The short answer
Half round is the traditional shape and sheds debris well. Square sits flatter and holds more water for its width, and deep flow or high-capacity versions carry more again. Capacity depends on the depth of the channel, the number of outlets and the slope as much as on the profile, so a bigger shape on a poorly drained run will still overflow.
The profiles on offer
Half round is a plain semicircle, the oldest and most familiar section. Square has flat sides and a flat bottom, and its crisp lines suit modern fascias. Ogee has a stepped, moulded face that echoes the cornice mouldings of Victorian terraces. Deep flow, sometimes sold as high-capacity, is a deeper version of either half round or square, made for larger roofs or heavier downpours. Some systems also offer a moulded, fascia-style profile that doubles as a board.
Plastic comes in all of these. Cast iron and aluminium are usually half round or ogee. Our page on cast iron gutters covers the traditional section in more detail.
Each shape also behaves differently when it is neglected. Half round lets leaves wash towards the outlet, while a flat-bottomed square channel lets silt lie where it falls and builds up faster.
How profile affects capacity
Capacity is how much water a run can pass before it spills. A deeper, wider channel holds more for a given length, which is why deep flow exists. Square gutters tend to hold more than half round of the same width because they do not lose volume to the curve at the bottom.
But the shape is only part of the sum. Water leaves through the outlet, so the outlet size and the number of downpipes limit the flow just as much as the channel. A long run feeding a single downpipe at one end can overflow even in a large profile, while a modest half round with a central outlet may cope. Slope matters too: plastic systems are generally laid with a very slight slope, roughly 1:600 to 1:350, and any dip along that line cuts what the channel can carry.
Matching the profile to the house
- Victorian and Edwardian terraces: ogee or half round in cast iron or a good imitation, to keep the character of the eaves.
- 1930s semis and post-war houses: half round is the usual and sits comfortably against a flat fascia.
- Modern estates and extensions: square or fascia-style profiles match plastic boards and clean lines.
- Large or complex roofs, or a big roof feeding a short run: deep flow, so the channel can carry the heaviest flow.
A listed building or a house inside a conservation area may need consent for a change of profile, since gutters show from the street. Before you order anything, ring the planning department of Swindon Borough Council, or of the council for your own town, and ask.
Finish counts as well as shape. Black, white, grey and brown are all common in plastic, and a downpipe should match the gutter it serves. Painted cast iron is usually kept to a dark colour that suits the fascia, and the choice shows more on a long run than you might expect. A mixed roofline is common in Swindon, where a Victorian main house may have a 1960s extension. Matching the new run to the old one on the street side, while using a more capable profile on the back, is a sensible compromise.
What limits capacity in practice
Roof area is the first limit. A large pitched roof delivers a lot of water to a short gutter, and an extension that adds a new slope to an old run adds to the burden without changing the gutter. A shared run between two houses compounds this, as described under shared gutters.
Brackets are another limit. A full channel is heavy, and if the brackets are too far apart the run sags and holds water. Our note on gutter bracket spacing sets out the typical manufacturer maxima.
Last comes the downpipe, which has to take the flow the gutter delivers. A narrow pipe, or one that bends sharply at the bottom, throttles the whole system however large the channel above it.
Fittings, makers and cost
Profiles are not interchangeable between makers. A bracket, corner or stop end made for one square system rarely fits another, so a repair to an old run often means finding the same system or changing the whole length. Metal gutters have their own fittings again.
Deeper channels need stronger brackets, because more water means more weight on each fixing. Square and deep flow runs also ask for neat corner units, and those are where leaks start if the sealing is poor.
On price, MyBuilder's national guide, updated in August 2026, gives gutter replacement at £30 to £70 per metre. Profile, material and the height of the elevation all move the final figure, which is why the figure that counts is the written quote that follows our survey of your house. Taller elevations, awkward side access and old boards that need repair first all add to the bill, while a short, easy run on a single storey costs far less to do.
Choosing, and what to ask for
Choose a profile that fits the look of the house, then check it against the roof area it has to drain. If a downpipe discharges into a water butt, the connection has to cope with the heaviest flow too, as explained in our piece on a water butt downpipe.
At the survey we measure up what drains where and photograph the runs, outlets and boards, then the written quote follows. Sometimes the right answer is a single extra outlet, not a new set of gutters, and tell you that plainly.
Work carries a 10-year workmanship guarantee in writing, and the site is tidy when we leave. Our gutters, soffits and fascias service covers the rest.