Should I remove the old subfloor entirely or just patch damaged areas before new flooring in my Vancouver home?

In most cases, patching damaged areas is sufficient and far more cost-effective than full subfloor replacement — but the decision depends entirely on the extent of damage, moisture levels, and what type of new flooring you are installing. A thorough inspection before making this call can save you thousands of dollars or prevent a costly flooring failure down the road.

Start with a systematic inspection of the entire subfloor. Walk every square foot and feel for soft spots, bounce, or areas that deflect noticeably under your weight. Use a pin-type moisture meter to test readings in multiple locations — focus on areas near exterior walls, bathrooms, kitchens, and any walls adjacent to the home's crawl space or basement. In Metro Vancouver's wet climate, moisture damage to plywood subfloors is extremely common, particularly in older homes across Burnaby, New Westminster, East Vancouver, and the North Shore where crawl space ventilation was often inadequate by modern standards. Plywood moisture content should be below 12% before any flooring installation.

Patching is the right approach when damage is localized — a section near a toilet where a slow leak went unnoticed, an area under an old dishwasher, or a spot where crawl space moisture concentrated. Cut out the damaged plywood back to the nearest joists on both sides so the replacement piece has solid joist bearing on all edges. Use plywood of the same thickness (typically 3/4 inch for most Vancouver homes built since the 1960s) and the same grade. Secure the replacement piece to the joists with 2-1/2 inch subfloor screws on a 6-inch grid. Feather the edges flush with the surrounding subfloor using a belt sander or floor patching compound so there is no height difference at the seams. Budget approximately $3–$8 per square foot for patching, including materials and labour.

Full replacement is necessary when the damage is widespread — when more than 30–40% of the subfloor shows moisture damage, delamination, rot, or structural compromise. Signs that warrant full replacement include visible mould on the underside of the plywood (check from the crawl space), widespread delamination where the plywood layers are separating, spongy or punky wood that a screwdriver pushes into easily, and moisture readings consistently above 16% across large areas. Full subfloor replacement in a Vancouver home typically costs $5–$10 per square foot for the subfloor work alone — a 1,000-square-foot home might run $5,000–$10,000 before any new flooring is installed.

There are also situations where adding a layer on top makes more sense than removing the existing subfloor. If the existing plywood is structurally sound but uneven, thin, or has minor surface damage, installing a new layer of 1/4-inch or 3/8-inch plywood over top can create a fresh, flat surface for your new flooring. This approach works well when the existing subfloor is 1/2 inch and you need 3/4 inch total for hardwood nail-down installation. Screw the new layer into the joists (not just into the old plywood) and stagger seams so they do not align with the layer below.

The type of new flooring also influences the decision. Solid hardwood nail-down installation demands the most from a subfloor — it must be plywood (not OSB for nail-down), structurally sound, flat, dry, and at least 3/4 inch thick. Floating floors like LVP, laminate, and click-lock engineered hardwood are more forgiving because they distribute loads across their locking systems and do not rely on direct fastening to the subfloor. Tile requires absolute rigidity and flatness but can go over a well-prepared subfloor with backer board or uncoupling membrane.

Before making your decision, address the root cause of any moisture damage. If a crawl space is damp, install or repair the vapour barrier and ensure adequate ventilation or encapsulation. If a plumbing leak caused the damage, fix the leak and verify it is fully resolved. Replacing subfloor without fixing the moisture source is throwing money away in Vancouver's climate. For a professional assessment of your subfloor condition and the best path forward, Vancouver Floor Installers can connect you with experienced contractors across Metro Vancouver.

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