How much does a sagging roof cost to fix?

Sagging rooflines in Greater Victoria cluster in two housing eras. Pre-1940s homes in James Bay, Fernwood and Victoria West were often framed with undersized rafters and plank sheathing, and a century of moss-held moisture has softened the planks between rafters into visible dips. Post-war bungalows in Esquimalt and Saanich sometimes sag where a later owner removed a wall or added a heavy second layer of roofing the framing was never sized for.

A third local cause is trees. A limb from a Garry oak or Douglas fir that landed years ago can leave a cracked rafter that only shows as a dip after the roof ages. Because the fix ranges from a few sheets of plywood to an engineered repair, the inspection report, not the estimate over the phone, is what tells you which bill you are facing. If a sag appeared suddenly after a snow load or a tree strike, keep people out of the room below and get professional help the same day.

A roofer can tell you what a re-roof costs from the driveway. Nobody can tell you what a sag costs without seeing the framing from the attic and, often, the decking from above once shingles are off. A written inspection ($150 to $400 in our model, frequently credited against the job) should say whether the sag is decking, rafters or ridge, whether it is stable, and whether an engineer's letter is needed. That letter is also what an insurer or a future buyer will ask for.

If the shingles are past 15 to 20 years, a decking-caused sag almost always means replacing the roof at the same time; you cannot replace sheathing without removing the roofing above it, so paying twice makes no sense. Our repair-or-replace tool uses a threshold of roughly 35 percent: once the repair approaches a third of a replacement, the replacement usually wins on a five-year view. Structural rafter work is different; it is done before or during the re-roof and priced as its own line.

• Under 10 years old, small dip: decking repair alone
• 15+ years, dip plus moss or curling: combined re-roof
• Sudden sag, snow or tree strike: emergency inspection first

Ask what caused the sag, whether the fix is decking or framing, whether an engineer is involved, what happens if more rot is found once open, and whether the quote is fixed or an allowance. Ask for photos of the framing before and after. A contractor who prices a sag without going into the attic is guessing with your money.