Wall Insulation: Insulating solid walls with internal dry lining – insulation boards fixed by battens

Solid stone wall

Existing plaster finish

Mannok Therm Wall / MW PIR insulation boards


Internal finish

The fitting of internal wall insulation can greatly improve the thermal performance in older buildings where solid walls are uninsulated. Insulating solid walls with internal dry lining is a common method of improving a building’s energy performance which is generally used in retrofit projects.

Insulating the walls in this way will also cut down on draughts through the walls and windows giving an overall more comfortable environment and significantly reducing energy costs.

Insulating an existing wall changes the heat and moisture patterns in the wall, so it is vital to carry out condensation risk analysis before undertaking any work on site.

It is essential to ensure the detailing and fitting takes account of water vapour and condensation risks to avoid issues with damp. Any existing problems with damp should be fixed before any work commences.

Mannok Therm Wall / MW insulation boards are high performance PIR insulation boards with a rigid thermoset insulation core, faced on both sides with a low emissivity composite foil facing. These foil facings increase the thermal resistance, therefore improving the overall thermal performance and U-values achievable.

How to install solid wall internal insulation: internal dry lining fixed by battens

1. Ensure the surface of the existing wall is prepared correctly for the fitting of the insulation layer by removing existing skirting, picture rails and window boards, as well as any wall coverings with high vapour resistance, such as vinyl wallpaper or gloss paint.

2. Fit the Mannok Therm Wall / MW insulation boards to the internal surface of the walls, ensuring the insulation boards are butted tightly together to form a continuous layer of insulation.

3. To minimise the risk of condensation the joints between Mannok Therm Wall / MW boards should be taped with metalised tape to form an AVCL which will prevent moisture from the building interior condensing on the cold side of the insulation.

4. Fix the treated timber battens to the insulation layer at 400mm centres using appropriate mechanical fixings. Mechanical fixings which penetrate the insulation boards result in additional heat loss. The screws which fix the battens and Mannok Therm Wall / MW insulation to the wall should be selected to minimise the additional heat loss.

5. Additional battens should be fixed to support cupboards, shelves and other fittings.

6. Fix the internal plasterboard layer to the timber battens without penetrating the insulation boards.

Calculating insulation thickness and U-values

Below are U-value calculations based on a number of typical wall constructions. The thickness of insulation will be dependent on the desired U-value. To calculate U-values specific to your wall construction, use our free online U-value calculator.

Required thickness of Mannok Therm Wall / MW

Mannok Therm Wall / MW insulation fixed by timber battens @ 400mm centres

Masonry Type
215mm Brick 500mm Stone 215 Dense Block 215mm Aircrete Thermal Block (B5)
Thickness (mm) U-value (W/m2K)
25 0.44 0.43 0.47 0.32
30 0.41 0.40 0.43 0.30
40 0.35 0.34 0.37 0.27
50 0.29 0.29 0.30 0.24
60 0.26 0.26 0.27 0.21
70 0.23 0.23 0.24 0.19
80 0.21 0.21 0.22 0.18
90 0.19 0.19 0.20 0.17
100 0.18 0.17 0.18 0.15

U-value results above based upon wall construction shown:

Masonry (see table); 15mm plaster; Mannok Therm Wall / MW; 25mm cavity; 12.5mm plasterboard. Calculations performed to BS EN ISO 6946, taking account of repeating thermal bridges.

Need technical support?

For help and advice on any of our products and how they might fit your needs please contact our Technical by Mannok team.

  • Floor Insulation
  • Pitched Roof Insulation
  • Flat Roof Insulation
  • Wall Insulation