How Is a Conservatory Roof Sealed to the House?

The roof needs something to bear on at the house end. That is the wall plate: a length of timber or metal fixed to the house wall, level and secure, onto which the top ends of the rafters or glazing bars rest.

How is the wall plate fixed?

It is bolted or screwed through into the masonry with proper plugs or anchors, and it must sit on sound brick or block, not on crumbling mortar or render that has blown. Where the wall behind is soft, the fixings pull out and the roof starts to creep away from the house, which opens a gap that no sealant can close for long.

A careful installer checks the wall before choosing fixings and levels the plate so the roof falls evenly towards the gutter. If the plate is out of line, the roof ends up out of line too, and you notice it later as an uneven bar or a sheet that will not seat. Fixing the plate properly costs little on the day and a great deal to put right afterwards. Ask whether the plate is treated timber or metal, and what it is fixed with, before the roof goes on top of it and hides it for good.

Flashing is the metal strip that covers the join between roof and wall, so rain running down the brickwork cannot get behind the roof. On conservatories it is nearly always lead, because lead can be folded into awkward shapes and it lasts. According to MyJobQuote, lead flashing can last for over 80 years, a lower bound and never a promise.

What is the groove in the brickwork for?

The chase is a narrow slot cut into a mortar joint above the roof line. The top of the lead is folded into the slot and wedged, then pointed with mortar or sealed. The sheet hangs from the chase and lies over the top of the roof covering, leaving water no way in. A line of mastic smeared across the face of the wall instead of a chase is a short-term patch.

Where the roof slopes against the wall, the lead is cut in steps that follow the brick courses. A pitched roof beside a chimney uses the same stepped arrangement.

Lead sheet is made in codes, numbered by thickness and weight. Code 4 is 1.80 mm thick and weighs 20.41 kg per square metre, and suppliers colour-mark it blue. Royston Lead's brochure lists code 4 among the weights used for flashings, soakers, valley gutters and dormers, so it suits the job here.

Is thicker lead always better?

Not necessarily. Code 5 is heavier and is also listed for flashings, but heavier sheet is stiffer and harder to dress tight into a corner, which can work against a neat seal on a small conservatory roof. The right code depends on the length of each piece and how exposed the wall is, and the lead has to be dressed tight but not stretched. Code 3, the lightest in the table, is listed for soakers only, so it is not the one for a wall flashing. Soakers are the little bent lead pieces tucked under each tile or slate where the roof abuts a wall or chimney.

Ask which code is going on and whether the pieces are kept to sensible lengths. Long runs of lead need joints that allow for movement, or the metal cracks as the seasons turn. A roofer who can name the code and the lengths has planned the job.

You can check the wall end of the roof from inside and from the garden without climbing on anything.

What does a failing junction look like?

Look for damp staining on the house wall above the roof line, drips or tide marks along the top of the glazing, flaking paint or crumbling plaster inside, and lead that has lifted or slipped from its chase. Silicone smeared along the join tells you someone has patched it before, and such patches rarely last.

Mending a flashing costs far less than repairing the rotted timber behind it. We check the flashing, the chase, the wall plate and the gutter together, and show you pictures of the join on your own roof. If the lead needs replacing, the written price comes after the survey.

For leaks that show up elsewhere on the roof, read why a conservatory roof leaks. For the wider choices, see our conservatory roofs page, or why a conservatory roof sags where a failing junction has gone unnoticed.