Materials
Winter Wood Movement in Calgary Homes
Updated 3 min read
The short answer
Indoor humidity in a heated Calgary home drops to 15–25% through winter from around 40% in summer. That 15–25% swing moves wood 3–6mm across a 300mm-wide board — enough to open mitres, crack paint at panel joints, make doors stick, and cup shelves finished on one face only. It is normal behaviour, not defective construction.
How much wood moves in a Calgary winter
| Board width | Humidity drop 40%→20% | Humidity drop 40%→15% | Visible effect |
|---|---|---|---|
| 100mm | ~1mm | ~1.5mm | Barely noticeable |
| 200mm | ~2mm | ~3mm | Visible at joints |
| 300mm | ~3mm | ~4.5mm | Mitre gaps open |
| 400mm | ~4mm | ~6mm | Significant movement |
| 600mm | ~6mm | ~9mm | Problems if restrained |
Approximate values for ring-porous species (oak, ash). Diffuse-porous species (maple, birch) move roughly 60% of these values.
What moves and what does not
- Solid wood moves significantly
- Any solid wood component — shelves, door panels, trim, treads — will move across the grain. The wider the board, the more total movement. This is unavoidable and must be designed for.
- Plywood moves very little
- Cross-laminated layers resist movement. A 600mm-wide plywood shelf moves less than 1mm across a Calgary winter. This is one of plywood's primary advantages for shelving and carcasses.
- MDF moves very little
- MDF is dimensionally stable across humidity changes, which is why it dominates painted trim. It does swell when wet, but it does not respond to humidity the way solid wood does.
- Movement is across the grain
- Wood shrinks and expands across its width and thickness. Along its length (the grain direction), movement is negligible — less than 0.1%. This is why a 2400mm-long shelf barely changes length but can move 4mm in depth.
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Where movement causes visible problems
- Mitred trim joints
- A 90-degree mitre in shrinking trim opens at the outside corner. This is the most common winter complaint. Coped inside corners do not have this problem.
- Paint cracks at panel joints
- A floating door panel contracts within its frame. The paint film, which cannot stretch as far as the wood, cracks along the joint line. It closes in spring.
- Cupped shelves
- A wide shelf finished only on its top face exchanges moisture unevenly. The unfinished underside releases moisture faster, causing the shelf to cup upward. Finish every face.
- Door alignment
- A solid-core door shrinks slightly across its width. The gap on one side opens while the other closes. Most doors self-correct in spring. Persistent rubbing needs hinge adjustment.
- Gaps at trim-to-wall junctions
- Trim shrinks across its width, pulling away from the drywall. This is particularly visible on wide baseboard and crown moulding. Flexible caulk accommodates the movement.
Answers
Frequently asked questions
- Is winter wood movement a defect?
- No. It is normal wood behaviour in a climate with extreme seasonal humidity variation. A hairline crack at a painted joint that appears in January and closes in spring is seasonal movement. A gap that persists year-round or a structurally separated joint is a construction issue.
- Can I prevent wood movement entirely?
- No, but you can reduce it significantly. Controlling indoor humidity to a narrow range (30–40%) limits the dimensional change. Using dimensionally stable materials (plywood, MDF) where movement would be visible reduces the effect. Designing joints that accommodate movement (coped corners, floating panels) prevents visible defects.
- Why do my cabinet doors stick in winter?
- Cabinet doors rarely stick in winter — they typically stick in summer when humidity rises and the wood expands. If doors are sticking in winter, check the hinge adjustment first. The issue may be hinge drift rather than wood movement.
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