Why an Old Front Door Loses Heat

Solid timber front doors on period homes are lovely things, but they were never designed with airtightness in mind. The wood dries out and shrinks over the summer, the door drops slightly on its hinges, the frame moves with the seasons, and by November you can feel a steady trickle of cold air around the edges. It is not just uncomfortable either — a draught you can feel with the back of your hand is a draught that is costing you money every hour the heating is on.

The most common culprits are the vertical gaps down the hinge side and the lock side, plus the gap along the bottom of the door. You may also find a gap across the top where the frame has lifted. A strip draught excluder — brush, foam or rubber — deals with all of these neatly and costs very little. The key is fitting it properly, because a badly fitted excluder will either fall off within a month or stop the door closing altogether.

Measure the Gap Before You Buy Anything

Never guess at the size of the gap. Close the door as you normally would, then work your way around the frame with a piece of stiff card. Slide it into the gap at the top, the middle and the bottom of each side. Where it slips through easily, the gap is wide; where it grips, the gap is tight. Note the readings in millimetres at each point.

For a more precise picture, wait until dark and shine a torch along the inside of the closed door while a helper stands outside. Any light showing through marks a genuine gap, and you can see exactly where the frame is out of true. Measure the widest point, not the average — the excluder has to cope with the worst spot.

As a rough guide:

• Up to 5mm — a foam or rubber self-adhesive strip is plenty.
• 5mm to 10mm — a brush strip or a rubber blade in a carrier works best.
• Over 10mm — the door or frame probably needs adjusting first, as no strip will bridge that gap without fouling the door.

While you are at it, check the frame for square by measuring the diagonals of the opening. If they differ by more than a few millimetres, expect to trim the strip at an angle rather than square.

Choosing Between Brush, Foam and Rubber

All three do the same job, but they suit different doors.

• Brush strips are the traditional choice for older doors. The bristles sweep against the door face and cope well with uneven timber and slightly warped doors. They are also quiet, and they let a little air move, which helps if your home needs to breathe.
• Foam strips are cheapest and easiest — usually self-adhesive, peel and stick. They work well on narrow, even gaps but compress over time and can perish in sunlight if fitted to an external face.
• Rubber or EPDM blades give the tightest seal and last for years, but they need a reasonably flat door face and a consistent gap. On a gappy old door they can make it stiff to close.

For most period front doors, a brush strip in a slim plastic or aluminium carrier, screwed to the inside of the frame, is the sensible answer. Buy a length long enough to do all three sides with a bit spare — usually one pack covers a standard doorway.

Cutting and Fitting the Strip

Start with the hinge side, since it is the easiest to get right. Close the door and mark the position of the carrier on the inside face of the frame, tight against the door stop if there is one. The bristles should just touch the door face without being crushed flat.

Measure each side separately — top, hinge and lock — and cut the carrier with a junior hacksaw, holding it in a vice or against a block of scrap wood so the cut stays square. For a neat corner, cut the two meeting ends at 45 degrees so they butt together rather than overlapping.

Fix the carrier with the screws supplied, drilling pilot holes first to avoid splitting the frame. Space the screws roughly every 150mm and always put one within 25mm of each end. If the strip has a self-adhesive backing as well, use it as a helper rather than the main fixing — screws hold, adhesive does not.

A few points worth remembering:

• Leave a small gap at the hinge side so the strip does not jam the door as it swings.
• Keep the strip clear of the latch and deadlock keeps, and check the key still turns freely.
• Cut the bottom strip slightly short at each end so it does not catch on the frame as the door closes.

Checking the Fit and Finishing Touches

Once everything is screwed in place, close the door slowly. It should shut with a firm push, not a shove, and it should not spring back open. If it is stiff, slacken the screws and nudge the carrier a millimetre or two away from the door, then retighten. If the door rattles, the strip is not making contact and needs to move closer.

Run the torch test again at night. Any remaining light means a spot you have missed, often at the top corner where the frame has dropped. A small offcut of brush strip glued behind the carrier will usually sort it.

Finally, remember that the strip is only part of the job. A letterbox flap, a keyhole cover and a decent door brush or threshold seal at the bottom will finish the draught-proofing properly. Check the excluder each autumn as the wood moves — a quarter turn on a screw is often all it takes to keep the whole thing snug for another winter.