Weatherstripping a door that still fits
Applies to: Assumes a timber external door hung on butt hinges in a timber frame, closing against a rebate or a planted stop.
Last worked on 2014-12-08
A door that closes cleanly and still lets air through is sealing on three sides and not the fourth, or sealing at the wrong depth. Diagnose before you buy anything.
Find the gap before choosing the seal
Close the door on a strip of paper at intervals around the perimeter and pull. Where the paper slides out freely there is no contact; where it tears there is heavy contact. Work around the whole perimeter, marking the frame as you go, and you will have the gap profile that determines which seal to use.
Seals are sized by the gap they close. A seal too small does nothing; a seal too large stops the door latching, which is the usual reason a seal gets removed a week after it is fitted.
The three sides and the threshold
Head and hinge-side stiles are usually the easiest, because the gap is consistent and the door does not move relative to them. The latch stile is the one that varies, because the door pivots and the gap closes last there.
The threshold is different in kind. The gap under the door has to accommodate the floor covering and has to survive being walked on, which rules out most of what works on the other three sides. A brush or a drop seal fitted to the door, rather than a strip fitted to the floor, lasts longer and does not become a trip edge.
When the door does not fit
If the paper test shows heavy contact on one stile and no contact on the other, the door is out of square in the frame and no seal will correct that. The usual causes are worn hinge knuckles, screws pulled in the frame leaf, or a frame that has moved with the opening.
Fix the hang first. Packing behind a hinge leaf, or moving to longer screws that reach the framing behind the lining, changes the gap profile enough that a smaller and less obtrusive seal will then work.
| Situation | What usually suits | Why |
|---|---|---|
| Consistent narrow gap, head and hinge stile | Compression seal in the rebate | Contact is even and the door does not slide against it |
| Variable gap on the latch stile | Wiper or brush seal on the stop | Tolerates a changing gap without preventing latching |
| Wide gap under the door, hard floor | Drop seal fitted to the door | Lifts clear when the door swings, so it does not drag |
| Wide gap under the door, carpet | Brush seal fitted to the door | Rides over the pile instead of catching on it |
| Door out of square in the frame | Re-hang before sealing | No seal corrects a gap that changes across the height |
Scroll the table sideways for the remaining columns.
Weatherstripping is the cheapest measurable improvement available on an opening, and the only common way to get it wrong is to fit a seal thicker than the gap and then remove it when the door will not shut.