How do I tell a plumbing leak from a roof leak?

Two-storey homes with the bathrooms stacked over the living room are the standard layout in Langford, Colwood and the newer parts of Saanich, and a stain in the middle of the living-room ceiling there is a plumbing suspect first: a failed tub drain gasket or a toilet wax ring sits right above it, and the attic is another floor up. In the one-and-a-half-storey homes of Fairfield, Fernwood and Oak Bay the bathroom is often tucked under the roof slope, so the same stain has a dormer wall, a vent pipe and a plumbing stack all within a metre of each other, and the fixture test matters more.

Victoria's dry summers make the timing test unusually clear. From June to September at Gonzales rain is rare (July averages about 14 mm), so a stain that keeps growing in August is not a roof leak. Conversely, a stain that appears only after the first November atmospheric river and goes quiet in a dry week points at the roof. Note the dates; a roofer or plumber will ask.

Wait for a dry day. Mark the edge of the stain with a pencil and photograph it. Run each fixture above it one at a time for ten minutes: fill and drain the tub, run the shower directed at the walls, flush the toilet several times, run the dishwasher and washing machine. Check the stain after each. If it darkens or spreads, you have found a plumbing source and should call a plumber, not a roofer. If nothing changes across all fixtures and the stain only moved after last week's storm, book a roof inspection.

• Pencil-mark and photograph the stain first
• One fixture at a time, ten minutes each
• Shower aimed at walls and the tub spout, not just the drain
• Check the attic above with a flashlight if safely reachable

A ceiling stain that appears in a cold, dry January week with no rain and no fixture link is often attic condensation: warm indoor air leaks into the attic, frosts on the underside of the sheathing or on nail tips, and melts in a thaw. Bathroom fans that vent into the attic instead of outside are the classic Greater Victoria cause. This looks like a roof leak, gets blamed on the roof, and is fixed by air sealing and ventilation instead.

If the fixture test is positive, a plumber. If it is negative and the stain follows storms, a roofer; an inspection with a written report is $150 to $400 in our model and is often credited against the repair. If neither fits and the timing is cold snaps, a roofer or home inspector who will look at attic ventilation and fan ducting. A stain that is actively dripping or sagging is urgent regardless of source; contain it and call whoever can come first.