What is the proper gap between composite deck boards in NB's climate?

For composite decking in New Brunswick, maintain a 6-8mm (1/4" to 5/16") gap between boards to allow for thermal expansion and contraction. This spacing is crucial in NB's climate where temperatures can swing 70°C from winter lows of -35°C to summer highs of +35°C.

Why Proper Spacing Matters in NB

Composite materials expand and contract significantly more than wood with temperature changes. In New Brunswick's extreme temperature swings, composite boards can expand up to 6mm per 12-foot length during hot summer days. Without adequate gaps, boards will buckle, warp, or push against each other, creating dangerous raised edges and potentially damaging the deck structure.

The Maritime humidity also plays a role — while composite doesn't absorb moisture like wood, the material still responds to temperature changes. Boards installed during cool spring weather (when most NB decks are built) will expand considerably once summer heat arrives. Conversely, boards installed during hot weather will contract significantly in winter, so gaps may appear larger during cold months.

Installation Best Practices

Use proper spacing tools during installation — most composite manufacturers provide plastic spacers, or you can use 16d nails (about 6mm) as temporary spacers. Install when temperatures are moderate (15-25°C) for the most consistent results. Never butt composite boards tightly together, even if gaps look large during cool installation weather.

For end-to-end joints where boards meet, maintain 8-10mm gaps and ensure joints are staggered across different joists. This prevents long continuous seams that could create weak points or water collection areas.

Drainage Considerations

Proper gaps also ensure water drainage between boards, which is essential in NB's wet climate with heavy spring runoff and frequent Maritime storms. Standing water on composite decking can lead to mold, mildew, and slippery surfaces. The gaps allow water to drain through to the ground below rather than pooling on the surface.

Manufacturer Specifications

Always check your specific composite brand's installation guidelines, as requirements can vary slightly. Premium brands like Trex Transcend, TimberTech Pro, and Fiberon Paramount may have specific spacing requirements that differ from the general 6-8mm rule. Some newer composite formulations have improved dimensional stability but still require proper gapping.

When to Hire a Professional

While gap spacing seems simple, composite deck installation requires experience with proper fastening techniques, joist spacing (composite typically needs 12" on center rather than 16"), and understanding how different composite formulations behave in NB's climate. Professional installers ensure proper spacing, drainage slopes, and structural support that prevents costly callbacks for buckling or movement issues.

Need help finding a deck builder experienced with composite installation? New Brunswick Decks can match you with local contractors who understand proper composite installation techniques for our Maritime climate.