There are several problems that can lead to sagging or wavy roofs. Finding the cause often requires close inspection of the roof and the attic by a roofing contractor. Below are some issues that promote sagging or wavy roofs.
Rotting and Weak Plywood
Moisture can wreak havoc on the plywood surface under shingles. Missing or damaged shingles allows water to seep through and soak plywood. Heavy snow that remains on a roof for several days, rain, and storm damage can worsen the problem. The weak, soft plywood can begin to sag between the rafters or appear lumpy or wavy. It is easy to spot signs of this type of moisture damage inside the home. Water stains on ceilings and mold and mildew are signs of a leaky roof. Roof repair for shingles and plywood can correct the problem.
Horizontal Ceiling Rafters and Sagging Roofs
With a sagging roof, the exterior walls of a dwelling appear to tilt outward. The cause may be a weak or damaged horizontal ceiling rafter. During a roof installation, it is not unusual for builders to join two ceiling rafters to create one long rafter. The process involves lapping the rafters and nailing them together. If the rafters are pushed together but not lapped, or if the lapped joints become loose, the roof can sag. Pressure from the roof’s weight or heavy snow can also push the rafters against the exterior walls, which causes them to tilt outward.
Incorrect Rafter Tie Placement
Builders use rafter ties to keep rafters connected and keep them from spreading. Installing rafter ties incorrectly or failing to nail them securely can allow the rafters to pull apart. As a result, the roof may appear wavy, as if it is sinking between the rafters.
Some structures contain a beam positioned perpendicular to the rafters and attached to the bottom of each rafter for support. If the nails are not secure or if the beam is damaged, or the wrong size, the result can be a sagging roof.
It is crucial to seek roof repair for structural issues as soon as possible to preserve the roof’s integrity, maintain property value, and keep the home safe.