What fall should a gutter have?

A fall is written as a ratio. A fall of 1:600 means the gutter drops 1mm for every 600mm of run, and 1:350 means a drop of 1mm for every 350mm. Brett Martin's installation advice puts it as 1mm for every 600mm towards the rainwater outlet. FloPlast's guide for its MiniFlo range says that if you fit to a fall, 1:350 is recommended. Both are manufacturer guidance, not a British Standard, and the Brett Martin page is undated.

The range is narrow in practice. On a 6m run, 1:600 gives a drop of 10mm from the high end to the outlet, while 1:350 gives about 17mm. That is roughly the thickness of a pencil against the width of a thumb. A fall that small cannot be judged by eye from the ground, which is why a gutter that looks level is often a gutter that is not draining.

Because the two makers differ, the sensible rule is to follow the fitting instructions for the profile on your house. Each profile sits differently in its brackets, and the spacing that goes with each figure varies as well.

Gutters are shallow. If the bed is level, rain that arrives faster than the outlet can take it just stands in the channel, and what stands there collects grit, moss spores and the silt washed off the roof covering. Some of that settles into a film along the bed. Over a season the film becomes a ridge that checks the flow further, so a small fault feeds itself.

Standing water does more damage than most people expect. It shortens the life of the joints, because sealant and rubber seals sit wet instead of drying between showers. In a hard frost it freezes and spreads the channel, and a joint that was only weeping in autumn can open in January. A bed that holds water also gives the fascia behind it a wetter life. Our answer on rotten fascia boards covers what follows when the timber stays damp.

Where overflow shows at a joint or a corner and the downpipe is clear, a flat or reversed run is one of the first causes to rule out. The full set of causes is in our guide to leaking gutters, joints, falls and overflow.

You do not need to climb to get a first impression. After a heavy shower, look along the run from the ground. Water standing in the bed, a damp line inside the back of the channel or algae streaking the wall under the lip all point to a stretch that is not draining. Do this from the ground only; anything that needs a ladder on an upper storey is a job for a roofer with access equipment.

A proper check is done with a spirit level and a line. The installer strings a line along the brackets, or lays a long level on the gutter bed, and measures the difference between the high end and the outlet. Against the manufacturer figures, a 6m run should fall roughly 10mm to 17mm. A run that falls the wrong way, or sags between brackets, shows up straight away.

We photograph the gutter from the scaffold or tower as part of a survey, so the picture shows where the water sits and not just where it overflows. Check the profile too, because the fall that suits one profile does not always suit another.

The fall is set by the brackets, not by the gutter. On a fascia board the brackets are fixed first, with the highest one at the far end of the run and each one stepped down towards the outlet. If a board is rotten or a bracket fixing has pulled, the fall changes with it. That is why a sagging stretch is nearly always a fixing problem, which we deal with in our answer on why a gutter sags.

Outlet position matters as well. An outlet at one end means the whole run slopes one way. An outlet in the middle lets a long run fall both ways, which halves the height difference needed. On a very long elevation, running the whole length to a single end outlet takes the high end a long way off the fascia line, so the sensible layout is often two shorter runs or a central outlet.

Fascia capping can change this if it is fitted over a board that is not true, a point covered in capping over old fascias. A crooked board under new plastic carries the crookedness straight through to the brackets.

Bracket spacing

Spacing interacts with fall. FloPlast gives a maximum of 500mm between fascia brackets on straight MiniFlo runs, and Brett Martin allows up to 900mm, or no less than 600mm in areas of heavy snow. Wide spacing lets the bed dip between brackets and form shallow pools.

A gutter with a wrong fall can sometimes be re-hung without being replaced. The brackets are loosened or moved, the run is lined up again and the joints are cleaned and resealed. That works where the gutter itself is straight and sound. It does not work where the plastic has warped in the sun or a cast section has cracked, and then new lengths are the better route.

Price is easier to judge by the metre. MyBuilder's 2026 roofline price guide lists guttering at £30 to £70 per metre and scaffold at £20 to £40 per m², so a full re-fall on an upper storey is dominated by access. Your written quote covers scaffold, labour and materials.

Where gutters are being renewed, the fall is set again as part of the job, and a 10-year workmanship guarantee is given in writing on the finished job. Photographs of the standing water and the elevation are the best starting point if you want an opinion before a visit. The wider picture of the work we do on the roofline sits on our guttering, soffits and fascias page.