Timber Frame Walls Insulation Blown-in Insulation - Technical Detail

Timber Frame Walls Built In
Timber Frame Walls

Tf05: Blown in Insulation, Between Studs

Knauf Insulation Timber Frame Wall Blown insulation

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

Earthwool FrameTherm Rolls and Slabs

  • 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 an insulation netting layer 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 Frame netting layer and Supafil Frame blowing insulation blown between studwork, plywood


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


The Supafil Frame netting 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 0.034 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 junction TF05 Timber Frame Walls

Typical specification

External wall panels to be insulated between studs using Supafil Frame Blow-in-Blanket System. 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. All external walls to be insulated during construction by partially filling the cavities with Earthwool DriTherm Cavity Slab 32 Ultimate TBCmm thick.

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 5628: Part 3: 2005. 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

Timber Studs filled with:Thickness (mm)Standard MembraneMasonry Outer Leaf (W/m2K)Tile/Timber Clad Outer Leaf (W/m2K)
Supafil Frame 20030.210.22
Supafil Frame 14030.270.29
Supafil Frame 200Low E0.180.21
Supafil Frame 140Low E0.230.28

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 0.29m2K/W and unventilated.

Find out more about Timber Frame Walls