How do I replace the rubber seal on a uPVC door?

uPVC door gaskets are extruded rubber pushed into a groove. They compress permanently over ten to fifteen years, and a flattened gasket is the most common reason a door that closes perfectly still lets a draught through.

What you'll need

• A sample of the old gasket
• New gasket, bought by the metre
• A blunt plastic tool or a seal-fitting wheel
• Soapy water
• Scissors

Step by step

1. Find which seal has failed.Close the door on a strip of paper at several points. Where it pulls out freely, the seal is not compressing. Do this at the top, both sides and the bottom.
2. Identify how many seals there are.Most uPVC doors have a gasket in the frame and a second in the leaf, sometimes with a third in the glazing bead. They are different profiles and are replaced separately.
3. Check the seal is actually flat before replacing it.Compare a section behind the hinge, which sees less compression, with a section by the lock. If they look the same, the problem is adjustment rather than the gasket.
4. Pull out a sample.Start at a corner and pull. Most gaskets come out by hand. Take a 100mm sample to a uPVC supplier or a builders' merchant — matching by shape is normal and they expect it.
5. Clean the groove.Years of grit sit in the channel. A vacuum and a damp cloth, because debris in the groove holds the new gasket high and stops it sealing.
6. Start at the top centre.Push the new gasket in with a blunt plastic tool or the back of a fitting wheel. A little soapy water makes it slide.
7. Never stretch it.Rubber pulled tight during fitting relaxes over the following weeks, and the extra length reappears as a wave in the middle and a gap at the corners. Feed it in loose.
8. Leave a little extra at the corners.A couple of millimetres of compression at each corner keeps the seal continuous when the rubber settles. Butt the ends rather than mitring them.
9. Finish where you started.Cut the final end 5mm long and squeeze it in so the joint is under compression, and put the joint at the top rather than at the bottom where water sits.
10. Recheck the closing pressure.A new, uncompressed gasket makes a door feel stiff for a few days. If it is genuinely hard to close after a week, ease the keeps rather than the gasket.

Tips

• Buy 10 percent more than you measure. Corners eat length and a short piece cannot be joined invisibly.
• Replace the whole run rather than a section. A new piece next to a flattened one leaves a step exactly where the draught was.
• Silicone grease on the finished gasket once a year keeps it supple and stops it sticking to the frame in frost.

Common mistakes

• Stretching the gasket as you fit it — Rubber has a memory. It will contract back to its original length over a few weeks, pulling the corners open and leaving a draught exactly where you have just worked.
• Sealing the gasket in with silicone — Gaskets are meant to be replaceable and to move slightly as the door closes. Silicone bonds them into the groove, stops them compressing evenly and makes the next replacement destructive.

If it doesn't work

Questions people ask