Draughts, Gaps and Good Air: Sealing Internal Doors Without Turning Your Home Into a Thermos

There's a particular kind of cold that lives in a British hallway in November. It sits at ankle height, curls round the door frame and makes the radiator in the front room work twice as hard as it should. Most people blame the front door. Often, it's the internal one.

Sealing up internal doors is a slightly awkward bit of home improvement, because the goal isn't actually to make the house airtight. Do that and you'll be wiping condensation off the windows by December and wondering why the bathroom never dries out. The trick is knowing which gaps cost you comfort and which ones are quietly doing you a favour.

First, find out what's actually cold

Before you buy a single strip of anything, spend an evening doing very little. Sit near the suspect door with a cup of tea and hold the back of your hand near the gap at the bottom, then the hinge side, then the top. A cheap smoke pencil or even a lit incense stick will show you the direction of travel.

Half the time the door is innocent. Cold air arrives through a chimney you never use, up through bare floorboards, down a disused flue, or from a hallway that's effectively a wind tunnel because the letterbox flaps. Sealing a door that isn't the culprit just makes the room quieter and no warmer.

The bottom gap does most of the damage

That horizontal slit under an internal door is usually 8–20mm, and it might as well be an open window. There are three sensible fixes and they suit different houses.

Brush seals are the workhorse. A slim aluminium carrier with a nylon brush, screwed or stuck to the face of the door, sweeps the floor as the door moves. They cope well with uneven Victorian boards and slight slopes, and they're cheap. The catch is that a stiff brush on a deep-pile carpet will fight you every time the door closes.

Blade or wiper seals are neater and quieter — a rubber fin rather than a brush — and they suit modern engineered floors where the gap is consistent.

Automatic drop-down seals sit inside a groove in the bottom of the door and lift as the door closes. They're the tidiest answer and the best choice where a fire door needs to keep its clearance, but they cost more and need a router and a bit of confidence.

Whatever you choose, test the door through its full swing before you commit. If it drags, the seal will be worn out within a season and the door will start rubbing on the floor instead.

Sides and top: a light touch

Foam or rubber compression strips in the rebate will stop the sneaky draughts around the frame. Don't overdo it. Thick foam in a thin rebate means the door no longer latches properly, and a door that sits proud of its stop is a door that whistles.

Self-adhesive E-profile strips are the renter-friendly option and work well on painted softwood frames. Clean the surface first, and avoid sticking anything to a freshly painted door — give it a week.

Now the part people get wrong: ventilation

This is where draught-proofing turns into a trade-off. Internal doors in older British homes often do some of the work that modern extractor fans and trickle vents do now. Block that and the moisture has to go somewhere — usually into the plaster.

A few things worth leaving alone:

• Letterbox-style vents set into a door, or grilles above it, are there for a reason. In a kitchen or bathroom especially, they may be the only path for moist air to leave.
• Air bricks and sub-floor vents aren't door-related but they're the classic casualty of a sealing spree. Never cover them.
• Bathroom and kitchen doors should have a gap or a vent so that extraction can pull air through the room. Seal the door completely and the fan just spins in a vacuum.
• Any room with a gas appliance — a boiler cupboard, a room with a gas fire — needs its ventilation exactly as designed. If in doubt, leave it and ask a Gas Safe engineer.

A useful rule: seal for draughts, not for air. If a room has no opening window, no extractor and no vent, and you've just sealed the door, you've created a condensation problem, not a cosy one.

Fire doors are a different conversation

The door between your kitchen and an integral garage, the one to a flat's communal corridor, the one at the top of a shared stair — these are fire doors, and they aren't ordinary doors with a bit of trim added.

Smoke and intumescent seals are usually a specified part of the door's performance. Adding a chunky brush seal at the bottom can stop it latching, interfere with the closer, or alter the gap the door was tested with. Never block or remove a vent in a fire door, and never assume a bit of draught-proofing is harmless just because it's small. If you rent a flat, ask the landlord or managing agent before touching any door on an escape route.

If you rent

Stick to things you can take with you. A fabric draught excluder sausage at the bottom of a door is unfashionable, deeply effective and costs about a tenner. Removable foam strips are fine; adhesive seals that peel paint off a frame are a deposit conversation waiting to happen. Anything involving a screwdriver needs a quick email first.

The room-by-room picture

• Hallway: the priority. Cold air pools here and leaks into every room off it. Seal the front door first, then the doors that open onto the hall.
• Living room: brush seal at the bottom, thin foam in the rebate. Worth doing properly — this is the room you notice.
• Bedrooms: keep the gap modest. A fully sealed bedroom with the window shut gets stuffy by 2am.
• Kitchen and bathroom: seal the sides if you like, but leave the ventilation path intact.
• Under-stair cupboards and box rooms: cold, damp-prone and usually unventilated. A little airflow is a good thing here.

The upshot

Draught-proofing internal doors works best as a targeted job rather than a campaign. Deal with the two or three doors you actually feel, leave the ventilation routes alone, and don't treat the house as something to be wrapped up. A period home that breathes is warmer, drier and considerably less grumpy than one that's been sealed shut.