Subfloor Repair & Preparation

The subfloor is the hidden foundation that determines whether your new flooring will perform flawlessly for decades or develop problems within the first year. In New Brunswick, subfloor issues are among the most common causes of flooring failure — and the most frequently overlooked during renovation projects. NB's Maritime climate creates specific subfloor challenges that differ from drier provinces.

Moisture migration through concrete basement slabs is nearly universal in NB construction, as the water table in many Maritime communities sits relatively close to the surface. Without a proper vapour barrier (6-mil polyethylene for plywood subfloors, or a dimpled membrane for concrete), moisture migrates upward through the slab and into the flooring above, causing hardwood to cup, laminate to swell, and carpet to develop mould.

Older NB homes built before the 1980s often have subfloors constructed from 1x6 or 1x8 softwood boards rather than modern plywood, and decades of seasonal movement have created gaps, squeaks, and uneven surfaces. These board subfloors must be evaluated for structural integrity and often require an overlay of 3/8-inch or 1/2-inch plywood to create a stable, flat surface suitable for modern flooring products.

In NB homes where the original subfloor has been damaged by water — from plumbing leaks, ice dams, or basement flooding — sections of rotted plywood must be cut out and replaced before new flooring can be installed. Ignoring soft or spongy subfloor areas leads to flooring that bounces, cracks (especially tile), and develops visible depressions over time.

Self-levelling concrete compound is used to flatten uneven concrete slabs and smooth transitions between different floor heights — a common need in NB open-concept renovations where walls are removed and floor surfaces at different levels must be brought flush.

Professional subfloor inspection and preparation in NB costs $1-$3 per square foot for basic levelling and moisture barrier installation, $3-$5 per square foot for plywood overlay on existing board subfloors, and $5-$10 per square foot for rotted plywood replacement requiring structural repair. A typical NB subfloor preparation project for a 500 square foot renovation area runs $500 to $2,500 depending on the extent of work required.

Investing in proper subfloor preparation adds 5-10% to your total flooring project cost but prevents failures that would require tearing out and reinstalling the finished floor.