Why Is My Conservatory Leaking Where It Meets the House?

Why the wall junction is the weak point

Where a conservatory roof meets a house, two different structures with different movement meet at a joint that must stay watertight for years. The house wall is solid brick or block, and it absorbs rain. The conservatory frame is light and moves with heat and cold. Water running down the house wall must be directed over the roof and off, not behind it. The detail that does this is a flashing, which is a strip of lead or a flexible sheet that is tucked into the wall and laid over the conservatory roof edge. If any part of that detail fails, the water finds its way in.

Many older conservatories were fitted with a bead of silicone along the wall instead of a proper flashing. Silicone ages, shrinks and peels, and within a few winters it lets water through. That is a very common reason for a leak that returns every time it rains hard against the wall.

The usual causes, one by one

A lifted or split flashing is the first suspect. Lead can be dislodged by wind or movement, or can crack where it has been bent repeatedly. A flexible flashing can lose its adhesive. The top edge of the flashing should sit in a cut chase, a groove cut into the mortar course, and be pointed up with mortar or sealed. If the chase has fallen out, the water runs behind.

Second is the cavity. Houses with cavity walls have an air gap, and water that gets into the wall above the conservatory roof can run down inside the cavity. A cavity tray, a strip of damp-proof material that directs that water out through weep holes, should be installed above the roof junction. If it is missing, or the weep holes are blocked by mortar droppings or bridged by new work, the water comes out inside the conservatory. Third is the house wall itself: cracked pointing, porous bricks, or failed render above the roof can let rain in and send it down behind the flashing.

Fourth are the gutters and downpipes. A blocked house gutter or a cracked downpipe above the conservatory sends a stream of water onto the junction. Last, an old roof can sag and pull away from the wall, creating a gap that the flashing cannot bridge. Our broader guide to leaking conservatory roofs describes the leaks that start at the glazing.

How to tell what is leaking

Look at when and where it leaks. Drips at the wall plate after any heavy rain suggest a flashing or chase problem. Leaks that appear only in strong wind-driven rain from one direction point to the pointing or cavity. A leak that appears even in light rain can be a blocked gutter. Staining on the house wall above the roof line, green algae or damp patches also give clues. Take photos from inside, and note the dates and weather.

A proper diagnosis can involve a water test. We direct water at one part of the junction at a time, starting low and working up, while watching inside, as a hose over the whole area proves nothing. Sometimes the flashing has to be opened up to see what is behind it. Do not try to seal it with a tube of sealant: that often hides the fault and makes the correct repair harder.

Putting it right

The repair depends on the cause. A failed flashing is stripped, the chase is cleaned and the wall is made good, and a new lead or flexible flashing is fitted with a proper step or apron detail, and pointed or sealed. A missing cavity tray requires opening the wall above the junction, which is more work and should be agreed with you before it begins. Pointing and render repairs go in at the same visit. Gutters and downpipes are cleared and repaired. If the conservatory roof has sagged or moved, it may be better to look at the roof as a whole, as discussed on our page about repairing a conservatory roof or replacing it.

If the roof is being replaced, the wall junction is rebuilt as part of the work, with proper flashings and cavity trays. The steps in a replacement are covered in what happens when a conservatory roof is replaced.

When we survey, we photograph the junction, the pointing above and the gutters, so you can see where the water is getting in. A repair is quoted at a fixed price in writing. The rest of our conservatory work is at conservatory roof replacement in Basingstoke.