![](https://greenbuildingencyclopaedia.uk/wp-content/uploads/2016/05/H21Outline.png)
GBE H21 Timber Weatherboarding Outline
GBE > Encyclopaedia > Code > Outline > G#10281
GBE H21 Timber Weatherboarding Outline
About:
GBE H21 Timber Weatherboarding Outline
Outline:
- Outlines are the essence of the topic in a hierarchical order
- They could become the core of an Expert System or Design and Decision Tool
- The colour coding in the word file highlights:
- Green Environmental Options
- Violet Normal Practice
- Red Missing information
- (in the book it was extracted from)
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
- 1st line of defence: Design to reduce risk
- 2nd 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
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
© GBE GBC GBL NGS ASWS Brian Murphy aka BrianSpecMan **
26th February 2016 – 7th November 2020
GBE H21 Timber Weatherboarding Outline
Images:
© GBE GBC GBL NGS ASWS Brian Murphy aka BrianSpecMan **
26th February 2016 – 7th November 2020
GBE H21 Timber Weatherboarding Outline
See Also:
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
GBE Outline
- GBE H21 OutlineFromTRADABook (Outline) DOCX
GBE CPD
- H21 Timber Weatherboarding (Handout) (CPD)
GBE Shop
- H21 Timber Weatherboarding (Show) (PDF)
GBS Robust Specification
- GBS H21 Timber Weatherboarding (Navigation) G#632
- GBS H21 Timber Weatherboarding (RSW) G#625
GBE Projects: Information
- H21 Timber Weatherboarding (Project) G#549 N#569
GBE Data Sets
GBE Shop
- Timber Species Schedule (Shop) G#10656
GBE 6 Core pages
GBE Suppliers
- FSC Suppliers
GBE Installers
- Company names
GBE Systems
- System Reference: __
GBE Accessories
- Accessory Reference: _
GBE Manufacturer
- Company name
GBE Materials
FSC Timber Suppliers
GBE Collaborative Services
© GBE GBC GBL NGS ASWS Brian Murphy aka BrianSpecMan **
19th April 2016 – 7th November 2020