Conservatory roof leaking where it joins the house

The line where a conservatory roof meets the house is the hardest joint on the whole structure to keep watertight. Two different buildings meet there, one of brick and one of frames and glazing, and rain running down the house wall arrives at it first. It is also where a leak is most often misdiagnosed, because the water may not be coming through the roof at all.

If your leak is somewhere else on the roof, see our main page on a leaking conservatory roof.

How a conservatory roof meets the house

At the back of the roof, a wall plate or wall bar is fixed into the house wall. Makers specify how closely: Guardian at no more than 300mm apart, Leka every 400mm with stainless screws. The joint is then weatherproofed from above. On polycarbonate and glass roofs that is usually a flashing set into the wall and sealed. On solid roofs the installation guides add more layers: Guardian runs the breathable membrane 100mm up the house wall and fits a soaker against it, and SupaLite forms a lead valley 70mm up the wall.

Some roofs also have a box gutter running along the house wall. Guardian’s guide says it must be fixed into brick, not mortar, and Leka recommends gallows brackets to support it.

Why is my conservatory roof leaking where it joins the house?

What you see	Likely cause	What fixes it
Drips along the wall plate in most rain	Flashing lifted, cracked or badly set; sealant failed	Reseal, re-dress or replace the flashing
Leak only in heavy or wind-driven rain; damp on the house wall inside the conservatory	Water getting into the house wall above and running down inside it	Repairs to the wall above, or a cavity tray
Overflow at a corner or along the wall	Blocked box gutter or gutter end	Clear it; check the joints and supports
A crack or gap between conservatory and house that is getting wider	Movement between the two structures	Structural check before any sealing
Damp on the house wall that was there before the roof	Existing damp in the wall	Investigate the wall itself

Which? lists problems with flashing among the most common causes of conservatory roof leaks. The cavity route is less obvious. In a cavity wall, rain that soaks through the outer brickwork runs down the inside of it. Where a roof meets the wall, that water needs a cavity tray to catch it and steer it out above the roof; without one it can come out below the roofline, inside the conservatory. Guardian’s guide says “it is always advisable to fit cavity trays”, with local authority advice sought where the roof is a replacement on an existing structure.

Movement is the one to take seriously. LABC warns that inadequate foundations “could move and cause settlement differences between the conservatory and the existing house, leading to cracks and water leakage”. Sealing over a moving crack only hides it.

How to fix a leak where the conservatory meets the house

1. Watch it in the rain. Note whether it leaks in every shower or only in heavy, wind-driven rain, and mark where the water appears.
2. Inspect from a ladder, not the roof. Look for lifted or split flashing, gaps in the sealant or mortar, and cracks in the wall just above.
3. Clear the gutters, including any box gutter along the wall.
4. Reseal or re-dress the flashing. A failed bead of sealant is a small job; lifting or replacing lead flashing is work for a roofer.
5. If the wall is the source, fix the wall above, or ask a roofer about a cavity tray. LABC’s guidance says building control cannot require one retrospectively on a replacement roof, so it will only happen if you ask for it.
6. If there is movement, get the structure checked before anything else. MyJobQuote puts a basic structural engineer inspection at £200 to £500.
7. If the wall is your neighbour’s, remember that cutting into it to insert a flashing falls under the Party Wall etc. Act 1996 in England and Wales, which requires a party structure notice at least two months before work starts.

What does it cost to fix?

MyJobQuote puts a typical conservatory roof leak repair at around £375, and Home Improvement Quote Today gives £500 to £2,000 for repairs. We found no published price specifically for re-flashing a conservatory or fitting cavity trays, which depend on the length of wall and access, so get a written quote that names the cause and the fix.

Insurance usually will not help: the ABI lists wear and tear and lack of maintenance among the things home insurance does not cover. If the roof is recent, go back to the installer, since a badly sealed abutment is a workmanship fault. Our guide to conservatory roof guarantees explains who covers what.

If you are replacing the roof, get the wall joint right

A new roof is the chance to fix a junction that has never worked. LABC’s guidance says its checks on a solid replacement roof include the “resistance of the roof together with any junctions to the existing structure to moisture”. An LABC news summary, now offline, said abutments should be treated like new-build detailing, with cavity trays, damp proof courses, membranes and flashings all linked.

Before you sign, ask each installer to explain in writing how their roof will meet your wall: how the wall plate is fixed, what flashing or lead valley they use, whether they will fit cavity trays, and what happens if the wall turns out to be out of plumb (Ultraframe’s guide allows for packing with aluminium shims). Guardian also advises checking the existing wall for damp before the roof goes on. Our guide to whether your conservatory can take a solid roof covers the other structural checks, and damp that has already got in may need tackling as conservatory mould.

A tiled roof costs about £7,400 to £12,100 for a medium conservatory, and our conservatory roof costs page has every option. When you get quotes, make sure the wall junction detail is written into each one, not left to the fitters on the day.