How do I repair a sagging garage roof in Riverview New Brunswick?

A sagging garage roof in Riverview is a structural problem that requires professional assessment before any repair work begins — do not attempt to fix this yourself, as the underlying cause determines the correct solution and an incorrect repair can lead to collapse. Roof sag in NB garages is almost always caused by one of three things: undersized or damaged rafters and trusses, excessive snow load accumulation beyond the roof's design capacity, or moisture damage that has weakened the structural members over time.

Riverview sits in the Petitcodiac River valley and receives significant snowfall each winter, with ground snow loads in the 2.8-3.5 kPa range (roughly 58-73 pounds per square foot). Older garages in Riverview — particularly those built before modern code requirements were enforced — may have rafters or trusses that were undersized for these loads. A garage originally framed with 2x6 rafters spanning 24 feet without adequate intermediate support will eventually sag under repeated snow loading, even if it does not fail catastrophically. Each winter adds cumulative stress, and the wood fibres gradually creep under the sustained load until the sag becomes visible.

Moisture damage is the other major culprit in Riverview's Maritime climate. A small roof leak that goes unnoticed — perhaps where flashing has failed at a roof-to-wall connection on an attached garage, or where a valley collects ice dam meltwater — can saturate the wood structure over several seasons. Wet SPF lumber loses significant structural capacity, and once rot sets in, the affected members must be replaced entirely, not simply reinforced. During your professional assessment, the contractor should probe all structural members in the sagging area with an awl or screwdriver to check for soft, punky wood that indicates rot.

Repair Options and Costs

The repair approach depends entirely on the cause and severity. For minor sag caused by undersized rafters (deflection of 1-2 inches over a 20-foot span), the most common fix is to sister new lumber alongside the existing rafters. This involves cutting new rafters to match the existing profile and bolting or nailing them to the originals, effectively doubling the structural capacity. Sistering costs approximately $1,500-$4,000 for a two-car garage depending on the number of rafters involved and access difficulty. The roofing does not need to be removed for this repair — the work is done from inside the garage.

For moderate to severe sag (more than 2 inches of deflection, or sag accompanied by cracking sounds, visible separation at connections, or spreading walls), the repair is more extensive. The roof structure may need to be jacked back to level — carefully, over several days to avoid cracking the sheathing — and then reinforced with engineered lumber, steel plates at connections, or entirely new trusses. This level of repair typically runs $4,000-$12,000 and should involve a structural engineer's assessment to ensure the repair meets NB Building Code requirements for the local snow load.

If the sag is caused by rot from water damage, the repair must address both the structural deficiency and the source of the moisture. Replacing rotted rafters or truss members costs $3,000-$8,000 depending on extent, and the roofing above must be removed and replaced to fix the leak source. Budget an additional $2,000-$5,000 for roofing repairs including proper ice and water shield membrane (minimum 36 inches from the eave, though 48-72 inches is recommended in Riverview given the ice dam risk).

As an immediate safety precaution, if your garage roof is visibly sagging, do not store heavy items in the garage or park vehicles beneath the sagging area until a professional has assessed the structure. If the sag appeared suddenly or worsened noticeably after a heavy snowfall, clear the snow from the roof using a roof rake from the ground (never climb onto a compromised roof) and call a contractor immediately.

For Riverview homeowners, this is not a DIY repair under any circumstances — structural roof work involves load calculations, proper fastening patterns, and understanding how forces transfer through the building. An incorrect repair can shift loads to walls and foundations that are not designed to carry them. Get matched with experienced garage contractors through the New Brunswick Construction Network at newbrunswickconstructionnetwork.com for a professional assessment and repair quote.