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

Timber Frame Walls Built In
Timber Frame Walls

Tf03: Between Studs with Insulated Plasterboard

Knauf Insulation 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 Insulated Plasterboard improves thermal performance.

Knauf Insulation FrameTherm® Rolls and Slabs

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


Knauf Insulation 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 Insulated Plasterboard is comprised of 9.5mm taper edged plasterboard bonded to a Polyisocyanurate (PIR) board.

Typical construction

A timber frame stud wall infilled with Knauf Insulation FrameTherm® and faced internally with Knauf Insulated Plasterboard and externally with plywood sheathing, or OSB, 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

Knauf Insulation FrameTherm® Roll 40 – 0.040 W/mK 
Knauf Insulation FrameTherm® Roll – 0.035 W/mK 
Knauf Insulation FrameTherm® Roll/Slab 32 – 0.032 W/mK

The insulation component of Knauf Insulated Plasterboard has a thermal conductivity of 0.023W/mK and the plasterboard has a thermal conductivity of 0.19W/mK. You can contact Knauf UK here.


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.

Knauf Insulation 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 Insulated Plasterboard 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.

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Reaction to Fire performance

Knauf Insulation FrameTherm® is classified as Euroclass A1 to BS EN 13501-1 which means that the product does not contribute to the development of a fire or flame spread

Building Regulations state that external walls in domestic construction shall achieve half hour fire resistance. To meet the half hour requirement using Knauf Insulated Plasterboard it will be necessary to line the wall with 12.5mm plasterboard before installing the Knauf Insulated Plasterboard. 

Typical junction of external wall and upper floor

TF03 With Insulated Plasterboard

Typical specification

External wall panels to be insulated between studs using Earthwool FrameTherm Roll*/ Slab* 40*/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

Stud Thickness (mm) Product with 35mm Knauf Insulated Plasterboard with 50mm Knauf Insulated Plasterboard with 65mm Knauf Insulated Plasterboard with 75mm Knauf Insulated Plasterboard
140 Knauf Insulation FrameTherm® 32 0.21 0.18 0.17 0.16
140 Knauf Insulation FrameTherm® 35 0.22 0.19 0.17 0.16
140 Knauf Insulation FrameTherm® 40 0.23 0.20 0.18 0.17
90 Knauf Insulation FrameTherm® 32 0.27 0.24 0.21 0.19
90 Knauf Insulation FrameTherm® 35 0.28 0.24 0.22 0.20
90 Knauf Insulation FrameTherm® 40 0.30 0.26 0.23 0.21

Notes: Default timber fraction BR443:2019. Timber studs fully filled with Knauf Insulation FrameTherm® Rolls. Thermal conductivity of timber studs is 0.12 W/mK. Calculated with masonry outer leaf and 50mm unventilated residual cavity with airspace resistance of 0.180m²K/W and 9mm sheathing board. Knauf Insulated Plasterboard comprises 9.5mm plasterboard facing at 0.19 W/mK where the remainder of the thickness is insulation with thermal conductivity 0.023W/mK. 

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