Thermal insulation existing timber stud external walls (QA) G#1803 N#1690

By February 23, 2015 November 29th, 2018 Code, Encyclopaedia, Q&A

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Thermal insulation existing timber stud external walls QA

Thermal insulation existing timber stud external walls QA


  • An old timber house in Harlow, which is being modernized.
  • Thermal insulation: there is none to the external wall and roof.
  • Wall construction:
    • Horizontal timber weatherboard external skin,
    • Structural stud and big cavity void,
    • inside lath and plaster.


  • Would you have any suggestions for appropriate material to pump or shove into stud zone, to improve performance without condensation?

Answer in stages:


  • Not removing outer cladding and inner lining
  • Lath has lime plaster
  • Weatherboarding has battens and or counter battens and ventilation void and some form of lining to the outer face of the studs


  • No rigid insulation to outer face of studs and then reinstall cladding
  • No rigid insulation to inner face of studs and then reline with lath and plaster
  • A rigid insulation board on outer or inner face would have maintained stud zone void for thermal flanking
  • A rigid insulation board on the outer face would form a good base for counter battened weather boarding


  • little scope or desire for adding membranes without removing and replacing inner or outer faces
  • NB: Membranes: Vapour barriers, breather membranes, airtightness layers etc.
  • would remove all the existing character
  • would be messy, dusty process
  • would cost lots of money to replace removed materials
  • would send materials to landfill if not reused


  • use a vapour permeable insulation:
    • not foamed plastic board,
    • not cellular glass slab or board
    • consider cellulose fibre/flake
    • consider wood fibre
    • consider sheep’s wool
  • use a hygroscopic insulation:
    • not glass, slag or stone fibre
  • Consider injected vapour permeable plant based resin foam insulation (but would require removal of one face)


  • Stud zone:
    • Old property may be imperial spacing studs
    • Even older property random spacing or random stud sections and random shaped studs
    • stud zone not easily accessible


  • Use formless insulation to fit void size or shape
  • cut small holes to access void and repair on completion
  • Injected, blown or poured in insulation
  • Not rigid or stiff insulation
  • Don’t use vapour permeable sprayed plant based foam insulation (requires removal of inner lining or external cladding)
  • Use cellulose flake (recycled newspaper) turbo blown in

Adding Conductivity Thermal Insulation:

  • Lightweight timber frame, timber weatherboarding and lath and lime plaster (assumed)
  • Lightweight fabric, little thermal mass, low solar protection
  • Likely to lead to overheating in summer


  • Use radiation thermal insulation
  • Use medium to high decrement delay insulation
  • Use cellular glass (previously excluded for being too rigid)

Use cellulose fibre/flake blown in


Excel Industries Insulation manufacturer recently went into liquidation


  • Find ex Excel supplier or installers
  • Find out what they are selling or installing now
  • Consider this

© GBE NGS ASWS BrianSpecMan aka Brian Murphy
22nd February 2015 – 29th November 2018

Thermal insulation of existing timber stud external walls QA

© NGS GBE BrianSpecMan aka Brian Murphy
22nd February 2015

Thermal insulation of existing timber stud external walls QA
See Also:

GBE Installers:

Warmcel Installers:

PYC Systems Ltd. Pen Y Lan, Meifod, Powys, SY22 6DA


Cellulose Fibre/Flake Blowers

  • PYC Systems use insulation blowing machines from X-Floc Ltd for all training courses.
  • X – Floc Ltd. SY22 6DA
  • Telephone 01938 500797

GBE Suppliers


GBE Manufacturer:

  • CIUR (Prague) Warmcel
  • Isocell Verdament Besser (Austria)


  • Thermal insulation of existing timber stud external walls (This page) G#1803 N#1690

GBE Installers

Cellulose Fibre/Flake Installers:

GBE Supplier


  • Isocell Verdament Besser (Austria)
  • CIUR (Prague) Warmcell


1320: THEMES

  • Thermal Insulation

705: Words + Phrases

  • Acoustic Insulation
  • Conduction Thermal Insulation
  • Conductivity
  • Decrement Delay
  • Insulation
  • Radient Thermal Insulation
  • Thermal Insulation

GBE Checklist

© GBE NGS ASWS BrianSpecMan aka Brian Murphy
22nd February 2015 – 29th November 2018

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