What is a chimney back gutter?

A chimney that rises through a pitched roof acts like a dam. Water coming down the slope reaches the uphill face of the stack and has nowhere to go. The back gutter, sometimes called a cricket or saddle, solves that by giving the water a shallow channel that falls away to each side of the stack, so it flows round and rejoins the roof below.

You cannot usually see it from the ground. It sits tucked against the back of the stack, partly hidden under the tiles or slates above. Because it is out of sight, it tends to be forgotten until a stain appears in the loft. Yet it works hard, since it takes the water from the whole width of roof above the stack, not just the rain that lands on the chimney itself.

That is why a leak behind a stack, during heavy rain, so often traces back to this one small detail.

The gutter is made from lead, shaped on site. The floor of the channel is set with a slope, so it falls to the two sides, and the lead is turned up against the brickwork behind. The upper edge slides under the tiles or slates, and the sides are lapped over the stepped flashing along each flank. Every joint in the lead has to overlap in the direction the water flows.

Royston Lead's cast-lead brochure lists code 5 and heavier for parapet, box and tapered valley gutters, which is the nearest category to a back gutter, and code 4 for lighter valley and flashing work. Thicker lead copes better where the gutter is wide or takes foot traffic. The right code depends on the size of the stack and the width of roof draining into it, and it is confirmed at survey.

The usual culprit is rubbish. Leaves, moss, bird droppings and bits of crumbled mortar collect in the channel because it runs level with the roof and is hard to see. Once it silts up, water stands in it, backs up under the tiles and finds the loft. Standing water also keeps moss growing, and that makes the blockage worse each season.

Splits are the second cause. Lead moves as it warms and cools, and a channel with too long a run, or fixed too firmly, can crack at a fold. A gutter laid with too little fall holds water instead of passing it on. Another failure is the joint between the gutter and the stepped flashing, where lead has lifted or been "fixed" with sealant. Our page on stepped flashing on a chimney shows how that joint should look.

If the lead is sound and only blocked, clearing the channel and checking the falls may be all that is needed. That is the smallest job that cures it, and the survey photographs show you the result. Where the lead has split, a repair is possible in some cases, but patching a tired gutter can fail again, so you get a plain recommendation when renewing it will last longer.

Renewal means lifting the covering above, removing the old lead and building the new gutter to a proper fall before dressing the tiles back. It is better done together with the other leadwork around the stack, since the stepped flashing and apron are touched anyway. Our overview of chimney flashing shows how those parts fit together, and the chimney repairs hub lists the rest of the work on a stack.

There is no separate national price for a back gutter. MyJobQuote (last updated 22 September 2026) gives typical ranges for chimney lead as a whole: a patch repair £150 to £250, and a full replacement £350 to £460 without scaffold or £700 to £920 with it. A back gutter forms part of that work.

What moves your price is the width of the stack, the length of the gutter, the lead code, whether the tiles above need lifting and relaying, and the access. The survey comes first. After it you receive a written quote with a single total. To trace where a leak is entering, see our page on water around a chimney in the loft.

A back gutter needs little attention once it is sound, but it does need looking at. Moss and leaf litter build up where trees overhang or birds perch on the stack, and a quick check after autumn and after a gale stops a small blockage turning into a stain in the loft.

Do not try to clear it from a ladder against the stack, and never lean on the lead, because it dents and tears. If you can see debris building up from a window or with binoculars, mention it when you next have the roof looked at. A roofer clearing it carefully, with the lead protected, takes far less time than repairing the damage that standing water causes. Where trees overhang the roof, expect the channel to need clearing more often than the roof around it.