Water is coming in where my veranda roof joins, what now?

First work out which joint is actually wet

Water rarely drops where it entered. It runs down the inside of an aluminium glazing bar until the bar changes angle, then it falls. That is why so many people replace the wrong seal. On the next wet day, or with a hosepipe run gently for a few minutes at a time, wet one area only and watch. Start at the lowest point and work upwards, because wetting the top first floods everything below it and tells you nothing.

1. 1Dry the underside of the roof completely and wipe the bars.
2. 2Run water on the gutter and front bar for three minutes and check.
3. 3Move to the panel joints, one row at a time, and check again.
4. 4Finish at the wall plate, the junction most likely to be responsible.
5. 5Photograph the first drip you see, since the entry point is above it.

The wall plate, where most veranda leaks begin

The wall plate is the aluminium section bolted to the house that the roof hangs from. It is sealed against the brickwork, usually with a flexible sealant and often with a cover flashing. Sealant is not a lifetime material. It hardens, shrinks back from one face and opens a hairline gap that only fills during sustained rain, which is why the leak seems to come and go. On rendered or pebbledashed walls the problem is worse, because the sealant has bonded to a surface that is itself only stuck to the wall.

A leak that appears after a dry spell followed by heavy rain is a classic sign of shrunken wall plate sealant rather than a failed roof.

Panel to panel joints and gasket shrinkage

Between each pane sits a rubber gasket held by the glazing bar. Over years the roof heats to a surprising temperature in summer and cools sharply at night, and the rubber moves with it. At the ends of a run the gasket can creep back by several millimetres, leaving a short open channel exactly where the bar meets the wall plate or the front beam. This is a genuinely small repair, and it is one of the few where replacing the gasket run properly is far better than pumping more sealant into the gap.

The front beam, gutter and end caps

The front of a veranda roof carries the rainwater, so anything wrong there shows up quickly. End caps that were pushed on rather than bedded, a gutter joint that has been nudged by a ladder, or a gutter running slightly the wrong way after ground movement will all put water where it should not be. Standing water in the gutter at the wrong end after rain is the giveaway, and it takes ten seconds to check with a torch.

• Water sitting still in the gutter long after rain stops
• Staining or green growth on the wall under one end cap
• Drips from the same spot on the underside of the front beam
• A downpipe that only trickles while the gutter overflows

What you can safely do yourself

Clearing the gutter of moss and leaves, checking the downpipe runs freely, and washing the roof from ground level with a soft brush on a pole are all sensible owner maintenance. Everything above that involves working at height over glass, and glass roofs are not walkable. Do not climb onto a veranda roof, do not lean a ladder against a glazing bar, and do not pressure wash a joint, because a pressure washer drives water past seals that were coping perfectly well.

• Never stand or kneel on the roof panels
• Avoid pressure washing near any junction
• Do not smear silicone over a gasket gap, it traps water behind it
• Do not drill new fixings into the wall plate to close a gap

When it is worth calling someone in

If the wall plate is involved, if the leak follows structural movement, or if the roof is an inherited structure with no records, a survey is the honest answer. We are asked to look at structures we did not install regularly, and often the outcome is a modest repair rather than a replacement. Where a leak has been running for a long time it is worth checking the fixings behind the wall plate as well, because sustained damp around anchors in a soft outer leaf is the one failure that does become serious.