Rainwater systems – choosing and replacing

Choosing in three steps

1. Size. Work out what area of roof each run of gutter drains into one downpipe, and choose the downpipe diameter and gutter width from that. The manufacturer’s table is on the Gutters page, and the calculator does the sums.

2. Material. Three questions decide it:

3. System. Buy all the parts from one manufacturer in one material and colour. Brackets, unions, hoppers and seals are designed to work together; mixing manufacturers is a common cause of leaks, and manufacturers’ warranty conditions often require original accessories.

Replacing gutters step by step

1. Check the fascia board and rafters – taking down the old gutter often reveals rot. Repair it now, not after the new gutter is up.
2. Downpipe positions – where there are existing gullies, keep the downpipes where they were; otherwise the drain connections have to be redone.
3. Brackets. The end brackets are fixed at the start and end of the run with a height difference to suit the fall (for example 30 mm over 10 m at 3 mm/m), a string line is stretched between them and the other brackets are added. KJG says bracket spacing follows the rafter spacing.
4. Gutters are laid in the brackets and joined with unions or soldered, depending on the material; KJG specifies a 5 mm gap for expansion at a union joint.
5. Hoppers, stop ends, angles, expansion pieces.
6. Downpipes – bends, pipes, pipe clips, connection to the gully.
7. Water test – pour water in at the highest point of the run and check that it flows to the outlet and does not stand anywhere.

When replacing, also think about

• the covering at the eaves – if the eaves flashing or underlay drip flashing is being replaced too, this is the ideal time,
• gullies and drains – new gutters will not help if the connection below ground is blocked,
• collecting water – water butts and tanks are connected with a diverter on the downpipe,
• scaffolding – on a two-storey house and higher, it makes a big difference to the price.

Budget

A worked budget with current prices is set out in the article Cost of a new gutter system. As a guide to labour: Numiq (14 May 2026) gives €8–20 per m for fitting gutters and €6–15 per m for downpipes, excl. VAT and materials.