A healthy roofline runs straight. When you see a dip or a sag, the roof is telling you something has given way underneath, and it is a structural issue, not just a surface one. The most common cause we find is water, since a leak that has run for a long time soaks the decking and framing, and wet wood softens and loses strength until the roof dips where it gave way. That ties many sags directly to an old, unaddressed leak.
The other causes are structure that was undersized or has weakened over the years, too much weight from layers of old roofing or heavy tile on framing not built for it, and simple age. Whatever the cause, a sag tends to grow, because the thing behind it, wet wood or overload, keeps acting on the roof. That is why it should be looked at rather than watched.
We start by examining the decking and framing through a roof inspection, and where water is the cause, leak detection and roof repair stop the source before more wood is lost. Our page on what causes a sagging roof goes deeper.
| Step | What to check |
|---|---|
| 1. Look at the roofline | Sight along the ridge and eaves from the ground. A straight roof should not dip or wave. |
| 2. Pair it with leaks | A sag over a known leak strongly suggests water has softened the wood beneath. Note any stains nearby. |
| 3. Watch for growth | A dip that is getting worse should be looked at without delay, since it can signal serious damage underneath. |
| 4. Check inside | New cracks in ceilings or walls can accompany a settling roof and are worth mentioning. |
Because a sag is structural, the fix depends entirely on what caused it, which is why the inspection comes first. If water is the cause, stopping the leak and replacing the softened decking during a repair may be enough. If the framing itself is undersized or failing, a structural engineer is brought in for that work. And if the damage is widespread, a full roof replacement that corrects the deck is the honest fix.
What we do not do is cover a sag with a new surface and call it done, since that leaves the real problem, wet wood or overload, still at work. The one constant is that a sag should not wait, because it only grows, as our page on delaying a repair covers. Ponding on a flat roof can also stem from a settled deck, which our ponding water page addresses.
We examine what is underneath. Request an inspection.
Call (310) 806-5959Tell us what you are seeing and we will inspect the structure and give you a written price for any work, with no obligation.