Prevent this unfortunate series of events by bracing your rafters to make them sturdy and resistant to snow loads and wind.
Sagging roof between rafters.
When the framing of the roof is put together quite frequently two of the ceiling rafters will be fixed together as this will create a much longer span.
When you notice a roof sagging in between trusses it is usually the result of a damaged or broken roof rafter.
If the roof sags between the rafters or trusses the most likely cause is sheathing that s too thin for the area it covers.
Also inspect the metal or plywood gusset plates used where your wood meets on a truss.
If so i bet the installers used 1 2 in.
In this case the problem was due to a combination of poor attic ventilation and two bathrooms with vent fans dumping moist air into the attic.
If you notice that there is a visible dip in your roof chances are you have a problem with one or several rafters and you may soon be facing more issues like water leaks bowed out walls or your roof caving in on you.
Determine where the sag is in your roof in relation to your attic.
The fix here is to replace the thin sheathing with thicker sturdier sheathing.
Sagging rafters can lead to serious problems with the entire roofing system.
Half inch drywall can sag if it s hung under roof trusses that are spaced every 24 in.
If your ceiling drywall is sagging between joists sometimes called pillowing it s probably on the top floor and attached to the roof trusses.
If the framing is sound and problems are not found elsewhere but the roof still sags the problem might have originated because of poor installation of the plywood sheathing or shingles.
Other potential causes include damaged roof decking or even an underlying foundation problem.
A sagging roof line may original from the ceiling s horizontal rafters.
Sagging rafters are a sign that a house is in serious trouble.
When sagging gets too severe it can lead to roof collapse and once the roof goes the house won t last for long.
Sagging sheathing between rafters may be due to rot delamination use of fiberboard or other materials that may not perform well over the life of a home or due use of too thin plywood roof decking to start with.
Typically they are lapped and then toe nailed together in its center so that the correct length can be achieved.
Here s another view of the same roof shown at the top of the page and you can see that the sagging extends over a large area.
