Some roofs sag because of decay to the inside beams and sheathing.
Roof rafer construction wall sag.
Sagging rafters may be the result of having framed the roof with lumber of dimensions smaller than current building standards such as using 2x4s or 2x6 s or there may be damage to the framing from insects or rot.
Should the bottom cord of one or more trusses be sagging or damaged it may be reflected in a sagging ceiling or if the roof is over loaded to heavy then the downward pressure may cause the sagging.
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.
Decay can occur over time due to a number of reasons including leaks in the roof or leaks from guttering or downpipes wet rot or even insect attacks such as termites damaging the ends of the bearings.
Sagging rafters can lead to serious problems with the entire roofing system.
Some roof framing designs include the use of a strut or beam that runs perpendicular across the bottom of the rafters inside the attic.
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.
Sagging ceiling could be an indication of framing issues some of which could be related to the roof.
We include photographs of collapsing wood framed roofs and photo sequences.