Gutters are sized for the roof area that drains into them and the rainfall intensity where you work. Placing the outlets well matters as much as the gutter size.
Common sizes
Domestic gutters are typically 112–115 mm half-round or square, with 150 mm or deep-flow profiles for larger roofs. Downpipes are usually 68 mm round or 65 mm square.
Outlets
Put an outlet roughly every 10–12 m of gutter, and close to valleys, which deliver a lot of water to one spot. A centre outlet with the gutter falling both ways doubles the capacity of a run.
Fall
About 1:350 to 1:600 (3 mm per metre or less) is typical. Some systems are designed to be laid level.
The full fitting list
- Gutter lengths and union brackets
- Fascia brackets every 1 m or less
- Stop ends, corners and outlets
- Downpipes, offset bends, clips and shoes
- Leaf guards, if wanted
This guide is general information for estimating. It is not engineering, legal or tax advice. Check the Building Regulations and Building Control for your project.