Floors account for around 10% of heat loss in UK homes. Whether you have suspended timber or solid concrete, find out which approach is right, what it costs, and whether it’s worth doing before other measures.
The right underfloor insulation approach depends entirely on your floor type. Most pre-1945 properties have suspended timber floors (wooden boards over a void). Most post-1945 properties have solid concrete floors. Both can be insulated, but the methods and costs are very different.
Floors typically account for around 10% of home heat loss — lower than roofs (25%) or walls (35%). This means underfloor insulation generally has a longer payback period than loft or wall insulation. However, there are good reasons to prioritise it:
Even though the energy savings are modest, many homeowners report that eliminating cold draughts through suspended floors makes their homes feel dramatically more comfortable, particularly in older properties.
If you’re renovating, replacing flooring or extending, the additional cost of underfloor insulation is marginal. It makes most financial sense when bundled with other work.
Underfloor insulation improves your EPC rating, which matters increasingly for mortgage compliance (EPC E minimum for rentals) and resale value.
If your loft is uninsulated or underinsulated, address that before underfloor insulation. The payback is faster, the savings are higher, and it’s the recommendation of the Energy Saving Trust for most UK homes.
For suspended timber floors with crawl space access, DIY installation is realistic for practical homeowners. Here’s how it’s done:
You need to be able to move through the crawl space comfortably. Clear the space and ensure adequate lighting and ventilation.
Measure the distance between joists and the available depth. Order mineral wool batts (typically 100mm) cut to match your joist spacing.
Fix netting between the joists to support the batts, or use timber battens to create a shelf. The insulation must not sit on the ground.
Cut and push mineral wool batts between the joists, ensuring no gaps. The batts should fit snugly but not be compressed.
Use draught-proofing tape around the perimeter and ensure any pipes in the floor void are also lagged.
DIY is not recommended for solid floors, properties with asbestos concerns, or where crawl spaces are very confined. Always check for asbestos before working in older properties.
Tap the floor with your knuckle. A hollow sound suggests a suspended timber floor. A solid sound indicates a concrete floor. You can also check at the edges — a skirting board that runs to the floor level with no gap typically indicates solid concrete, while air bricks on the external wall near ground level suggest a suspended floor with a ventilated void beneath.
Incorrectly installed underfloor insulation can cause moisture problems if it restricts ventilation in the floor void or creates cold spots that allow condensation. It is important to ensure the floor void remains ventilated and air bricks are not blocked. Mineral wool is the preferred material as it allows moisture movement.
Underfloor insulation can be funded through ECO4 for eligible households, though it is less commonly installed as a standalone measure than loft or wall insulation. It may be included as part of a broader ECO4 package. Eligibility depends on household income, benefits received and EPC rating.