Why does my composite door stick in hot weather?

A composite door has a timber or foam core in a GRP skin, and a uPVC door has a steel-reinforced plastic frame. Both expand when the sun heats one face and not the other, and both come back at night.

What you'll need

• A tape measure or a straight edge
• An Allen key set
• PTFE lubricant

Step by step

1. Test the door cold.First thing in the morning, before the sun reaches it. If it locks and unlocks easily, the door is fine and you have a thermal problem rather than a mechanical one.
2. Check which way it bows.Hold a straight edge against the face in the afternoon. A door bowing outwards at the middle is being heated on the outer skin, which is normal on a south or west-facing dark door.
3. Use the lift-and-lock technique.Lift the handle firmly and fully before turning the key. That lifts the leaf and engages all the hooks together instead of forcing one at a time.
4. Lubricate the hooks and keeps.PTFE spray on every hook, roller and keep, twice a year. Friction is what turns a millimetre of bow into a door you cannot lock.
5. Resist the urge to adjust for the hot day.Adjust for a 30°C afternoon and the door rattles in a 2°C January. Set the door up for its cold state and manage the hot days.
6. Ease a specific keep only if it is consistently tight.If one hook is always the one that binds, backing that keep off a fraction is reasonable. Do not back off all of them.
7. Reduce the heat on the door.Shade from a porch, a canopy, a tree or an awning is the actual fix. So is a lighter door colour when the time comes to replace it.
8. Check the frame is properly fixed and packed.A frame that is not packed behind its fixings can be pulled out of shape by the leaf as it expands, which makes a mild bow into a real problem.
9. Watch for it getting worse year on year.A door that used to be fine in summer and now is not may have a failing hinge or a sagging leaf underneath the thermal effect.

Tips

• Dark grey and anthracite doors on a south-facing wall are the classic case. Surface temperatures well above 50°C are normal on a summer afternoon.
• Never pour cold water on a hot door to close it. The thermal shock can craze the skin and it does nothing lasting.
• Most manufacturers' warranties explicitly allow a few millimetres of thermal bow, which is worth knowing before you call them out.

Common mistakes

• Adjusting the hinges to fit the door on the hottest day — Every adjustment made in a bowed state is wrong when the door returns to shape. By October the door rattles, the seal does nothing and the whole set-up has to be redone.
• Forcing the key when the hooks are binding — The key is the weakest part of the chain. Forcing it against a bound hook is how cylinders and gearboxes break, and it usually happens on the hottest day of the year.

If it doesn't work

Questions people ask