Every winter, the calls come in: “My door was fine yesterday, now I can’t lock it.” Sound familiar?
uPVC doors and cold weather have a complicated relationship. Understanding the science helps you manage the problem—and prevents panic when your door suddenly becomes difficult. For maintenance tips, see our uPVC door maintenance guide.
uPVC contracts in cold weather by approximately 0.8mm per metre for every 10°C drop. A standard door can shrink several millimetres in height and width. If your door was already marginally aligned, this contraction pushes it into sticking. The fix is usually hinge adjustment to account for seasonal movement.
The Science: Thermal Expansion and Contraction
How uPVC Responds to Temperature
uPVC (unplasticised polyvinyl chloride) has a relatively high coefficient of thermal expansion—meaning it changes size noticeably with temperature.
The numbers:
- Expansion coefficient: approximately 80 × 10⁻⁶ per °C
- For a 2-metre door height: roughly 1.6mm change per 10°C
- UK winter swing: potentially 20-30°C range = up to 5mm total movement
What This Means for Your Door
| Temperature | Door Behaviour |
|---|---|
| Summer (25°C) | Door at maximum size |
| Autumn (15°C) | Door begins contracting |
| Winter (5°C) | Significant contraction |
| Frost (-5°C) | Maximum contraction |
Why Doors Stick When They Contract
Counterintuitively, a smaller door can be harder to lock. Here’s why:
Hinge Geometry Changes
When the door shrinks:
- The hinge attachment points move relative to each other
- This changes the door’s hang angle slightly
- The lock side of the door shifts position
- Hooks and bolts no longer align perfectly with keeps
Frame and Door Contract Differently
The aluminium or steel reinforcement inside uPVC has a different expansion rate than the plastic. This creates:
- Internal stress in the door slab
- Potential for slight warping
- Unpredictable dimensional changes
Keeps Become Misaligned
Even millimetre shifts matter:
- Hooks miss their keeps
- Bolts strike keep edges instead of entering cleanly
- Rollers create friction instead of smooth compression
Immediate Solutions for a Stuck Winter Door
If the Door Won’t Close
- Pull the door towards you while lifting the handle
- Push at the hinge side while lifting
- Try with door slightly ajar—identify where it’s catching
If the Door Won’t Lock
- Lift handle fully with door open—confirm mechanism works
- Close door gently, feeling for resistance points
- Apply pressure at the locking side while lifting handle
- Locate specific catch points—often top or bottom shootbolts
Temporary Fixes
Lubrication:
- Silicone spray on keeps and locking points
- Reduces friction while misaligned
- Works immediately, buys time
Slight adjustment:
- Loosen hinge screws slightly
- Allow door to self-position
- Retighten in new position
Proper Adjustment for Winter Issues
Adjustable Hinges
Most modern uPVC doors have flag hinges with adjustment:
| Adjustment | Direction | Effect |
|---|---|---|
| Lateral | Side-to-side | Moves door closer/further from frame |
| Vertical | Up-down | Raises or lowers door |
| Compression | In-out | Affects seal and latch engagement |
Professional hinge adjustment accounts for seasonal range—setting the door to function year-round rather than perfectly in one season.
Keep Adjustment
If hinges can’t fully compensate:
- Keeps can be repositioned (unscrew, move, re-fix)
- Strike plates can be filed or built up
- Replacement keeps may offer different positions
When Adjustment Isn’t Enough
Sometimes the door or frame has moved beyond adjustment range:
- Frame fixings may need resetting
- Door sash may need professional realignment
- In extreme cases, mechanism or door replacement
Preventing Frozen Locks
Cold temperatures cause a separate problem: ice forming inside the lock mechanism. For detailed solutions, see our frozen lock guide.
How Locks Freeze
- Moisture enters the cylinder (breath, humidity, rain)
- Temperature drops below freezing
- Water becomes ice inside the mechanism
- Pins can’t move, key won’t turn
Prevention
Graphite lubrication:
- Apply graphite powder to cylinder annually (autumn)
- Graphite doesn’t attract moisture like oil
- Creates dry barrier against ice formation
Lock covers:
- External cylinder guards reduce moisture entry
- Particularly useful on exposed doors
De-icer:
- Keep lock de-icer accessible (not inside the locked house!)
- Apply at first sign of stiffness in cold weather
When to Call for Help
DIY-Appropriate
- Basic hinge adjustment (quarter-turn increments)
- Lubrication of moving parts
- De-icing frozen cylinders
- Minor keep repositioning
Professional Required
- Door consistently won’t lock safely — see our uPVC door won’t lock guide
- Mechanism making unusual noises
- Visible damage to hooks or gearbox
- Frame appears to have moved
- Multiple adjustment attempts haven’t resolved issue
Long-Term Solutions
Upgrade Worn Components
If your door regularly struggles in winter:
- Hinges may be worn beyond adjustment
- Mechanism may be at end of life—see when to repair vs replace
- Replacement restores full adjustment range
Consider Environmental Factors
Dark doors:
- Absorb heat, expand more in sun
- Cool rapidly in shade
- Experience greater thermal cycling
Sheltered vs exposed:
- Exposed doors experience fuller temperature range
- Sheltered doors have smaller swings
Draft excluders:
- Quality seals accommodate some movement
- Worn seals require perfect alignment
The Seasonal Reality
Your uPVC door experiences significant physical stress every year—contracted in winter, expanded in summer, cycling between extremes. This is normal and manageable.
Key principles:
- Adjustment for middle ground, not perfection
- Never force stuck mechanisms
- Lubricate before winter
- Address issues before they cascade
With proper setup and maintenance, your door can handle British winters for decades. The science is against you, but engineering solves the problem—when applied correctly. For ongoing care, follow our lock maintenance tips.