Why does my conservatory roof leak at the ridge?

Where the two slopes of a conservatory roof meet, the ridge closes the joint along the top. On a conservatory it is a metal or plastic cap that sits over the joint between the roof sheets or glass units, with seals, gaskets and fixings below it. All of that has to stay watertight while the frame expands in the sun and shrinks at night, and while wind lifts the roof. Hold a joint closed through those cycles for years and something eventually gives.

The ridge is also where several parts join up. The glazing bars from each slope meet at the top, the ridge cap closes over them, the end of the ridge meets a gable or wall, and often a flashing finishes against the house. Any one of those details can let water in. Because the ridge is also the part of the roof people see least, small leaks are rarely noticed until a drip stains the ceiling or the wall below, or until the carpet at the centre of the room is damp.

The most common fault is the seal under the ridge cap. Many conservatories were built with a bead of silicone and a rubber or foam gasket that is meant to seal the cap against the roof sheets. In time the sealant dries, shrinks and splits. Gaskets harden and lose their grip, so water is pulled under the cap by wind and capillary action. Birds and insects can also pick at the material and leave gaps.

You can often see it from inside, as a line of staining or damp running along the underside of the ridge, or water collecting at the glazing bar ends. Outside, the sealant is cracked, missing in places or pulling away from the surface. Resealing is possible if the surfaces are clean and the cap is firmly fixed. A thick layer of silicone over a loose cap is not a repair, because the next gust shifts the cap again. A proper repair strips the old material, refits the gaskets and uses the correct sealant for the materials involved.

At the back of a lean-to or the top of a gable-end conservatory, the ridge runs into the wall of the house. Here a flashing closes the gap. A flashing is a length of lead or similar metal pushed into a groove in the wall and dressed over the roof so that water runs off instead of in. If it is loose, split or short, water runs down behind it, and it often shows as a leak at the top of the ridge or in the corner.

Lead is the usual material, and Royston's cast-lead brochure lists code 4 among the weights suited to flashings. It should be dressed neatly, tucked into the mortar joint or a chase cut into the brick, and fixed in lengths short enough to move with the frame. Where the previous fix was a smear of mastic, the answer is to replace it with proper lead. Our page on lead flashing where a conservatory meets the house describes the detail. We check this joint on every ridge leak, because it is so often the true cause.

Sometimes the cap is fine and the trouble is below it. A frame that has moved can open a gap between the roof sheets and the ridge. Cracked glazing bars let water run along the bar and appear at the ridge. A split polycarbonate sheet, or one that has shrunk away from its channel, leaks wherever it ends. HomeBuilding gives a typical polycarbonate lifespan of 10 years and Eco Experts 10 to 15, so a roof of that age is on borrowed time.

Condensation can be mistaken for a leak. Water that forms inside the room and runs down the roof lining looks the same on the ceiling but has a different cause, and our page on conservatory roof condensation shows how to separate them. A pointer is timing. A real leak appears during or after rain and dries out in dry weather. Condensation follows cold, damp mornings and is worst around the glass edges, where it forms in beads. If you are not sure, photograph the stain through a wet spell.

If the frame is sound, the roof sheets or glass are in good order and the fault is a seal, cap or flashing, a repair will hold. It is a matter of stripping, refitting and resealing with the right materials. Our survey photographs each fault, then ends with our view on the ridge: fix the seal, buy time with a temporary measure, or renew the roof, and why.

If the roof is old, brittle and leaking in several places, patching becomes a loop of small fixes. In that case we would rather tell you so and move on to a new roof. Our guide to a leaking conservatory roof explains how the decision is made, and you can read about the alternative on the conservatory roof replacement page. Our price arrives in writing as one total figure, and we advise the least work that will cure the leak.