What thickness of plywood subfloor do I need under tile for a Vancouver bathroom renovation?

For tile installation in a Vancouver bathroom, you need a minimum total subfloor thickness of 1-1/8 inches — typically achieved with 3/4-inch plywood plus 1/2-inch cement backer board on top. This combination provides the rigidity that tile demands. Tile and grout are inflexible materials, and any subfloor flex or bounce will crack grout lines and eventually loosen tiles, wasting your entire investment.

The plywood layer should be exterior-grade or better — CDX plywood or tongue-and-groove subfloor plywood rated for structural use. OSB (oriented strand board) is acceptable under tile in dry areas, but in a Metro Vancouver bathroom where moisture exposure is inevitable, plywood is the strongly preferred substrate because it handles moisture better than OSB over the long term. The plywood must be securely fastened to the joists with screws on a 6-inch grid pattern. Any bounce or flex in the plywood needs to be addressed before proceeding — this may mean sistering joists, adding blocking, or installing thicker plywood if the existing subfloor is only 1/2 inch.

Cement backer board is the critical second layer. Use 1/2-inch cement backer board (such as HardieBacker, Durock, or PermaBase) installed over the plywood with thin-set mortar and 1-1/4 inch backer board screws spaced every 8 inches. Tape and thin-set all backer board seams with alkali-resistant fibreglass mesh tape. Never use green-board drywall or regular drywall as a tile substrate in a bathroom — it is not moisture-resistant enough and will eventually fail in Vancouver's humid climate.

An increasingly popular alternative to traditional backer board in the Metro Vancouver market is the Schluter DITRA uncoupling membrane. DITRA is a polyethylene membrane with a grid of square cavities that bonds to the plywood subfloor with thin-set, and the tile bonds to the top of the membrane. It serves as an uncoupling layer (preventing tile cracks caused by subfloor movement), a waterproofing membrane, and a vapour management layer — all in one product about 1/8 inch thick. DITRA can be installed directly over 3/4-inch plywood without additional backer board, saving height and simplifying the installation. At $2.50–$4.00 per square foot for the membrane alone, it adds cost but provides superior performance, particularly in shower surrounds and wet areas.

Waterproofing is absolutely essential in any Vancouver bathroom tile installation. Whether you use backer board or DITRA, the substrate must be waterproofed before tiling. Options include liquid-applied waterproofing membrane (RedGard, Hydroban, or Mapei AquaDefense) painted over backer board, or sheet membrane systems like Schluter Kerdi. Pay particular attention to floor-to-wall transitions, drain connections, and any penetrations. In Metro Vancouver's marine climate, bathroom moisture that penetrates behind or below tile will cause mould, subfloor rot, and structural damage — proper waterproofing is not optional.

For cost planning, expect to pay approximately $10–$25 per square foot installed for bathroom tile, which includes substrate preparation, backer board or membrane, waterproofing, thin-set, tile, grout, and sealer. Subfloor prep and backer board installation alone typically add $3–$6 per square foot to the project. A typical Vancouver bathroom renovation (40–60 square feet of floor tile) runs $1,500–$4,000 for floor tiling including all prep work.

Bathroom tile installation is not a project to cut corners on, and it is one of the areas where professional installation makes the biggest difference. The waterproofing, substrate prep, and precise tile work required in a wet environment demand experience. Vancouver Floor Installers can match you with tile professionals across Metro Vancouver who specialize in bathroom renovations — get matched for a free estimate on your project.

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