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Internal Wall Insulation
Installing Internal Wall Insulation (IWI) can help to improve the thermal performance of a building. It can be particularly helpful to refurbish solid walled properties.
Why choose internal wall insulation?
Internal wall insulation is applied to the internal walls of a building and can be mechanically fixed or adhesively bonded to the wall. It is ideal for retrofit projects and improving the thermal performance of existing solid wall buildings, particularly if you cannot insulate a building externally.
Can internal wall insulation cause damp?
When designed and installed correctly, internal wall insulation should not lead to damp problems.
Before carrying out work, installers should carry out a pre-assessment of the building to ensure it is in good condition and dry. Installers should carefully plan and design the installation with close attention paid to junctions around features, such as windows and doors. They will also need to look carefully at junctions around the floor and ceilings and any penetrations such as joists or pipework to ensure a continuous layer of insulation and vapour protection.
As internal wall insulation applications will mean that external walls remain cold at all times, there may be cases where installers advise that solid wall insulation cannot be fitted. This may be the case where the materials used to construct the wall are particularly porous and planning restrictions prevent effective external weatherproofing.
To find an installer for your project, take a look at the Trustmark website. Trustmark is the only Government endorsed quality scheme that promotes reputable tradespeople.
What internal wall insulation systems are available?
Internal wall insulation systems can be either 'moisture open' or 'moisture closed'. Whether to use moisture open or closed materials is dependent on the specifics of a project, including its use, location, construction, condition, ventilation, moisture load and level of heating. A full assessment and development of a plan for improvement is crucial.
Moisture open systems, such as wood fibre, can allow moisture to pass in and out of the wall, preventing them from being saturated and allowing the construction to dry more easily. However, they still rely on heat escaping from the property to help evaporate moisture within the wall. This means that walls must typically be insulated to a lower level than might be preferred. These systems can also be unsuitable where the walls are likely to be exposed to severe weather conditions such as driving rain.
Moisture closed systems, such as our Kooltherm K118 Insulated Plasterboard, work on the principle of occlusion. This ensures that moisture doesn’t get trapped within the wall construction. The external leaf is designed to prevent driving rain entering the construction and a vapour control layer should also be installed internally to prevent condensation forming behind the insulation layer. A condensation risk analysis can be used to then determine whether a construction in a particular location can handle any residual interstitial condensation that might form. As moisture closed internal wall insulation systems are not reliant on internal heat to warm walls, more thermally efficient insulation specifications can be used.
For more information, see our article on moisture open or closed internal wall insulation.
Do Kingspan Insulation have a product suitable for internal wall insulation systems?
Yes, our Kooltherm K118 Insulated Plasterboard can be either mechanically fixed or adhesively bonded and provides insulation, drylining and vapour control in one board. It can be used with solid stonework or brickwork, with or without an existing lining. Kooltherm K118 has a thermal conductivity of just 0.019 W/mK - making it one of the thinnest commony used insulants for internal walls. This makes it ideal for maximising the internal space of a room when installing internal wall insulation.
On this page you will find a number of useful links to help with your project, including installation advice and where to buy Kooltherm K118.
If you are a homeowner don't forget to take a look at our Homeowner Hub where you can find a wealth of advice and support for your project!
Need more information?
Ezy Fit design and sell internal wall insulation systems. They can provide you with support on which insulation system is right for your home, and can point you in the direction of approved installers.
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Page updated 20/02/2026