Blisters, cracks and splits are the flat roof's way of telling you something underneath has changed. This guide explains the usual causes on Montpelier's bays, extensions and rear additions, and what can be done about them.
Flat roof coverings are sealed skins, so when one bubbles or opens there is always a reason. Trapped moisture, movement, sun and age are the usual causes. Montpelier's Victorian houses carry plenty of small flat roofs over bays, back additions and porches, and each of them lives in a different position and takes a different amount of weather.
Blisters and what is inside them
A blister is a pocket of trapped air or moisture between layers, or between the covering and the deck. The sun warms it and it grows. A small one on a sound roof may be left alone and watched, but a blister that is soft, wet or sitting on a joint can split and let water into the deck underneath, so it is worth having looked at.
Cracks and splits from movement
Roofs move as they heat and cool, and as timber dries or swells. A covering that has stiffened with age cannot follow that movement and cracks, usually first at corners, upstands and over deck joints. On old bay tops attached to a Victorian wall, small movements between the bay and the main house also open up the junction, which is why that line is always checked first.
Water pooling and poor edges
Standing water speeds up wear. Where it lies, the covering stays wet, softens and copes less well with frost and sun. Blocked outlets, low spots in the deck and badly formed edges all feed the problem, and several of these often turn up together on the same roof.
- Water sitting on the roof long after rain
- Loose, lifted or open edge trims
- Blocked or sagging gutters and outlets
- Debris gathering on the surface and at outlets
Rot underneath
Sometimes the covering is not the true culprit. A deck that has become damp and weak can move and push up through the covering. Under a bay or an extension, ceilings that mark or boards that flex suggest the deck needs attention as well, so a patch on the surface would only be a short-term answer. We lift a small area where needed to see what is really there.
Repair or replace
Where the damage is local and the deck is sound, a repair to the blister, split or joint can be reasonable. Where cracks are widespread or the roof has failed in several places, a new covering usually makes more sense than repeated patching. We show you what we found and explain which route we would take and why, so you can decide with the facts.
- Local damage on a dry, firm deck: repair
- Widespread cracking or lifting: new covering
- Soft or rotten boards: deck renewed first
Frequently Asked Questions
Can a blister be popped and sealed?
Not as a rule. Cutting a blister open lets water in and rarely leaves a lasting patch. We check whether it is dry and stable and, if it is not, repair it properly with new material rather than sealing over it.
Do cracks always mean a new roof?
No. A few cracks on a sound roof can be repaired. But widespread cracking, or cracks over a damp deck, usually means the covering is nearing the end of its useful life and a new one is the sensible option.
What can I look for from the ground?
Stains on ceilings below the roof, water that lingers after rain, and visible bubbles or lifted edges from an upstairs window. Do not climb up to inspect; call us for a proper look and a clear view of what is wrong.
Talk to our team about flat roofing in Montpelier
Every roof is different — the fastest way to get an accurate answer is a quick chat with our team.