Should I add attic ventilation when re-roofing?

The 1940s–50s bungalows of Esquimalt, Vic West and Oaklands were built with narrow or closed soffits and a couple of gable vents, and many have since had blown-in insulation pushed into the eaves. The result is an attic with no intake at all, warm moist house air rising through ceiling gaps and condensing on cold plywood in January. Re-roofing those homes without adding intake and a ridge vent puts new shingles over the same wet sheathing.

Fernwood and Fairfield multi-suite conversions add another source: bathroom fans and kitchen hoods from added suites that were ducted into the attic rather than out through the roof. A roofer on the roof for a replacement can terminate those ducts through proper roof jacks in an hour, which is the single biggest condensation fix available on that housing stock. In newer Langford and Bear Mountain homes ventilation is usually to code and the question is only whether baffles were crushed by insulation.

Cold-climate attics fail with ice dams; ours fail quietly. Winter here sits a few degrees above freezing with high humidity, so the plywood is cold enough to condense the moist air that leaks up from bathrooms, kitchens and pot lights, but never cold enough to freeze it into an obvious frost layer. The sheathing stays damp for months, the nails rust, and the first sign is often a ceiling stain that looks like a roof leak but appears on cold, dry days.

Balanced ventilation moves that moist air out: intake low at the soffits, exhaust high at the ridge, and a clear path between them over the insulation. Air-sealing the ceiling plane matters as much, because ventilation cannot keep up with an attic that is being fed warm air from below.

The crew is already on the roof with the old shingles off, so the marginal cost of doing ventilation properly is small.

• Continuous ridge vent along the main ridges, replacing scattered box vents
• Soffit intake confirmed open, with baffles installed where insulation touches the roof deck
• Bathroom and kitchen ducts terminated through insulated roof jacks, not into the attic
• Old gable vents evaluated; they can short-circuit a ridge-and-soffit system
• Plumbing stacks and pot-light penetrations air-sealed from the attic side if accessible
• Ventilation area checked against the manufacturer's requirement, which many shingle warranties assume

If the attic is wet because a fan is blowing into it or the ceiling leaks air like a sieve, adding a ridge vent alone does little. Equally, a low-slope or cathedral roof with no attic space cannot be ventilated the same way and may need a different assembly. And a stain that appears only during heavy rain is more likely a roof or flashing leak than condensation, which is a job for the leak assessment rather than a vent.

Ask the roofer to look in the attic before quoting, and to write the ventilation scope as its own line so you can see what is being added.