Replacing a lean-to conservatory roof

A lean-to, sometimes called a sloping or mono-pitch conservatory, has one plane of roof running from the house wall down to the front frame. There is no ridge and no hip, so the job looks simpler than a multi-sided design. The catch is that every drop of water, and every gust, meets the roof at just two lines: where it joins the house and where it ends at the gutter.

For general advice on the solid roofs that might replace it, see solid and tiled conservatory roofs for Stroud homes. This page covers only what belongs to a lean-to.

The wall plate is a timber beam bolted to the house wall to carry the top ends of the new rafters. It has to be fixed into sound masonry, never into render or a loose course of old brickwork. On Stroud's older stone cottages and terraces we look first at what the wall is built from, because soft lime mortar between stones asks for different fixings than modern brick does.

The front frame must take its share as well. Homebuilding and Renovating notes that frames which once held polycarbonate are being asked to bear heavier roofs, and MyBuilder puts structural reinforcement at £500 to £2,000 when it proves necessary. The survey records whether the frame, the cill and the dwarf wall need attention before any heavier roof is chosen.

The plate is also levelled and packed where the wall is uneven, so the rafters sit true along the whole slope.

Every covering has a minimum pitch, the angle below which it should not be laid. Polycarbonate and glass systems cope with shallow slopes, but tiled and slate-effect systems want more. Marley lists concrete tiles from 12.5 degrees up to 35 degrees depending on the profile, so the product's own data sheet decides, not a rule of thumb. If your slope is too low for the covering you like, the choice is another covering or a change to the structure.

Marley's reading of BS 5250 asks for a continuous 5 mm vent at high level when a roof is a single slope, so air can pass over the whole of it. We build that into the detail from the start. A lean-to is also the shape most likely to overheat in summer; see fixing a hot conservatory for the choices.

At the house wall, a strip of lead or a made-up proprietary section closes the gap. It is cut into a mortar joint in the masonry and dressed over the roof covering. Get it wrong and water tracks behind it, showing up later as damp patches on the inside of the house wall. MyJobQuote gives a long life, over 80 years, to correctly installed lead flashing, and Leadworx names Code 4 as the usual general choice, though we match the code to each detail.

At the foot of the slope, a gutter gathers the water. Manufacturers generally advise a slight fall towards the outlet, somewhere between about 1:600 and 1:350 depending on the system. A lean-to often has a single gutter run and one downpipe, so a blockage matters more than on a larger roof, and we plan a clear route to a drain or soakaway.

Cover strips and end caps are another place to look. On the sides of a lean-to, where the roof meets a return wall or a neighbour's boundary, a stepped or continuous flashing is needed, and these side junctions leak just as readily as the top edge. The survey notes each of them so the quote does not leave one out.

A solid roof over a conservatory is a material alteration, which brings it under the Building Regulations and means a building control application (Homebuilding and Renovating, 2023). Planning permission can also come into play when a change alters the building's structure or appearance in a significant way, according to the Planning Portal, so ask Stroud District Council's planning team when in doubt.

A written quote follows the survey, taking in access, the strip, frame work, the new roof, finishing and waste. The look of the inside is a further choice; see plastered ceilings inside a solid conservatory roof. If your conservatory has several facets, not one slope, our page on Victorian-style conservatory roofs may suit better. Costs and options for the whole service sit on the conservatory roof replacement page.

A lean-to roof comes off in one plane, which makes the order of work straightforward but the weather risk real. The old covering and roof bars are lifted away, the wall plate is fixed and levelled, and the new rafters are set before the room is closed in again. We plan to have each stage covered before the day ends, with temporary sheeting where it cannot be.

Access can be awkward. Many Stroud houses stand on steep lanes or terraced hillsides, where a skip cannot sit close and materials have to be carried a distance. We work that into the survey and the quote, not on the day, so there are no surprises when the lorry arrives. The old sheets, bars and sealant are taken away when we leave.