GBE H21 Timber Weatherboarding Outline

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GBE H21 Timber Weatherboarding Outline
Outline:

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GBE H21 Timber Weatherboarding Outline

NB: %%% Requires formatting (indenting)

Performance requirements

• Resist wind load and uplift
• Resist defection and creep
• Weatherboarding
  • Exclude wind driven rain
  • Ventilation through space behind weatherboarding
  • Drainage through space behind weatherboarding
• Rainscreen
  • Permit limited rain passage but drain out at base
  • Pressure equalisation though open joints
  • Ventilation tough space behind rainscreen
• Not generate wind noise or rattling
• Fire performance
• Fire resistance at site boundaries
• Low spread of flame in escape routes
• Combustibility
• Design life & Durability
• Meet design life
• 30 years treated softwood
• 40 years durable hardwood
• Maintain good appearance
• Fade to grey/silver
• Avoid corrosion staining
• Avoid rainwater splash staining/fading
• Require redecoration at intervals
• Maintenance
• None
• Frequent and predictable
• Replacement after design life
• Damage at low level
• Rain splash discolouration
• Trapped contact water damage
• Persistent gutter overspill?
• Security
• Prevent removal of screen
• Prevent entry into building
• Flora and Fauna exclusion or inclusion
• Exposure Conditions & Fire characteristics
• Hazard Class:
• Hazard class 3: Above ground, not covered
• Timber of durability class 1 2 or 3
• suitable without treatment
• sapwood removed
• Timber of durability class 4 & 5 not suitable
• Preservative treated timber including sapwood is suitable
• Heat treated timber suitable
• Internal
• Fire
• No requirements
• Escape route
• Surface spread of flame BS 476:Part 7: Class 1
• Building Regulations Approved Document B: Class 0
• Splinter free passage or touching
• Sawn, planed and arises removed
• Sawn, planed arises removed and sanded
• Sawn planed arises removed and sand blasted
• External
• Weather
• Undercover
• Not covered
• Sheltered
• Severe
• Wind driven rain index
• Humidity
• Precipitation
• Fire
• No requirement
• Boundary proximity condition (fire)
• Surface spread of flame BS 476:Part 7: Class 1
• Building Regulations Approved Document B: Class 0
• Shading (Differential fading)
• Avoid projecting eaves
• Shading to top of cladding and soffits below fascias
• Avoid projecting verges
• Shading to cladding and soffit below barge board
• Consider pre-fading boards
• Consider coloured decorative coating
• Long term maintenance
• Proximity to horizontal splash surface
• Contact (avoid always)
• Window sills
• Door thresholds
• Cladding sills/flashing/drips
• Handrails
• Copings
• Close (Avoid if possible)
• Cladding sills/flashing/drips
• Minimum 15 mm. gap and sloping down and out
• Clearance sufficient for ventilation of batten zone
• Insect mesh at base and top of batten zone
• 200 splash height
• Ground level
• Consider planting or gravel mulch to disturb splash
• Balconies
• Consider open grille decking against building
• Access walkways
• Consider open grille decking against building
• Flat roofs
• Consider loose gravel solar shading
• 200-250 mm. (avoid textured surfaces (sawn): risk of capillary attraction, provide drip profile)
• 450 mm. (suitable for most choices of surface finish)
• Framing:
• Generally
• Metal: Not in contact
• Timber:
• Not in contact
• Joinery framed (in contact)
• Mild steel frames
• Hot dip galvanized
• Sacrificial Zinc rich coating
• Stainless steel frames
• Grade: 316 Marine grade
• Timber
• Same species, treatments, Surface, Finish, MC,
• Different species, treatments, surface, finish, same MC
• Flashings:
• Material compatible with adjacent roofing/cladding
• Material compatible with acidic tannin
• Coated metal:
• Leave protective films in place
• (not exceeding manufacturer recommendation)
• Aluminium (high % recycled content)
• Polyester Powder coated
• Anodized
• PVF2 coated
• Steel
• Hot dip galvanized
• Hot dip galvanized and sacrificial zinc rich coating
• Hot dip galvanized and Polyester powder coating
• Hot dip galvanized and painted
• Alternative splash zone materials (recessed)
• Overhang cladding beyond wall
• Concrete plinth shown
• Concrete plinth/DPM/Protection
• Slates placed against plinth, dry joint, soil retained
• Paving slab turned up forming skirting, dry joint, soil retained
• Reconstructed stone plinth units, lime mortar
• Brick in lime mortar
• Plastics wood substitutes
• Durability
• Natural durability BS EN 350 Parts 1 & 2
• Class 1 Very Durable
• Remove sapwood
• European Oak (exceptional)
• Achievable using acetylation treatment
• Class 2 Durable
• Remove sapwood
• European Oak (normal)
• Class 3 Moderately Durable
• Remove sapwood
• Class 4 Slightly Durable
• Remove sapwood
• European Redwood (Pinus sylvestris)
• Scots Pine (Pinus sylvestris)
• Requires preservative in cladding applications
• Class 5 Not Durable
• Remove sapwood
• Requires preservative in cladding applications
• Life Expectancy
• Treated Softwood: 30 years
• Durable Hardwood: 40 years
• Maintenance Regimes (desired frequency and complexity)
• None
• No decoration, fade to silver (external exposed)
• Intensive
• Regular sanding/stripping and over coating
• Regular staining/oiling/waxing
• Guarantee Requirements
• Certification
• NHBC
• 10 years normally
• Zurich
• 15 years normally
• Other
• BLP
• Supplier/Installer back to back?
• Timber sourcing certification
• Treatment Certification
• Strength ad suitability certification
• PII covered engineer with reclaimed timber
• Moisture movement
• General:
• not all timbers fit these groups neatly
• frequent uptake and loss of moisture in unfinished wood can lead to surface checking (small cracks)
• Small movement timbers: 1% for 5% change in MC
• Medium movement timbers: 1% for 4% change in MC
• Home grown Oak
• Will develop small surface cracks but will not affect durability
• European Redwood (Pinus sylvesris)
• Heat or chemical treatment without preservatives
• Large movement timbers: 1% for 3% change in MC
• Avoid in cladding
• Sustainable Certification
• FSC
• FSC Certified
• FSC Chain of Custody
• FSC Project Chain of custody
• FSC Recycled content (applicable to panel products)
• FSC Reclaimed (not yet formally established)
• Non-FSC Local source, sustainable forestry
• PEFC
• PEFC Certified
• PEFC Chain of Custody
• PEFC Project Chain of custody
• PEFC Recycled content (applicable to panel products)
• Non-PEFC Local source
• Timber Quality
• Sapwood General
• Treated sapwood is acceptable
• Exclude sapwood if untreated
• Durable hardwoods
• Knots BS 1186 Part 3
• Classes dictate size and frequency of knots
• Class CSH
• maximum 6 mm. diameter knots
• Intended for small sections
• Not appropriate for cladding
• Class 1
• For planed and unfinished boards
• For prestigious buildings
• Easily available
• Douglas Fir
• Western Red Cedar
• Tropical hardwoods
• More difficult to obtain
• May prove expensive in otherwise low cost species
• European redwood
• European whitewood
• European Larch
• European Oak
• Class 2
• Increasingly accepted for cladding
• Unfinished and transparent finishes
• Temperate hardwoods
• European oak
• Class 3
• Traditionally acceptable for cladding
• BS EN 15146
• Addresses knots
• Also addresses:
• Acceptability of end splits
• Shakes and checks
• Presence of resin pockets
• Relates to each species and defines two grade
• Grade A
• Grade B
• Profiles: Take care:
• many profiles not commercially available
• not necessarily represent good practice in design or purpose made profiles
• BS EN 14915
• Characteristics, evaluation of conformity and marking
• Reaction to fire
• Formaldehyde content
• Pentachlorophenol content
• Water permeability
• Largely irrelevant to claddings with ventilated cavity
• Thermal conductivity
• Largely irrelevant to claddings with ventilated cavity
• Preservative treatment
• Manufacturing controls
• Good practice in construction
• Species
• Species Applicable
• Softwood
• Local
• Native
• European Larch (Larix deciduas)
• care with Sustainable Certification
• Class 3 moderately durable
• Small movement
• Less dense, strong and knot-free
• Also suitable for shingles and shakes
• Spruce (European whitewood) (Picea abies)
• Class _ durability
• ____ movement
• Scots Pine (European redwood) (Pinus sylvestris)
• Class 4 Slightly durable
• Heat or chemical treatment not preservative
• Medium movement
• Non-native
• Western Red Cedar (Thuja plicata)
• (UK grown less durable than North American class 2) (Remove sapwood)
• Small knots common in UK grown
• Small movement
• BS 8417: 60 year service life
• Resistant to preservative treatment
• High tannin content corrosive: protect porous and steel or iron materials below
• Soft and brittle: Avoid applications prone to mechanical damage: low level
• Avoid unfinished where high levels of pollution present (traffic and industrial processes)
• Also suitable for shingles and shakes
• Douglas Fir (Pseudotsuga menziesii)
• (UK grown less durable Class 3-4 moderately to slightly durable than North American Class 3)

• Moisture movement: _
• Resistant to treatment
• Can be left unfinished to fade
• Requires preservative treatment
• European Larch (Larix deciduas)
• care with Sustainable Certification
• Class 3 moderately durable
• Small movement
• Also suitable for shingles and shakes
• Scandinavia,
• Native
• European redwood (Pinus sylvestrius)
• Class 4 Slightly durable
• Heat or chemical treatment not preservative
• Medium movement
• European whitewood (Pinus abies)
• Class 4 Slightly durable
• Heat or chemical treatment not preservative
• Medium movement
• European Larch (Larix deciduas)
• care with Sustainable Certification
• Class 3 moderately durable
• Small movement
• Also suitable for shingles and shakes
• Russia, Latvia
• Native
• European redwood (Pinus sylvestrius)
• Class 4 Slightly durable
• Heat or chemical treatment not preservative
• Medium movement
• European whitewood (Pinus abies)
• Class 4 Slightly durable
• Heat or chemical treatment not preservative
• Medium movement
• Siberia
• Native
• European Larch (Larix deciduas)
• care with Sustainable Certification
• Class 3 moderately durable
• Small movement
• Very slow grown
• Dense, straight grained and less knotty
• Also suitable for shingles and shakes
• Alpine
• Native
• European Larch (Larix deciduas)
• care with Sustainable Certification
• Class 3 moderately durable
• Small movement
• Very slow grown
• Dense, straight grained and less knotty
• Also suitable for shingles and shakes
• North American
• Native
• Californian Redwood
• Class 2 durable
• infrequent use in UK
• Also suitable for shingles and shakes
• Douglas Fir (Pseudotsuga menziesii)
• Aka Oregon Pine, British Columbian Pine
• Acidic with high tannin content
• Small movement
• Class 3 Moderately durable
• Straight grained, robust wood
• Can be untreated and unfinished
• Western Red Cedar (Thuja plicata)
• Durability Class 2) (Remove sapwood)
• Straight grained, largely free of knots
• Small movement
• BS 8417: 60 year service life
• Resistant to preservative treatment
• High tannin content corrosive: protect porous and steel or iron materials below
• Soft and brittle: Avoid applications prone to mechanical damage: low level
• Avoid unfinished where high levels of pollution present (traffic and industrial processes)
• Expensive
• Also suitable for shingles and shakes
• Asia/Pacific
• Native
• Radiata Pine
• Class 4 slightly durable
• requires treatment
• Don’t know
• Western Hemlock
• Class 4 slightly durable,
• requires treatment
• Temperate
• Southern Yellow Pine
• Class 4 slightly durable,
• requires treatment
• Temperate Hardwood
• Local
• Native
• English Oak (Quercus robur)
• Shorter lengths than European
• 2.4 m long normally
• 150 mm. maximum width
• Durability Class 1 Very Durable (Remove sapwood)
• Medium movement
• Can be used green (un-dried)
• Soft and workable whilst green
• Once dry becomes extremely hard and resistant to mechanical damage
• High tannin content corrosive: protect porous and steel or iron materials below
• Resistant to coatings
• Can be left unfinished to fade to grey
• FSC and PEFC
• Also suitable for shingles and shakes
• Welsh Oak (Quercus robur)
• Source: Coed Cwmry, Small section?
• As English Oak
• Sweet Chestnut (Castanea sativa)
• 2.4 m long normally
• 150 mm. maximum width
• Durability Class 1 Very Durable (Remove sapwood)
• Small movement
• Can be used green (un-dried)
• Soft and workable whilst green
• Once dry becomes extremely hard and resistant to mechanical damage
• High tannin content corrosive: protect porous and steel or iron materials below
• Resistant to coatings
• Can be left unfinished to fade to grey
• FSC by the forestry commission
• Available in relatively small quantities
• Also suitable for
• shingles and shakes,
• post and beam construction
• Elm
• In short supply
• classed as 5 non durable
• but performs better than that
• Used in waney edge boarding
• European
• Oak (Quercus robur)
• France, Germany, Eastern European
• Longer lengths than UK Home grown
• ___ m long normally
• 150 mm. maximum width
• Durability Class 1 Very Durable (Remove sapwood)
• Medium movement
• Can be used green (un-dried)
• Soft and workable whilst green
• Once dry becomes extremely hard and resistant to mechanical damage
• High tannin content corrosive: protect porous and steel or iron materials below
• Resistant to coatings
• Can be left unfinished to fade to grey
• FSC and PEFC
• Also suitable for shingles and shakes
• North American
• Native
• American White Oak (Quercus Alba)
• Kiln dried suitable for internal use
• Can lead to problems if used externally
• Can lead to extensive shakes
• PEFC
• Tropical Hardwood
• General Issues
• Take particular care with Certification
• Durability Class 1 Very durable or 2 durable
• Dense or very dense
• Small or medium movement
• Some will darken upon exposure initially
• avoid treatment: probably unnecessary
• Suitable for use undecorated
• Will bleach to grey after exposure for long period
• African
• Small amounts of certified wood
• Far East
• Illegal Logging rife
• Primary species
• Iroko
• Endangered species
• Plantation grown with certification available
• Teak
• take care with sourcing and certification
• Central & Southern America
• FSC Certified available
• Seek detailed performance characteristics of subspecies
• Seek availability information
• Seek length and sizes information
• Secondary species (less well known)
• Angelim
• Cumaru
• Louro
• Itauba
• Jatoba
• Kauri
• Massaranduba
• Purpleheart
• Tatajuba
• Options and Alternatives
• Designer Preference
• Species to avoid
• Alternatives
• Greenpeace and FoE have lists
• Performance Specification of timber (avoiding species specification)
• Treatment
• General issues
• Service life BS 8417
• Durable species or treatment
• Up to 60 years (normal building design life)
• Untreated
• Durability to match or exceed exposure class
• Preservative pre-treated (BS 8417)
• Chemical
• CCA (Copper Chrome Arsenic)
• no longer permitted
• (in domestic applications)
• Where children present
• Where food growing may occur
• No longer made?
• Water-borne Copper-Organic
• Up to 60 years
• Organic-Solvent
• Up to 60 years
• Water-borne micro emulsions
• Up to 60 years
• Mineral
• Boron Salts
• Up to 30 year life
• WPA Manual
• Methods:
• Immersion in liquid
• Pressure and vacuum in liquid in vessel
• Pressure and double vacuum in liquid in vessel
• Low pressure spraying
• Unacceptable except:
• Local application to previously treated timber
• after cutting planning and drilling
• end grain sealer
• Applicability:
• If timber to be left unfinished:
• Water-borne copper-organic
• Affect moisture content of the wood
• Greenish tinge to wood
• Will fade over time
• Must be fully dried before handled or used
• If the timber to be coated or stained
• Light organic solvent
• Do not increase moisture content of the wood
• Less risk of distortion of profile
• Must be fully dried before handled or used
• Water-borne micro-emulsions
• Do not increase moisture content of the wood
• Less risk of distortion of profile
• Must be fully dried before handled or used
• Boron salts
• 30 year life
• Water soluble and susceptible to leaching
• Fire Treatment
• Modified timber
• Generally:
• Allows cheaper and readily available timber of lesser durability to be used without preservatives
• Modification is throughout the section
• Reduces moisture absorption and moisture movement
• Process tends to darken the wood
• Preservative treatment only penetrates to a limited depth
• Chemically Modified timber
• Process
• Impregnate wood
• Chemical reaction with wood
• Effect
• Render the wood more durable
• Improves moisture resistance
• Improves dimensional stability
• Improves coating performance
• Extends coating maintenance frequency
• Raises timber durability
• European redwood
• European whitewood
• Acetylation
• Pressure impregnate wood with acetic anhydride
• derivative of acetic acid (Vinegar)
• Raises pine to Durability Class 1
• Proprietary
• Product Reference: Accoya
• Manufacturer: BSW timber
• Heat treated timber
• Process:
• Dries the wood
• Heats the wood
• Reduces the natural nutritional content of wood
• Discourages fungi and insects
• Effect
• Timbers suitable for hazard category 3
• (above ground, not covered)
• Suitable for cladding
• 30 year life
• Advantages
• Throughout whole section
• Halves the moisture movement of timber
• Disadvantages
• Darkens appearance
• This should fade due to sun bleaching if unfinished
• Makes the timber softer and more brittle
• Similar to Western Red Cedar
• Use adequate number of fixings
• Loss of fastener pull out strength
• Proprietary
• Finland
• Product Reference: Thermowood
• Manufacturer: Finnforest UK Ltd.
• Holland
• Product Reference: ___
• Manufacturer: ____
• Additional opportunities
• Similarly modified softwood battens are available
• But they are softer and more brittle than unmodified
• Consider unmodified softwood
• Fire Protection
• Fire treatment
• Requirements
• Limit “Unprotected cladding”
• Within 1 m from site boundary:
• Of greater height than __ m.
• Building Regulations Approved Document B Class 0
• European Class B
• Or better
• Applications
• Vacuum/Pressure treatment
• Type:
• External exposure
• Leach resistant
• Humidity resistant and maintained protective coating
• Internal exposure
• Effectiveness
• Natural permeability of wood
• Sapwood easily treated
• Heartwood can be resistant to treatment
• Softwoods
• European Larch quite resistant
• Hardwoods mostly resistant to treatment
• Manufacturers know the species and thicknesses that can be treated to Class 0/Class B
• WPA Manual: Industrial Flame retardant for solid timber and panel products
• Treated
• Treated and kiln dried
• Cavity barriers
• Requirements
• Building Regulations Approved Document B
• Different in each country?
• Smoke and flame
• Counterproductive for ventilation and drainage cavities
• Stop and start the cavity above and below
• Provide drips etc. at each floor
• Locations
• Party walls
• Solid 50 x 50 mm. batten can be used at party walls
• Party floors
• Intumescent honeycomb
• Intumescent strip or tape
• Intumescent paint
• Around window openings
• Boundaries
• Edges at change of materials
• Breather membranes
• At re-entrant
• In line
• No need for vertical DPC
• Turn breather membrane to close wall
• Hold in place with batten
• Damp proof course from cavity wall closing
• In-line or behind a vertical DPC
• Extend the DPC to cover joint between any framing or sheathing of the wall
• Pre-compressed foam sealing strip
• Instead of gunned sealant or mastic
• Maintain good contact over uneven surfaces
• Will continue to expand to fill any gaps
• Even if there is shrinkage or movement at interface of wall and timber
• Metal flashings
• Malleable metal flashings
• Lead
• Avoid below Acidic timber
• Avoid below WRC
• Avoid below mosses and algea
• Dressed over solid base
• Below windows
• Dressed back behind base of timber boarding
• Capping
• Not suitable as a capping or it will block ventilation of cavity
• May be used with open joint boarding
• Finishes
• Patination oil on face
• Bitumen coating on rear face against alkali materials
• Pressed metal
• General
• Profiled to self support and span
• Project from base and background
• Materials and finishes
• Aluminium
• Powder coated
• Anodized
• Copper
• Unfinished
• Pre-patinated
• Avoid below acidic timber
• Avoid below WRC
• Zinc
• Unfinished
• Recycled aluminium
• Powder coated
• Protective temporary peel off strip
• Anodized
• Protective temporary peel off strip
• Mild steel
• Unfinished not suitable below acidic species
• Galvanized
• Galvanized and powder coated
• Pre-drill before protection
• Protective temporary peel off strip
• Bitumen coating
• Bimetallic and electrolytic corrosion
• Avoid
• Copper below green acidic timber
• Lead below green acidic timber WRC & Oak
• Zinc below western red cedar (acidic)
• Zinc below green oak (tannin)
• Unprotected mild steel below green acidic timber
• mixing metals on one building
• different metals in contact
• Consider
• Temporary protection during tannin release
• More base metals towards the top
• More nobel metals towards bottom
• Copings
• Project over top edge of boarding
• Particularly exposed ends of vertical boarding
• Drip profile downstand
• 10 mm. clearance minimum
• Any further will not ensure clearance of the cladding below
• Shed water away from top edge
• Overshadowing will prevent the boarding below bleaching (if desired)
• Window opening top flashing
• Requires careful detailing
• Vertical boarding
• Flashing to extend into adjoining boards
• Boarding to be cut back to accommodate
• Flush boarding difficult
• Board on board okay
• Base of claddings
• Sloping top surface to drain out and down
• Projection beyond wall below
• Steep enough that any rain splash misses bottom of boarding
• Maintain 15 mm. gap
• Between bottom of board and top of flashing
• For drainage and ventilation
• Important with vertical boarding end grain absorption
• Prevent excessive wetting and discolouration
• Flashing to extend back full depth of cavity
• Dressed or pressed up, drilled and screwed to backing wall
• Breather membrane to overlap upstand onto flashing
• Gap between ends of boarding and other material
• 8-10 mm. gap for ventilation
• End grain of horizontal boarding
• Do not fill with any sealant
• Changes of direction, plain or angle
• external corners
• Strong visual impact
• Consider detailing at openings when detailing corners
• Horizontal boarding
• Solid timber set flush
• Create re-entrant corner with vertical battens
• Stop boards 8-10 mm. short of batten face
• Requires high quality workmanship
• Fix solid timber to battens
• 8-10 mm. shadow gap between boards and solid timber
• No sealant
• Covered corner
• Create corner with vertical batten
• Stop boards 8-10 mm. short of batten corner
• Cover ends of boards with corner piece
• Form L shaped corner piece
• tongued and grooved together
• 8-10 mm. anti capillary groove on two hidden faces
• No sealant
• Solid capped set flush
• Create re-entrant corner with vertical battens
• Fix solid timber corner batten to vertical battens
• Stop boards 8-10 mm. short of vertical batten face
• Requires high quality workmanship
• Form L shaped corner piece
• tongued and grooved together
• 8-10 mm. anti capillary groove on two hidden faces
• Cover corner batten with corner piece
• 8-10 mm. shadow gap between boards and corner piece
• No sealant
• Re-entrant corner
• Create re-entrant corner with vertical battens
• Stop boards 8-10 mm. short of vertical batten face
• Requires high quality workmanship
• Cover re-entrant corner battens with two boards of different dimension,
• First board widest
• Second board narrower by first board width
• one to each face
• 8-10 mm. shadow gap between corner boards and horizontal boarding
• No sealant
• Mitred corners
• Mitreing is not recommended
• Shrinkage will leave gap for moisture retention
• Moisture will lead to selling and moving apart
• Open joint Rainscreen horizontal boarding
• Mitred open joint corner
• Maintain normal vertical joint width at corner
• Accommodate tolerance and any variation
• Visible fasteners will be set back from corner
• Diagonal boarding
• Treat similarly to horizontal boards
• Exposing ends of boards needs accurate cutting
• High water run off
• 12 mm. gaps recommended
• Seal space behind vertical gap to prevent water entry
• Vertical boarding
• Board on board
• Cladding to corner
• Outer board at corner of one elevation
• Inner board (cut) at end of one elevation
• internal corners
• At openings
• Dimensional coordination is essential for appearance sake
• Work with board/lap/joint width
• Position openings to coordinate with boarding
• Avoid notches and split boards (poor appearance)
• Consistency is important
• Varying board widths or laps can solve dimensions but appearance may suffer
• Ribbon windows may simplify detailing
• Minimise cutting to minimise labour intensity (costly)
• Minimise cutting to minimise waste (costly)
• 3D consideration of flashings, DPC and sills essential
• Maintain integrity of defence against water entry
• Maintain pattern of visible fasteners around openings
• Eaves
• General
• The greater the overhang the more pronounced the shading and likelihood of differential bleaching of unfinished surfaces
• Projecting eaves
• Horizontal soffit
• Sloping soffit
• Fascia
• Verges
• Bargeboards
• Fascia
• Soffit
• Parapet
• General
• No overhang avoids shading and ensures consistent weathering
• Capping with lead will seal ventilation zone
• Capping with self supporting metal maintains ventilation
• See
• Moisture Content
• Green
• Seasoned
• Kiln dried
• Surface Texture
• Sawn
• risks of splinters
• Capillary attraction of splash water up surface
• More surface coating required for coverage
• Better protection with more coating
• Fine sawn
• Suitable for stains
• Sawn Planed
• Sawn Planed Arises eased
• Removes risk of splinters during handling
• Sawn Planed Sanded
• Sawn Planed Sand blasted
• Decoration
• Types
• General
• No decoration will lead to:
• timbers bleaching to grey/silver
• some friability of the surface
• particularly with softwood
• Decoration should be applied as early as possible
• Maximise the performance of the coating
• Uncoloured decoration is poor UV protection
• generally not suitable externally
• pigments are necessary
• Opaque coatings
• Offer best protection
• Translucency
• Can permit the figure, texture, grain and colour show through
• Colours:
• Can simulate natural colours
• Can contrast with manmade colours
• Dark colours offer greatest UV protection
• Dark colours raise the temperature
• Raised temperature will drive out moisture
• Drying timber may suffer cracking or checking
• Raised temperature can lead to resin exudation
• Permeability
• Can enhance the ability of the timber to dry out through stains and low build finishes
• Can protect from moisture uptake
• Film forming coatings
• Paints and varnishes
• Can resist moisture uptake
• Are too brittle upon aging
• Will crack as moisture movement occurs
• Lets moisture in
• Can trap moisture under surface in the wood
• Possible degradation of the wood
• Possible blistering, flaking and peeling of the finish
• Should ideally be extensible:
• To cope with moisture movement of timber
• Micro-porous coatings
• Are flexible enough to follow moisture movement
• Are permeable to permit loss of moisture from under the surface
• Apply to fine sawn surfaces for longer life than planed
• More coating needed for sawn surfaces
• Can help the wood retain its colour
• Application
• UK worst practice
• prime timber before building in
• Absorbent surface against permeable construction
• Scandinavian best practice
• full coating system on all faces
• Compromise
• Minimum one full topcoat on all faces
• Consistent moisture uptake and loss possible
• Shrinkage will not reveal uncoated surfaces
• Location
• Factory
• Controlled moisture content (if timber)
• Controlled humidity (in factory)
• No Precipitation
• Controlled wind movement
• Controlled sun (exposure of wood)
• Machine applied
• Controlled application rates
• Controlled drying
• On-site
• Uncontrolled moisture, humidity, wind, sun exposure, precipitation,
• Unpredictable on site labour skills
• Timber exposed to ultra violet light degraded
• Risk of inconsistent factory undercoat and site top coats
• Diminished life expectancy
• On-site maintenance
• Do not let bare timber to be exposed before maintenance
• Poor UV affected surface will lead to poor adhesion
• Hardwoods more difficult to gain penetration or adhesion
• Sand down or strip all film forming coatings
• Unfinished
• Weather and bleach naturally in UV sunlight
• General
• No further maintenance
• Long life possible
• Sun (UV light) bleaching to grey or silver colour
• Some will go to brown
• Bleaching will not affect the durability of the timber
• High levels of UV light do not reduce life expectancy
• More movement in the surface
• due to fluctuating moisture content
• Some surface checking (small cracks) may occur which will open and close
• Pollution and dirt accumulations higher on un-finished
• Can lead to blackening of the surface
• Low moisture movement species best
• Partial bleaching
• Affected by shading
• Eaves, verges, balconies, solar shading, rainwater goods, lights, signs, sills and drips
• Can be high contrast, unexpected and unacceptable
• It is a design failure rather than a materials failure
• Consider pre-bleached timbers
• Consider different detail in sheltered no-bleach zone
• Orientation affects rate of bleaching
• Slow: north east, north, north west
• Fast: south east, south, south west
• Shading by other buildings can affect rate
• Brake dust containing metal dust can react with tannin resulting in iron staining
• Blackening
• A number of causes
• Cladding in the vicinity of trees or heavy vegetation or where there is unusually high run off of moisture
• Exhaust fume pollution
• Brake dust from cars and trains containing metals can react with tannin resulting in iron staining
• Cement dust from local construction work
• Mild steel fasteners in acidic timbers reaction blackens fastener and timber
• Avoid all such risks
• Cleaning fluids are available but remove the source of the problem first
• Moisture content affecting colour or appearance
• Shading can maintain moisture content higher that that warmed by the sun
• Contact surfaces at base of cladding and other penetrations
• Maintain timber in wet condition
• Splash zones can keep moisture content high
• Splash 200 mm. and capillary attraction up sawn surfaces a further 250 mm.
• Eaves abutment with gables, blocked gutter overflow zone
• Consider different fastening regime to permit easy replacement
• Tannin
• High tannin content acidic timbers
• Run-off during bleaching process
• Porous materials below cladding
• Stone, brick, concrete, precast stone, renders
• Staining potential
• Avoid by design or temporary protection
• Softwoods
• Western Red Cedar
• Douglas Fir
• Hardwoods
• European Oak
• Finished
• Vapour tight
• Lacquered
• Painted
• Micro porous vapour permeable
• Low build stain high solids
• high build stain
• Stained
• Stain and wax (dangerous on decking)
• Oiled
• Waxed (dangerous on decking)
• Limed (traditionally on oak)
• Health issues
• Plant based
• Plant based solvent
• Water based solvent
• Mineral based
• Synthetic
• High VOC
• Low VOC (more chemicals)
• Installation appearance
• Co-ordinated design
• Corners
• Changes of level
• Parapets
• Openings
• Soffits
• Junctions with other materials
• Board layout
• Orthogonal shapes
• Non-orthogonal shapes
• Curved on plan
• Lends itself to vertical boarding
• Board on board works well
• T&G difficult
• Tight radii
• Lends itself to narrow boards
• Battens
• Can be made up in thin layers capable of negotiating curve
• Successive layers can be fixed together
• Nails
• Screws
• Joints must not coincide
• Curved on section
• Lends itself to horizontal boarding
• Overlap and shiplap work well
• T&G difficult
• Shallow angles can permit capillary attraction leading to water entry
• Tight curves open up joints to water entry into joint
• Sustained moisture content will lead to failure
• Curved on elevation
• Angled facades
• May accept vertical horizontal or sloping boarding
• Shallow angled façade or gable
• Cut end of vertical boards
• Avoid tapering horizontal boards
• Horizontal boards
• Additional batten to support tapered ends of boards
• Use of diagonal boards can sometimes simplify junction
• Combinations of the above
• Geometry may dictate board layout
• Vertical horizontal or diagonal board layouts
• Combination of the above
• Surface coverage
• Random length and joint locations
• Controlled length and joint locations
• Random width(s) and joint spacing
• Controlled width(s) and joint spacing
• Framed panels
• Unframed panels
• Off-site panelised prefabrication
• Boarded
• Vertical
• Diagonal
• Horizontal
• Mixed
• Battened
• Louvres
• Solar shading
• Rainscreen
• Tiled
• Shingles
• Shakes
• Tiles (appear like ashlar stonework)
• Boundaries
• Profiles, overlapping, gaps, butting T&G or TG&V
• Profiles
• Spaced battens
• Weathered top edge
• Drip profile
• Rain-screen open joint profiled edge boards
• Anti-capillary profiles
• Joint layout
• Board length limitations
• Softwood
• Species
• European redwood
• European Whitewood
• European larch
• Douglas fir
• Lengths
• Up to 4.8 m.
• Temperate Hardwood
• Species
• Sweet chestnut
• 2.0 – 4.0 m.
• Maximum: 5.0 m.
• European Oak
• 2.4 m. generally
• 2.0 – 4.0 m.
• Maximum: 5.0 m.
• Tropical hardwoods
• Species
• Varies
• 2.1 – 4.2 m.
• Maximum: 4.8 m.
• Width limitations
• European Oak
• 150 mm.
• Spacing and size and patterns
• Surface profiles
• Joint patterns & batten spacing
• Random or standardised lengths
• Random colour mixing
• Fixing appearance and spacing
• Joints
• Horizontal boarding
• Vertical end-joints
• Coincident with battens
• Standard batten widths insufficient for end joints
• Insufficient width batten
• Insufficient edge distance on batten
• Insufficient end distance on board
• Consistent length boards and all occur on same batten
• Use two battens side by side
• Spaced to match joint between board ends
• Timber frame background
• Use wide batten fixed in centreline of stud
• Panelised boarding
• On structural grid lines
• Lends itself to prefabrication
• Requires coordination of openings
• Labour intensive
• Requires accuracy for good visual effect
• Invites rejection by designers
• Wasteful of timber cutting to length
• Invisible joints
• Random location
• Coincident with battens
• Length of batten nailed to side of main batten
• To support ends of two boards
• Length 3 x board width
• Butt joint positions randomly staggered
• 5 mm. gap for ventilation and drainage of end grain
• Vertical boarding
• Horizontal end-joints
• Increasingly visible over time
• Wetting and swelling of lower board end grain
• Run-off from upper board
• Chamfer ends of boards outwards
• Seal top of lower board
• Gap: 5 – 8 mm.
• Coincident with battens
• Standard batten widths insufficient for end joints
• Insufficient width batten
• Insufficient edge distance on batten
• Insufficient end distance on board
• Consistent length boards and all occur on same batten
• Use two battens side by side
• Spaced to match joint between board ends
• Panelised boarding
• Storey heights
• Most species can be accommodated
• Lends itself to prefabrication
• Floor level joints can accommodate shrinkage, deflection, creep and structural settlement
• May accommodate cavity barriers between floors
• Requires coordination of openings
• Offcuts can be used under window openings
• Labour intensive
• Requires accuracy for good visual effect
• Invites rejection by designers
• Wasteful of timber cutting to length
• Jointing
• Finger jointing and end dowelling
• Will become economic
• Will become more commonplace
• Longer lengths overcome need for butt joints
• Reduce off-cut waste
• Invisible joints
• Random location
• Coincident with battens
• Length of batten nailed to side of main batten
• To support ends of two boards
• Length 3 x board width
• Butt joint positions randomly staggered
• 5 – 8 mm. gap for ventilation and drainage of end grain
• Chamfered outward and downward
• It may be difficult to exclude all sapwood:
• Permissible relaxations:
• No sapwood should be visible in exposed board face
• No sapwood should be present in board edges, lapping or jointing profile
• No sapwood should be present in end grain
• Sapwood which occupies less than 5 mm. width of the hidden face may be of unlimited length
• Sapwood which occupies more than 5 mm. width of the hidden face should be less than 500 mm. long
• Check the class specification and modify if required
• may be difficult to identify sapwood
• Board Orientation & Profile
• Horizontal
• General issues
• Most common
• Profiles: simple overlap, feather or square, rebated feather, shiplap
• Square edge
• thickness: 16-19 mm.
• overlap 25 mm.
• Heart side outwards
• Feather edge
• thickness: minimum 8 mm. to 16-19 mm.
• overlap 25 mm.
• thin edge at top
• Heart side outwards
• Rebated feather edge
• Thickness: minimum 8 mm. to 19 mm. low edge: 10 mm.
• Overlap 15 mm.
• Gap: 2 mm.
• Heart side outwards
• Ship lap
• Thickness: minimum 16 – 19 mm.
• Overlap 15 mm.
• Gap: 2 mm.
• Heart side outwards
• Horizontal T&G Jointed
• tongue uppermost
• Heart side outwards
• Thickness: 19-22 mm.
• Recommended board face width: 100 mm.
• Maximum board face width: 125 mm.
• T&G overlap 10 mm.
• Gap: 2 mm.
• Not V joint (used internally or vertically)
• Better with a rebated profile
• Open joint
• 30 degree sloping top and bottom edges
• Heart side outwards
• Widening gap towards back is better
• gap 8-15 mm.
• thickness 16-19 mm.
• Insect mesh behind
• Suitable for green timber, shrinkage less obvious
• strong shadow line
• UV light penetration effect on breather membranes to be taken into account
• Reduced spacing battens to reduce shrinkage movement
• Butted boards
• risky for capillary attraction
• end grain water penetration
• Diagonal (take care with profiles)
• General issues
• Longer span between H or V battens
• Diagonal battens?
• Reduce V or H batten spacing
• Thicker board (How thick?)
• Avoid V pattern abutments
• Consider A pattern abutments
• Avoid simple overlapping boards
• Avoid open butt joints in lengths
• Avoid butt joints use longer boards
• Heart side outwards
• Ship lap
• Thickness: minimum 16 – 19 mm.
• Overlap 15 mm.
• Gap: 2 mm.
• Heart side outwards
• Diagonal T&G Jointed
• tongue uppermost
• Thickness: 19-22 mm.
• Recommended board face width: 100 mm.
• Maximum board face width: 125 mm.
• T&G overlap 10 mm.
• Gap: 2 mm.
• Not V jointed (used internally or vertically)
• Heart side outwards
• Overlapping
• Vertical
• General Issues
• Consider lengths available and horizontal joints
• Avoid top of board below joints absorbing water
• Consider stopping and starting at floor levels
• Consider fire barriers at floor levels
• Allow for creep, deflection and settlement of the structure
• Consider a weather drip between storeys or panels
• Consider prefabrication of panels
• Vertical T&G Jointed
• Recommended width: 100 mm.
• Maximum width: 125 mm.
• Thickness: 22 mm.
• Shrinkage risks disengagement of T&G
• T&G overlap 10 mm.
• Gap: 2 mm.
• Can use V jointed
• Alternative: Rebated overlapping
• Heart side outwards
• Rebated overlapping boards
• Maximum width: 150 x 19 mm.
• Heart side outwards
• Board on Board
• Minimum 20 mm. overlap
• With or without Capillary grooves near the outer edges of both board touching faces
• Suited to curvilinear plan walls
• Tolerant of dimensional variation
• Gap created provides ventilation and drainage
• Gap created avoids need for counter-battens
• Wide boards on wide board
• 150 and 150 x 16 mm.
• Wide boards on narrow board
• 100 on 75 x 16 mm.
• Narrow boards on wide board
• 75 on 100 x 16 mm.
• Variety of board widths permits surface modelling
• Outer board: Heart side outwards
• Inner board: Heart side inner
• Open joint board
• Widening gap towards back is better
• gap 8-15 mm.
• thickness 16-19 mm.
• Insect mesh behind
• Heart side outwards
• Suitable for green timber, shrinkage less obvious
• strong shadow line
• UV light penetration effect on breather membranes to be taken into account
• Use of breathing sheathing board appropriate
• Reduced spacing battens to reduce shrinkage movement
• Open joint battens
• Widening gap towards back is better
• gap 8-15 mm.
• Size: minimum ex 50 x 50 mm.
• Insect mesh behind
• Suitable for green timber, shrinkage less obvious
• strong shadow line
• UV light penetration effect on breather membranes to be taken into account
• Use of breathing sheathing board appropriate
• Reduced spacing battens to reduce shrinkage movement
• Sloping
• Board on Board
• Minimum 20 mm. overlap
• With capillary grooves near the outer edges of both board touching faces
• Wide boards on wide board
• 150 and 150 x 16 mm.
• Wide boards on narrow board
• 100 on 75 x 16 mm.
• Narrow boards on wide board
• 75 on 100 x 16 mm.
• Outer board: Heart side outwards
• Inner board: Heart side inner
• Reduced spacing battens to reduce shrinkage movement
• Reduced batten spacing or sloping battens
• Fixing & Fastenings
• Choices
• Hardwood
• Screws (normal practice)
• At or close to 16% MC
• Allow for seasonal variation in MC
• Oversize drill holes
• Small movement timbers: 2 mm.
• Medium movement species: 2 mm.
• Clearance around shank
• Use countersunk screws
• Use oversize screws with bigger heads
• Maximum 150 mm. board width
• Locate screws ¼ board width in from edges
• Green timber
• Allow for considerable initial shrinkage
• Oversize drill holes
• Green timber: 4 mm.
• Washer needed
• Slotted hole washers
• Not easy to obtain
• Require alignment to permit movement
• Require positioning to maximise possible movement
• Recessed holes in timber face
• Oversized to permit movement of washer over timber in recess
• screw heads for use with washer
• Round head or pan head
• Sheeting screws with built in washers
• Rear face fixing
• Hardwood open joint boards
• Panelise boards with battens
• Screws through clearance holes
• Front face fixing
• Hardwood boards
• Panelise boards with battens
• Screw through front face and pellet or plug holes
• To treated softwood battens (normal practice)
• To same hardwood battens
• Expressed
• Demountability
• Single lap with exposed Phillips head screw
• Square edge board, horizontal boarding
• Feather edge board, horizontal boarding
• Socket in timber oversized hole, washer and screw
• open joint boarding
• Flat head nails at surface
• board on board
• Hidden
• Limited demountability
• Hidden J profile stainless steel fixing clips
• Fixed to vertical batten
• Horizontal shiplap or Open joint boarding
• With added slot in underside
• J profile hooks into slot
• Screw top of boards to battens through shoulder
• Similar principle to T&G
• Can allow for considerable shrinkage in board width
• Easy to engage in Joint
• Less liable to damage tongue
• Board can be held and aligned with wide clip
• Requires careful design for each application
• Taking in to account:
• Species, shrinkage, thickness, other characteristics
• Softwood
• Nails (normal practice)
• To treated softwood battens (normal practice)
• Non-demountable
• Lost head nails
• Horizontal boarding
• Open joint
• Square edge
• Feather edge
• Rebated feather edge
• Shiplap
• T&G
• Diagonal
• Vertical
• Secret fix nails
• Not recommended in T&G Joint
• Risk of tongue splitting
• Recommended in rebated T&G Joint
• Nail through shoulder
• Metals
• Acidic species e.g. Oak, WRC, Sweet chestnut
• Austenitic stainless steel
• Marine Environment: (tidal estuary and sea) Grade 316
• Otherwise Grade 304
• Weathers down to matt grey
• (Quercus Fencing fastenings)
• Galvanized steel
• Prone to damage when driving
• Mild steel
• Will stain timber and fastener purple-black
• Stain not removable
• Non acidic species
• Avoid ferrous if uncoated softwood boarding
• Galvanized steel
• Prone to damage when driving
• Protect by coating timber
• (Quercus Fencing fastenings)
• Brass
• Un finished hardwood
• Austenitic stainless steel
• Marine Environment: (tidal estuary and sea) Grade 316
• Otherwise grade 304
• Weathers down to matt grey
• Clips or washers same metal and grade
• Coated hardwood
• Austenitic stainless steel
• Marine Environment: (tidal estuary and sea) Grade 316
• Otherwise Grade 304
• Weathers down to matt grey
• (Quercus Fencing fastenings)
• Galvanized steel
• Prone to damage when driving
• Fastener sizes: Dictated by board thickness
• Nails
• Nails normally driven just below the surface
• allow for timber shrinkage
• avoiding nail becoming proud of surface
• Nails 20 mm. from end of board
• Nails 15 mm. from edge of board
• Spacing: batten spacing dictates.
• Small head or siding nails can pull through soft WRC
• Larger heads recommended for WRC
• Standard round wire nails:
• 2.5 x thickness of board
• T&G: 19-22 mm. = 48-55 mm.
• Other: 16-19 mm. = 40-48 mm.
• Annular ring-shank nails
• Improved holding power
• 2 x thickness of board
• T&G: 19-22 mm. = 38-44 mm.
• Other: 16-19 mm. = 32-38 mm.
• Pneumatically driven nails
• D shaped heads may not be visually acceptable
• Virtually headless pins are not recommended
• Screws:
• 2 x thickness of board
• T&G: 19-22 mm. = 38-44 mm.
• Other: 16-19 mm. = 32-38 mm.
• Batten size, spacing and direction
• Batten Size:
• Minimum 2 x board thickness
• T&G: 19-22 mm. = 38-44 mm.
• Other: 16-19 mm. = 32-38 mm.
• Minimum: 38 x 38 mm.
• Batten profile:
• Horizontal boarding vertical batten
• Square
• Vertical boarding horizontal batten fixed to counter-batten
• 15 degree sloping top face to throw off water into ventilation cavity
• Vertical board on board horizontal batten
• 15 degree sloping top face to throw water away from sheathing and breather face
• Metal framing and fasteners
• Avoid different metals in direct contact if possible
• Introduce timber battens between boards and metal framing
• Fix boards with stainless screws to battens
• Fix galvanised framing with galvanized or plated screws to battens
• If unavoidable:
• Galvanized framing and stainless steel fasteners
• Never:
• Stainless framing and galvanized steel fasteners
• Avoid self drilling, self tapping, self countersinking fasteners
• Unprotected mild steel swarf will corrode
• Iron staining of timber and stainless steel
• Electrolytic action between different metals
• See Background and counter-battens
• Insect mesh
• Cavity behind boards can be warm and dry home to insects
• Insects: wasps, woodlice, flies
• Risk factors:
• Urban v rural
• Proximity of trees
• Height above ground
• Etc.
• Guidance:
• TRADA do not advise on need
• Precautionary principle could apply (do it anyway)
• Mesh over openings:
• Bottom and top of cavity
• Close jointed horizontal boarding
• Fix mesh vertically to back wall of cavity
• Fold up and attach to underside of vertical battens
• Spanning between battens
• Close jointed vertical boarding
• Fix mesh vertically to back wall of cavity behind counter-battens
• Fold up and attach to underside of horizontal battens
• Board on board vertical cladding
• Fix mesh to horizontal bottom battens
• Extend out to run continuously across the inner boards
• Sealing gaps behind the outer boards
• Horizontal overlapping boards
• Square and feather edge boards
• Triangular gaps at ends of boards
• Alternate solutions:
• Compressible foam tape
• Between last vertical batten and boards
• Fabric mesh
• Stapled to whole facade battens before boarding
• Open jointed boarding
• Fabric mesh
• Excludes insects
• Stapled to whole facade battens before boarding
• Reduces rain penetration
• Shades cavity from UV light
• Restricts visibility into cavity
• Products
• Perforated metal sheet
• If metal cladding is also used,
• Obtain from installer
• Metal
• Acidic timber
• Stainless steel
• Terne coated stainless steel
• Zinc
• Copper
• Perforation size: __ mm. maximum
• Free air area: __ %
• Fastener:
• Screw if adequate access room
• Same metal as perforated sheet
• Staple if limited access
• Same metal as perforated sheet
• Metal mesh
• Mesh spacing: ____
• Hole size: ____
• Metal
• Acidic timber
• Stainless steel
• Non-acidic timber
• Zinc coated mild steel
• Galvanized chicken wire (small mesh)???
• Non-ferrous metal
• Fastener:
• Screw with large washer if adequate access room
• Same metal as perforated sheet
• Staples if limited access
• Same metal as perforated sheet
• Fabric mesh
• Mesh spacing: ____
• Hole size: ____
• Material:
• UV Resistant plastic mesh
• Nylon
• _____
• Fastener:
• Staples:
• Acidic timber
• Stainless steel
• Non-acidic timber not coated
• Stainless steel
• Non-acidic timber coated
• Zinc coated steel
• Supporting Biodiversity:
• Occupation v Infestation
• What is the consequential risk of occupation?
• Can we encourage without risk?
• Bats?
• Bat droppings and urine on outer face of insulation
• Suits hygroscopic insulation
• Dense cellulose fibre
• Bat droppings and urine on outer face of breather membrane
• Used with open surface hydrophobic insulation
• Moisture resistant vapour permeable membrane
• Paper may not be suitable
• Polymeric may be acceptable
• Tyvek are working with BCT
• Bat droppings and urine on outer face of breathing sheathing boards
• Suits hygroscopic boards
• Dense cellulose fibre and wood fibre boards
• Entry slots
• Higher level (base of upper floors) may be ideal
• Roots
• Trapped warm air is ideal for maternity roots
• Sunny elevations
• Ventilated spaces are ideal for winter hibernation roosts
• Shaded elevations
• Or should we hang bat boxes on outer face?
• Bees and other pollinators?
• Lone bees
• Drill holes in perimeter battens and horizontal board ends
• Various diameters
• Probably not be deep enough
• Build in bee and insect nest box in panels
• Swarms
• Probably discourage
• Avoid honeycomb building inside construction
• Encourage separate weather-boarded hive construction (mobile)
• Or build hives on apex of roofs (not collecting honey)
• Spiders?
• Insect mesh will exclude some and permit others
• But excluding insects will deny them food
• Birds?
• Permitted behind cladding by poor detailing or unfinished work
• House martins
• Fix manufactured nests to cladding below eaves
• Other bird boxes
• Fix to cladding out of reach of cats
• Background
• Solid
• Counter battens to provide ventilation zone
• Battens to accommodate tolerances
• Rainscreen Insulation & DPM
• Insulation and breather membrane or board
• Breathing Sheathing Board
• Airtightness layer
• Spaced
• External walls
• Studs and insulation
• Avoid if possible creates cold bridge through insulation
• Decrement in timber: impact on infrared survey?
• Cold bridge analysis: Psi values
• 400 mm. thick walls
• 400 mm. timber stud and 400 mm. insulation
• psi negligible
• (but metal stud would remain a big problem)
• Studs, insulation and sheathing board
• Sheathing board with insulating properties will reduce cold bridge effect
• External insulation covering the studs wraps up the cold bridges
• Dense cellulose fibre boards
• 2 layer studs and cross battens with insulation in both layers
• Cold bridge minimisation
• 400 mm. thick over all
• Psi value minimised further
• Breather membrane
• Essential to prevent warm air being drawn out of insulation into ventilation space and blown away
• Breathing sheathing board
• Essential to prevent warm air being drawn out of insulation into ventilation space and blown away
• May be essential to hold the insulation in place
• Can have racking strength to add to wall stability
• Can provide additional or substantial thermal insulation for the wall
• Breathing wall construction
• Internal lining
• airtightness layers
• Studs
• Thermal insulation: Hygroscopic with decrement property
• Dense cellulose fibre
• Breathing sheathing board
• Battens
• Weatherboarding
• Pitched roof
• Rafters, eaves & verge framing
• Rafters and boarding (Scottish practice)
• Counter-battens and battens essential
• BRE confirmed that breathing roof construction is also possible
• Rafters and insulation between
• Avoid if possible creates cold bridge through insulation
• Decrement in timber: impact on infrared survey?
• Cold bridge analysis: Psi values
• 400 mm. thick roof
• 400 mm. timber rafters and 400 mm. insulation
• psi negligible
• (but metal rafter would remain a big problem)
• Internal ceiling
• Ceiling joists with thermal insulation
• Ceiling Joist, thermal insulation and board
• Ideally a breather membrane is used over
• Ceiling to flat roof
• Decrement insulation important
• Thermal mass important
• Ceiling to pitched roof with attic space
• Decrement insulation important
• Thermal mass important
• Ceiling to pitched roof with sloping ceiling
• Decrement insulation important
• Thermal mass important
• Ceiling to room in a roof
• At eaves (beyond room)
• Insulated
• Decrement insulation important
• Thermal mass
• Below room
• Insulated
• Decrement less important
• Thermal mass less important
• Floor
• Suspended ground floor
• Suspended upper floor
• Suspended floor over external passage/carport/garage
• Floor joists
• Floor joists and soffit boards
• Rainscreen framing
• See Metal flashings for corrosion issues
• See batten, metal framing and fastenings for corrosion issues
• Access panels and doors
• To service risers
• Water, Gas, Electricity, Telephone, Broadband, Satellite
• RWP, RWHP, SW&VP
• Meters: Electric, Gas, Water
• Gas ventilation issue and Gas Regs.
• Water stop valves, drain cock, outdoor taps,
• Gulley below (low risk of sewer gas)
• Easy replacement areas
• Eaves abutting gable
• Rainwater gutter persistent overflow risk area
• Splash zone
• Detail Design
• General
• Meet service life with minimal maintenance
• 1^st line of defence: Design to reduce risk
• 2^nd line of defence: Durable – sapwood or + preservatives
• Control of moisture
• Generally
• Always assume rain-screen principle
• Cladding largely protects membrane from wind, rain, daylight and sunlight
• Amount of rain penetration depends upon design of cladding
• Open jointing more rain penetration
• Overlapping less rain penetration
• Open cavity should always be provided
• Drain any moisture penetration
• Ventilate to dissipate any internally generated vapour
• Maintain equal moisture content in both faces of boarding
• Avoid distortions
• Minimum 19 mm. wide
• Usually dictated by the batten size (minimum 38 x 38 mm.)
• Minimum 15 mm. at flashings
• Maintain moisture content (MC) below 22%
• No risk of Fungal attack (UK)
• Little risk of Insect attack (UK)
• Risk of Termite attack (Not UK)
• Wetting to higher than 22% will not instigate decay
• Sustained exposure above 22% increases risk of attack
• UK typical ambient humidity and direct exposure to rain unprotected externally
• Not raise MC above 20%
• BS 1186:Part 3 suggests 19%
• Climate change increase?
• Principles
• Avoid contact with porous surfaces
• Avoid contact with wetted non-porous surfaces
• Prevent wood from absorbing moisture
• Particularly the absorbent end grain
• Waterproof membranes or air gaps required
• Protect top edges of vertical boards
• Ventilate bottom edges of vertical boards: 15 mm.
• Ventilate side edges of horizontal boards: 8 – 10 mm.
• Ventilate bottom ends of diagonal boards: 12 mm.
• Sloping flashings to splash away from board ends
• Avoid sealants
• Backgrounds
• Masonry background
• Waterproof membrane not needed
• Other backgrounds
• Waterproof membrane behind battening
• Bases
• 15 mm. clearance above flashings
• Abutments
• 8 – 10 mm. clearance
• 12 mm. clearance from diagonal boarding
• Ensure water runoff cannot enter behind this joint
• Overhangs
• Generally
• Largely protect walls from direct wetting
• Wind driven rain gets everywhere
• Extend the life of surface finishes
• Not affect the durability of the wood
• Unfinished
• Will slow or prevent natural weathering and bleaching
• Result in uneven colouring between shaded and unshaded
• Horizontal surfaces
• Ground, pavement, flat roofs, decking, etc.
• Smooth surface splash higher
• Irregular large gravels disperse splashes
• Water can sit on surface
• Consider permeable surface
• Indirect wetting from splashing
• Greater wetting of lower boards
• Deterioration of surface finishes
• Possible algal growth
• 200-250 mm. clearance advisable
• Allowing for moisture movement (MM)
• General
• Organic material: Moisture Content (MC) varies with environmental conditions
• MC varies:
• Maximum 22% North face winter
• Minimum 10% South face summer
• Higher and lower % are occasionally recorded
• Seasonal variation on one face varies: 6-8%
• Change in moisture content won’t affect strength or durability
• Avoid restraining fixings or tight jointing
• Risk of splitting cupping or bowing
• Excessive moisture movement: T&G can disengage
• May compromise the fixing to the building
• Design to accommodate MM Moisture Movement
• Design in allowances for MM Moisture Movement
• Match MC in use to MC at construction
• UK normal MC range: 12% – 20%
• BS 1186:Part 3 suggests: 13% – 19%
• Aim to obtain timber of 16% mean MC
• Aim to fix timber at __% mean MC
• Design joints to accommodate shrinkage and swelling
• Generally
• Limit board widths to 150 mm. to limit variation in size
• Especially if used Green
• Overlapping
• Overlapping more tolerant and remain watertight
• Open joint
• Open joints more tolerant remain watertight
• Rebated
• Rebated less tolerant and may not remain watertight
• T&G Tongue and Groove boarding
• Limit board widths to preferably 100 mm. maximum 125 mm.
• Tongue uppermost
• T&G less tolerant and may not remain watertight
• Movement in T&G boards can make assembly difficult
• T&G boards movement can lead to tongue splitting off
• Only kiln dried to recommended MC should be used
• Fixing and fasteners to accommodate moisture movement
• Board Widths
• Below 100 mm. single fixed
• Reduce batten spacing
• Up to 100 mm. single fixed
• Shrinkage either side of fastener
• Over 100 mm. double fixing to help them stay flat
• Stresses between fasteners
• Changes in shape
• Moisture content variations
• Natural tendency
• Predictable
• Turn to advantage
• Section cut from tree
• side nearest the heart of the tree expands relatively (heart side)
• side furthest from the heart side shrinks relatively
• edges cup away from the heart side
• Arrange for joints between board to tighten against each other
• Most boards:
• Heart side to face outward when section installed
• Board on board
• Inner board
• Heart side inwards to face building
• Outer board
• Heart side outwards to face away
• Quarter sawn boards have least risk of changing shape
• Uneconomical to use quarter sawn throughout
• Cladding support: battens and counter-battens
• Battens to which boards are fixed
• Battens usually dictate the ventilation zone depth
• (minimum 19 mm.)
• Vertical cladding, Horizontal Battens Size:
• Dictated by board fastener and board thickness
• Nails
• Nails normally driven just below the surface
• allow for timber shrinkage
• avoiding nail becoming proud of surface
• Nails 20 mm. from end of board
• Nails 15 mm. from edge of board
• Spacing: batten spacing dictates.
• Small head or siding nails can pull through soft WRC
• Larger heads recommended for WRC
• Standard Round wire nails:
• 2.5 x thickness of board
• T&G: 19-22 mm. = 48-55 mm.
• Other: 16-19 mm. = 40-48 mm.
• Annular ring-shank nails
• Improved holding power
• 2 x thickness of board
• T&G: 19-22 mm. = 38-44 mm.
• Other: 16-19 mm. = 32-38 mm.
• Pneumatically driven nails
• D shaped heads may not be visually acceptable
• Virtually headless pins are not recommended
• Screws:
• Minimum 2 x thickness of board
• T&G: 19-22 mm. = 38-44 mm.
• Other: 16-19 mm. = 32-38 mm.
• Batten Size:
• Minimum 2 x board thickness
• T&G: 19-22 mm. = 38-44 mm.
• Other: 16-19 mm. = 32-38 mm.
• Minimum: 38 x 38 mm.
• Batten profile:
• Horizontal boarding vertical batten
• Square
• Vertical boarding horizontal batten fixed to counter-batten
• 15 degree sloping top face to throw off water into ventilation cavity
• Vertical board on board horizontal batten
• 15 degree sloping top face to throw water away from sheathing and breather face
• Counter-battens, studs, joists or rafters
• Spacing of nails or screws dictated by this spacing
• Usually fixed vertically or running down slope
• Reduced centres
• Helps reduce tendency for boards to twist, bow or cup
• Green timber cladding
• Centres reduced to 400 mm. (maximum 500 mm.)
• Narrow boards (less than 100 mm.)
• Centres reduced to 400 mm.
• Vertical or horizontal boards
• Not greater than 600 mm. centres
• Diagonal boards
• Vertical or horizontal battens
• Not greater than 400 mm.
• Diagonal battens
• Not greater than 600 mm.
• Counter-batten size:
• To maintain 19 mm. ventilation zone
• Vertical boarding:
• Counter-batten size: 16 x __ mm.
• Perimeter battens
• Omit or reduce thickness of any perimeter battens (top and bottom of horizontal boarding)
• Maintain 19 mm. ventilation zone
• Resource Efficiency
• Reduce waste in design
• Obtain knowledge of what is available: width and length
• Design with available width and length in mind
• Choose species according to preferred design width and length
• Design for Demountability
• Fasteners
• Screws
• Accessible heads
• Corrosion resistant to enable unscrewing later
• Nails: Avoid
• Metal
• Future reuse as screw essential
• Corrosion resistant
• Austenitic stainless steel
• Grade: 304 or 316 (marine grade)
• Corrosion resistant finish
• Susceptible to damage when driving
• Reclaim for reuse
• Care with fixings avoid damaging boards
• Use screwdriver in reverse to remove screws
• Assemble multiple pallets to support lengths
• Strapping to secure, timber strips to protect
• Waste issues
• Hazardous waste (treated or coated)
• Active Virgin timber
• Compostable waste (perishable species)
• Mixed waste (treated or coated)
• Samples & Mock-ups
• Samples
• Require sufficient samples prior to purchase
• Purpose
• Agree visual quality of profile
• Check size of section
• Agree visual quality of timber
• Knots
• Sapwood
• Colour range
• Agree finish: surface texture, transparency, colours, gloss level
• Timing
• In advance of purchase deadline to meet programme
• Programme may include mock-up construction and approval process
• Mock-ups
• Position:
• as if in real building
• Height, distance and viewing angles
• for accurate judgement
• in the real building
• if acceptable, as part of the final works
• Large enough to include:
• Long lengths of timber, butt joints
• Background build-up, framing,
• boundaries, edges
• Internal and external changes of direction,
• Openings,
• Changes in design
• Purpose
• Check interfaces with other trades
• Ensure required quality can be achieved
• Agree acceptable quality if different
• Timing
• In advance of purchase deadline to meet programme
• Drawings
• Standard Details
• Show the proposed construction details (fixed)
• Principle Details
• Show the ideal details (fixed)
• but offer designers some choices about:
• size, profile, species, finishes (unfixed)
• Materials handling and storage
• Materials can be spoiled and repairs may be impossible or unacceptable
• Wasting materials is unacceptable practice
• Risks
• Exposure to excessive wetting
• Exposure to mud splashes
• Exposure to cement slurry splashes
• Damage by foot traffic boot marks
• Damage by impact
• Protection
• Protection is essential in transportation, storage and once installed
• Storage
• Avoid over tight banding
• Protect edges of boards from damage
• T&G vulnerable
• On solid flat (shallow slope to self drain) surface
• Dry concrete suitable
• Lime stabilised soil suitable
• Avoid soil base (mud splashes)
• Away from traffic flows (mud splashes)
• On battens or pallets to prevent contact with soil and ground water
• Batten spacing to prevent deflection of stack or individual boards
• Undercover and ventilate
• Exclude moisture but encourage moisture egress
• Green timber
• Consider stacking with sticks between layers
• Ventilation to reduce moisture content
• Sticks must be clean and dry to avoid stick marking
• Unfinished installation boards
• Special care to keep clean and dry and free from soil and cement splashes and damage
• Sawn finishes impossible to sand to remove marks
• Natural weathering of any marks: long slow process
• Prefinished boards or panels
• Avoid damage of finish
• Avoid touching up as it is difficult to do well
• Colour matching
• Gloss level matching
• Blending in
• Loss of durability compared with factory applied
• Installation
• Moisture content
• At time of installation is important
• As specified
• Check and record immediately before installation
• It may be different to when delivered
• Condemn timber for use on the project if MC drops by _ %
• Heartside arrangement
• Normal boarding
• Symmetrically profiled boards
• If growth rings are visible in cross section of boards
• Ensure heartside is on outer face
• Board on board
• Inner board heartside to face inwards to wall
• Outer board heartside to face outward
• Care with kiln dried and sawn timber this may reverse requirements
• Allow for moisture movement: Expansion
• 2 mm. gap for up to 150 mm. wide T&G
• What gap for larger?
• Allow for moisture movement: Shrinkage
• Green timber will shrink on drying
• Provide less gap
• T&G not suitable for Green Timber
• Open joint setting out should make joints narrower so they are correct once dry
• X mm. per xxx mm.
• Determined by calculation
• Butt jointing boards
• Unfinished timber: 5 mm. gap
• Coated timber: 8 mm. gap
• Always occur on doubled battens
• Random length: add additional batten, length: ≥ 3 x board width
• Expressed joint in panels: add second batten
• Thicker or narrow hardwood boards
• Form lap joint by rebating ends and overlap
• Labour intensive and requires good workmanship
• Nominal and finished sizes
• Allow nominally 6 mm. reduction in section size (3 mm. from each face)
• If cladding is based on nominal size and coordinated with openings
• increase joint sizes to compensate
• Unfinished boards and fasteners
• Drive nail or screw heads flush after initial drying has taken place
• Coated boards
• Arrises
• Removal of sharp square arises will prolong the life of the coating
• Planning chamfers or sanding
• Coating cannot negotiate sharp corners
• Surface tension in liquid coating pulls them back from corners
• Benefits horizontal boards in particular
• fasteners
• Drive nail or screw heads slightly below the surface for slight paint build up
• Application on site
• Minimum of first coat to be applied before installing
• Apply thickly to exposed end grain
• Pre-coating on all faces will even out moisture absorption
• help even out distortion across the section
• Avoid uncoated material showing when shrinkage occurs
• Open joint boarding
• Coat battens as well
• Maintenance
• Unfinished boards
• Unfinished shingles and shakes
• Little or no maintenance
• Surface cleaning from pollution or foliage
• Surface cleaning
• Cleaning agents
• For removal of surface staining or soiling
• For removal of beached surface
• For removal of iron staining in acidic timber
• Stubborn stains may require a clear coating
• Clear coating have low UV resistance
• Will need recoating frequently
• 2-3 years or less
• Wetting stains may benefit from clear coating
• To reduce water uptake
• Only apply after drying out
• Clear coating have low UV resistance
• Will need recoating frequently
• 2-3 years of less
• Test small patch to check appearance
• Life expectancy
• Depends on many factors:
• Level of exposure
• Initial application method
• Factory applied will outlast site applied
• Factors include:
• Tightly controlled process
• Controlled moisture content
• Limiting exposure to UV light before application
• Cleanliness of environment
• Standards of workmanship
• Long life coating may require special preparation for maintenance
• Consult manufacturer of coating and component
• Always check for compatibility of all layers
• Check O&M manuals (Operation and maintenance manuals)
• Do not overcoat micro porous coating with film forming coatings
• If reapplying same coating check preparation rules
• Patchy clear stain will need to be stripped back to bare wood
• Minimise preparation time by maintaining before deterioration sets in
• Hardwoods coating for first time after being left unfinished
• Hardwood vary considerably
• Some are not suitable for coating
• Need for decoration depends on exposure
• The most exposed will require more frequent redecoration
• Less exposed need not be coated at same frequently as exposed
• Survey and determine needs
• Update O&M manuals

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H21      TIMBER WEATHERBOARDING

BACKGROUND INFORMATION

• Environmental Issues
• Forest as Resource
• Support for people
• Home for people
• Medical resource
• Food resource
• Shade grown coffee
• Support Biodiversity
• Home for nature
• Food source for nature
• Food for nature when dead
• Timber
• Biomass Fuel
• Building material Carpentry and Joinery
• Furniture and Cabinet making
• Carbon sink (Carbon Sequestration) when growing
• Consumes Carbon dioxide
• Produces Oxygen
• Mature trees reduce efficiency
• Harvesting of plantation is good if replanting
• Occupants
• Occupation by indigenous tribes
• Occupation by wildlife
• Legality
• Legal ownership of land forest plantation
• Occupation rights
• Legacy
• Clear felling destroys most future opportunities
• Clear felled land rainwater runoff overwhelms rivers
• Runoff deposits soil in river estuaries
• Soil in solution in rivers can starve fish of oxygen
• Soil deposits pollute and kill corals
• Farming chemicals create dead zones in rivers, estuaries and coastal waters
• Plantations
• Plantations can restore status quo and avoid many of these issues
• Plantations likely to be monocultures
• Limited support for biodiversity
• Trees may not be indigenous species
• Coffee, Chocolate, Poppies, Drugs, Soya bean,
• for animal feed or bio-fuels, soap
• recreational drugs
• Resource if maintained
• Medical resource
• Food resource
• Shade grown crops in harmony with forest canopy
• Wildlife habitation/resource
• Indigenous tribes
• Carbon sequestration & oxygen generation
• Selective cropping
• Removal of individual trees can be done
• Leaving forest to heal in relatively short time
• Access roads give farmers access
• Farmers burn and clear fell to make farms for cattle
• A few years in the soil fertility is gone
• Soil erosion after cattle disturbance
• Farmers moves on to repeat process in new location
• Environment Sustainability
• Rapidly renewable coppicing for biomass fuel
• Rapidly renewable forest thinning timber
• for some construction applications
• Renewable tree growing 40 – 100 year cycle
• Use of sun, water and minerals from ground
• Energy for loggers
• Energy for transportation
• Energy for milling and craftsmen
• Energy for shipping and transport
• Factors influencing choice of species
• Local sourcing
• Home grown v imported
• Local employment
• Local economy
• Transport minimised
• Fuel use
• Pollution
• Congestion
• Manufacturing
• Energy
• Emissions
• Simple sawn profiles v profiled
• Energy used
• Waste generated
• Efficient use of resource
• Reduce
• Reuse
• Recycle
• Recovery: Composting v energy from combustion
• Reject Waste: Disposal
• Erection
• Local labour v imported
• Finishes
• None v stained v painted
• Natural v Synthetic
• Plant extract v Petrochemical
• Perfume v VOCs
• Materials:Waste 1:20
• Compostable v Hazardous waste
• Durability
• Durable v Preservatives
• Maintenance
• None v over-coating v stripping and repainting
• Disposal
• Composting of untreated unfinished timber
• Hazardous waste if treated or finished
• Performance in use
• Desired performance
• Service life
• Appearance
• Costs
• Zones of influence
• Sun
• Sundial
• Solar shading in summer
• Solar penetration in winter (deciduous)
• Light
• Shading
• Dappled light
• Colour from translucency of leaves
• Reflection on leaves and wet leaves
• Wind
• Shelter
• Wind noise in leaves and through branches
• Wind shadow
• Rain
• Temporary shelter
• Long term shower
• Dry spot slowly disappears
• Lightning
• Tall trees: lightning magnet
• Root zone
• Water harvesting
• Soil shrinkage
• Building settlement in extreme droughts
• Pavement disruption
• Production
• Pollen drift
• Sap
• Perfume
• Allergic reactions: Hey fever
• Seed drop
• Leaf drop in autumn
• Biodiversity support
• Nectar bar
• Fruit and nuts
• Home for flora and fauna
• Cost plan
• Treated Softwood: £60-69/m2
• Durable Hardwood: £64-75/m2
• Sustainable Definition?
• England
• Domestic
• Code for Sustainable Homes
• Non-domestic
• Pending
• Not England
• Domestic
• BRE EcoHomes
• Others?
• Non-domestic
• BREEAM, etc.
• LEAD
• DREAM
• CEEQUAL
• BRE Green Guide to Specification
• (2002 EcoHomes & BREEAM))
• Treated SW: 2002 A rated
• Durable HW: 2002 A rated
• Reclaimed and reused timber: A rated
• (2008 CfSH Green Guide)
• Treated SW: 2008 A+ rated
• Durable HW: 2008 A+ rated
• Reclaimed and reused timber: A rated
• Timber types
• Coniferous (Softwood)
• Durable softwood
• Green Softwood
• Perishable softwood
• Treatment
• Acidic Softwood (tannin staining/corrosion potential)
• Western Red Cedar
• Deciduous (Hardwood)
• Durable Hardwood
• Green Hardwood
• Perishable Hardwood
• Acidic Hardwood (tannin staining/corrosion potential)
• Oak
• Sweet chestnut
• Timber merchants
• Need to be familiar with numerous issues
• Strength grades (is not enough)
• Quality grades
• Sustainable Forestry Certification
• Chain of custody
• Treatment certification
• H21 Sector
• Manufacturers or suppliers
• Softwood for batten
• Treatment for battens
• Hardwood for battens
• Softwood for boards
• Treatment for boards
• Hardwood for boards
• Decorative coatings
• Fasteners
• Meshes
• Membranes???
• Installers and applicators
• Treatment
• Installation
• Applications
• Maintenance
• Contractors
• Designers

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© GBE GBC GBL NGS ASWS Brian Murphy aka BrianSpecMan **
26th February 2016 – 7th November 2020

Images:

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© GBE GBC GBL NGS ASWS Brian Murphy aka BrianSpecMan **
26th February 2016 – 7th November 2020

See Also:

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More about Timber Weatherboarding

• GBS H21 Timber Weatherboarding (Navigation) G#632
• H21 Timber Weatherboarding (Checklist)  G#11946
• Jargon Buster: H21
• GBE CPD H21 Timber Weatherboarding (Shop) G#11855
• GBS H21 Timber Weatherboarding (RobustSpecW) G#625
• H21 (RSGuidanceNotes)
• H21 (RSAppendix)
• Portfolio: Leapfrog Day Nursery Royal Docks East London (CaseStudy) G#11864
• GBE H21 Timber Weatherboarding (Outline) G#10281 (this page)
• H21 Timber Weatherboarding (Project) G#549 N#569

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GBE Outline

• GBE H21 OutlineFromTRADABook (Outline) DOCX

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GBE CPD

• H21 Timber Weatherboarding (Handout) (CPD)

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GBE Shop

• H21 Timber Weatherboarding (Show) (PDF)

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GBS Robust Specification

• GBS H21 Timber Weatherboarding (Navigation) G#632 
• GBS H21 Timber Weatherboarding (RSW) G#625

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GBE Projects: Information

• H21 Timber Weatherboarding (Project) G#549 N#569

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GBE Data Sets

GBE Shop

• Timber Species Schedule (Shop) G#10656

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GBE 6 Core pages

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© GBE GBC GBL NGS ASWS Brian Murphy aka BrianSpecMan **
19th April 2016 – 7th November 2020

GBE H21 Timber Weatherboarding Outline G#10281 End