Sagging roofs to your roof

A visible dip or wave in the roofline is one of the few roof problems you should treat as urgent.

What causes a roof to sag

Common causes are rotten or undersized rafters, failed or removed structural supports, water-damaged decking, too much weight (for example heavier tiles fitted to a structure built for slate), or simply age. Occasionally it's a foundation or wall-plate issue.

How serious is it?

A sag can range from cosmetic to a genuine structural risk. Because you can't tell which from the ground, a sagging roof should be inspected promptly by a roofer or, if needed, a structural engineer. Don't delay — a sag tends to get worse, not better.

Putting it right

Fixing a sag may mean replacing or sistering rafters, renewing decking, adding support, and re-covering the affected area — often alongside a re-roof if the covering is also at the end of its life. Cost depends entirely on the cause and extent, which is why a survey is essential.