Floor Insulation: The Snugg 2024 Guide

Floor Insulation: The Snugg 2024 Guide (updated November 2023)

Around 10% of a home’s heat can be lost through the floor.¹ But adding or improving floor insulation can minimise the amount of heat that’s lost, reducing energy bills and making your home more comfortable to live in.

In this guide, we cover:

1. How does floor insulation work?

2. What are the benefits of installing floor insulation in your home?

3. What types of floor insulation are there?

4. How much does floor insulation cost?

5. How efficient is floor insulation?

6. Are there any grants or incentives for floor insulation?

7. How to lay floor insulation

8. Floor insulation FAQs

How does floor insulation work?

Floor insulation works like a barrier that sits underneath the flooring of your house and helps to keep the warm or cool air inside. It helps your home stay at a comfortable temperature throughout the seasons.

The insulation is installed underneath your flooring, typically in the crawlspace. But this can also be done by pulling up the floorboards if you don’t mind the disruption.

There are different types of insulation materials, including fibreglass, cellulose and natural materials. The insulation works by trapping small pockets of air within their fibres, which slows down the movement of heat.  

What are the benefits of installing floor insulation in your home?

There are lots of benefits to installing floor insulation, including:

• Cheaper energy bills: Floor insulation helps reduce the amount of energy needed to heat or cool your home, resulting in significant savings on your energy bills over time.
• Lower carbon emissions: By lowering energy consumption, floor insulation can help reduce your carbon footprint and have a positive impact on the environment.
• Increased property value: By installing floor insulation, you can improve your home’s EPC rating which can increase its value on the housing market.
• More comfortable: Insulation can help to keep your home at a more consistent temperature, making it more comfortable to live in, especially during extreme weather conditions.
• Low maintenance: Once installed, floor insulation doesn't require regular maintenance, making it a cost-effective solution for your home.

What types of floor insulation are there?

There are several different types of floor insulation, and your options will vary depending on the type of flooring you have.

Floorboards

If you have suspended flooring (i.e. the floorboards are suspended over joists) then your options include:

• Insulation boards: These can be placed between the joists, underneath the floorboards, and supported with netting. The boards can be made from several materials including polystyrene, polyurethane and cork.
• Loose-fill insulation: This type of insulation is poured or blown into the space between the joists. It can be made from cellulose, mineral wool or fibreglass.
• Reflective insulation: Reflective insulation is made of a reflective material that reflects heat back into the room. It can be installed on top of the joists before the floorboards are laid.
• Natural wool insulation: Wool insulation can be bought in batts or rolls, making it relatively easy to install between the joists of a suspended floor. It’s breathable and can manage moisture very well, making it particularly effective in spaces where ventilation and dampness are potential issues.
• Recycled textile insulation: Insulation made from recycled textiles like denim can be used in suspended floors. It’s usually treated for fire and pest resistance, and it can be cut to fit tightly between floor joists.
• Hemp insulation: Hemp insulation has excellent thermal properties and moisture management, making it a good choice for naturally damper areas.
  

Insulation boards made from polyurethane or polystyrene are generally considered to be some of the most efficient insulation options for suspended flooring. They have a high R-value, which measures their ability to resist heat flow, and can provide a consistent insulation barrier that isn’t affected by settling or compression.

Loose-fill insulation can also be efficient, but it can settle over time which can reduce its insulating properties.

Reflective insulation can provide good thermal performance, but they’re not as common as insulation boards when it comes to suspended flooring insulation.

Concrete flooring

If you have a concrete floor in your home, you’ll need to bear in mind that installing any type of insulation will raise the height of your floor, meaning that skirting boards and plug sockets may need refitting.

To insulate concrete floors, your options include:

• Insulation slabs: This is a lightweight and easily cut insulation form, often made from rock wool, that can be fitted between wooden beams that form a suspended floor above the concrete.
• Rigid foam insulation boards: This type of insulation is made from a solid plastic material, usually polyisocyanurate (PIR), expanded polystyrene (EPS) or extruded polystyrene (XPS). It can have a high R-value and be cut to fit most spaces.
• Cork insulation: Cork is a natural, renewable material that’s made in rigid board form. It has good thermal insulation properties and is also resistant to moisture (ideal for concrete floors).

Insulation slabs are generally very dense and can offer extra sound insulation (although concrete floors are usually very good at blocking sound from travelling between floors). Being lightweight, they’re also easy to move where you need them. Slabs are the best option if you’re insulating between the beams of a suspended floor.

Rigid foam insulation comes in a variety of materials. And while they’re all lightweight, that’s where the similarities end. Pound for pound, PIR has the highest insulation value (primarily because PIR is sandwiched between two foil sheets). XPS can bear the most weight, which makes it ideal for floor insulation. XPS is also the most resistant to water vapour, while PIR is the least resistant. EPS and XPS are the most environmentally friendly, as PIR can’t be recycled.

How much does floor insulation cost?

The cost of floor insulation can vary a lot depending on the type of insulation you buy. It will also vary depending on the amount you need, as the price per square metre will drop the more total square footage you need.

You can use the following as a rough guide:² (Prices sourced November 2023)

• Rock wool slab: £3 per square metre
• Foil roll: £2.50 per square metre
• EPS board: £10 per square metre
• Cellulose loose-fill bag: £11 per square metre
• PIR board: £16.50 per square metre
• XPS board: £13 per square metre
• Natural wool slab: £17 per square metre
• Hemp insulation slab: £16 per square metre

How efficient is floor insulation?

Floor insulation is an efficient way to improve the energy efficiency of your home. But how efficient is it? It will depend on the type of floor insulation you choose and its thickness.

A material's R-value measures its resistance to heat flow. Essentially, the higher its R-value, the better job it will do at keeping the heat in.

Here are some R-values of a selection of 100mm-thick products:³

• Rock wool slab: 2.78m2K/W R-value
• EPS board: 2.78m2K/W R-value
• PIR board: 4.5m2K/W R-value
• XPS board: 2.94m2K/W R-value

PIR has one of the highest R-values of any insulation material available, and the highest of any floor insulation material. But you’ll need to consider which type of insulation is more suitable for the job at hand. For example, PIR board might not be suitable if you plan on storing heavy items or are conscious of its recycling potential.

Floor insulation thickness

You can buy floor insulation of different thicknesses. As you’d expect, thicker insulation will be more effective at slowing heat transfer than thinner insulation.

The thickness required for your specific needs will influence the type of insulation you’ll want to buy. For example, if need to maximize insulation in a compact area, you may want to consider insulation with a high R-value per inch. But if you have more room to work with, you may prefer thicker insulation with a lower R-value per inch.

So it's not always best to choose the material with the highest R-value. Other factors such as cost, installation complexity and environmental impact should also be considered when selecting insulation.

Are there any grants or incentives for floor insulation?

A grant is money given to you that you don’t have to pay back.

There are several grants available in the UK that could help you pay for loft insulation. You can find an up-to-date list of available grants on our grants page.

How to lay floor insulation

Laying floor insulation is something you could do yourself, depending on the project’s complexity. But if you’d prefer an experienced professional to do it for you, you may want to find an installer.

There are many ways to lay floor insulation, depending on the insulation used and the type of flooring already in place. So bear in mind that the following examples may not be suitable for all scenarios.

Floor insulation on concrete

Follow these steps to lay rigid foam insulation on concrete:

1. Prepare the surface: File down any protrusions in the concrete. Then clean the surface to remove any dirt or dust. ‍
2. Lay a membrane: Lay a damp-proof membrane (usually polythene) to cover the floor from wall to wall. This will prevent any moisture from building up between the concrete and the insulation above. ‍
3. Install the insulation: Measure the room and lay down the rigid foam insulation boards. You may need to cut them down to size. Start in one corner and work across and down to the diagonally opposite corner. ‍
4. Tape the insulation: As a precautionary measure, tape the boards to prevent the potential for them to move out of place over time. ‍
5. Lay chipboard flooring: Lay the chipboard on top of the insulation using a tongue-in-groove technique and glue so that they lock in place. This will provide extra strength to the floor. You may want to leave space around the edge of the wall for a skirting board.

Floor insulation for a suspended floor (from above)

Follow these steps to lay mineral wool insulation on top of a suspended timber floor:

1. Pull up the floorboards: Pull up any carpet as well as the floorboards to access the timber joists below. ‍
2. Lay a membrane: Lay a damp-proof membrane (usually polythene) over the joists and push it down to cover the bottom of the gaps between the joists. This will prevent any moisture from coming up from the ground below and disturbing the insulation. Attach the membrane in place using galvanised staples that won’t rust. ‍
3. Install the insulation: Measure the space between the joists and cut the insulation to size. Then place them down. ‍
4. Lay the floorboards: With the insulation in place, simply return the floorboards where they were before.

Floor insulation for a suspended floor (from below)

Follow these steps to install rigid foam insulation boards from within the crawl space under a suspended timber floor:

1. Access the crawl space: You may need to pull up some floorboards to access the crawl space below. ‍
2. Install a support structure: Fix either wooden batons to the sides of the joists, or netting under the joists, so the insulation has something to rest on. ‍
3. Install the insulation: Measure the space between the joists and cut the insulation to size. Then rest it on top of the batons or netting. ‍
4. Fix a membrane: Fix a damp-proof membrane (usually polythene) under the joists. This will prevent any moisture from coming up from the ground below and disturbing the insulation. Attach the membrane in place using galvanised staples that won’t rust.

Floor Insulation FAQs

How much floor insulation do I need?

How much floor insulation do I need?

The amount of floor insulation you need will depend on several factors, including:

• The climate where you live
• The size of your home
• The existing energy efficiency of your home
• The type of flooring you have
• Your energy usage
• Your energy efficiency goals
• The type of insulation material you choose

How much does floor insulation help?

Floor insulation can greatly improve the energy efficiency of your home. By reducing heat loss through the floor, insulation can help lower your energy bills and increase the comfort of your home.

The exact amount of energy savings will depend on several factors including the type and thickness of insulation used, the climate where you are, and your energy usage patterns.

Given that around 10% of an uninsulated home’s heat is lost through the floor, you could expect to reduce around 10% of your energy bill by installing floor insulation.

Which underfloor insulation is best?

For suspended flooring, insulation boards made from polyurethane or polystyrene are generally considered the best options due to their high R-value and consistent insulation properties. Loose-fill insulation can be efficient but may settle over time reducing its properties. Reflective insulation can provide good thermal performance but are less common for suspended flooring.

For concrete flooring, insulation slabs made from rock wool are a good option as they’re dense, provide extra sound insulation and are easy to move. But rigid foam insulation boards made from PIR, EPS or XPS can also be used, with PIR having the highest insulation value, XPS being best for weight-bearing and most resistant to water vapour, and EPS and XPS being the most environmentally friendly.

What are the floor insulation thickness regulations for the UK?

If you’re replacing at least half of a room’s flooring, building regulations in England, Wales and Norther Ireland require the floor insulation to achieve a U-value (a measurement of how quickly heat will pass through the floor) of 0.25 W/m2K or less. You’ll need approximately 70mm-thick high-performance insulation or 150mm-thick mineral wool insulation to achieve this.

In Scotland, building regulations require floor insulation to achieve a U-value of at least 0.18 W/m2K. A lower U-value is more efficient.

What funding options can you use to pay for loft insulation?

Loft insulation can be purchased from most high-street and online hardware stores using cash, debit or credit card.

If you’re hiring an installer who buys the material on your behalf, the installer will usually ask you to pay their invoice by bank transfer or debit card.

If you don’t have the cash to hand or prefer to finance (borrow money) the payment, you could consider taking out a personal loan or an instalment plan. We’ve more details on this in our Funding Options Guide.