Draught Proofing: Door Sweeps, Weather Seals and Thresholds

Draft stoppers: the cheapest fix

A draft stopper is a strip of foam, often with a fabric or rubber casing, that you push or screw into the gap under the door. It works by compressing. When the door opens it squashes and springs back; when it closes it fills the gap.

This is the right answer when the gap is small and the floor is level. The is the simplest version, at a price that makes it an obvious first thing to try. It also does a genuinely good job on noise, because a tight strip blocks sound as well as air.

The limitation is obvious once you meet it: foam cannot fill a large gap, and on an uneven floor it either leaves a gap or drags. If your door has more than about 10mm underneath, you need something else.

Under-door seals: foam with a hard backing

An under-door seal is a refinement on the same idea. The foam sits in a rigid or semi-rigid carrier that screws or slides into the door itself rather than sitting on the floor, which means it stays correctly positioned as the door opens and closes and it looks tidier.

The is a good example, with the twin profile giving more contact area than a single strip. If you can only fit one thing, this is the most versatile option for a standard internal door.

Door sweeps: hanging brush or rubber

A door sweep hangs from the bottom of the door and rests against the floor or threshold. Because it hangs, it flexes to follow uneven surfaces and it can seal a much larger gap than foam.

Brush seals are quieter because the bristles compress rather than sliding. Rubber sweeps seal better against wind and rain but can be noisier on some floors. The is the durable choice for a door that gets used hard, and the is the typical choice for a standard front or back door.

For an exterior door on a step, a is the correct product. The expander compresses as the door closes, which is what makes it work on a threshold that is not perfectly smooth.

Thresholds: sealing the gap between two surfaces

A threshold seal does a different job. It seals where the door lands, rather than under the door itself — the strip on a step, or the sill between a tiled hallway and a wooden room. If you can feel a line of cold air across a step rather than under a door, this is the product you need.

The is a typical example. A related product worth knowing about is the , which is sold in lengths and is a much larger job than any interior door.

If your draught is coming from a sliding door, none of the above is the right answer. Sliding doors cannot take a sweep that hangs, and the seal runs vertically down the overlap between the two panels.

Getting the measurement right is the difference between a seal that works and one that rattles. Four numbers to take with a tape measure.

• Door opening width. Measure across the frame, not the door leaf. Add a few millimetres if the listing is at the edge of a range.
• Gap height. Close the door and measure from the bottom of the door to the floor. Do this at three points, because floors are not straight.
• Material of the threshold. Carpet needs a different seal from tile or concrete. Carpet compresses and holds a brush seal; tile needs something that will not slide.
• How the door closes. If it has a threshold the door lands on, you want a sweep that rests on it. If it swings onto carpet with no sill, you want an under-door seal.

Also check whether you are going to fit more than one. A house with three external doors is a different project from a single internal door, and buying in pairs is often cheaper than buying separately. The is the obvious example.

Surface preparation

Most failures are adhesive failures, and almost all adhesive failures come from a dirty surface. Wipe the bottom of the door and the threshold with a degreasing cleaner, let it dry fully, and then apply the seal. If the door is painted, a light sanding to break the gloss gives adhesive something to grip.

Measure twice on the door leaf

If you are screwing a sweep on, mark the position with the door open, on the face of the door rather than the edge. Set it so the seal touches the threshold when the door is closed but does not scrape when it opens fully.

Adhesive versus screws

Adhesive is faster and reversible. Screws hold better and survive a heavy door slamming. If you have an external door that gets pushed hard in the wind, screws are worth the extra five minutes.

Check it closes

Open and close the door several times after fitting. A seal that catches is worse than no seal, because it either lifts the door or will not let it shut. If it catches, take it off, trim a few millimetres with scissors and refit.

The most commonly reported benefit after draught proofing is not warmth, it is noise. A tight brush seal under a door cuts a surprising amount of hallway, corridor and street sound, because the gap under a door is an excellent path for sound as well as air.

If noise is your main problem, prioritise brush seals over rubber ones and prioritise the gaps under internal doors between rooms, because those are usually the shortest paths sound takes. The is designed with exactly this in mind.

If you also have gaps around the door frame rather than under the door, you are looking at a different product — self-adhesive foam weather strip that runs up the frame. That is a fifteen-minute job with a tape measure and is worth doing at the same time.

The door is usually where people start because it is the biggest gap, but there are four openings in a typical wall that cost you heat in the same way, and an afternoon spent on all of them changes the result far more than a £40 door sweep does.

• The letterbox. A standard letterbox leaks air straight into the hall. A brush strip or letterbox brush costs very little and is the single highest-return item in this list. It also stops insects getting in, which is a bonus in summer.
• Keyholes and unused sockets. A euro-cylinder keyway and external sockets are small but constant. Insulating tape over an unused socket and a cover plate on a keyhole take five minutes.
• Gaps around the frame. Self-adhesive foam weather strip run up the frame and across the top rail seals the sliding gap that lets air move even when the sweep is doing its job at the bottom.
• The gap beside a garage or outbuilding door. Larger and usually worse than the house, and it is the one people forget entirely because they never walk past it.

The principle is the same for all four: you are stopping warm air moving from inside to outside. The largest opening gives the biggest return, so measure them in order of size rather than tackling them in the order you think of them.

Under $15 gets you a draft stopper that will do most of the job on an internal door. The is the best value in this guide if you have one problem door.

Between $15 and $35 covers a proper sweep or a pair of seals, which is the right spend for a front or back door that is the main source of a draught. The is a straightforward, well-specified choice at that level.

Above $35 you are buying durability rather than a better seal. That is worth it on external doors exposed to weather and to being dragged over a threshold, and not worth it anywhere else.

One caution on very wide doors. Anything over about 1.2m wide usually needs two sweeps side by side rather than one oversized one, because a single long sweep twists and stops sealing at one corner.

Buying a draft stopper for a large gap. It will compress to nothing and you will assume it is faulty. Match the product to the gap.

Fitting onto a wet or dusty surface. This is the number one cause of failure and takes thirty seconds to avoid.

Ignoring the threshold. If the door lands on a step, sealing under the door alone will not stop the draught coming across the step.

Assuming one size fits all doors. They do not. Door widths, gaps and floor levels vary more than the packaging suggests.

Leaving the seal on a door that needs to be dragged across a carpet. Brush handles it. Rubber on carpet will wear out and then catch.

Doing one door and stopping. If the front door is the problem, the garage and the bathroom are usually close behind. A house-wide pass in one afternoon is cheaper per door than doing them individually.

Sealing draughts is one of those jobs where the result is immediately obvious and the measurement is hard to photograph. You will feel the difference at floor level within a day, and you will notice the noise reduction before you notice the temperature change.

It is also reversible, cheap per door, and does not require a tradesperson. That combination puts it well ahead of most other home comfort spending, which is why it has become a standard autumn job on both sides of the Atlantic.

For the wider picture of staying comfortable through a cold snap, our guide to winter power outage preparation covers the things that matter when the heating stops for a different reason, and our space heater guide covers the other half of the problem — adding heat back into a single room cheaply.

eBay prices move daily and sellers vary widely in condition and description, so check recent sold listings before you commit rather than trusting the first price you see.