How are bay window roofs repaired?

A bay window sticks out from the front of the house, and its roof can take several forms. Victorian and Edwardian bays often have a lead-covered flat or shallow-pitched roof, with a lead apron running up the wall behind. Interwar houses, including many 1930s semis, may have a tiled hipped roof over the bay, matched to the main roof. Later or altered bays may carry felt, EPDM or GRP.

Whatever the material, the roof is small and exposed, with a short run to the gutter. The joints are where it fails: the line where it meets the wall above, the junctions at each angle of the bay, and the edge over the window head. Our page on lead roofing explains the sheet metal commonly used on older bays, and the flat roofing page covers the other coverings.

A lead bay roof often fails at the seams or the upstand against the wall. Lead moves with the temperature, and old bays may have cracked at the folds where the metal has been stretched and flexed over the years. A flashing can also lift where the mortar line it was fixed into has crumbled, letting water run behind it. Staining on the plaster below the bay window head is the typical sign that something is wrong above, and it often shows first on the inside corner nearest the wall.

Felt and single-ply bays tend to split along the edges or around the corners, where the material is folded tightest. On a tiled bay, the weak spots are the hips and the lead-lined valleys at each angle, and the ridge where the bay meets the wall. Blocked outlets or small gutters can also back up on a roof this size. The guide to causes of roof leaks lists the faults in general.

The work begins with a survey, from safe access, to find the fault and its extent. Photographs of the lead, the seams, the upstand and the outlet go into the verdict, so the finding rests on pictures you can look at yourself. If the lead is sound apart from one failed seam or loose flashing, a local repair is possible: the joint is cleaned, the lead re-dressed or a section replaced, and the flashing tucked back into a groove raked out of the brick joint above and wedged tight.

If the lead has cracked across a wide area, renewing the sheet is the better value, because patching metal that has lost its flexibility tends to fail beside the repair. Where new sheet is laid, the thickness is chosen for the use, and Royston Lead's brochure lists codes 4 to 8 for different jobs. Our chimney page on lead codes for flashings shows how the codes work.

A felt or single-ply bay is repaired by cutting out the damaged area and fitting a new section with lapped joints, so water runs over the seams. If the covering has aged across the whole roof, recovering such a small roof is not a large job, and it often makes better sense than a patchwork. Typical lifespans are published for each covering, and our answer on repair lifespan covers how long a mended roof is expected to last.

A tiled bay is repaired like any pitched roof: slipped tiles re-fixed, the hips and ridge checked and the lead valleys renewed if they have failed. When hip or ridge pieces are disturbed they are refixed mechanically and not on mortar alone, in line with BS 5534. For a bay that has a shallow, near-flat top, the finished fall matters just as it does on a larger flat roof, because standing water is what wears a small covering out first.

Many bays in the older parts of Bognor Regis, Chichester and Arundel stand in conservation areas, and a front-facing roof may be visible from the street. A straight swap of old lead for new, or felt for felt, is rarely a planning matter, but a listed building has its own rules. Check with Arun District Council's planning team, or the council for your area, before altering the material or the look of a bay that faces the street.

The cost depends on the covering, the access and what the survey finds. Scaffold may be needed to reach a first-floor bay, and our price is given as one written sum. Ask any roofer whether their figure includes VAT and scaffold. Start with the roof repairs page, then book a survey to get pictures of your own bay roof. For a neighbouring job of similar size, see our answer on porch roof repair, where the same joints and coverings turn up.