It's a common complaint: a UPVC door that works perfectly fine in winter suddenly becomes stiff, hard to close, or impossible to lock on a hot summer's day. This isn't a coincidence — thermal expansion is almost always the cause. Here's what's happening and what can be done about it.
Thermal Expansion in UPVC
UPVC expands when it gets hot and contracts when it cools. A dark-coloured UPVC door facing south can reach surface temperatures of 70°C or more on a hot sunny day — significantly higher than the ambient air temperature. This expansion is enough to cause the door to bind against the frame or the locking points to misalign with the keeps.
Is It Just a Summer Problem?
If a door only sticks in summer and works normally in winter, the expansion is likely minor and the door may be close to the threshold of acceptable performance. However, if the problem is getting worse each summer, or the door is becoming difficult to lock even at moderate temperatures, it indicates the door alignment needs addressing. Ignoring it risks damage to the lock mechanism from forcing.
The Fix: Hinge and Keep Adjustment
The solution is to adjust the door hinges and, where necessary, the positions of the keeps (the plates in the frame that the locking bolts engage with) to give more clearance at the temperatures where the door expands. This is a precise job: too much clearance and the door will rattle in winter; too little and it will still stick in summer. A specialist UPVC engineer can calibrate this correctly.
Prevention for Dark Doors
Dark-coloured composite and UPVC doors absorb more heat and therefore expand more than white doors. If you're having a dark door fitted, ensure the installer accounts for thermal expansion during commissioning. For existing dark doors that are expanding significantly, a specialist can adjust the hinge positions to accommodate the greater movement.
Need a UPVC Repair in Birmingham or the Black Country?
The Glass Guardian provides fast, affordable UPVC window and door repairs across Birmingham, Dudley, Walsall, Wolverhampton, and the surrounding area. Call for a free quote.