How to fit guttering: fall, brackets and downpipe

Which way should the gutter fall, and how much?

Fall towards the outlet at 3mm per metre. Over a 10m run that is 30mm of drop from the high end.

Set it with a string line, never by eye. Fix the highest bracket first, then one at the outlet end at the correct drop, then pull a taut line between the two. Every bracket in between lands on that line. Too much fall looks wrong from the ground and drops the gutter away from the tile line. Too little and the run holds standing water, silt and moss, which is what most blocked gutters actually are.

How far apart do the brackets go?

1000mm maximum, and 800mm on exposed sites or where snow sits. Add a bracket within 150mm of every union, outlet, corner and stop end.

The brackets carry everything; the gutter is just a channel sitting in them. A union with no bracket beside it is the joint that leaks after the first hard frost, because the gutter flexes there and the seal rolls out of its seat. A 4m length needs five brackets at 1m centres before you count the ones next to fittings. Fix into solid timber. On a 16mm replacement fascia the board itself takes the screw. On an 8mm cover board, go through into the rafter end behind it.

Where does the outlet go?

Directly above the gully the downpipe will discharge into. Everything else in the run is set out from that point.

You have two choices. A running outlet sits mid-run and takes water from both directions, which suits runs over about 8m and gullies part-way along an elevation. A stop end outlet closes the end of a run and drains one way only, which suits short runs and corner gullies. Check where the gully actually is before ordering, because on rear elevations and extensions it is often not where you expect. If there is no gully at all, that is a drainage job before it is a gutter job. Ring us.

What are the setting-out numbers?

Setting out	Figure
Fall towards the outlet	3mm per metre (30mm over 10m)
Bracket spacing	1000mm maximum; 800mm on exposed sites
Bracket beside a fitting	Within 150mm of each union, outlet, corner, stop end
Half round gutter	112mm section, 4m lengths
Expansion allowance	Fit gutter to the moulded insertion mark, not hard to the stop
Tile overhang into the gutter	25-50mm
Downpipe	68mm round, 5.5m lengths
Pipe clip spacing	1.8m maximum, plus one at every socket
Shoe clearance above the gully	About 50mm
Wastage allowance	5-10 per cent on gutter length

How do unions and stop ends go together?

Clip one gutter end fully into the union, then lever the second in against the seal. Do not push gutter past the moulded insertion mark.

Every union and outlet has a raised mark or stop inside it. The gap that mark leaves is the expansion allowance, and it is not optional. Butt the gutter hard against the stop in January and the run bows out of its brackets in July. Wet the seal with plain water so the second end goes in without rolling the rubber. Never seal a leaking union with silicone. Replace the union; a smeared joint fails again within a year, further along, and wetter. External stop ends close a visible run end. Internal stop ends sit inside the gutter where the run finishes tight against a wall.

How do I set out the downpipe?

Plumb down from the outlet, offset back to the wall, then clip at 1.8m maximum and at every socket.

A pair of 92.5° offset bends brings the pipe from the outlet back to the wall face. The distance between fascia and wall varies house to house, so measure it before buying offsets rather than after. Keep every socket facing up the run so water cannot creep out of a joint. Cut with a fine-tooth saw and take the burr off the cut end. Finish with a shoe about 50mm above the gully, so it discharges clear and you can see it running. 68mm round pipe comes in 5.5m lengths, which covers most two-storey drops in one piece.

Is a gutter job safe off a ladder?

Not above single storey. Gutter work happens at the roof edge, which is precisely where people fall from.

Never lean a ladder against uPVC gutter. It distorts the section, and it slips. Use a ladder stand-off at low level, a tower or scaffold above that. Full 4m lengths need two people in any wind at all. If the fascia behind the gutter feels soft, stop and deal with that first. Brackets in rotten timber hold fine empty and let go under a gutter full of water, usually taking the fascia with them.