Is floor insulation worth it?

Floor insulation is one of the less-obvious retrofit measures. You can't see it, and the savings are modest compared to loft or wall insulation. But if you have a draughty suspended floor and you've already done the higher-priority work, floor insulation can make a noticeable difference to comfort and heating bills.

What type of floor do I have?

UK homes have two main floor types:

• Suspended timber floor: Floorboards or chipboard sit on timber joists, with a void (air gap) underneath. The void is usually 400mm to 600mm deep and ventilated via air bricks in the external walls. Common in houses built before 1950, and still used in some modern houses for ground floors.³
• Solid concrete floor (solid slab): A concrete slab sitting directly on the ground, with no void underneath. Common in houses built after 1950, and almost universal in flats and new-builds.³

To tell which you have:

• Lift a corner of carpet or check under a floor vent (air brick).
• Tap the floor. Timber floors sound hollow. Concrete floors sound solid.
• Check your EPC certificate. It often states the floor construction type.

The insulation approach is completely different for each type.

How much does floor insulation cost?

Costs depend on your floor type and whether you have access to the void:

• Suspended floor, access from below: £700 to £1,500 for a typical living room (20m²). The installer works from the cellar or crawl space, fitting rigid insulation boards or mineral wool batts between the joists, held in place with netting or battens. Whole ground floor: £1,800 to £3,500.
• Suspended floor, access from above: £1,200 to £2,500 for a room. More expensive because you have to lift the floorboards, fit insulation between the joists, and re-lay the floor. Only worth it if you're already lifting the floor for another reason (rewiring, replumbing, damp treatment).
• Solid concrete floor: £2,500 to £6,000 for a whole ground floor. You have to lift the existing floor (screed, tiles, or boards), lay rigid insulation boards (100mm to 150mm PIR or EPS), pour a new screed on top, and re-lay the flooring. This is disruptive and only makes sense during a major renovation.⁴

The work takes 1 to 3 days for a single room (suspended floor, access from below). Solid floor insulation takes 5 to 10 days for a whole floor due to screed drying time.

Can I get floor insulation for free?

Floor insulation is not usually covered by the ECO4 scheme, which prioritizes loft and cavity wall insulation.⁵ However, you may qualify for help if:

• Home Upgrade Grant (HUG): Available to low-income households with off-gas heating (oil, LPG, electric). HUG can cover floor insulation as part of a whole-house deep retrofit. Apply through your local authority.⁶
• ECO4 Flex: Some energy suppliers offer floor insulation under ECO4 Flex if your local authority nominates you as a vulnerable household. Check with your council.
• Interest-free loans: Scotland's Home Energy Scotland and Wales's Nest schemes offer interest-free loans for insulation work.⁷

If you don't qualify, you pay the full cost. Given the long payback (12 to 25 years), floor insulation is usually done after loft and wall insulation, not instead of them.

How much will I save?

The Energy Saving Trust estimates floor insulation saves:

• £40 to £60 per year for a suspended timber floor
• £50 to £100 per year for a solid concrete floor

These figures assume gas central heating and 2026 energy prices (6.24p/kWh for gas).^1,2 Electric heating savings are higher in pounds (about 4x) but electric heating is expensive either way.

Your actual savings depend on:

• How draughty your floor was before. If you could feel cold air blowing up through gaps in the floorboards, floor insulation will make a big difference to comfort and cut draughts by 80% or more. If your floor was already fairly airtight, savings will be lower.
• Ground temperature. Floors lose less heat than walls or roofs because the ground underneath is warmer than the outside air. A floor at 10°C is losing less heat than a wall exposed to 0°C wind.
• Room use. Living rooms and bedrooms benefit most because you heat them regularly. Utility rooms and hallways see smaller savings.

Should I insulate my floor or prioritize something else?

Floor insulation should come after loft and cavity wall insulation, not before. Here's the priority order:

1. Loft floor insulation (270mm): £300 to £500, saves £200+ per year, payback 2 to 3 years. Do this first. Often free via ECO4.⁵
2. Cavity wall insulation: £500 to £1,200, saves £160 to £260 per year, payback 2 to 5 years. Do this second. Often free via ECO4.
3. Draughtproofing (windows, doors, letterbox): £200 to £400, saves £25 to £50 per year, payback 5 to 10 years. Cheap and makes a noticeable comfort difference.
4. Floor insulation: £700+, saves £40 to £100 per year, payback 12 to 25 years. Do this after the above.

Floor insulation makes most sense if:

• You've already done loft and wall insulation.
• You have a suspended floor with easy access from below.
• Your floor is noticeably draughty (you can feel cold air through gaps).
• You're doing other work that requires lifting the floor anyway.

Skip floor insulation if:

• Your loft or walls are still uninsulated (do those first).
• You have a solid concrete floor and no plans for major renovation (too expensive and disruptive).
• Your floor already has insulation (check your EPC or look underneath if you have access).

What type of insulation is best for floors?

The material depends on your floor type:

Suspended timber floors

• Rigid PIR boards (100mm): Most common. Cut to fit between joists, supported by netting or timber battens. Good thermal performance, easy to handle. Cost: £25 to £35 per m².
• Mineral wool batts (150mm): Flexible, fits snugly between joists. Breathable (good for older houses where you want moisture to escape). Cheaper (£15 to £25 per m²) but bulkier.
• Sheep's wool or wood fibre batts: Natural, breathable, lower embodied carbon. More expensive (£30 to £50 per m²). Good for eco-renovations.

Solid concrete floors

• EPS (expanded polystyrene) boards (100mm to 150mm): Cheap, good compressive strength (can take the weight of the screed and floor finish). Cost: £20 to £30 per m².
• PIR boards: Thinner (80mm to 120mm for the same performance), more expensive (£35 to £50 per m²). Better if you're tight on floor height.

For suspended floors, you must leave a 50mm air gap between the insulation and the underside of the floorboards to allow ventilation and prevent condensation.³ Don't block the air bricks. The void needs to stay ventilated.

Can I DIY floor insulation?

Yes, if you have a suspended floor with access from below (cellar or crawl space) and you're comfortable working in a confined space. The steps are:

1. Measure the joist spacing (usually 400mm or 600mm centres).
2. Cut rigid insulation boards or mineral wool batts to fit between the joists.
3. Fix netting or timber battens under the joists to support the insulation.
4. Push the insulation up into place, leaving a 50mm air gap to the floorboards above.
5. Check you haven't blocked any air bricks or underfloor ventilation.

Materials cost £300 to £600 for a typical room. You'll need a dust mask (mineral wool is itchy), gloves, safety glasses, and a saw or knife to cut the boards.

Solid floor insulation is not a DIY job. You need a builder to lift the floor, lay the insulation, and pour a new screed to the correct level.

Do I need to worry about damp?

Suspended floors rely on ventilation to prevent damp. The air bricks in the external walls let air flow through the void, carrying away moisture. If you insulate the floor, you must:

• Keep the air bricks clear. Don't block them with insulation, soil, or paving.
• Leave a 50mm air gap between the insulation and the underside of the floorboards.
• Check for existing damp before you start. If the void is already damp (standing water, rotten joists, musty smell), fix the damp problem first (improve drainage, repair air bricks, install a damp-proof course if missing).⁸

If you insulate a floor with an existing damp problem, you'll trap moisture and make it worse. Any reputable installer will check the void for damp before starting work.

Summary

Floor insulation is worth it if you have a suspended timber floor with accessible void, you've already insulated your loft and walls, and you're comfortable with a 12 to 25 year payback. It costs £700 to £1,500 for a typical room and saves £40 to £60 per year.

Solid concrete floor insulation is expensive (£2,500 to £6,000 for a whole floor) and only makes sense during a major renovation. Prioritize loft and cavity wall insulation first, which have 5 times faster payback.