The decking surface is the part of the structure most exposed to winter. It takes the freeze-thaw cycling, the meltwater, the shovel and, in many provinces, months under snow. The framing below is governed by the building code, but the surface material is a choice with real trade-offs in cold conditions.
What winter actually does to a board
Two mechanisms dominate. The first is moisture: wood absorbs water, and when that water freezes it expands inside the board, working at the grain until the surface checks and splits. The second is dimensional movement: every material expands and contracts with temperature, and a board that swings from deep cold to summer heat moves more than one in a mild climate.
Both effects are made worse by the number of freeze-thaw cycles a region sees rather than by the lowest temperature alone. A surface that crosses 0°C repeatedly is stressed more often than one that simply stays frozen all winter.
The three common choices
Pressure-treated lumber
Pressure-treated softwood is the most widely available and the least expensive option per square foot. The preservative treatment resists rot and insects, but it does not stop the board from absorbing water. Used outdoors in a freezing climate, treated lumber generally needs periodic cleaning and sealing to slow moisture uptake, and even then it tends to check and require board replacement sooner than the alternatives.
Cedar
Cedar contains natural oils that give it some resistance to moisture and decay, and it is dimensionally stable for a softwood. It is more expensive than treated lumber and, like all wood, benefits from periodic sealing in a wet, freezing service condition. It is chosen most often where the natural appearance matters.
Capped composite and PVC
Composite boards combine wood fibre and plastic; capped composites add a protective polymer shell, and full PVC or mineral-core boards reduce moisture uptake further. The defining advantage in cold climates is low water absorption, which limits the freeze-thaw splitting that affects wood. The trade-offs are a higher up-front cost and the need to follow the manufacturer's expansion-gap guidance, because the boards still move with temperature.
A note on surface colour
Dark composite boards can reach high surface temperatures in direct summer sun. On south- and west-facing decks, lighter colours or PVC lines that run cooler are often preferred so the surface is comfortable underfoot in the warm months as well.
Side-by-side comparison
| Material | Moisture behaviour | Maintenance | Relative cost |
|---|---|---|---|
| Pressure-treated | Absorbs water; prone to checking | Periodic clean and seal | Lowest up front |
| Cedar | Some natural resistance | Periodic sealing | Higher than treated |
| Capped composite | Low absorption | Occasional cleaning | Higher up front |
| PVC / mineral core | Near-zero absorption | Occasional cleaning | Highest up front |
Practical points for installation
- Follow the manufacturer's expansion-gap spacing for the temperature range at install time, since a board fitted in summer behaves differently than one fitted in winter.
- Keep fasteners and connectors corrosion-resistant, and confirm any metal in contact with treated lumber is compatible with the preservative used.
- Clear heavy snow with a plastic shovel rather than metal, and avoid de-icing salts that can damage some surfaces.
- Match the material to the deck's exposure: full-sun decks favour lighter or cooler-running surfaces.
Reference notes; confirm product-specific guidance with the manufacturer and current requirements with your local building authority.
References
- Canada Construction Network, Deck Materials Compared: Pressure-Treated, Composite, and Cedar.
- National Research Council Canada, National Building Code of Canada 2020.