Applications
• Where external walls are poorly insulated.
• Where external walls are deteriorating or are insufficiently weather-tight, causing damp, draughts and heat loss.
• Installing external insulation would adversely effect the appearance of the building.
• Where the building is in a conservation area.
NB
• The wall insulation methods illustrated below are for general guidance only. The performance of products and methods of fixing vary. When specifying, confirm with the product manufacturer their installation methods and expected performance.
• Beware when combining different insulation materials. Check with respective manufacturers regarding possible condensation risks.
Insulation applied directly to the wall
Application
• The relatively small depth of the build up makes this solution particularly suitable for applications where internal floor area is at a premium.
• Where walls are dry.
Preparation:
• Ensure that the wall is dry.
• If not defective, the background plaster can be retained. If the plaster is removed, a parge coat is recommended to seal the masonry, rendering it airtight
• If maintaining existing plaster and applying plasterboard thermal laminate using adhesive or plaster dabs, strip any gloss paint or vinyl wallpaper.
Fixing methods:
• Adhesive: Using plaster adhesive as recommended by the board manufacturer, this method is applicable where the background plaster is smooth, level and dry. The adhesive is applied to the board in strips. To prevent air movement behind the board, it is important to seal the perimeter and the surround of any openings with a continuous band of adhesive. In addition to adhesive, boards incorporating plastic insulation should be secured using screw fixings.
• Plaster dabs: Using plaster dabs, the plasterboard thermal laminate is attached directly to the background wall. As for the adhesive, plaster is applied to the board perimeter to seal prevent air leakage. Mechanical fixing should also be included as for adhesive applications (above).
• Timber batters or metal furrings: Used where the background is uneven or has been previously damp. Treated timber battens are screwed or nailed to the wall.
Insulation materials and typical U-values*
| Insulation material | Thickness of insulation | |||
| 50mm | 100mm | 125mm | 150mm | |
| Expanded polystyrene | 0.55 | 0.33 | 0.28 | 0.24 |
| Polyurethane / Phenolic foam / Polyisocyanurate | 0.65 | 0.39 | 0.33 | 0.28 |
| Foamed glass (with plaster finish) | 0.57 | 0.33 | 0.28 | 0.24 |
* Values assuming construction: 215mm existing solid brickwork with plaster finish (U = 2.1W/m2K) (Source: EST)
Insulation fitted between battens
Application:
• Where space permits, the combination of battens and rigid / semi-rigid insulation can provide optimum thicknesses of insulation.
Preparation:
• Ensure that the wall is dry.
• If not defective, the background plaster can be retained. If the plaster is removed, a parge coat is recommended to seal the masonry, rendering it airtight.
Fixing methods:
Timber battens, at least the thickness of the insulation, are screwed or nailed to the wall (there are proprietary timber battens available that include a cork laminate to reduce thermal bridging).
Insulation cut to fit tightly between the battens.
A vapour protection membrane is fitted across the face of the studwork and covered on the internal face by plasterboard or alternatively a service zone and plasterboard.
Insulation materials and typical U-values*
| Insulation material | Thickness of insulation | |||
| 50mm | 100mm | 125mm | 150mm | |
| Mineral wool1 | 0.55 | 0.39 | 0.33 | 0.28 |
| Polyurethane / Phenolic foam / Polyisocyanurate2 | 0.30 | 0.18 | 0.33 | 0.28 |
* Values assuming construction: 215mm existing solid brickwork with plaster finish (U = 2.1W/m2K)
1 Source: EST; 2 Source: Celotex
Improving the u-value and reducing thermal bridging
Battens with plasterboard thermal laminate fixed to the face of the battens. This has the effect of reducing thermal bridging through the timber whilst offering the potential to increase the thickness of insulation.
Separate inner lining
Application:
• Appropriate for where the existing wall is subject to rain penetration.
• Appropriate for where the existing wall is distorted (bowed or uneven)
Preparation:
• Ensure that the new cavity is at least 30mm wide and is ventilated top and bottom
• Ensure that new timber studs are treated with preservative, particularly on exposed end grains.
Fixing:
The timber studwork (usually at 600mm centres, possibly increased to 400mm where heavy internal fittings are hung on the wall) is braced between the floor and the ceiling.
Various insulation materials are possible, but all must fit tightly between the studs.
A vapour protection membrane is fitted across the face of the studwork and covered on the internal face by plasterboard or alternatively a service zone and plasterboard.
Air tightness
Sealing penetrations;
Vapour membranes once installed are vulnerable to tearing and leakage through the actions of other building trades. Penetrations must be made good through rigorous on-site monitoring. Air leakage through service penetrations can be prevented by the use of flexible grummets attached to the membrane; tears in the fabric can be mended using tapes recommended by the membrane manufacturer.
Forming a service zone
To avoid penetrating the Vapour Protection Layer entirely, battens can be added to the room side of the membrane to form a small cavity between the membrane and the plasterboard. Services such as pipes and wiring can be run through this zone.
Sealing perimeter conditions
To avoid penetrating the Vapour Protection Layer entirely, battens can be added to the room side of the membrane to form a small cavity between the membrane and the plasterboard. Services such as pipes and wiring can be run through this zone.
Thermal bridging
Insulating the reveals
Window and door reveals are common areas of thermal bridging unless insulated. Return the plasterboard laminate into the reveal to butt the window frame. Ensure that the butt-joint is sealed. In many cases there will be insufficient space to accommodate the thickness of insulation used elsewhere - in which case it might be necessary to strip off the existing plaster to the reveal and also reduce the thickness of insulation.
In window openings, ensure that the sill board is insulated and is of sufficient size to cover the wall lining.
Publications
Building Research Establishment (BRE)
• Thermal Insulation: Avoiding Risks, C.Stirling, BRE Press, 2001
• Installing Thermal Insulation, BRE Press, 2006
Standards
British Standards Institute (BSI)
• British Standards associated with wall insulation (.doc)
Further information
• Insulation materials compared
• Insulated Render & Cladding Association
• TRADA
• National Insulation Association
• British Urethane Foam Contractors Association
Insulation wall lining products on GreenSpec
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