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

Solid stone wall

Existing plaster finish

Plaster dabs

Adhesive strip

Mannok Therm Laminate-Kraft / MLK PIR insulated plasterboard

Internal finish

Insulating a solid masonry wall can be done by the fitting of insulated plasterboard fixed by adhesive dabs to ensure a continuous layer of insulation on the interior of the wall’s surface. Commonly used as a method of insulating walls in retrofit projects, using PIR insulation boards with a plasterboard finish eliminates the need for an additional layer of plasterboard to finish.

Fixing the insulation boards using adhesive dabs is only suitable for masonry walls which are even and free from moisture. It is not suitable for uneven surfaces or walls with a risk of moisture penetration, such as timber frame or steel frame construction.

Mannok’s insulated plasterboard, Mannok Therm Laminate-Kraft / MLK  is a high performance, fibre free insulated board, with a kraft paper facing on one side and plasterboard bonded to the other side which is suitable for fixing using dot-and-dab adhesive or mechanical fixings.

How to insulate solid walls with internal dry lining: insulation boards fixed by dabs

1. Prepare the wall surface for 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. Measure and cut the insulation boards to allow for a 15mm clearance gap at the floor and ceiling joints.

3. Apply adhesive around the perimeter of the wall and around any openings such as windows and doors.

4. Apply the adhesive dabs directly to the wall in vertical rows. Each dab should be around 250mm long and minimum 50mm thick. Enough dabs should be applied to the wall to ensure a minimum of 20% of the insulation surface area will be fixed to the dabs.

5. Fix Mannok Therm Laminate-Kraft / MLK insulation boards to the wall with the edges are tightly butted together to ensure continuity of insulation and avoid thermal bridging issues.

6. Secure the insulation boards with 2 secondary mechanical fixings at mid height and at a minimum of 15mm from the board edge. The screws which fix the Mannok Therm Laminate-Kraft / MLK insulation to the masonry structure should be selected to minimise heat loss. U-value calculations for the wall should account for the additional heat loss resulting from mechanical fasteners.

7. Seal the 15mm clearance gap at the floor and ceiling with a continuous strip of drylining adhesive.

U-Values and Insulation Thickness

The required thickness of Mannok Therm Laminate-Kraft / MLK insulation boards will be dependent on the U-Values to be achieved. For project specific U-values, use our U-value calculator.

Required thickness of Mannok Therm Laminate-Kraft / MLK:

Masonry Type
215mm Brick 500mm Stone 215 Dense Block 215 Aircrete Thermal Block (B5)
Thickness (mm) U-value (W/m2K)
37.5 0.55 0.53 0.58 0.38
41.5 0.50 0.48 0.52 0.35
50.5 0.41 0.40 0.43 0.31
62.5 0.34 0.33 0.34 0.27
72.5 0.29 0.29 0.30 0.24
82.5 0.26 0.25 0.27 0.21
92.5 0.23 0.23 0.24 0.20
102.5 0.21 0.21 0.21 0.18
112.5 0.19 0.19 0.20 0.17

U-value results above based upon wall construction shown:

Masonry (see table); 15mm plaster; plaster dabs; Mannok Therm Laminate-Kraft / MLK with 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