What to consider before installing Internal Wall Insulation (IWI)

Who can carry out an IWI installation?

What to look for when checking the condition of the property

• Any planning restrictions on the property.
• A full moisture risk assessment following the guidance in BS 5250: 2021 (Management of moisture in buildings. Code of practice)  - learn more about what to consider when carrying out a moisture risk assessment for solid walled properties.
• Local weather conditions including the exposure zone (level of driving rain exposure for the area) and building specific factors such as aspects which are open to prevailing conditions and local sheltering.
• How the work will impact ventilation within the property, as installation of insulation measures can improve airtightness dramatically. Any existing provisions (such as air bricks) will need to be considered and the overall ventilation strategy may need to be improved.
• A survey of the building characteristics (such as whether walls are vapour open or vapour closed) and the materials used in all constructions. For example, fines concrete constructions are not suitable for IWI.
• The condition of external walls, including any cracks in bricks or render, missing pointing and broken guttering or downpipes.
• Suitability of sill overhangs, roof eaves and verge overhangs.
• Planning detailing for penetrations such as pipes, cables or ducts.
• Current insulation levels in neighbouring properties and if other elements (floors, roof or ventilation) could receive upgrades in the future.
• Whether a damp proof course is present and if so, its type, if it is sufficiently raised above paths and that paths run away from the external wall.
• Whether there are any signs of damp (such as mould or peeling paint) or insect attack in any part of the wall, floor or roof construction including the timbers.

How to prepare a property for IWI

• Removing all external and party wall (if being insulated) fittings, including skirting boards, picture rails, wallpaper, gloss/silk emulsion paint, kitchen cabinets, toilets etc.
• Determining whether sockets, radiators or pipes need to be relocated.
• Confirming if window reveals can be insulated if the existing plaster is removed (it is not recommended to leave any wall areas uninsulated).
• Sealing any gaps including around windows and doors and at the perimeter of the room (including junctions between the wall and floor and ceiling).
• Depending on the approach taken and the condensation risk analysis, system specific issues will need to be addressed e.g. with a moisture closed system, there should be a high level of vapour resistance on the warm side of the construction; alternatively with a moisture open system, the insulation thickness may need to be restricted to avoid moisture becoming trapped within the construction beyond its buffering capacity.
• Ensuring there is adequate protection against driving rain. This may include applying cladding, render or a barrier cream to the external face of walls. Or it could mean ensuring that render drips and parapets throw rainwater away from walls and making sure that all penetrations are effectively closed.
• Checking walls are dry (a typical masonry wall should have around 6-8% moisture content by volume).

• Related Products

• Kooltherm K118 Insulated Plasterboard

• Related Articles

• Important clarification to BEIS ‘Retrofit Internal Wall Insulation Best Practice Guide’
• Should I install moisture open or moisture closed internal wall insulation?
• What to consider when assessing moisture risk for IWI applications?