What causes trim gaps after renovation?

Trim gaps after renovation are primarily caused by wood movement due to moisture changes, settling of new materials, and temperature fluctuations — all common issues in Toronto's variable climate with hot, humid summers and dry winters.

Wood is a living material that expands and contracts with humidity changes, and Toronto's seasonal swings from 20% winter humidity to 70%+ summer humidity create significant movement. When contractors install trim during one season, gaps often appear months later as the wood adjusts to different moisture levels. This is especially noticeable in newer renovations where fresh lumber hasn't had time to acclimate to your home's specific conditions.

Structural settling also plays a major role, particularly in Toronto's older housing stock. Century homes in neighborhoods like Cabbagetown or The Annex naturally shift over time, and any new framing or drywall work will settle slightly as it bears load. Even in newer homes, fresh 2x4 framing can shrink as it dries, pulling trim away from walls or creating gaps at joints.

Installation factors contribute significantly to gap formation. If trim wasn't properly back-primed (sealed on the back side), it will absorb moisture unevenly and warp. Inadequate fastening — using too few nails or placing them incorrectly — allows pieces to pull away from the wall. Many contractors also fail to account for Toronto's climate by not leaving appropriate expansion gaps at long runs of baseboard or crown molding.

Temperature cycling in Toronto homes, especially those with forced-air heating, creates constant expansion and contraction. Trim near heating vents or in rooms with large temperature swings (like three-season porches) are particularly susceptible. The Ontario Building Code requires proper vapor barriers, but if moisture is getting behind the trim, it will cause more dramatic movement.

Professional solutions include using pre-finished trim that's been kiln-dried to local moisture content, proper caulking with paintable acrylic caulk that remains flexible, and strategic placement of expansion joints on long runs. Quality contractors will return for a "callback" visit 6-12 months after installation to address normal settling gaps — this should be discussed upfront.

Next steps: Small gaps (under 1/8") can be filled with paintable caulk, but larger gaps or recurring issues indicate underlying moisture or structural problems requiring professional assessment. Document the gaps with photos and contact your contractor if the work is under warranty.