Gutter / eavestrough

Frequently asked questions

What is the vertical pipe called, and does that differ too?

Yes, and it catches people more often than the gutter itself. The pipe taking water from the gutter to the ground is a downpipe in British and Australian usage, a downspout in American and Canadian usage, and a rainwater pipe in formal British specification. A "leader" is the American plumbing-code word for the same pipe. All four describe one component. The related word that does NOT map is "gutter" in the highway sense — the channel at the edge of a carriageway beside the kerb — which is a completely different element of a completely different trade, and is the one meant in kerb and gutter work on a road.

Why is gutter sizing a calculation rather than a standard size?

Because the flow depends on the roof, the rainfall intensity and the outlets, none of which is constant. The water a gutter must carry is the plan area draining into it multiplied by a design rainfall intensity for that location and return period, and the capacity available depends on the gutter's cross-section, its fall, and crucially the number and position of outlets — a long gutter with one outlet at one end carries far less than the same gutter with outlets at both. That is why roof drainage is designed rather than picked from a catalogue, and why a gutter perfectly adequate in one climate overflows in another beneath an identical roof.

Is a box gutter the same thing?

It is a gutter, and it is a considerably more demanding one, which is why it has its own word in all four markets. A box gutter runs within the roof — in a valley, behind a parapet, or between two roof planes — rather than at an eaves edge, so an overflow does not spill harmlessly outside the building but into it. Because of that, box gutters are designed with a larger margin, with overflow provision as an explicit requirement, and with attention to the outlet's capacity rather than just the channel's. The failure mode is different too: an eaves gutter that blocks drips down a wall, while a box gutter that blocks floods a ceiling.