Loft insulation gets all the attention. Heat pumps get all the grants. But if you ask a building physicist what the highest return-on-investment home energy improvement is, a lot of them will say draught proofing. It costs almost nothing to do properly, you can do most of it yourself in a weekend, and the savings are immediate and real.

The Energy Saving Trust estimates that properly draught-proofing a three-bedroom semi costs around £200 in materials and saves roughly £125 a year on energy bills. That’s a payback period of under two years. No other home energy measure comes close to that ratio.

So why don’t more people do it? Partly because it’s not dramatic — there are no panels on the roof or new systems to show off. Partly because it’s easy to underestimate how much air is leaking through a seemingly solid house.

Where the Draughts Actually Are

The places most people think to seal — around window frames, under doors — are correct but incomplete. The biggest sources of uncontrolled infiltration in a typical UK semi are often less obvious.

Loft hatch: The hatch into the loft is almost always poorly sealed. Warm air rises, and if there’s no seal around the loft hatch, you’re pumping heat directly into the cold loft space. A rubber draught excluder strip around the frame, combined with 100mm of rigid insulation board fixed to the back of the hatch itself, addresses both air sealing and conductive heat loss through the hatch. This is the single highest-impact thing you can do that takes under an hour.

Floorboards: Old suspended timber floors in Victorian and Edwardian houses can have extraordinary amounts of infiltration through the gaps between boards and around the skirting. Filling the gaps with a flexible filler (not rigid caulk, which will crack as boards move seasonally) and sealing the junction between floor and skirting board with a draught-excluding sealant addresses this. On floors over cold void spaces, a breathable membrane under the floor provides an air barrier without trapping moisture.

Pipes and cables entering from outside: Every pipe, cable, and duct that passes through an exterior wall is potentially a draught pathway. Gas pipes, electric cables, TV aerials — look around the outside of your house and check whether the penetrations are sealed. Expanding foam or proprietary fire-rated sealant (use fire-rated sealant on electrical cables, as per regulations) sorts these out quickly.

Chimney breasts: Open fireplaces that aren’t in use are essentially a hole in your exterior wall. A chimney balloon — an inflatable draught excluder fitted inside the flue — is the standard fix. Leave a note on the fireplace saying it’s fitted; removing it before lighting is essential. Blocked chimneys can also cause damp issues if the flue can’t breathe at all, so a vent cap at the top is worth considering if sealing permanently.

Letterboxes and cat flaps: A standard letterbox leaks a surprising amount of air. Fitting a brush seal behind it costs around £5 and takes ten minutes. Cat flaps are harder — they’re inherently leaky — but energy-efficient models with magnetic seals are available for around £40-60.

Windows and Doors

External doors should have a combination of a threshold strip (the strip along the bottom that seals when the door is closed) and compression seals on the sides and top. Brush seals are good for doors; foam strips degrade quickly and need replacing every few years. For French doors or patio doors with a gap in the middle between the two panels, draught-excluding brush strips on the overlapping edge help significantly.

For windows, draughts typically come from failed putty or sealant around the frame rather than through the glass. Run your hand around window frames on a windy day to find cold spots. A tube of low-modulus silicone sealant or flexible external mastic addresses frame gaps. Sash windows are a separate challenge — the traditional rattling sash has multiple draught pathways (the sash runners, the central meeting rail, the top and bottom of travel). Brush seals inserted into routed channels in the sash runners are the proper fix and are available as DIY kits for around £50-80 per window.

What Not to Seal

Here’s the thing that causes problems when people get overenthusiastic: some ventilation is essential. Houses need a certain air change rate to avoid damp, condensation, and indoor air quality problems. Sealing everything tightly without providing controlled ventilation causes issues — particularly in older properties that rely on background infiltration for moisture management.

The NHBC rule of thumb is that you should never seal below the damp-proof course level (this keeps the subfloor dry), you shouldn’t seal airbricks or cavity vents, and you should ensure bathrooms and kitchens have adequate extract ventilation if you’re significantly tightening the envelope. If you’re fitting secondary glazing or serious draught sealing throughout a whole house, consider getting a professional air pressure test to understand what your actual infiltration rate is and whether supplementary ventilation is needed.

What to Buy

For most draught proofing jobs you need:

  • Compression foam draught strips — cheap and easy for loft hatches and internal doors
  • Brush draught strips — better for external doors and sash windows, longer-lasting
  • Low-modulus silicone or flexible frame sealant — for gaps around window frames and pipe penetrations
  • Expanding polyurethane foam — for larger gaps around pipes and cables, use low-expansion foam for gaps near windows where structure matters
  • Chimney balloon — sized to your flue diameter
  • Threshold draught excluder — for external doors

The total material cost for a thorough job on a three-bed semi is usually £100-200. The Energy Saving Trust’s DIY guides are the best free resource for working through each location systematically, and NHBC has guidance specifically on moisture management implications of tightening.

Getting Help With It

If you’re not keen on DIY, or if you want a professional assessment of where the draughts are, several local authority and housing association schemes include draught proofing as part of a broader home energy package. Under the ECO4 scheme, households that qualify on income grounds can get draught proofing funded as part of a whole-house measure package, though it’s rarely offered as a standalone service. A local Trustmark-registered energy assessor can identify the most impactful locations if you’re not sure where to start.

The key point is that draught proofing doesn’t require grants or government programmes to be worth doing. At £200 all-in and a sub-two-year payback, it’s the rare home energy improvement that makes sense regardless of what else you’re planning or not planning to install.