How do I deal with a subfloor height difference when transitioning from an old section to a new addition in a Shediac home?

Subfloor height differences between old and new construction sections are extremely common in Maritime homes, especially in Shediac where many properties have been expanded over decades. The key is creating a smooth, structurally sound transition that accounts for different joist systems, settling patterns, and the coastal moisture conditions that affect dimensional stability.

Assessment comes first — measure the exact height difference with a straight edge and level across the transition zone. Differences under 6mm can often be handled with underlayment adjustments or self-leveling compound. Gaps of 6-19mm typically require plywood overlay or sleeper systems. Differences over 19mm need structural solutions like sistering joists or installing a transition beam.

In Shediac's coastal environment, moisture management is critical during this process. The salt air and persistent humidity mean any exposed wood framing absorbs moisture quickly, so seal cut edges of new lumber with primer immediately. Check that the existing subfloor isn't showing signs of moisture damage — older sections near the coast often have softened areas around the perimeter where condensation has accumulated over years.

For moderate height differences (6-19mm), installing a plywood overlay on the lower section is usually the most cost-effective solution. Use 3/8" or 1/2" exterior-grade plywood, screwed every 6-8 inches into the existing subfloor. This creates a smooth transition plane and adds structural stability to older subfloor assemblies that may have loosened over time. In coastal Shediac, choose plywood with moisture-resistant adhesive — standard interior plywood can delaminate in high-humidity conditions.

For larger gaps, you'll need to build up the lower section with a sleeper system — 2x3 or 2x4 lumber laid flat and shimmed level, then topped with plywood. This approach lets you run utilities (electrical, plumbing) through the transition zone if needed. Use pressure-treated lumber for sleepers in Shediac's moisture-prone environment, and ensure adequate ventilation underneath to prevent trapped moisture.

Transition strips become crucial for the final flooring installation. A multi-level transition strip can handle remaining height differences up to 12mm while providing a clean, finished appearance. For hardwood or engineered flooring, choose solid wood transitions that can be stained to match. For LVP or laminate, use manufacturer-matched transitions that snap into their track systems.

Professional help is recommended for height differences over 25mm or when the transition spans a load-bearing wall. Structural modifications in coastal areas require understanding of Maritime building practices and proper moisture barriers. A flooring contractor experienced with older Shediac homes will recognize common foundation settling patterns and know which solutions work long-term in the salt air environment.

The investment in proper subfloor leveling — typically $2-4 per square foot for overlay work — prevents flooring problems that would cost far more to fix later. In Shediac's challenging moisture environment, taking shortcuts on subfloor prep leads to cupping, gaps, and premature failure regardless of the flooring product chosen.

Need help finding a professional flooring installer familiar with coastal Maritime conditions? New Brunswick Flooring can match you with contractors experienced in Shediac's unique challenges.