Timber Frame Walls Insulation Single Layer with Service Void - Technical Detail

Timber Frame Walls Built In
Timber Frame Walls

Tf02: Single Layer Between Studs with Service Void

TF02 Wall Build Up

Earthwool® FrameTherm Rolls & Slabs

  • Friction fitting between timber studs closes joints, preventing airmovement and infiltration through or around the insulation
  • Much quicker to install than rigid foam boards which require very accurate cutting
  • Flexible products which accommodate movements in timber frame ensuring all joints remain closed

Earthwool FrameTherm Rolls and Slabs

  • Non-combustible with a Euroclass A1 reaction to fire rating
  • A+ Generic BRE Green Guide rating


Earthwool FrameTherm Rolls and Slabs are lightweight glass mineral wool products available in a range of thermal conductivities, their manufacture has a very low impact on the environment.

Typical construction

Standard timber frame construction, with a brick outer leaf and a low emissivity vapour control layer to the inner face of the timber frame. A service duct is formed by nailing 50x25mm timber battens to the timber frame before fixing the 12.5mm plasterboard internal lining. Other cladding options, such as tile hanging and timber boarding can be utilised.


Earthwool FrameTherm Rolls and Slabs are dimensioned to suit 90mm or 140mm studs at standard 600mm centres. The nominal thickness of the insulation should not be greater than the nominal stud depth.

Earthwool FrameTherm Rolls and Slabs are friction fitted between studs at standard centres and are self supporting. Generally, two slabs fully fill the space between sole and head plates for standard floor to ceiling height.

A low emissivity vapour control layer is stapled to the studs across the inner face of the wall with the low emissivity side facing internally. 50x25mm vertical timber battens are nailed to the timber


studs before fixing the plasterboard. The vapour control layer should be free from holes, any gaps should be made good, with tears repaired and overlaps sealed with aluminised tape.

A vapour permeable membrane or low emissivity vapour permeable membrane should be stapled or nailed to the sheathing board in accordance with the manufacturers instructions. It should be lapped so that each joint is protected, with upper layers lapped over lower layers to shed water away from the sheathing board.

Generally, horizontal laps should be at least 100mm wide and the membrane should extend below the lowest timber member. Vertical laps should be at least 150mm and be staggered.


Thermal performance

  • Earthwool FrameTherm Roll 40 – 0.040 W/mK.

  • Earthwool FrameTherm Slab 38 – 0.038 W/mK

  • Earthwool FrameTherm Roll/Slab 35 – 0.035 W/mK

  • Earthwool FrameTherm Roll/Slab 32 – 0.032 W/mK.

Fire performance

Earthwool FrameTherm Rolls and Slabs are classified as Euroclass A1 to BS EN 13501-1.

Please contact Knauf Insulation Technical Support Team for calculations that include specific products.


Typical junction of external and party wall

TF02 Typical junction of external and party wall

Typical specification

External wall panels to be insulated between studs using Earthwool FrameTherm Rolls* or Slabs* - 40*/38*/35*/32*/ mm thick.

Form service void with 50x25mm timber battens as shown on the drawings.

Insulation to be cut as necessary and friction fitted between studs. The vapour permeable membrane stapled*/nailed* to the sheathing and extending below the lowest timber member. (*delete as appropriate).

Cavity barriers and fire stops should be installed as required to meet the Building Regulations.

Alternatively, consult the National Building Specifications, Standard version clause/clauses P10/210 and 310.

Knauf Insulation specification clauses can be downloaded from our NBS Plus page.

Typical U-values for pre-fabricated timber framed walls with a service void and insulation between the studs

Thickness (mm)Low E MembraneVaour Permeable MembraneProductMasonry Outer Leaf (W/m2K)Tile/Timber Clad Outer Leaf (W/m2K)
140  Earthwool FrameTherm 320.190.22
140  Earthwool FrameTherm 350.200.23
140  Earthwool FrameTherm 380.210.24
140  Earthwool FrameTherm 400.210.25
140  Earthwool FrameTherm 320.220.25
140  Earthwool FrameTherm 350.230.26
140  Earthwool FrameTherm 380.240.28
140  Earthwool FrameTherm 400.250.28
90  Earthwool FrameTherm 320.250.30
90  Earthwool FrameTherm 350.260.31
90  Earthwool FrameTherm 380.260.32
90  Earthwool FrameTherm 400.270.33
90  Earthwool FrameTherm 320.290.35
90  Earthwool FrameTherm 350.310.37
90  Earthwool FrameTherm 380.320.38
90  Earthwool FrameTherm 400.320.39

Notes: Timber bridging is assumed as 15% and the stud depth is taken to be the same as the thickness of insulation specified. Thermal conductivity of timber studs is 0.12W/mK. Ventilated low emissivity airspace assumed to increase the R-value of the cavity to 0.29 m2K/W[ using Protect VC Foil VCL and unventilated low emissivity airspace assumed to increase R-value of cavity to 0.77 m2K/W using TF 200.

Find out more about Timber Frame Walls