Underfloor Insulation: How to Stop Heat Escaping Through Your Floors

15 July 2023

If your feet feel cold on the floorboards even when the heating is on, your home could be losing a surprising amount of warmth through its ground floor. Underfloor insulation is one of the most overlooked upgrades in home energy efficiency, yet it can dramatically improve comfort and reduce heating bills. In this guide, we explain how it works, what your options are, and how to get the job done properly.

Why Floors Lose Heat

Warm air rises, which is why most homeowners focus insulation efforts on the loft. But a significant amount of heat still escapes downwards through the ground floor, especially in homes with suspended timber floors. Cold air can also be drawn in through gaps between floorboards, skirting boards and under floor vents, creating noticeable draughts.

Older properties built before modern building regulations are particularly vulnerable. If your home has an unventilated or poorly insulated floor void, the ground beneath it stays cold all year round, pulling heat out of your living space like a silent drain on your boiler.

Check What Type of Floor You Have

Before spending any money, it helps to know what you are working with. Most homes have one of two floor types:

Suspended timber floors – typically found in older houses, with floorboards resting on joists over an air gap. You can often tell by the slight bounce underfoot, visible floorboards, or air bricks on the outside wall.
Solid concrete floors – common in newer builds and ground-floor extensions. These feel hard and unyielding and cannot be insulated from below.

Suspended timber floors are usually the easiest and cheapest to insulate, because the work can be done from underneath. Solid floors require insulation to be added on top, which raises the floor level and usually means lifting carpets or replacing flooring.

Your Insulation Options

Suspended Timber Floors

If you have reasonable access from below, say via a crawlspace or cellar, the job is relatively straightforward. The most common approach is to fit insulation between the floor joists, held in place so it cannot sag or fall out over time. Popular materials include:

Mineral wool rolls or slabs, supported by netting stapled to the joists
Rigid foam boards cut to fit snugly between joists
Natural fibre options such as sheep's wool or wood fibre, favoured for breathability and sustainability

Whichever material you choose, aim for a snug fit with no gaps. Even small voids let cold air wash straight through and undo much of the benefit.

Solid Floors

Insulating a solid floor means adding a layer of rigid insulation board on top of the existing slab, followed by a new floor covering. This is a bigger job, usually done during a renovation or when replacing flooring anyway. Even a modest thickness of high-performance board makes a real difference, and it also makes the floor feel warmer underfoot.

Don't Forget Draught-Proofing

Insulation alone will not stop draughts. Gaps between floorboards, around pipework, and where skirting boards meet the floor can let in cold air that chills your feet no matter how well insulated the void is. Seal visible gaps with flexible filler or draught-proofing strips, and make sure any underfloor ventilation vents are preserved, they are essential for preventing damp and timber rot in suspended floors.

DIY or Call a Professional?

Insulating between joists from a cellar or crawlspace can be a manageable DIY project for a confident homeowner, though working overhead in a cramped space is physically demanding. If access is only possible by lifting floorboards, or if the job involves solid floors, electrics or plumbing, a professional installer is the safer bet. It is also worth checking whether government energy-efficiency grants or schemes in your area could help cover the cost.

Done well, underfloor insulation is a one-time upgrade that pays you back every winter, in lower bills and feet that stay warm.