Insulating your ground floor is a great way to install a layer of protection between your warm home and the cold ground underneath. An uninsulated concrete subfloor, for example, can absorb up to 30% of your home’s heating, so it makes sense to invest in floor insulation if you’re a long-term homeowner. You can generally recoup your investment within 3 to 10 years, depending on what type of floor you have.
This guide will explore all the floor insulation options available to you, whatever type of property you own. For a more general look at home insulation, take a look at our ‘How to insulate a house’ article. And for more detail on other types of home insulation, read ‘How to insulate your water tanks and cylinders’ and ‘How to install cavity wall insulation’.
What is floor insulation?
About 30% of heat from an average home is lost through the ground floor. Underfloor insulation stops heat from escaping through your ground floor by placing an effective barrier between the cold ground underneath, and your warm home. You have a number of different options for effective insulation material, which we’ve listed below.
Generally speaking, you only need to insulate the ground floor. If you’re on an upper floor, you don’t usually need to insulate your floor. However, we recommend that you consider insulating any floors that are above unheated spaces, such as garages, as you may be losing a lot of heat through them.
Do I need floor insulation?
Well, it depends. The air under your house is actually warmer than the air around your house. This makes cavity wall insulation a higher priority for most people than underfloor insulation.
However, if you’ve already installed cavity wall insulation and you’re looking for the next way to save on your heating bills, underfloor insulation is your ticket.
Does carpet insulate the floor to some degree?
If you have a fitted carpet on your floors, then yes. Most houses already have a form of insulation; carpet, so underfloor insulation is, again, actually a low priority.
Does installing floor insulation affect building regulations?
Yes, installing floor insulation can affect building regulations. If you’re going to install floor insulation you need to make sure you meet all the requirements – we advise you to check the Energy Saving Trust website before carrying out any works.
How can I improve floor insulation?
There are a few different ways to insulate your floor, some cheaper than others whilst others are a lot less committal.
An extremely low-fi (but better than nothing) lesson in how to insulate your floor from cold air beneath would be the humble rug. Put it on top of bare floorboards or tiles to help block some draughts and keep your toes warm. Great budget option!
You can use sealant or caulking to fill the gaps between your floorboards and between skirting boards and the floor. Read more on draught-proofing your home with our guide.
If you’re having new carpets fitted, consider installing an additional insulating underlay beneath them. If you’re having new wood flooring installed, put a layer of mineral wool insulation under the floorboards first. Vinyl floors are themselves good insulators but can be improved by adding another insulating layer underneath. Ensure the vinyl is free from tears and cracks, especially around the edges, as this can reduce its insulating properties.
Insulation that sits beneath your floorboards/tiles etc: this is the biggest commitment and what you end up doing will depend on your home and its floors.
How heat is lost in three different types of homes
In the UK there are three significant classes of homes with differing levels of heat loss. Depending on what type of home you have will mean insulation for your floors will be different.
Older houses with ‘suspended’ timber floors
If you have timber joists suspended above a void, this is the type of floor that’s more likely to lose more heat. Suspended timber floors are also the easiest to insulate – and the Energy Saving Trust says you’ll see a return on your investment within 3 to 5 years.
Homes with solid (concrete) floors
Concrete floors have been common in homes since the 1930s and have less heat escaping than the timber joist type. Concrete floor insulation can help and usually consists of adding a layer of solid insulation placed directly on top of the floor.
Insulation for concrete floors is harder to install than suspended floors and the payback time for return on investment is a little longer, estimated to be within 8 to 10 years.
Modern houses built in the last 10 years usually tend to incorporate slabs of polystyrene insulation a few inches below the concrete floor surface, effectively reducing this type of heat loss.
Solid floor insulation
As mentioned, solid floor insulation (usually found in homes built since 1930) is laid on top of the existing flooring and then covered with your chosen finish. One of the big benefits of this floor insulation is that not only is it effective and relatively easy to install, it’s also affordable.
Suspended floor insulation
Suspended floor insulation is usually found in older houses with timber floors. If you have a basement or an access hatch that allows you to get into the crawlspace (void) below the floorboards, it’s a relatively easy process to install underfloor insulation. It can be placed between the joists and battens and then held in place with netting. It’s essential to cover any pre-existing holes created by old pipes or cables.
If you don’t have a basement or access hatch, you will need to take up the floorboards and use either netting or wooden battens to hold the glass, mineral or sheep’s wool insulation in place beneath the floorboards.
Two main benefits of floor insulation
1. Save on your heating bill
The Energy Saving Trust says homeowners can save £30–£75 a year on heating their homes (£30 for a terraced house and £75 for a detached house. If all houses in the UK saved 30% of energy lost through their floor, that’s a huge energy saving!
2. Reduce draughts and make your home warmer
This makes you home all the more pleasant to live in.
Free floor insulation
Did you know you can get a floor insulation grant from the government? To qualify, you must have the following
The ground floor of your home MUST have suspended wooden floors, NOT concrete floors.
You must also be already receiving a type of state benefit, tax credits or allowances.
As part of the free floor insulation service, the installer will also seal the gaps between the floors and the skirting boards to reduce draughts. To find out if you’re eligible and how to apply, visit The Affordable Warmth Scheme.
DIY floor insulation installation
What’s great about floor insulation is that the majority of the time, it can be a DIY job. However, if you’re not confident to install floor insulation yourself, it’s best to call a professional. If you’re more than a little bit handy, let’s get to it:
DIY suspended floor insulation
You’ll know you have a suspended floor by looking at the external brickwork of your home. If you have air ventilation bricks below the damp-proof membrane, ie. below floor level, then your home has suspended floors. The air bricks allow ventilation below your ground floor, which isn’t possible with concrete floors.
Another way to check is to peel up the carpet in a corner of a ground floor room to see whether the floor is concrete or wood. It might be wooden floorboards or wooden sheets.
What you’ll need: Suspended Floor Insulation
- Rolls of insulation – For suspended floors, you’ll need to insulate with rolls of glass, mineral or sheep’s wool insulation.
- Floor insulation boards: Alternative to rolls – An alternative to rolls of insulation material is to use solid insulation ‘batts’ or boards. Batts typically also have the advantage of having a slightly higher U-value. U-value is the measurement of the insulating material’s effectiveness, so the higher the U-value, the more effective the material at insulating. So it’s very worth considering.
- Insulation netting – You’ll need some insulation netting to hold the insulation in place, which is inexpensive to buy.
- Insulation foam/draught excluder – To seal any tiny gaps between your insulation boards and the joists with foam draught excluder.
- Damp-proof membrane – If there is bare earth under your joists in the crawlspace, it may be advisable to apply a damp-proof membrane on the ground to aid humidity control.
- Craft knife – Cutting insulation boards is fairly easy with a sharp craft knife. It’s best to buy a couple of extra boards as mistakes are likely to happen; most shops will be happy to take back any boards you end up not using.
- PPE (Personal Protection Equipment) – Protect the air you breathe and your eyes with a mask and a pair of goggles.