Can i replace the subfloor in my Saint John bathroom myself if the boards are rotted from a slow leak?

Replacing rotted bathroom subfloor is definitely a DIY-capable project, but you'll need to address the moisture source first and potentially deal with structural modifications that require permits.

The good news is that subflooring replacement falls within what homeowners can legally do themselves in New Brunswick. However, before you start ripping up boards, you must identify and fix the leak source — whether it's a toilet seal, shower pan, or plumbing connection. Continuing with rotted subfloor replacement while ignoring an active leak is like putting a bandage on a broken pipe.

Assessing the damage scope will determine your approach. If the rot is localized around a toilet or small area, you can often cut out the damaged section and patch with new 5/8" or 3/4" plywood or OSB subflooring. For extensive damage affecting multiple joists or spanning large areas, this becomes a more complex structural repair. In Saint John's older housing stock — particularly homes built in the 1970s-1990s — bathroom subfloor rot often extends beyond what's initially visible due to the city's humid coastal climate.

Here's where permits come into play: If your repair requires modifying or reinforcing floor joists, adding blocking, or making structural changes, you'll need a building permit from the City of Saint John Growth & Community Services department (506-658-2835). Simple subfloor replacement typically doesn't require a permit, but structural modifications do. The work must comply with the National Building Code of Canada 2020 edition, which New Brunswick adopts.

Safety considerations are critical — rotted subfloor often means compromised structural support. Before stepping on questionable areas, probe with a screwdriver to test joist integrity. Wear respiratory protection, as older Saint John homes may contain asbestos in flooring adhesives or insulation. If you discover extensive joist damage, sagging, or structural issues beyond simple board replacement, this moves into professional territory requiring an experienced carpenter or structural assessment.

The typical process involves cutting out damaged sections with a circular saw, ensuring cuts land on joist centers for proper support, treating any affected framing with wood preservative, and installing new subflooring with construction adhesive and screws. Factor in $150-400 for materials depending on the affected area size, plus any plumbing repairs needed to address the original leak.

Your next step should be thoroughly documenting the damage with photos, then getting quotes from licensed plumbers to permanently fix the leak source before touching the subfloor. Contact the City of Saint John building department if you're unsure whether your specific repair scope requires a permit.