How Much Guttering Do I Need? Lengths, Brackets and Fall (UK)
Plastic half round guttering (112 mm gutter with 68 mm round downpipe) comes in 2, 3 and 4 m lengths. 12 m of gutter takes 3 lengths of 4 m, 2 unions and 16 brackets at 800 mm, and must fall 20 mm along its length. The guttering calculator works out the parts for your roof.
Parts for a run of gutter
For one run in 4 m lengths, with a bracket every 800 mm:
| Run of gutter | Gutters (4 m) | Unions | Brackets | Fall at 1 in 600 | Fall at 1 in 350 |
|---|---|---|---|---|---|
| 4 m | 1 | 0 | 6 | 6.7 mm | 11.4 mm |
| 6 m | 2 | 1 | 9 | 10.0 mm | 17.1 mm |
| 8 m | 2 | 1 | 11 | 13.3 mm | 22.9 mm |
| 10 m | 3 | 2 | 14 | 16.7 mm | 28.6 mm |
| 12 m | 3 | 2 | 16 | 20.0 mm | 34.3 mm |
| 16 m | 4 | 3 | 21 | 26.7 mm | 45.7 mm |
| 20 m | 5 | 4 | 26 | 33.3 mm | 57.1 mm |
| 25 m | 7 | 6 | 33 | 41.7 mm | 71.4 mm |
Downpipe and clips, by height
For one downpipe, in 2.5 m lengths with a clip about every 1.5 m:
| Height | Downpipe lengths | Clips |
|---|---|---|
| 2.5 m | 1 | 2 |
| 5 m | 2 | 4 |
| 7.5 m | 3 | 5 |
| 10 m | 4 | 7 |
Brackets, by spacing
| Spacing | 6 m run | 12 m run | 20 m run |
|---|---|---|---|
| 600 mm | 11 | 21 | 35 |
| 800 mm | 9 | 16 | 26 |
| 1000 mm | 7 | 13 | 21 |
The closer brackets are the safer choice: they hold the gutter better when it is full of water and leaves.
A house, front and back
Two runs of 9 m each (18 m in all), two downpipes 5 m high and two corners come to 5 gutters, 3 unions, 25 brackets, 4 stop ends, 2 outlets, 4 downpipe lengths and 8 clips.
Fitting the gutter
- Fall. Fix the bracket at the highest point first and the one at the outlet lower by the fall, then use a string line between them. The gutter must fall at least 1 in 600, which is about 3 mm in every 2 m.
- Position. The edge of the roof, or of the felt, should overhang the middle of the gutter, so that the rain falls in and not behind it.
- Brackets. Put one close to each joint, corner and outlet, and space the others evenly.
- Joints. Push the gutter into the union as far as the mark, leave a small gap for expansion, and snap the clip closed.
- Downpipe. Fit the clips at about 1.5 m, and never more than 1.8 m apart, with one close to each bend and joint.
- Test. Pour a bucket of water into the highest point and check that it all runs to the outlet.
Before you start
- Take down the old gutter and look at the fascia boards. Replace any that are rotten, since the brackets need something solid to hold.
- Use parts from one system, since the sizes and the joints are not all the same.
- Use a safe access tower or a scaffold for anything above one storey, and never lean over from a ladder.
A water butt on a downpipe collects free water: see the water butt calculator. See the roof tile calculator if the roof needs work too. Estimates only: check the quantities with the supplier.
Frequently asked questions
How many lengths of guttering do I need?
Divide the run by the length of each gutter and round up. 12 m of gutter in 4 m lengths is 3 gutters and 2 unions.
How far apart should gutter brackets be?
Most plastic systems say 600 to 1,000 mm. 12 m of gutter takes 16 brackets at 800 mm, and 21 at 600 mm. Use the maximum in the maker's instructions.
What fall should a gutter have?
At least 1 in 600, and 1 in 350 is better. Over 12 m that is 20 mm and 34 mm.
How many downpipes do I need?
At least one for each run, and more for a long run or a large roof. A gutter with an outlet in the middle falls both ways.
How do I measure for guttering?
Measure the length of the fascia where the gutter will go, add the corners and the stop ends, and measure from the gutter to the ground for each downpipe.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.