I suspect that the plywood used was cheap quality or too thin.
Fix sagging roof between trusses.
If your ceiling drywall is sagging between joists sometimes called pillowing it s probably on the top floor and attached to the roof trusses.
After measuring the damaged area between your roof trusses or rafters cut a piece of 1 2 plywood that will cover the area.
Measure the damaged area between your roof rafters or trusses.
The expanding roof stretcher used to push out the sag in the roof frame is mounted in place between a rafter pair.
Drywall instead of 5 8 in.
The fix here is to replace the thin sheathing with thicker sturdier sheathing.
The free ends of the expander are bolted below mid span on a pair of sagged opposing rafters.
Driving nails into it might make it worse place the plywood and styrofoam side up against the damaged roof decking.
Half inch drywall can sag if it s hung under roof trusses that are spaced every 24 in.
Sagging roof lines can originate with the horizontal ceiling rafters.
From the inside there doesn t appear to be any water damage or rot.
The first one is the rated span in inches for roof sheathing the second number is for flooring and the stamp will be visible from inside the attic.
Our roof sags a little between the trusses near the peak on the west facing side of the house.
The span between trusses exceeds rating of the sheathing each panel of plywood or osb has a grade stamp on one face like the example shown at below with two big numbers near the top.
Cut a piece of 1 2 inch plywood that will cover the area.
Remedies for a sagging roof there are a number of remedies for traditional rafter style roof frames depending on the problem and its severity.
If the roof sags between the rafters or trusses the most likely cause is sheathing that s too thin for the area it covers.
Drill holes in angle iron to keep the rafter from buckling again you will need to secure it with a piece of 1 2 inch angle iron.
Often the framing can be bolstered and beefed up internally but if the roofing material needs replacement anyway it may be best to tear off.
Multiple layers of shingles and new roofing material that s heavier than the roof was designed for can cause sagging even in a well constructed roof.
Glue a piece of 1 rigid styrofoam to the plywood.
You can simply have the old sheathing replaced with better material when it s time for new roofing.
If a roof dips in between rafters or trusses it s probably because the sheathing is too thin for the span.
If so i bet the installers used 1 2 in.
I was thinking about putting additional.
If your roof is sagging under the weight of too many shingles ideally all the shingles should be removed and a new set installed.
This will give some added strength and take care of any cracks in the wood itself.
When the roof framing is assembled two ceiling rafters are often joined together to create a longer span.
