A dip can come from several different layers
When you notice a dipping roof line, it helps to separate what you can see from what may be happening underneath. The issue here is a local low spot visible in the roof slope or ridge. With a dipping roof line, a small visible defect can sometimes have a simple explanation, while a wider pattern may point to something that needs a closer inspection.
Before arranging work, note whether the dip is between supports or directly over one, whether tiles follow the dip smoothly or look recently disturbed, and whether the dip is old and stable or newly noticeable. For a dipping roof line, this sort of simple information often tells more than a close-up picture because it shows when and where the defect is active.
First decide whether the structure or covering is uneven
The main possibilities are natural long-term deflection in timber, a weakened rafter or purlin, and settlement at a support.
Other causes worth considering are poorly aligned battens during previous reroofing, and local decay from an old leak. With a dipping roof line, the important thing is to match the cause to a local low spot visible in the roof slope or ridge, rather than treating it as a general roofing fault. For a dipping roof line, that distinction can prevent work being carried out on a nearby detail that happens to look worn but is not responsible for what you are seeing.
Photographs are useful if you suspect change
From a safe position, you can photograph the roof line from the same viewpoint over time. You can also look in the loft for a bowed or damaged member beneath the low spot.
It is also useful to compare the dip with ceilings or walls below for related signs. For a dipping roof line, write down what you can see and, where relevant, what the weather was doing at the time. A short sequence of photographs of a dipping roof line from the same safe viewpoint can show whether the condition is changing. When checking a dipping roof line, avoid walking on the roof or leaning out of windows; the aim is to collect useful information without creating another problem.
A stable old dip is different from new movement
This becomes more urgent if the dip is becoming more pronounced, cracking or splitting is visible in supporting timber, and a recent impact or alteration preceded the change. With a dipping roof line, those signs suggest that waiting for a convenient time could allow more water entry, falling material or further damage.
If those warning signs are absent, a dipping roof line may not need an emergency call-out, but it is still worth arranging a proper look before the condition gets worse. In this case, change over time matters: a local low spot visible in the roof slope or ridge that has been stable for a long period is a different situation from something that has appeared recently or is becoming more obvious after each spell of bad weather.
Inspection should work from tiles down to supports
A roofer looking at a dipping roof line should identify whether the unevenness is in the covering, battens or main structure, then check supports on both sides of the dip.
They may also need to decide whether structural advice is needed before reroofing work. Because this page is about a dipping roof line, the inspection should stay focused on that problem and the nearby details that could realistically produce it. For a dipping roof line, ask what they think has failed, what evidence supports that view, and whether the proposed work is local or part of a wider defect. A clear explanation of a dipping roof line is more useful than a quotation that simply lists materials.
Correct the layer that is actually out of line
Depending on what is found, a suitable repair might refix local coverings if the structure is sound, strengthen or repair the supporting timber if it has failed, or avoid cosmetic levelling that masks ongoing movement.
For a dipping roof line, the best option is the one that deals with a local low spot visible in the roof slope or ridge and leaves the surrounding roof working as it should. If wider work is proposed for a dipping roof line, ask why a local repair would not be reliable, what condition the adjoining materials are in, and whether access costs make it sensible to combine closely related repairs. The answer should make sense for a dipping roof line, not read like a standard reroofing recommendation.
This guide is general information about a dipping roof line. The cause of a dipping roof line at an individual property can only be confirmed by inspecting the relevant roof area.