Timber Frame Walls Insulation Blown-in Insulation - Technical Detail

Timber Frame Walls Built In
Timber Frame Walls

Tf04: Blown in Insulation, Between Studs

Knauf Insulation Timber Frame TF04

Supafil® Frame

  • Fully fills the timber stud void, preventing air movement and infiltration through or around the insulation
  • Installed quickly between studs of any width with no product wastage
  • Installed by trained and approved technicians monitored by the BBA

Supafil® Frame

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


Supafil® Frame blowing insulation is an unbonded glass mineral wool which is blown into the cavities between the frames in timber frame walls. It requires no mixing on site and is dry when installed, adding no water to the building.

Supafil® Frame blowing insulation is the insulation component of the Supafil® Frame Blow-in-Blanket System. This system is installed by a network of nationwide approved installers. The Blow-in-Blanket system also includes Supafil® Veil that retains the insulation in the frame cavity during the blowing process and before the wall is lined with the vapour control layer and plasterboard.

Typical construction

Inner leaf comprising 12.5mm standard plasterboard, vapour control layer, Supafil® Frame Blow-in-Blanket System consisting of the Supafil® Veil and Supafil Frame blowing insulation blown between studwork, plywood


or OSB sheathing and a vapour permeable membrane. A 50mm cavity separates the timber frame from the outer leaf, typically of brick.


The Supafil® Veil layer is stapled across the entire wall area creating discrete cavities of each stud void. A hole is then cut in the netting just large enough to accommodate the nozzle of the Supafil Frame Blow-in-Blanket System.

The nozzle is inserted into the cut and the cavity is filled with Supafil® Frame blowing insulation. The Supafil® Frame Blow-in-Blanket System includes sensors that determine when the cavity has been filled to the required density and cuts off the flow automatically. Continue filling all the cavities until the entire wall area is insulated.

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 tears repaired and overlaps and apertures for services effectively sealed. Particular care is necessary around electrical boxes.

A vapour permeable membrane or a low emissivity vapour permeable membrane should be stapled or nailed to the sheathing board in accordance with 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. 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

Supafil® Frame blowing insulation has a thermal conductivity of 0.033 W/mK.

Fire performance

Supafil Frame blowing insulation is classified as Euroclass A1 to BS EN 13501-1.

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

✔  Installed by approved installing technicians

Typical junction of external and party wall

Typical specification

External wall panels to be insulated between studs using Supafil Frame. 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. 

The first run of wall ties to be located at 600mm centres horizontally at a level to be determined by the specifier. Subsequent runs of wall ties to be at not more than 900mm centres horizontally (or as otherwise required by the structure) and at 450mm vertically.

All work under construction must be protected overnight and during adverse weather conditions in accordance with BS EN 1996-2:2006. 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 Supafil Frame

Stud Thickness (mm) Product Vapour Permeable Membrane  Masonry Outer Leaf (W/m2K) Tile/Timber Clad Outer Leaf (W/m2K)
140 Supafil® Frame Standard 0.27 0.29
140 Supafil® Frame Low Emissivity 0.23 0.27
200 Supafil® Frame Standard 0.20 0.21
200 Supafil® Frame Low Emissivity 0.17 0.20

Notes: U-values calculated assuming Supafil® Frame installed with a density of 30Kg/m³ and having a thermal conductivity of 0.033 W/mK. 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. 9mm sheathing and 12.5mm Standard wallboard internal finish. 

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