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

Knauf Insulation Timber Frame TF02

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

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.

Typical 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.


Knauf Insulation 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.

Knauf Insulation 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

  • Knauf Insulation FrameTherm® Roll 40 – 0.040 W/mK.

  • Knauf Insulation FrameTherm® Roll 35 – 0.035 W/mK

  • Knauf Insulation FrameTherm® Roll/Slab 32 – 0.032 W/mK.

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


Typical junction of external and party wall

Typical specification

External wall panels to be insulated between studs using Knauf Insulation FrameTherm Rolls* or Slabs* - 40*/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 timber framed walls with single layer insulation between studs and low emissivity breather membrane and service void 

Stud Thickness (mm) Product Masonry Outer Leaf (W/m2K) Cavity Unventilated Tile/Timber Clad Outer Leaf (W/m2K) Cavity Ventilated
140 Knauf Insulation FrameTherm® Roll 32 0.19 0.22
140 Knauf Insulation FrameTherm® Roll 35 0.20 0.23
140 Knauf Insulation FrameTherm® Roll 40 0.21 0.25
90 Knauf Insulation FrameTherm® Roll 32 0.25 0.29
90 Knauf Insulation FrameTherm® Roll 35 0.25 0.31
90 Knauf Insulation FrameTherm® Roll 40 0.27 0.32

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, Ventilated low emissivity airspace assumed to increase the R-value of the cavity to 0.29m²K/W for tile/ timber clad and 50mm unventilated low emissivity airspace assumed to increase R-value of cavity to 0.77m²K/W for masonry outer leaf. Low emissivity airspace assumed to increase R-value of service void to 0.78m²K/W. 9mm sheathing and 12.5mm Standard wallboard internal finish. 

Contact our TST Team Today