Timber Frame Walls Insulation Single Layer with Insulated Lining - Technical Detail

Timber Frame Walls Built In
Timber Frame Walls

Tf03: Between Studs with Insulated Lining

Knauf Insulation Built Up Timber Frame Wall insulation Glass Mineral Wool.

Earthwool® FrameTherm Rolls & Slabs

  • Friction fitting between timber studs closes joints, preventing air movement 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
  • Inclusion of Knauf PIR laminate improves thermal performance

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.

Knauf PIR Laminate* is comprised of 9.5mm taper edged plasterboard bonded to a Polyisocyanurate (PIR) board.

*Knauf PIR Laminate is available from Knauf Drywall. Please find contact details for Knauf Drywall here.

Typical construction

A timber frame stud wall infilled with Earthwool FrameTherm and faced internally with Knauf PIR Laminate and externally with plywood sheathing and a vapour permeable membrane. The use of a thermal laminate improves the thermal performance and reduces thermal bridging through the timber studs. A 50mm cavity separates the timber frame from the outer leaf, typically of brick.


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

The insulation component of Knauf PIR Laminate has a thermal conductivity of 0.023 W/mK and the plasterboard has a thermal conductivity of 0.19W/mK.


Knauf Insulation products are dimensioned to suit studs of 90 or 140mm at standard 600mm centres. The nominal thickness of the insulation should not be greater than the nominal stud depth.

Earthwool FrameTherm is friction fitted between studs at standard centres and is self-supporting. A vapour control layer is stapled to the studs across the inner face of the wall before fixing the plasterboard. The vapour control layer should be free from holes, any gaps should be made good with any tears repaired and overlaps and apertures for services effectively sealed. Particular care is necessary around electric sockets and boxes.

Subsequently, Knauf PIR Laminate is screwed to the timber frame at maximum 150mm centres. The boards are taper edged and should be finished using standard drylining techniques.

A vapour permeable membrane should be stapled or nailed to the sheathing board at maximum 500mm centres. It should be lapped so that each joint is protected, with upper layers lapped over lower layers to shed water away from the sheathing. 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.

For more information on installation of our products, contact our Technical Support Team today.

Contact Technical Support

Fire performance

Earthwool FrameTherm is classified as Euroclass A1 to BS EN 13501-1.

Building Regulations state that external walls in domestic construction shall achieve half hour fire resistance. To meet the half hour requirement using Knauf PIR Laminate it will be necessary to line the wall with 12.5mm plasterboard before installing the Knauf PIR Laminate. (CHECK WITH KNAUF UK)


Typical junction of external wall and upper floor

Typical junction of external wall and upper floor

Typical specification

External wall panels to be insulated between studs using Earthwool FrameTherm Roll*/ Slab* 40*/38*/35*/32*mm thick.

The wall panels to be lined internally with Knauf PIR Laminate, TBCmm thick with integral 9.5mm plasterboard screwed to the timber studs at maximum 150mm centres.

A 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 and K10/205

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

Typical U-values for pre-fabricated timber framed walls with an internal lining

Thickness (mm)Knauf PIR Laminate Thickness (mm)ProductMasonry Outer Leaf (W/m2K)Tile/Timber Clad Outer Leaf (W/m2K)
14050Earthwool FrameTherm 320.170.18
14050Earthwool FrameTherm 350.180.19
14050Earthwool FrameTherm 380.180.19
14050Earthwool FrameTherm 400.190.20
14035Earthwool FrameTherm 320.200.21
14035Earthwool FrameTherm 350.200.22
14035Earthwool FrameTherm 380.210.21
14035Earthwool FrameTherm 400.220.23
9050Earthwool FrameTherm 320.220.23
9050Earthwool FrameTherm 350.220.23
9050Earthwool FrameTherm 380.230.24
9050Earthwool FrameTherm 400.230.25
9035Earthwool FrameTherm 320.250.27
9035Earthwool FrameTherm 350.260.28
9035Earthwool FrameTherm 380.270.29
9035Earthwool FrameTherm 400.280.30

Notes: Studs assumed to be 38mm wide at 600mm centres (allowances for sole plates etc, give a 15% bridging area for the timber). Stud depth is taken to be the same as the thickness of insulation specified. Thermal conductivity of timber studs is 0.12W/mK. Plywood thickness = 12mm

Find out more about Timber Frame Walls