What is a secret gutter?

What a secret gutter is

A normal gutter hangs on the eaves where you can see it. A secret gutter does not. It follows the base of a wall, a parapet or a chimney, or along a hidden valley, and the last course of slates or tiles laps over the edge of the lead, so only a thin joint shows from outside. The same idea is sometimes called a concealed or hidden gutter.

The gutter itself is a trough of sheet lead laid on a timber deck, a boarded surface on the rafters, with a fall to an outlet or a downpipe. At its sides the lead turns up under the covering on one side and against the wall on the other. A parapet gutter and a box gutter are cousins of it, each a lead-lined channel, but those are generally open to view from the roof, while a secret gutter sits under the covering and only its mouth is visible.

Builders used it because it keeps a roof edge clean. There is no gutter on the wall face, no bracket and no downpipe running down a fine elevation, so the architecture stays intact. On historic terraces and larger houses that mattered, and it is why you meet secret gutters in older roofs where appearance dictated the design.

Why secret gutters block

The features that make the gutter neat also make it fragile. It is narrow, because it has to hide under the covering. It is shallow, because there is little depth to spare between the deck and the slate above. And it is covered, so no one looks at it from year to year.

Debris arrives from several directions. Moss and grit loosen from the roof above and wash into the channel. Leaves blow into the mouth. Birds and insects use the sheltered gap as a nesting place. Because the channel is narrow, even a small amount of material forms a dam, and because it is shallow, water overflows almost at once.

When that happens the water has nowhere obvious to go. It can lift over the lip of the lead and run under the slates or tiles into the roof timbers, or it can soak into the wall at the back of the gutter. Neither shows straight away. A stain on a ceiling or damp along the top of an internal wall is typically the first clue, and by then the timbers have already been damp for a while.

A smaller number of leaks come from the lead rather than a blockage. If the sheet was laid too thin for its width, or the joints were poorly formed, it can crack where it bends against the wall. Our page on lead underlay explains one reason that happens.

Signs that one is failing

Because you cannot see the gutter, you look for what it does to everything around it. These are the signs we check.

• Damp or staining on an upper ceiling or wall. A mark that grows after heavy rain and dries in dry weather usually points to a gutter overflowing or leaking at one point.
• Green growth or dark runs on the wall below the covering. Water spilling over the edge leaves an algae trail.
• Slipped or lifted slates at the base of the slope. The last course sits over the gutter and is the first to be disturbed when the timbers below soften.
• Water sound in a downpipe long after rain stops. Slow draining suggests the channel is partly blocked.
• Soft or dark timber seen from the loft. Rafter ends and wall plates at the edge of the roof are the first to rot when a hidden gutter leaks.

No single sign proves the fault, and the cause may be a lead flashing or a valley rather than the gutter. That is why we open the covering at the suspect point and look, instead of guessing from the ceiling stain.

How a secret gutter is cleared and repaired

Access is the difficulty. To clear a secret gutter properly, the slates or tiles along its edge are lifted and set aside, which exposes the full width of the lead. Debris is removed by hand, the channel is flushed with water to confirm it drains, and the condition of the lead is checked for splits, pinholes and worn areas.

If the metal is sound, the covering is refixed and the job is a clean. If it has failed in a small area, a repair may be possible, but lead that has cracked along a bend or aged evenly is better replaced. A new gutter is formed to the correct width and fall, with the lead dressed up under the covering and into the wall, and the roof covering put back over it. The fall matters because a channel that holds water will wear sooner, and one manufacturer's guidance quoted for flat roofs is a design fall of about 1 in 40 so that a finished fall of 1 in 80 is achieved.

A lead code is chosen to suit the width and the exposure. Thicker codes are used for wider gutters, and our guide to lead flashings explains how the thicknesses compare. If the covering is old natural slate or stone, it is lifted carefully and matched when it goes back, since reusing sound pieces keeps the roof true to its original build.

Secret gutter or open alternative

Where a secret gutter keeps failing, owners sometimes ask whether it can be replaced with something easier to maintain. It depends on the property. Where a building carries a listing or falls within a conservation area, changing the way the roof edge looks is a question for B&NES planning, and a concealed gutter often belongs to the original design. Rebuilding it in lead to the same pattern is usually the safest route.

On a plainer building, a larger or deeper channel, a parapet-style gutter with an overflow, or a different lining may be possible. A fibreglass lining is one option, and our page on GRP box gutters sets out when it is and is not suitable.

Whichever route is taken, the aim is the same: a gutter that drains freely, a lining that can move without tearing, and a way for you to check it. We can add a small access point or an overflow where the design allows. If you suspect yours is leaking, our free survey records what the opening shows in photographs, and a fixed quote follows in writing. Repair or relay falls under our lead roofing work.