How to Fix a Sagging Roof

A sagging roofline is one of the few roof problems you should never wait on. It means something under the shingles, the decking or the framing, has weakened. Here is what causes it, how serious it is, and how it gets fixed.

What sagging looks like

What causes it

Water damage

The most common cause. A long-term leak rots the plywood decking, and eventually the wood under it. Rotted decking sags between rafters, and rotted rafters or trusses can let a whole section drop.

Too much weight

Two or three layers of old shingles add a lot of weight. Heavy tile installed on framing not designed for it causes the same problem. Occasionally, a heavy ice storm or a fallen limb adds load the structure cannot carry.

Undersized or damaged framing

Rafters or trusses that were undersized, spaced too far apart, cut for later work like ductwork or an attic ladder, or cracked over time can bend under the load.

Poor ventilation

Years of trapped heat and moisture in the attic weaken decking until it delaminates and sags.

Foundation movement

In North Texas, clay soil movement can shift walls and pull on the roof framing. A sag that appears along with cracks in brick and drywall and doors that stick may start below the house.

How serious is it?

It depends on the cause and the extent. Sagging decking between two rafters is a repair. A ridge that has dropped or framing that has cracked is a structural problem that can get worse quickly, and it needs attention right away.

How the extent is found

A roofer inspects from above and from the attic:

If framing is involved, a structural engineer may be brought in to specify the repair.

How it gets fixed

The shingles over the repaired area are replaced, and often the whole roof, if it is near the end of its life anyway.

What not to do

Do not walk on a sagging roof, and do not store heavy items in the attic above it. If the sag appeared suddenly or is getting worse, call right away.

Call (855) 741-ROOF for an inspection.