Floor insulation

Many homes – especially newer ones – will have a ground floor made of solid concrete. This can be insulated when it needs to be replaced, or can have rigid insulation laid on top.

Older homes are most likely to have suspended timber floors. 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.

Do NOT block up air bricks in your walls. They are needed to help ventilate the space under your floor and stop your floorboards rotting.

If you have a basement or cellar beneath your house that you can get into safely, take a look down there to see what type of floor you have. If the floor is a suspended wooden floor, you will probably be able to see wooden joists and the undersides of the floorboards.

If you don’t have access to the space underneath your house, you will need to lift a corner of the carpet and underlay to have a look.

Timber floors can be insulated by lifting the floorboards and laying mineral wool insulation supported by netting between the joists. Insulating under the floorboards on the ground floor could save you about £70 a year in GB and £80 in NI in an average property. 

If you live in a detached house, you could save up to £110 a year in GB and £130 in NI.

Not all home insulation work has to be carried out by a professional; it may work out cheaper to do the smaller jobs yourself.

You can seal the gaps between floors and skirting boards to reduce draughts yourself quite easily, with a tube of sealant bought from any DIY store.

It’s even easier to insulate your timber floor if you have an unheated cellar or basement space underneath that you can get into. Check that the joists supporting the floorboards are in good condition and don’t show any signs of wet or dry rot.

If the joists are okay, you can fit insulation in between them and hold it in place with netting if necessary. The basement’s ‘ceiling’ should then have plasterboard fixed directly to the undersides of the joists, to provide fire resistance – and you can then fit more rigid insulation underneath the ‘ceiling’ to benefit from even more insulation.

Try to seal up any gaps between and around the floorboards when you put them back.

Rugs and carpets on the floor will also help your feet feel warmer, which might mean you don’t feel the need to put the heating on as much. We’ve got more information about energy saving home improvements here.

If you don’t feel confident lifting your floorboards yourself, you can get a professional to do this as well as fit the insulation and replace the boards afterwards. Costs will vary depending on how big your house is and how easy the floorboards are to lift and replace.

For solid concrete floors, make sure that if they need to be replaced, your builder puts in insulation – you have to insulate a floor when it is replaced in order to comply with building regulations.

Solid floors are insulated using rigid insulation foam, which can be fitted either above or below the concrete. If the concrete is above the insulation it can sometimes store heat during the day, which helps keep the room warm at night. If the insulation is above the concrete the room will heat up more quickly in the morning.

You can still insulate your solid floor even if it doesn’t need replacing. Rigid insulation can be laid on top of the original floor, then chipboard flooring can be placed over it. This will raise the level of the floor, so you will need to make sure doors are trimmed shorter to make room for the insulation. Skirting boards and some electrical sockets may need to be moved.

If you are looking for someone to insulate your floor, Energy Saving Trust recommends you look for an installer who is a member of the National Insulation Association.

If you want to insulate your floor as part of a bigger refurbishment job, you will probably want to use your existing builder.

If you are adding extra insulation to your floors, the work will need to comply with the relevant building regulations for where you live. Although your installer will normally arrange this for you, 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, contact your local Building Control Office or Building Standards Department before starting work.

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