Walk down a street of Victorian and Edwardian houses and you will see the same detail repeated: a bay window with a shallow roof above it, or a porch hood sheltering the front door. Both roofs are small, often only a few square metres, and most are covered in lead. They sit close to the ground, so they are easy to inspect, yet they are also the roofs most often left alone until a stain appears on the ceiling inside the front room.
Here we look at how these roofs are built, the faults at the abutment (the joint with the house wall behind), splits and ponding, and when renewal is the sensible choice. Larger lead roofs get their own treatment in our guide to lead flat roofs. If you want a tour of every place lead appears on a house, read what leadwork is first, or go to the lead roofing hub.
Anatomy of a bay or porch roof
Despite the small size, a bay or porch roof is built from several layers, and each does a separate job. Knowing the sequence makes it easier to see where a leak starts.
The structure
Timber joists span the bay or porch, and boards are laid over them with a slight slope, called the fall, to carry water towards the front. The fall is usually shallow, which is why water lingers on these roofs when anything goes wrong.
The covering
Over the boards goes a separating layer, then sheets of lead. On a bay of any width the lead is divided into bays of its own by wooden rolls, rounded battens the metal is wrapped over, and where one run ends a drip, a low step cut into the deck, passes the water down to the next section. A short porch hood might need only a single sheet.
The edges
Along the front the metal folds down over a timber drip batten and hangs clear of the gutter or fascia. At the sides it rises against any upstand. At the back, where the roof meets the main wall, a flashing runs up the brickwork or stone and tucks into a joint cut for it, with a cover flashing hanging over the upturned edge of the roof lead.
Canted bays
A bay with angled sides has hips, the sloping lines where two planes of roof meet at an outward corner. Lead is dressed over each hip and then tied to its neighbours, which makes the corners the most skilled part of the job.
The abutment: where a bay roof meets the wall
If we could pick one place to inspect on a leaking bay, it would be the back edge. The abutment is the line where the roof meets the vertical wall of the house, and it has to deal with water running down the wall as well as water landing on the roof.
How the junction is built
Two pieces of lead work together. An upstand, a vertical turn-up of the roof lead, rises against the wall. Over it hangs the cover flashing, a separate strip tucked into a groove or mortar joint in the masonry. The lap between the two has to be generous, and the cover flashing must be held tight to the wall with wedges or clips and sealed with fresh pointing mortar or a sealant.
How it fails
Pointing is the weak link. Mortar shrinks, cracks and drops out, leaving a gap behind the flashing that lets rain track in behind the lead. Moss and plant roots can pry the metal away. On older houses, the chase itself may be eroded, so there is little to hold the flashing at all.
What we do about it
On a survey we run a hand along the cover flashing to find loose lengths, look for dark staining on the wall above, and check the joint for open mortar. Repairs range from re-pointing and re-wedging the existing lead to renewing the whole abutment. On brick and stone alike, the chase is cleaned out first so the new pointing has something solid to grip.
A stain on the front-room ceiling just inside the window head often traces back to the abutment above, not to the lead on the roof itself.
Splits, cracks and the movement of lead
Lead expands in warm weather and contracts as it cools, and over the years that cycle works at any weak point. A bay roof is exposed to the sun on its flat top and shaded underneath, which means movement can be significant for its size.
Why lead splits
Splits tend to appear in a handful of places. One is at the base of a roll, where the sheet turns a corner and is under tension. Another is along a seam that was nailed through the face, which held the lead fixed when it needed to slide. A third is at a sharp fold that was beaten flat instead of dressed round a curve. In all three cases the cause is a detail, not the lead itself.
Sheets that are too large
Lead can only move freely over a limited length. MyJobQuote says correctly fitted flashing comes in lengths of about 1.5 metres, and the same thinking applies to roof bays: long runs without a drip or a roll give the metal no relief, and cracks follow.
Foot traffic and damage
Lead is soft. Ladders, window cleaners and people climbing out of a window can leave dents and kinks, and a kink becomes a crack with time. Falling branches and stones from a neighbouring chimney do similar harm.
Patch or renew?
A single split in sound lead can be mended: the area is cleaned back, a new piece is let in and the joint is made watertight, usually with a welded or lapped repair. When there are splits at several rolls, or the lead has become thin and crazed across the surface, a patch becomes a distraction. Our answer on patching a lead flat roof goes further.
Ponding, blocked outlets and the deck beneath
A lead covering is thin. It relies on a flat, sound deck below it, and on the water draining quickly off the surface. On a bay or porch roof, both can go wrong.
A dip in the boards
If a board has rotted or the joists have sagged, a shallow dip forms, and rain collects in it. Standing water on lead leaves white deposits and can find its way into any seam. Rockwool, citing BS 6229, says to design a flat roof at 1:40 so the finished fall reaches 1:80, and a bay roof that has lost its fall has lost that margin.
Gutters and downpipes
Most bay roofs shed into a small gutter at the front. Leaves, moss and bird debris block it, water backs up onto the lead and rises over the edge of the drip. The fix is cleaning and, where the gutter has dropped, re-fixing it so it falls to the outlet.
Timber rot
A damp deck rots from the underside, and the first sign may be a soft board or a darkened ceiling plaster in the room below. If the timber has gone, renewing the lead alone is a waste of money, so we probe the boards and joists wherever we can reach them from above or below.
Porches
Porch roofs have the same problems with one addition: a pitched porch roof may be tiled or slated, with lead confined to the ridge, the wall junction and the sides. The lead details are smaller, but they carry the same risks of loose flashings and failed pointing. The gap between the porch and the front wall often takes the full flow of water from the main roof above.
Renewing a bay or porch roof in lead
Renewal is a small job on paper, and a precise one in practice. The first step is access, which for a ground-floor bay may be a scaffold tower or a short lift of poles, rather than the full scaffold of a re-roof. MyBuilder gives about £1,125 as a typical scaffold cost for a full re-roof, and we price the actual scaffold your bay needs on the survey.
The sequence
The old lead is lifted and checked, since it may need keeping if the building is protected. The boards are inspected, soft sections are cut out, and any dips are corrected with new boards or tapered battens. A fresh separating layer goes down, the rolls and drips are set out, and the new sheets are cut, fixed at the head and dressed over the rolls. At the abutment, the cover flashing is re-set into a clean chase, wedged and pointed. Last, the front edge is dressed over the drip batten and the gutter is checked.
Choosing the code
The Royston Lead brochure lists parapets, box gutters and flat areas among the uses of Codes 5 to 8, and Code 4 is the standard general-purpose choice according to Leadworx. A bay roof of ordinary size often sits in the middle of that range. The code is named in the quote, so the metal is never a mystery. The lead codes guide has the full table.
Costs and life
MyBuilder's 2026 flat roof guide gives lead at £150 to £200 or more per m², and Less gives 50 to 100 years for a lead flat roof. As national ranges they are a guide only, since a bay of a few square metres has fixed costs for scaffold, set-up and waste that do not scale down. Your own written quote follows the survey and covers the whole job.
Finish, appearance and protected houses
New lead on a bay roof is bright and will stay visible from the street for a while. It weathers to a dull grey, and applying a patination treatment helps the change happen evenly and stops white run-off marks on the stone or brick below. Our guide to lead patination oil explains the process.
Listed houses and conservation areas
On a listed house the lead over a bay or porch counts as protected fabric, and a repair that changes its look may need consent. Renewal in the same metal and pattern is the usual starting point, with the council making the call. Stroud District has 41 conservation areas, and in five of them Article 4 Directions remove some permitted development rights. Ask the planning team before you start if your street is in one.
Why not a cheaper covering?
EPDM or GRP will keep water out of a small flat roof, and they are sold for exactly that. On a Victorian front bay, however, the finish, the colour and the junction with the stone will look different from lead. If cost is the issue, tell us and we will explain what the options mean for the look of your house.
What you get from us
At the survey we photograph your own bay or porch roof and annotate the faults on the prints. The quote that follows covers scaffold, stripping, boards, lead, labour, waste and making good. Older houses get like-for-like materials, the site is cleared on completion, and a 10-year workmanship guarantee comes in writing. Phone 01453 933613, or send a photograph of the bay through WhatsApp or the enquiry form.