Underfloor Insulation Guide: The Facts

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There are countless ways to insulate your home and multiple incentives to do so, from reducing the cost of your energy bills to significantly shaving your carbon footprint.

Underfloor insulation is a common method of insulation and is less costly than some other methods of insulation (but it saves you slightly less, too).

Generally, you’ll only need to insulate your ground floor, and if you live in an upper-floor apartment, for example, you don’t usually need to insulate your floor space. If your house is on top of an insulated space like a garage, for example, you should insulate it to avoid heat loss.

Does Your Home Need Underfloor Insulation?

Generally, if your home fits the following criteria it will benefit from the installation of underfloor insulation.

  • You feel draughts coming up through your floor.
  • You live in an old home without floor insulation.
    Your existing insulation is damaged or no longer effective.
  • Your home experiences significant fluctuations in temperature, getting extremely cold in winter and very hot during the summer months.
  • You’re already planning on replacing your floor.

How Do I Know What Type Of Floor I Have?

If you live in a new property, the chances are your ground floor will be made of solid concrete. With this material you’ve got two options – insulate ground floors when they need replacing or lay rigid foam insulation on top.

This rigid foam insulation can be fitted either above or below the concrete floor. If you are insulating your solid floor without replacing it, bear in mind that this will raise the level of the floor, so you’ll have other factors to consider.

If you live in an older property, you’re more likely to have suspended timber floors. One easy way to check is to look for air bricks or ventilation bricks below floor level on your home’s exterior. These usually indicate that you have suspended floors. You can also check by lifting a corner of the carpet or looking for wooden floors from underneath in your home’s basement or cellar.

Suspended timber floor insulation can be easily fitted by lifting the floorboards and fitting mineral wool insulation between the wooden joists.

Pros and Cons of Underfloor Insulation

By comparing the advantages and disadvantages of underfloor insulation to other insulation methods, you can figure out which is best for your property. Here are the pros and cons of installing underfloor insulation.

Pros of using underfloor insulation

When you’re able to keep your home naturally cooler in the summer and warmer in the winter, you don’t need to use as much energy on things like central heating, electric heaters and air conditioning.

Reducing your energy consumption significantly lowers your energy bills, helping you to save money across the year. Not to mention your carbon footprint will be lower, because keeping our homes warm often requires burning fossil fuels, so the less energy you use, the fewer fossil fuels you’ll need to burn.

While underfloor insulation can in some instances cost up to £3,000 (for the biggest detached homes), in general, it’s much cheaper than some alternatives such as solid wall insulation.

The good news is, your underfloor insulation should pay for itself multiple times over during its lifespan, while having it in your home can even increase the value of your property. Thanks to floor insulation, you can keep saving well into the future.

While underfloor insulation’s main purpose isn’t soundproofing, it can reduce the noise you make when you walk across your floor, which is particularly useful if members of your home use a garage with a room above it.

Cons of using underfloor insulation

Whether you’re replacing your floor or simply installing insulation material on top of your floor, the reality is the process is more disruptive than cavity wall insulation, for example. You can expect the floor in whichever room(s) you’re insulating to be out of order while the installation takes place.

While we do lose heat through our floors, not as much is lost as through our loft or walls, for example. This means that the energy efficient bill savings aren’t as significant as those associated with other types of insulation like loft insulation or wall insulation.

On the other hand, floor insulation is significantly cheaper than methods such as internal or external wall insulation, even if you opt for spray foam insulation, so if you want to insulate part of your property but have a limited budget, flooring insulation could be a good option.

While installing underfloor insulation certainly doesn’t guarantee condensation, damp, or mould, incorrectly installed insulation can definitely cause problems for your home. To reduce the risk of condensation, a vapour barrier or damp proof membrane may be required when you insulate floors, but a professional will advise on this as they aren’t recommended for every situation.

If you are planning on installing the floor insulation yourself, be sure to install the right type of insulation, and not one that easily absorbs and releases water. You should make sure not to block any ventilation spaces, as doing so could increase the levels of condensation.

How Much Does Underfloor Insulation Cost?

Naturally, the cost of your insulation will depend on a few different factors. Underfloor insulation can be installed using DIY methods, although this is much easier to do with timber floors than it is with solid floors. A tradesperson will usually charge between £150 and £250 for the day depending on where in the UK you’re located. Below is a table of the costs you can expect to pay for floor insulation and how long you can expect the process to take, broken down by the size of the property. These figures relate to professional insulation – for DIY insulation installation you can expect to reduce these prices by a few hundred pounds.
PropertyApproximate costEstimated time
Flat£450-£7001 day
Terraced house£800-£12001-2 days
Semi-detached house£1200-£17502-3 days
Detached house£1500-£30003-5 days
While underfloor insulation isn’t cheap, it will pay for itself multiple times over in its lifespan – which is however long your floor lasts. Plus, it’s generally cheaper than insulating some other parts of your home.

How Much Can I Save By Installing Underfloor Insulation?

According to the Energy Saving Trust an insulated floor could save a typical gas-heated detached property as much as £135 per year, or up to £80 annual in a semi-detached house (based on fuel prices as of January 2024).

When it comes to boosting your eco credentials, floor insulation can knock up to 310kg of carbon dioxide per year off carbon footprints (based on a gas-heated detached property). Naturally, you could save the most carbon dioxide in a bungalow (330kg annually) because the insulation will cover all your floor space.

How Can I Save Money on Underfloor Insulation?

A simple way to save money is by opting for a DIY installation rather than relying on a professional. Unfortunately, DIY installation isn’t always suitable, and if you’re trying your hand at solid floor insulation with little to no previous experience, you might spend more in the long run on fixing any mistakes.

If you’re already planning on replacing your floor, installing insulation as part of the new floor installation will save you money. It’s more expensive to install solid floor insulation on top of your floor if you’re not replacing it.

If floor insulation is out of your budget, consider draught-proofing measures you can take instead, that might cost you less but be effective at keeping your house warmer and keeping your energy bills low.

Can I Install Underfloor Insulation as a DIY Project?

One of the benefits of floor insulation versus other types of insulation is that you can install it yourself, especially if you have access to your floor from a basement or cellar.

If you have access beneath the floor, you’ll simply need to fit floor insulation boards or blankets of insulation between the floor joists. Semi-rigid insulation tends to be held up by battens or friction fitted, while blanket insulation can be held up by netting and tacks.

Want extra padding and draught-proofing? If there’s a big enough crawlspace beneath your floor, you can screw solid insulation board into the bottom of the joists.

If you can’t access your floor from below, you’ll likely need professional help to take up the floorboards. With this in mind, consider underfloor insulation as part of other renovations to reduce costs and disruption.

Does Insulating Underfloor Space Affect Ventilation?

When installing floor insulation, it’s crucial to be mindful of any underfloor ventilation systems located in the crawlspace. If you spot any grilles or air blocks, make sure you don’t block them, as doing so can lead to hazards such as rotting floorboards.

Not blocking grilles and vents doesn’t mean you have to have draughts, though. You can block cold air from coming up through your floor by using sealant to fill gaps around the skirting boards or between the floorboards.

Things to Consider Before Installing Underfloor Insulation

Naturally, we don’t tend to spend a lot of time rooting around under the floorboards in our homes. This means when you explore installing insulation, you might find rotting floorboards or joists which will need replacing as part of the renovation.

Obviously, work like this throws up extra costs, so it’s worth considering whether you have the budget for any unforeseen expenses that might arise during the installation process.

The thickness of the insulation you install is something to think about before going ahead. Install too little, and it won’t be effective. Install too much, and you’ll raise the height of your floor too much, which can require adjusting door frames, skirting boards, and even electrical wiring.

If you’re feeling nervous about getting the right approach, consult with a professional who can help you measure up before you get started.

Any huge changes you make to your home will need to meet your local authority’s building regulations, and failing to check them before you get started can cause serious problems down the line.

If you replace more than half your floor, you’ll need to install a certain thickness of insulation to meet building regulations. The effect can usually be achieved with foam or mineral wool insulation, but it’s best to consult with a professional insulation installer to confirm the best approach.

How Do I Insulate a Solid Floor?

Naturally, insulating a solid floor is significantly trickier than the alternative. With concrete floor insulation, the installation requires you to actually raise the height of the floor unless you’re already planning to replace your floor.

If you’re replacing your solid floor, you can fit rigid insulation foam either above or below the concrete floors. If the concrete is fitted on top of the insulation, it helps to keep the room warmer at night. If you fit it above the concrete, you’ll find that the room heats up more quickly in the morning. Establish your priority before deciding where to fit the rigid insulation foam.

If your concrete floor doesn’t need replacing but you want to insulate it regardless, things get a little more complicated. You’ll have to lay rigid insulation on top of your original floor and then place chipboard flooring over it.

Doing so, however, raises the level of the floor, so you’ll need to adjust doors and skirting boards accordingly. You may even need to carry out some electrical rewiring, but it’s best to check with a professional before going ahead.

How Do I Find a Professional Underfloor Insulation Installer?

If you decide to opt for installation by a professional, you’ll want to find somebody trusted, with a reputation for excellence to carry out the project.

Insulation Advisor can help you with your search by providing you with trusted insulation installers in your local area. You will be provided with a no obligation highly competitive quote which, if agreeable, will boost your home’s energy efficiency and bring you savings on your heating bills for many years to come.

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