Blisters, cracks and splits are the visible signs of something underneath. Here is what causes each on flat roofs over extensions, bays and dormers in Bishopston, and what the right repair looks like.
A flat roof covering is a thin skin working hard. Sun, frost, standing water and building movement all pull at it. When it blisters, cracks or splits, the surface is telling you about moisture, stress or age below. Bishopston has plenty of flat sections: extensions, bay tops and dormer roofs among them, so these faults turn up often.
Blisters and trapped moisture
A blister is a pocket where the covering has lifted. Usually moisture or air got trapped beneath and warmed in the sun, pushing the skin up. Small blisters may be left alone and watched. Large ones, or any that have burst, let water in and need attention. We press and check the surrounding area, because a blister often has others nearby that have not yet shown. Pressing gently around the edge of a blister tells us whether the moisture is local or has spread under the surrounding covering.
Cracks from movement and age
Cracks form where the covering stretches, hardens or is pulled at a joint. Bay tops and dormer cheeks sit where different parts of a house move at different rates, and the covering has to follow. Over time sun and frost make the surface brittle, so a hairline crack can open into a split. Cracks along upstands often point to failed edge details.
- Hardening of the surface from sun and frost.
- Movement between extension and main house.
- Poor jointing where sheets meet.
- Foot traffic on a covering never meant for it.
Splits and ponding
Standing water does damage over time. Where a roof holds a puddle, the covering takes constant load and the water finds any weakness. Splits often follow ponding patches. Blocked outlets and poor falls both play a part, so we check the drainage as well as the surface. Fixing a split without curing the pond means it will probably return. Where a roof ponds in more than one place, the fall of the whole deck is usually the underlying cause.
Hidden decks and edges
Sometimes the real cause lies below. A rotten or uneven deck shows up as soft spots, ridges or sagging lines under the covering. Failed edge trims let water creep under at the perimeter. We check by feel and sight, and from inside where there is a ceiling stain, before deciding what to do.
- Soft deck boards under the covering.
- Loose or missing edge trims.
- Failed joints at walls and upstands.
- Debris blocking outlets and gutters.
Repair or replace
Where the covering is sound over most of the roof, a local repair is honest and sensible. Where blisters, cracks and splits are spread over the whole surface, patching is a short-term fix and replacement is better value. We explain which applies, show you what we found, and describe the materials we would use. Ask any roofer to show you photos of the damaged areas so you can see what is being proposed.
Frequently Asked Questions
Can a blister be popped and sealed?
Small, intact blisters are often left and monitored. Cutting one open without understanding the cause can let water in. If it has split or keeps growing, it needs proper repair, which may include drying out the area first.
Are cracks always a sign the roof has failed?
No. A few surface cracks on an otherwise sound roof can be sealed or patched. Many cracks across the whole area, or ones with water behind them, suggest the covering is at the end of its useful life.
Why do splits keep coming back after repair?
Usually because the cause was not fixed. Ponding, movement at a joint or a poor edge detail will tear a new patch just as it did the old covering. A lasting repair deals with the cause as well as the split.
Talk to our team about flat roofing in Bishopston
Every roof is different — the fastest way to get an accurate answer is a quick chat with our team.