Duncan Roofing FAQ

Most asphalt re-roofs on a typical Cowichan Valley home run one to three working days — a day for tear-off and deck repair, then the underlayment, flashing and shingle courses. Steeper or more cut-up roofs take longer because staging slows every stage, and metal systems generally run longer again. Weather sets the real schedule here: work is sequenced into a dry window rather than started and left open.

Late spring through early autumn, for a straightforward reason. Duncan averages about 30 mm of rain in July against 221 mm in November, so the dry window is wide in summer and effectively gone by late autumn. Asphalt shingles also need warmth and sun to seal down properly after installation. Roofs do get replaced through the wet months when a failure forces it, in shorter weather-dependent stages — but planned work belongs in the dry season.

Physically yes, and it is usually a false economy. Laying over an existing layer hides the sheathing entirely, so rot, delamination and previous leak damage stay undiscovered. It traps heat against the new shingles and shortens their life, and it turns the next re-roof into a two-layer tear-off at higher cost. Full tear-off to the deck is the specification here, and the reason a deck inspection appears in the scope.

The deciding factor is remaining service life in the surrounding shingle field, not the size of the damage. Asphalt is rated 15 to 30 years, and on the coast the lower half of that range is common. A failed chimney flashing on a twelve-year-old roof is a repair at $500 to $3,000. The same failure on a twenty-six-year-old roof showing granule loss and curling edges is money spent immediately before spending it again. An assessment with photos of deck condition and shingle wear is what settles it.

Seven things, at minimum: how many existing layers come off, what underlayment is specified, whether flashing is new or reused, whether ventilation is being brought to the BC Building Code minimum of 1/300 of the insulated ceiling area, what allowance covers replacement sheathing, what disposal and cleanup include, and what the manufacturer's system requires. A quote naming all seven can be compared against another. A single number cannot. Full ranges are in the roof cost guide.

A like-for-like repair or re-roof generally does not require a building permit in the Municipality of North Cowichan, which lists re-roofing and re-cladding as exempt unless structural repairs are required or insulation is replaced or upgraded. The City of Duncan publishes no roofing-specific exemption and directs homeowners to its building inspector. Anything touching structure, sheathing over damaged framing, or insulation should be treated as permit work until the local authority confirms otherwise.

Roofing service runs across the Cowichan Valley Regional District — Duncan, North Cowichan including Chemainus, Crofton, Maple Bay and Westholme, Lake Cowichan, and Cowichan Bay, plus the rural areas toward Sahtlam, Glenora, Cobble Hill, Mill Bay and Shawnigan Lake. Conditions differ enough across that ground that specification is set per property: Duncan averages roughly 1,500 mm of precipitation a year while Lake Cowichan takes about 2,048 mm.

Yes, using the method the shingle manufacturers specify. The Asphalt Roofing Manufacturers Association calls for a 50:50 mix of laundry-strength liquid chlorine bleach and water, applied by sprayer, left 15 to 20 minutes, then rinsed at low pressure, with dead moss loosened by a leaf blower rather than scraped. ARMA also warns that pressure washing an asphalt shingle roof causes granule loss and very likely premature failure of the roof system — which rules out a good deal of what is sold locally as roof cleaning.