How are lead box gutters and parapet gutters relined?

A box gutter is a channel set between two roof slopes, or between a roof and a wall, with a flat bottom and upright sides. A parapet gutter is the same idea tucked behind a short wall that rises above the eaves. Both are lined in lead and often hidden from the ground. They carry all the rain from the slopes beside them, and they are a common place for a leak because the channel is narrow and easily blocked.

Because they are hidden, they tend to be forgotten until water comes through a ceiling. Many older terraces, shops, chapels and larger houses have them. If your roof has a parapet or a valley between two pitches that you cannot see into, this page probably applies. A careful look with a torch, from a safe position, will often show the state of the lead. Overflowing water on a wall face below the parapet is another sign.

Relining starts with removing the old lead and any worn felt beneath it. This is when the real condition shows. Water that has run through cracks for some time can rot the boards, the bearers and the ends of the rafters. The deck is repaired or relaid, and the fall is checked or reformed.

This is where the final cost is often set. The lead is predictable. The carpentry is not, until the old lining is off. We photograph what is found, then tell you which timbers must be replaced and which can stay, before going further. Our guide to a lead flat roof covers the build-up beneath the metal. Dry, sound boards with a clean surface are the base for any lining that is meant to last. We also look at the ends of the gutter, where it meets walls and chimneys, since leaks often start there. Any rot we find is shown to you in photographs before it is cut out.

BS 6229:2025 sets a minimum finished fall of 1:80 for internal gutters among other areas, but that standard covers continuously supported flexible coverings such as felt and single-ply. Lead follows its own practice, so ask your roofer what fall they are working to and how the drips are spaced.

For gutters of this kind, Royston recommends lead codes 5 to 8. The higher the code, the heavier and stiffer the sheet. The lead is laid in lengths with a drip at each step, as shown in our answer on rolls and drips, and turned up each side under the roof covering or against the wall, with cover flashings finishing the top edge. A gutter that is wider needs more care over how the sheet is supported. Where the channel is long, the number of drips is higher. Ask how the lead will be supported at each drip, because that is where the sheet is most stressed.

A relined gutter has to empty somewhere. The outlet is formed in the lead, usually a sump with a downpipe beneath it, and kept clear of leaves and moss. An overflow set a little above the outlet gives a warning, because water will show at the overflow before it rises over the sides of the gutter.

Once the lead is laid, the roof covering on either side is made good, and the cover flashings or soakers are fixed back. The new gutter is then tested by running water through it. The finished job should drain freely with no standing water, and it should be easy to clear in future. Our answer on lead soakers covers one of the pieces that finishes the edge, where the roof slope meets the gutter side. If the channel is awkward to reach, clean it twice a year, once in autumn and again after any big storm.

Less, in a guide dated March 2026, gives 50 to 100 years for a lead flat roof, and MyJobQuote gives lead flashing more than 80 years. These are published ranges, not promises, and a gutter that is kept clear lasts longest.

Cost depends on how long the channel runs, which lead code is chosen, the condition of the timber beneath, and the height at which everything has to be done. Checkatrade, in a guide table dated October 2026, lists scaffolding on a two-storey semi at around £875 per month. That is a national figure for an ordinary house, and a tall parapet may cost more to reach. The quote follows the survey, in writing, with the whole job priced as one sum. See the lead roofing and leadwork page for the rest of our lead work. A roof with a concealed gutter is also worth a look every couple of years, since catching a blockage early costs very little.