What the abutment flashing does
Where the conservatory roof stops against the house wall there is a join that rain tries to get into. A flashing is waterproof metal laid over that join. One edge is tucked into the wall and the other lies over the roof, so water running down the wall is carried onto the roof surface instead of behind it. Built well, it seals the roof and the wall along their whole length.
The wall edge is the part to watch. It is usually set into a joint cut in the brickwork, called a chase, and sealed with mortar or sealant. Over time the mortar crumbles, the sealant shrinks and the metal lifts, and a path opens behind the flashing. Rain runs down the face of the brick, finds the gap, and enters at the top of the roof frame.
Roof movement adds to it. A conservatory frame flexes slightly with temperature, and the house wall does not move with it, so the joint between them takes the strain each time the weather changes. Signs inside include a stain on the house wall above the glazing and drips along the top bar, often worst after a day of driving rain from one direction.
Lead, and the alternatives
Lead is the traditional flashing metal because it is soft enough to dress tightly to the wall and the roof, and it lasts. MyJobQuote's figure for lead flashing is over 80 years, which is a minimum and not a forecast of its life. The specification for the job decides the lead code, meaning the thickness, and lead sheet work follows BS 6915 through Approved Document C.
Alternatives exist, and the choice depends on the roof system:
- Lead, dressed into a chase and pointed or sealed.
- Aluminium or other formed metal flashing, sold with some conservatory roof systems.
- Self-adhesive or flexible flashing strip, which is simpler but less durable at an exposed edge.
A flexible strip stuck over a failed joint is a quick fix that often leaves the cause in place. On a conservatory with a tiled or glazed roof we favour metal that is fixed into the wall and tucked under, because a line of sealant on its own relies on sticking to old brick and soon gives up. Our guide to a leaking conservatory roof shows where else water gets in.
Fixing it properly
A lasting repair deals with the cause, not just the gap. The steps, in the order they are done, are:
- Open the joint and remove the old sealant, loose mortar and any perished flashing.
- Check the roof bars, the top cap and the timber behind for water damage.
- Fit new flashing, tucked into a clean chase and lapped over the roof.
- Fix it with wedges, repoint or seal the chase with a suitable material, and test it with water.
The pointing step matters as much as the metal. A flashing set into brick that is crumbling will fail again, so loose bricks and old mortar are made good first. Where the house wall is rendered, the render is cut back to give the flashing a clean edge, and the cut is sealed so water cannot track behind it.
If the leak has soaked the frame or the plaster inside, we flag that at the survey instead of covering it over, because damp left behind a new flashing comes back as a stain. Read more about the work on our repairing a conservatory roof page, and about the wider service at conservatory roofs.
Telling a flashing leak from other leaks
Not every wet patch near the house wall is the flashing. A few checks help narrow it down before anyone gets on a ladder.
| Where | Likely cause |
|---|---|
| Along the top bar at the house wall | Abutment flashing or its pointing |
| Down a glazing bar mid-roof | Failed glazing seal or cap |
| At the eaves or gutter end | Gutter joint or overflow |
| On the house wall above | House roof or wall, not the conservatory |
A wet patch on the house wall above the conservatory can come from a blocked gutter or a defect on the house roof above, so the repair may be needed on the main roof. Our page on conservatory gutter leaks covers the eaves case.
A photo of the join where the conservatory meets the brickwork, taken after rain, tells us a good deal before we visit. The single written price comes after the survey itself, once we have seen the flashing close to, because the amount of repointing or brickwork repair only shows then.
