Thin Internal Wall Insulation (TIWI)
Looking to make your home more comfortable, but limited on space? Thin internal wall insulation (TIWI) could be the answer. It’s a practical way to cut heat loss and reduce condensation without the disruption or bulk of standard insulation.
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What is TIWI?
TIWI refers to insulation materials under 25mm thick. These are typically applied directly to internal walls, like wallpaper or plaster, and are ideal for spaces where thicker insulation isn’t an option.
Common types include:
- Wallrock Thermal Liner KV600 (around 4mm)
- Sempatap Thermal (around 10mm)
- Slim insulation-backed plasterboards (up to 22.5mm)
These materials can also be used on sloped ceilings and window reveals, helping to improve comfort in tricky areas.
How much difference does it make?
TIWI doesn’t match the performance of full internal wall insulation, but it can still reduce heat loss by up to 15%. In some cases, that’s enough to noticeably improve warmth and comfort, especially in colder rooms or older properties.
Natural alternatives like spray-on cork or cork rolls can offer slightly better performance, cutting heat loss by 20–30% while also helping manage moisture. For example:
Breathable insulating plasters such as Breathaplasta and ProofTherm can also help improve wall performance. When applied more thickly (usually 40–80mm), they can reduce heat loss by up to 60%.
Best for older or harder-to-insulate homes
If you live in a solid wall or heritage property, breathable solutions are especially important. Some specialist products can be applied at 15–25mm thickness and still improve a wall’s U-value by up to 50%. These are often trowel-applied and work well with traditional building materials.
Options include:
Don’t forget the window reveals
It’s vital to insulate around window reveals as part of any internal wall insulation work. This reduces the risk of cold spots, heat loss, and condensation forming around the edges.
Want it to count on your EPC?
To have your new insulation reflected in your Energy Performance Certificate (EPC), the wall’s thermal performance (U-value) must be calculated and certified. We recommend taking clear photos during installation and keeping receipts as proof of the work done.
You can find more detailed guidance in the government’s official best practice guide to internal wall insulation.
Need support with insulation or retrofitting?
If you’re considering internal wall insulation or any other energy-saving home improvements, get in touch with our expert advisors. We offer free, impartial advice tailored to your home, including which retrofit measures could work best for you.
