Internal wall insulation is a great option in properties where external wall insulation is not practical or permissible; for example in listed buildings, conservation areas, or in blocks of flats.
What is Internal Wall Insulation?
Internal wall insulation involves the application of insulation to the interior face of external walls in order to improve the thermal performance of the property.
Internal wall insulation can, however, be disruptive and require the removal and re-fixing of items such as electrical switches, radiators and kitchen units, so you need to be sure it is the best insulation solution for your home. Creating an airtight layer is vital, so awkward areas, such as reveals and floor voids, require particular care.
Figure 1: Internal wall insulation being installed.
Achieving U Values and Airtightness with Internal Wall Insulation
The U value of a material is the rate at which heat (in watts) is lost through each square meter of the surface. A lower figure means better thermal performance.
An uninsulated cavity wall will have a U value of around 1.5W/m² and there will also be a relatively high level of cold bridging due to the cavity ties
A solid 225mm brick wall will be around 1.9W/m²
A solid stone wall 1.7W/m² to 1.4W/m² (depending on the thickness)
Current Building Regulations require a maximum U value of 0.3W/m² and realistically 0.2W/m². Achieving that U value for solid walls will mean installing at least 100mm of rigid insulation (eg. Celotex, Kingspan or similar).
Internal insulation and damp
Unfortunately, internal insulation will not be particularly effective against damp, when compared to external insulation. We recommend that any damp issues be dealt with before insulation is installed.
How Internal Wall Insulation is installed
A cut-away model of internal solid wall insulation.
1 | Surface coating (green)
This is the new plasterwork that covers the insulation layer. Just like a normal internal wall, it can be painted or papered.
2 | Insulation (orange)
This is the layer that prevents heat escaping through the outside walls of your home. We normally use PIR insulation boards for IWI.
3 | Internal wall (white)
This is the old internal plaster which is now covered by the new insulation board and plasterwork.
4 | Windows
We always try, where practical, to insulate the inside of the window recess to prevent cold spots in the system.
5 | External wall (brickwork)
From the outside, your property will look exactly the same.
Funding for Internal Wall Insulation
We currently have access to funding to help towards the cost of Internal Wall Insulation. To qualify for funding you will need to meet certain criteria (please see our ECO Grant funding page for more details).
If you have questions or need advice on Internal Wall Insulation, please get in touch with us on 0121 663 6123 or complete your details in our Call Back Box and one of our advisors will be in touch with you.
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