Yes, and on Cwmbran's shallower postwar roofs it happens for a reason that is worth understanding, because it points at a completely different repair from the one most people assume they need.
A pitched roof is not sealed and was never meant to be. It works by overlap: each tile covers the head of the one below, so water running down the surface never reaches a joint. The whole arrangement rests on one assumption — that water leaves faster than it arrives.
Break that assumption and the roof leaks without anything being wrong with it. In prolonged heavy rain, water that cannot get away backs up, rises above the level of a lap and goes through it. Nothing has broken. The roof simply could not drain fast enough.
Steep roofs have a large margin here. Shallow ones have much less, which is why this shows up on postwar housing more than on the Victorian terraces in the valleys.
Two things happen as a roof gets shallower, and they compound.
Water moves down the slope more slowly, so at any moment there is more of it sitting on the roof. And wind-driven rain arriving at an angle can be pushed UP a shallow slope against the direction of fall — something it cannot do on a steep one, where gravity wins comfortably.
Combine them and driven rain can be worked back up under a lap, past the overlap the roof relies on, and into the space beneath. On a mono-pitch roof, where the entire surface drains to a single edge, the loading on that edge is higher still.
This is why the timing of a leak is the single most useful thing you can tell us. A roof that leaks in all rain has a route in — a hole, a gap, a failed detail. A roof that leaks only in prolonged heavy rain, and stays dry the rest of the time, has a capacity problem. Those are different diagnoses and different repairs, and knowing which you have saves a great deal of time on the roof.
Driven rain pushed up the slope gets past the overlap. It shows inside as damp appearing during sustained wind-driven rain from one particular direction, and not otherwise — which is why it goes unexplained for years.
The bottom edge of a shallow roof handles the whole slope's water in a narrow band. If the underlay does not carry water properly into the gutter — because it has torn, sagged or was never dressed in correctly — water goes behind the gutter instead and into the top of the wall.
A good share of what gets reported as a roof leak after heavy rain is guttering. When a gutter is blocked or overwhelmed, water goes over the back edge and runs down the wall, saturating the wall head, the fascia and the roof timber ends. Because it soaks rather than drips, it appears as damp at the TOP of an upstairs wall, not as a wet ceiling.
Canopies, integral garages, porches and the links between blocks. These drain to an outlet, and storms deliver the debris that blocks outlets at the same moment as the water. Standing water then finds any weakness in a seam and puts weight on the structure.
Next time it rains hard, put a coat on and walk round the outside. It takes two minutes and it is genuinely diagnostic.
If the answer to any of those is yes, tell us. It may well be the whole story, and it is a considerably smaller job than a roof repair.
Water entering at a lap can run along the underside of the covering, cross a batten, travel down a rafter and drop through a ceiling several metres from where it got in. Following a stain straight upwards is the most reliable way to repair the wrong part of a roof.
If somebody proposes to work directly above your damp patch without having established how water could be getting there, they are guessing, and a guess that misses means paying for the same leak twice.
Since tracing a leak is the job rather than a preliminary to it, it is fair to say what it involves.
We start inside, at the stain, because its position, shape and behaviour narrow things down considerably — whether it is a ceiling or a wall head, whether it is near a chimney breast or an external corner, whether it grows during rain or holds steady. Then the loft, where the underside of the roof shows the route the water has taken far better than the outside does: a wet rafter tells you where water has been travelling, and it usually points uphill from the stain rather than straight up.
Only then the roof itself, and by that point we are checking a specific hypothesis rather than wandering about looking for something wrong. That is why the questions below are worth answering before we arrive — they do a real part of the work.
T & T Roofing South Wales traces storm leaks across Cwmbran and works back from where water shows to where it is getting in. Assessment is free and without obligation.
Usually a capacity or drainage problem rather than a hole — a blocked gutter or outlet, or a shallow lap being overwhelmed. It is a different repair, so tell us when you call.
That points at guttering rather than the roof covering. Water going over the back of a blocked gutter saturates the wall head and the eaves, and it soaks rather than drips.
It has less margin. Water leaves more slowly and driven rain can be pushed up the slope against the fall, so a worn lap or a blocked gutter matters more than it would on a steep roof.
Yes. Driven rain gets past laps and into junctions that ordinary rain never reaches, so a roof can leak in one storm with nothing broken and nothing missing.
Storm damage in Cwmbran? T & T Roofing South Wales will assess the roof, explain what needs repairing and give you a free, no-obligation quotation. Storm Damage Roof Repairs Cwmbran has the full detail, or call us on 07766 547309.
Tell us what the weather has done and what you can see from the ground. We will come back to you — usually the same day.
If water is coming in now, please call rather than email — 07766 547309.
