How much does wood deck shrinkage cause gaps between boards in Calgary's dry climate and can it be prevented?

Wood deck boards in Calgary's extremely dry climate will shrink significantly more than in humid regions, creating gaps of 3-5mm between pressure-treated boards and 2-3mm between cedar boards by the first winter. This shrinkage cannot be prevented but can be planned for during installation.

Calgary's indoor winter humidity drops to just 15-20%, and outdoor humidity remains low year-round compared to coastal cities. This extreme dryness causes lumber to shed moisture rapidly, and pressure-treated lumber arrives at the lumberyard with very high moisture content (often 19-25%) that must dry out. As the wood dries, it shrinks across the grain, opening gaps between boards that were installed tight together.

Pressure-treated lumber experiences the most dramatic shrinkage because it's kiln-dried after treatment, then absorbs moisture during the pressure treatment process. When installed fresh from the yard, PT boards may have 20%+ moisture content. As Calgary's dry air pulls this moisture out over 6-12 months, boards can shrink 3-5mm in width. If you install PT boards with no gaps in summer, you'll have significant gaps by winter. The solution is to install pressure-treated boards with minimal gaps (1-2mm) knowing they will open up to 4-6mm spacing.

Cedar shrinks less but still moves significantly in Calgary's climate. Cedar typically arrives at lower moisture content than pressure-treated lumber, so it shrinks 2-3mm per board. Install cedar with standard 3mm gaps using a nail or spacer, and expect final gaps of 5-6mm after the first year. Cedar also develops surface checking (small cracks along the grain) in Calgary's dry air, which is normal and doesn't affect structural integrity.

The timing of installation affects shrinkage patterns. Decks built in spring with lumber that's been stored outdoors through winter will shrink less than decks built with fresh, wet lumber in summer. However, you can't completely avoid shrinkage - even kiln-dried lumber will adjust to Calgary's specific humidity levels. Most experienced Calgary deck builders plan for maximum shrinkage and space boards accordingly during installation.

Composite and PVC decking eliminate shrinkage issues entirely. These engineered materials are dimensionally stable and won't shrink, swell, or gap over time. While the upfront cost is higher ($10-18/sqft for composite vs $3-6/sqft for pressure-treated), you avoid the gapping, checking, and maintenance issues that plague wood decks in Calgary's climate. For homeowners concerned about appearance consistency, composite decking maintains uniform gaps year-round.

Proper installation technique minimizes problems. Use a consistent spacing method - either a nail for minimal gaps on pressure-treated lumber or a 3mm spacer for cedar. Ensure boards are straight and properly fastened to prevent cupping and warping as they dry. Pre-drilling end grain prevents splitting, and using corrosion-resistant fasteners prevents staining as the wood weathers.

When to Hire a Pro: Experienced Calgary deck builders understand local shrinkage patterns and install boards with appropriate spacing for the lumber type and season. They also know which lumber suppliers provide the most consistent moisture content, reducing unpredictable shrinkage. For DIY builders, the key is planning for shrinkage rather than trying to prevent it - Calgary's climate will win every time.

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Looking for experienced contractors? The Calgary Construction Network connects homeowners with qualified professionals:

• G.D.K Drywall LTD.
• BOND CONTRACTING & CONSTRUCTION INC
• Royland Stucco
• Mike’s Restoration Service
• True North Overhead Doors