Insulating under the floorboards on your ground floor will save you around £60-£75 a year, and you can seal the gaps between floors and skirting boards to reduce draughts too.
Gaps and droughts around skirting boards and floors are simple to fix yourself with a tube of sealant bought from any DIY store. Floorboards will rot without adequate ventilation, though, so don’t block under-floor air-bricks in your outside walls.
Older homes are more likely to have suspended timber floors. Timber floors can be insulated by lifting the floorboards and laying mineral wool insulation supported by netting between the joists.
Many homes – especially newer homes – will have a ground floor made of solid concrete. This can be insulated If it needs to be replaced, or can have rigid insulation laid on top.
You don’t need to insulate the floors of upstairs rooms in your house if they’re above heated spaces (like the living room). But you should think about insulating any floors that are above unheated spaces such as garages, as you could be losing a lot of heat through those.
Complying with building regulations
If you are adding extra insulation to your floors, the work will need to comply with the relevant Building Regulations for where you live. Your installer will normally arrange this for you but if you are doing it yourself, it is your responsibility to comply.
If you live in England or Wales, the floor should achieve a U-value of 0.25 W/m2K or less, if possible. The U-value is a measure of how quickly heat will travel through the floor. To achieve this standard you will normally need at least 70mm of high-performance foam insulation, or 150mm of mineral wool, but this will vary depending on floor type, shape and size.
If you are replacing at least half of a floor then you have to insulate to these standards whether you planned to or not.
For further information, and for regulations in Northern Ireland and Scotland, we recommend that you contact your local Building Control Office before starting work.
How do I tell what kind of floor I have?
If you have a basement or cellar beneath your house that you can get into safely, go and take a look. If the floor is a suspended wooden floor, you will probably be able to see wooden joists and the undersides of the floorboards. Also, if you have air bricks or ventilation bricks on the outside wall(s) of your house that are below floor level, you probably have a suspended timber floor. (If you do have these airbricks in your walls, don’t block them up. They are needed to help ventilate the space under your floor and stop your floorboards from rotting.)
If you don’t have access to the space underneath your house, you will need to lift a corner of the carpet and underlay and have a look. If you live in a flat (apart from the ground floor) then you will also need to lift the carpet to see what kind of floor you have. However, you don’t need to insulate your floor if there is another flat beneath you.