What is underfloor insulation?
Underfloor insulation is a way to make your home warmer, more efficient, and more comfortable by placing thermal materials directly beneath your floorboards or concrete slabs. Unlike loft or wall insulation, which primarily address heat escaping upwards or sideways, underfloor insulation acts as a barrier against the cold air and draughts sneaking up from below.
The installation method will depend on your property’s build:
- Homes with suspended timber floors (often found in older properties) typically have rolls or rigid boards fitted snugly between the joists underneath the boards.
- In contrast, modern homes with solid concrete floors usually need rigid insulation boards or an insulated screed layered on top of the slab.
Done properly, underfloor insulation not only cuts heat loss but gives rooms that extra warmth underfoot, helps reduce sound transfer from downstairs, and lowers your long-term energy bills.
Building regulations for new homes and major refurbishments will often require a minimum standard of floor insulation to help properties achieve a better EPC rating. Insulating floors can also play a key role in meeting government net-zero targets.
How it works
Underfloor insulation works by slowing heat transfer from the inside of your property to the cold ground beneath. Without it, warmth naturally escapes through the floor, meaning higher energy costs and a chillier home. By fitting insulation materials below, you reflect heat back upward, reducing draughts, and keeping more warmth in the room.
Because heat takes the path of least resistance, any uninsulated surface (walls, roofs, or floors) can become the weak link in your overall energy efficiency strategy. Upgrading an underfloor insulation is one of the quickest ways to fill these gaps for a cosier, more affordable home.
Why it’s important for energy efficiency
Up to 15% of the heat in your home can escape through uninsulated floors, especially if you have timber boards and noticeable gaps. Fitting underfloor insulation helps reduce this wasted energy and brings a noticeable improvement in overall comfort.
It’s not just about saving money on heating bills, though most homeowners start to see reductions within the first year. Proper insulation also boosts your property’s EPC rating, which makes it more attractive to buyers and renters, and helps meet newer standards for rental properties and public buildings.
For architects, developers, and housing associations, specifying the right underfloor insulation can make the difference between compliance and costly retrofit work in the future.
Underfloor insulation vs other insulation types
Floor vs wall insulation
Wall insulation addresses heat loss through external walls, which is significant given their surface area. Floor insulation, however, tackles cold spots, draughts, and the discomfort you feel directly underfoot through the long winter months, crucial in older or poorly insulated homes.
Floor vs loft insulation
Loft insulation is usually the first upgrade because heat rises, but after that’s sorted, solid underfloor insulation is a logical and highly effective next step. If you still feel cold drafts or your lower rooms are chilly, it’s likely that heat is being lost through the floor.
Which flooring should you prioritise?
Most homes will benefit from following this order of priorities: loft insulation first, then walls, and then floors. But if you have particularly draughty timber floorboards or experience cold ground floors, this could bump underfloor insulation up the list.
Builders and contractors working on refurbishments can often tackle floor insulation as part of wider upgrades, saving cost and hassle. Energy assessors may recommend floor insulation first in properties with severe ground level heat loss or cold bridging.
How to install underfloor insulation
DIY installation: Step-by-step
If you’re handy and want to try it yourself, fitting underfloor insulation in a suspended timber floor is a rewarding project. You’ll need to lift the floorboards or access the crawl space and fit insulation (like mineral wool, rigid PIR boards, or specialist underfloor rolls) between the joists.
Key steps include:
- Clear and prepare the area (check for any signs of damp or pests).
- Fit insulation tightly between all joists, ensuring full coverage.
- Maintain ventilation, making sure not to block air bricks or vents.
- Reseal and relay floorboards, filling any gaps to prevent future draughts.
- Seal edges and around pipework with expanding foam or tape for best performance.
Wear gloves, a dust mask, and kneepads. If working in a crawl space, safety goggles and overalls help keep things comfortable.
Professional installation process
For solid floors, or if you want maximum performance and minimal disruption, professional installation is recommended. Installers should:
- Advise on the best material for your floor type (PIR, EPS, XPS, or mineral wool).
- Handle vapour barriers, edge detailing, and fire regulations.
- Check that all work meets current building standards for safety and efficiency.
- Guarantee quality from start to finish, saving you time and avoiding costly mistakes.
For large buildings, listed properties, or multi-unit developments, it’s almost always quicker and more reliable to use professionals.
Tools and materials needed
- Insulation boards or mineral wool rolls (PIR, EPS, or eco-friendly options).
- Staple gun or board fixings.
- Vapour barrier membrane (especially for solid floors).
- Expanding foam or insulation tape.
- Hand tools (crowbar, saw, utility knife).
- Protective gear: gloves, mask, goggles.
Some underfloor insulation kits are now available, which bundle materials, fastenings, and instructions, making DIY simpler for homeowners and time-saving for builders.
Common questions about underfloor insulations
Is underfloor insulation worth it?
Underfloor insulation boosts comfort, slashes heating bills, and improves your EPC rating. The benefits become noticeable, especially in winter and in homes with noticeably cold floors or draughts.
How long does underfloor insulations last?
Most underfloor insulation will last for decades, often 40 years or more. Modern products are moisture and rot-resistant, delivering savings for the lifetime of your home.
Can it cause damp or condensation?
Only if incorrectly installed can underfloor insulation cause damp or condensation. It’s essential to maintain airflow under suspended timber floors and use vapour barriers on solid floors. Breathable insulation materials are available for heritage or older homes.
What’s the best insulation for wooden floors vs concrete floors?
For suspended wooden floors, mineral wool rolls or PIR boards fitted between joists are most effective. For concrete floors, rigid PIR, EPS, or XPS boards laid above or below the slab work best. Discuss options with your supplier for your specific property.
Many architects and specifiers now use underfloor insulation as part of wider low-energy building strategies, pairing it with double glazing, modern heating systems, and renewable energy generation. Third-party certifications, such as BBA and Green Deal approval, are worth looking for when purchasing insulation products.
Underfloor insulation for different property types
- For homeowners: It’s a straightforward way to cut energy costs and increase property value, especially in older houses with original floorboards.
- For builders and contractors: Knowing which materials are suitable for suspended versus solid floors saves time and helps with site planning.
- For architects/specifiers: Modern insulation boards support compliance with new energy and sustainability standards, and detailed technical data is available for design calculations.
- For property developers and housing associations: Scaling up installations for multiple properties improves EPC ratings portfolio-wide and helps access government funding.
- For government, regulatory, and sustainability professionals: Promoting underfloor insulation supports public policy targets for energy saving and climate action.
Ready to insulate your floors?
Underfloor insulation is one of the most effective ways to make British homes and buildings cosier, greener, and less expensive to run. Whether you’re tackling a DIY job in one room or planning a large professional installation, the results are well worth it.
Explore more of our floor insulation guides to find the best solution for your home.