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Wall Insulation: Insulating timber frame walls with weatherboards

Weatherboarding

Vapour open membrane

Mannok Therm Wall / MW PIR boards between studs

Plasterboard

Mannok PIR boards across studs

  • Weatherboarding

  • Vapour open membrane

  • Mannok Therm Wall / MW PIR boards between studs

  • Plasterboard

  • Mannok PIR boards across studs

PIR insulation boards provide excellent thermal performance for the insulation of timber frame dormer cheeks to significantly improve the energy efficiency of the structure and provide greater comfort levels internally. Mannok Therm Wall / MW insulation boards are suitable for application between the studs, and Mannok Therm Wall / MW or Mannok Therm Laminate-Kraft / MLK insulation boards can be used across the studs.

Mannok Therm Wall / MW insulation boards are faced on both sides with a low emissivity composite foil facing which increases the thermal resistance and helps achieve excellent U-values whilst minimising the thickness of insulation required.

Mannok Therm Laminate-Kraft / MLK insulation boards have a kraft paper facing on one side and plasterboard bonded to the other side. This means a separate plasterboard finish is not required so it is quicker and easier to install.

How to insulate timber frame walls with weatherboards with insulation between studs at dormer cheek

1. Precisely cut the Mannok Therm Wall / MW insulation boards to fit snugly between the studs and to window framing.

2. Fit the cut insulation boards between the studs ensuring a tight fit and fill any gaps with expanding polyurethane foam.

3. Timber stud dormer checks require an appropriate vapour control layer to prevent interstitial condensation forming on the back of the sheathing. Where Mannok Therm Wall / MW insulation is fitted only between the studs, install a vapour resistant membrane, such as 500 gauge (125µm) polyethylene, across the face of the studs. Condensation risk analysis should be carried out to ensure the specified AVCL has a sufficiently high vapour resistance for the project. Laps should be sealed and the vapour control layer itself sealed to the vapour control layers in the adjoining elements and to the frame of the dormer window.

4. Where insulation boards are specified between and across the timber studs, install Mannok Therm Wall / MW or Mannok Therm Laminate-Kraft / MLK insulation boards across the inner face of the studs with the edges butted tightly together to ensure a continuous layer of insulation. If using Mannok Therm Wall / MW insulation across the studs, a vapour control barrier may be formed by taping the joints between boards with metalised tape.

5. The junction between the dormer cheek and the roof plane should be designed and constructed so as to minimise thermal bridging. This is most easily achieved where both the dormer and the roof plane have a layer of insulation drawn over the internal faces of the studs and rafters. The insulation on the dormer face can then be carried down the face of the supporting rafter to meet the insulation to the underside of the rafter.

U-Values and Insulation Thickness

Calculate your insulation thickness required based on the desired U-values to be achieved. The below tables show calculations based on a typical construction detail, but you can calculate U-values specific to your construction detail using our free U-value calculator.

Required thickness of Mannok Therm Wall / MW:

89mm x 50mm studs @ 400mm centres. 60mm Mannok Therm Wall / MW between studs.

Mannok Therm Wall / MW between + across studs
89mm stud U-value (W/m2K)
60 + 20 0.27
60 + 25 0.25
60 + 30 0.24
60 + 35 0.23
60 + 40 0.21
60 + 45 0.20
60 + 50 0.19
60 + 60 0.18

100mm x 50mm studs @ 400mm centres. 75mm Mannok Therm Wall / MW between studs.

Mannok Therm Wall / MW between + across studs
100mm stud U-value (W/m2K)
75 + 20 0.24
75 + 25 0.23
75 + 30 0.21
75 + 35 0.20
75 + 40 0.19
75 + 50 0.18
75 + 60 0.16
75 + 70 0.15

140mm x 50mm studs @ 400mm centres. 110mm Mannok Therm Wall / MW between studs.

Mannok Therm Wall / MW between + across studs
140mm stud U-value (W/m2K)
110 + 20 0.19
110 + 25 0.18
110 + 30 0.17
110 + 40 0.16
110 + 45 0.16
110 + 50 0.15
110 + 60 0.14
110 + 70 0.13

U-value results above based upon wall construction shown:

Weatherboarding; 25mm air cavity formed by battens; vapour open membrane; 12mm plywood sheathing; Mannok Therm Wall / MW between timber studs @ 400mm centres; Mannok Therm Wall / MW; AVCL; 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.

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