Sagging or dipping roof: what it means
Old roofs move. The question is whether the movement finished decades ago or is still happening, and that is answered inside the loft rather than from the pavement.
A gentle, even sag in an old roof is usually historic timber settlement and is not dangerous. A new dip, a sharp local hollow, or a sag with cracked plaster or sticking doors below it is structural and needs looking at quickly.
Historic settlement
Victorian and Edwardian roofs were built with undersized rafters by modern standards. Many settled into a gentle dip within their first few decades and have been stable ever since. The tell is that the sag is smooth and even along the whole slope.
Rafter or purlin failure
A sharp local hollow usually means a purlin has deflected, a rafter has split, or a wall plate has rotted where water has been getting in. This is progressive and needs support rather than paint.
Too much weight on the roof
Old roofs designed for slate sometimes had heavier concrete tiles laid on them at a later re roof. The added load slowly bows the purlins. If your roof was re covered in a different material, this is worth checking.
Removed or cut timbers
Loft conversions and old water tank removals sometimes left struts cut or braces removed. We see this often, and the fix is usually reinstating support rather than anything dramatic.
What an inspection involves
We look along the slope from outside, then go into the loft and check rafters, purlins, struts, the wall plate and the condition of the timber where it bears. You get a plain description of what is holding the roof up and whether anything has moved.
FAQs
Long settled sags rarely are. New or worsening movement, especially with cracking below, should be inspected promptly. If you are unsure, treat it as urgent and let us look.
The line can be improved during a re roof by packing and reinstating support, but perfectly straightening an old roof is rarely realistic or necessary.
Yes. Where a defect is structural rather than a roofing matter, we say so and tell you what to ask for rather than quote around it.
Related reading
More on repairs & problems and the jobs that usually come with it.
- Moss on a roof: does it actually matter?Repairs & problems
- Ridge tile replacement: mortar bedding vs dry-fix ridge
- GRP fibreglass flat roofs: pros, cons and when to choose them
- Scaffolding for roof work: when you need it and what it costsCosts & budgeting
Looking for something specific? See our roofing services, cost guides, common roof problems or the areas we cover.
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