How do I know if my Calgary home's subfloor needs replacing before new flooring?

The most reliable signs that your subfloor needs replacing are soft or spongy spots when you walk across the floor, visible water damage or staining on the underside, persistent squeaking that does not respond to screw-down repairs, and noticeable dips or humps that you can feel through the existing flooring. Any of these indicate the subfloor has been compromised and should be addressed before new flooring goes down — installing over a failing subfloor is a recipe for premature failure of your new floor.

The walk test is your simplest diagnostic tool. Remove the existing flooring (or walk on it carefully if it is still in place) and pay attention to how the floor feels underfoot. A solid subfloor should feel firm and uniform. If you feel soft spots, bouncing, or flexing between joists, the plywood or OSB has likely delaminated from moisture exposure. This is particularly common in Calgary homes where basement moisture has wicked up into the subfloor over years, or where a plumbing leak went unnoticed. Calgary's extreme dry winters followed by humid spring thaw create a seasonal moisture cycle that stresses subfloor materials, especially in homes without proper vapour barriers.

Visible damage indicators include dark staining (water damage), white or greenish patches (mould), swollen or crumbling edges on OSB panels, and delamination where the layers of plywood are separating. Pull up a section of old flooring in a suspect area and inspect the subfloor surface directly. In older Calgary neighbourhoods — Hillhurst, Sunnyside, Capitol Hill, Forest Lawn — homes built before the 1970s sometimes have plank-style subfloors made of individual boards rather than sheet goods. These plank subfloors often have gaps between boards, are not tongue-and-groove, and may be too uneven for modern floating floors without overlaying with new plywood.

The straightedge test checks for flatness. Lay a 6-foot straightedge or level across the subfloor in multiple directions. For floating floors like LVP, laminate, or engineered hardwood, the subfloor must be flat to within 3mm over 1.8 metres. For tile, the tolerance is even tighter. If you find dips or humps beyond these tolerances, the subfloor may need patching with self-levelling compound, sanding down high spots, or replacement of damaged sections.

Moisture testing is essential in Calgary basements and any area where water damage is suspected. A pin-type moisture metre should read below 12% for plywood subfloors before any wood-based flooring is installed. Readings above 14% indicate an active moisture problem that must be resolved before proceeding. Calgary basement slabs are notorious for transmitting moisture upward, especially in spring when snowmelt saturates the soil around foundations.

If your subfloor shows any of these warning signs, have a professional flooring installer assess the situation before committing to new flooring. A thorough subfloor inspection typically costs nothing as part of a flooring estimate, and it can save you thousands in avoided failures. Calgary Floor Installers can match you with local flooring professionals who will evaluate your subfloor and recommend the right preparation for your project.

---

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

• Wise Abatement
• Jk Stucco
• Calgary Custom Concepts
• Premium Built Structures
• Venkor Group Inc