How does the Ontario Building Code regulate drywall in areas with high moisture like GTA home laundry rooms?

The Ontario Building Code requires moisture-resistant materials in high-humidity areas like laundry rooms, but the specific drywall requirements depend on whether the space is a new build, a renovation requiring a permit, or a cosmetic upgrade. For laundry rooms in GTA homes, the key concern is protecting the wall cavity from moisture that can lead to mould growth and structural damage behind the drywall.

The Ontario Building Code (OBC) does not explicitly mandate a specific drywall type for laundry rooms the way it does for fire-rated assemblies in garages or party walls. However, several code provisions directly affect what goes on your laundry room walls. First, the vapour barrier requirement applies to any insulated exterior wall in Ontario's Climate Zone 6 — a 6-mil polyethylene vapour barrier must be installed on the warm side of the wall, between the insulation and the drywall. This prevents warm, moist air from your laundry room (which can be extremely humid when the dryer is running or clothes are air-drying) from condensing inside the wall cavity. Second, the OBC requires adequate ventilation in rooms that generate moisture. Laundry rooms should have either mechanical ventilation (an exhaust fan vented to the exterior) or a window that opens. Your dryer must be vented directly to the exterior through rigid or semi-rigid metal ductwork — never into the wall cavity or attic.

For the drywall itself, best practice in GTA laundry rooms is to use moisture-resistant (green board) drywall at minimum, which runs $20–$28 per 4x8 sheet in the GTA market. Green board has a moisture-resistant paper facing and core treatment that resists humidity better than standard drywall. For even better protection, especially in laundry rooms that also house a utility sink or are located in basements where ambient humidity is already higher, mould-resistant (purple board) drywall at $24–$32 per sheet is the superior choice. Purple board uses fibreglass facing instead of paper, eliminating the organic food source that mould feeds on. This is particularly important in older GTA homes — post-war bungalows across Scarborough, North York, and Etobicoke often have basement laundry rooms with chronic humidity issues, and standard drywall in these spaces frequently develops hidden mould behind the wall surface.

Behind the drywall matters as much as the board itself. If your laundry room shares an exterior wall, ensure the insulation meets the minimum R-20 for below-grade walls (or R-24 for above-grade walls in renovations) and that the vapour barrier is continuous with all seams sealed using acoustic sealant or Tuck Tape. Any penetrations — dryer vent, water supply lines, drain pipes — must be sealed around the vapour barrier to maintain its integrity. In basement laundry rooms, verify there is no active water infiltration before installing any drywall. Water seeping through foundation walls will saturate drywall from behind, and you will not see it until mould has spread extensively through the wall cavity.

For laundry rooms behind the washer and dryer, consider installing a waterproof membrane or cement board on the lower portion of the wall (the first 4 feet) as extra insurance against washing machine leaks and splashes. This is not code-required but is a smart precaution that GTA contractors increasingly recommend, especially after seeing the damage that a single washing machine hose failure can cause — which typically means tearing out all the drywall, remediating mould, and starting over at triple the cost.

The cost to properly drywall a typical GTA laundry room (roughly 80–120 square feet of wall area) with moisture-resistant board, proper vapour barrier, taping, and finishing runs approximately $1,200–$2,500 depending on the scope and condition of the existing walls. If you are finishing a basement laundry room as part of a larger basement renovation, the drywall work will require a building permit, and the inspector will check for proper insulation, vapour barrier installation, and ventilation before you can close up the walls.

A capable homeowner can handle replacing damaged drywall in an existing laundry room with moisture-resistant board as a like-for-like repair without a permit. However, if you are creating a new laundry room or finishing an unfinished basement space, hire a professional drywall contractor to ensure the moisture management system — insulation, vapour barrier, ventilation, and board selection — works together as a complete assembly. Get matched with a drywall contractor for a free estimate through Toronto Drywall Installers.