The short answer
Half-round is the traditional profile: a simple curve that sheds debris well and suits older and period houses. Square gives a crisp modern line and, for the same width, more room for water, but corners can catch leaves and silt. Both work if they are the right size for the roof, hung to a proper fall and kept clear, so the choice is largely one of looks and matching.
Two profiles compared
Half-round guttering has a semicircular cross-section, like a pipe cut lengthways. It has been used for centuries in cast iron and now comes in uPVC, aluminium and other materials. The curved bottom has no corners for debris to settle in, and the flow settles in the centre and runs along it.
Square guttering has a flat bottom and straight sides, forming a rectangular or slightly rounded box. It gives a sharper, more contemporary line and sits tidily against a flat fascia. Variants include deep or box profiles that hold more water.
Other shapes exist, including ogee profiles with a decorative curve on the face, and deep-flow or high-capacity versions for large roofs. Many are available in the same materials as the two main shapes.
Each profile has its own matching fittings: brackets, stop ends, corners, unions and outlets. They do not interchange, so a square gutter cannot be joined to half-round parts and vice versa. That limits repairs and mixing on one house.
Downpipes come in round and square forms too, usually paired with the gutter profile, and the outlet has to suit both. Our page on downpipe replacement explains the connection between pipe and gutter.
Looks are the main difference most owners notice, and the choice is about what suits the building.
Capacity, debris and cleaning
For the same width, a square or box gutter usually has a larger cross-section than a half-round one, because a rectangle fills the space a semicircle leaves empty. It can carry more water before it overflows, which helps on big roofs or steep pitches. The width and depth of any gutter should still be chosen for the roof area it serves.
Capacity depends on the size and number of outlets as much as on the gutter, and BS EN 12056-3:2000 is the drainage standard behind it. A large gutter with one small outlet will still overflow. A roofer sizes the gutter, outlets and downpipes together.
Debris behaves differently. A half-round gutter has no flat bottom for silt, so leaves tend to wash to the outlet, though they can still jam there. A square gutter has two corners where grit and moss settle, and needs a little more attention when it is cleared.
Cleaning is simple in either: lift debris out by hand, flush with a hose and check the outlet. Leave powerful washing equipment off the roof, since Marley advises against it for tiles and slates.
A clear-out of both elevations costs £75 to £350, ex VAT, according to Which? (Nov 2025), a typical UK range that applies to either shape.
Fall matters more than shape
A well-hung gutter of either profile drains. A poorly hung one of either does not. The slope along the gutter is what moves water to the outlet, and Brett Martin's guide is 1 mm for every 600 mm of run, a gentle gradient that must be consistent along the whole length.
Bracket spacing and strength matter as well. A square gutter full of water is weighty and needs supports that hold its line, and half-round runs droop in the same way when brackets are spaced too widely or the fascia has rotted.
Outlets matter just as much. Their size, number and position decide how quickly water leaves, and an outlet set too high or blocked will cause overflow whatever the profile.
So when the question is why a gutter overflows, the shape is rarely the cause. Check for blockages, the fall, the size and the outlets, as our page on why gutters overflow explains.
The material matters more than the shape for life and cost. Our page on aluminium against uPVC guttering compares them, and MyJobQuote gives gutter replacement at around £1,000 to £1,600 (MyJobQuote, Oct 2026), a typical UK range for either profile.
Matching the profile to the house
Start with what is there. Replacing like for like keeps the look and avoids mismatched parts, particularly on a terrace or a semi where neighbours' gutters sit alongside yours. A mixture of profiles along a roofline looks untidy.
Period houses usually suit half-round, with brackets and a profile in keeping with the age of the building. Modern houses with flat, square-edged fascias often suit square. In a conservation area or on a listed building, the profile and material may be controlled, so ask the council before changing them.
Consider capacity. If an existing gutter has overflowed in heavy rain with the outlets clear, a larger profile, or more outlets, may be the answer. Do not assume a different shape alone will cure it.
Think about what you want to maintain. Both need clearing, and the difference is slight. Check availability of fittings, since it is easier to repair a common profile in future.
The visit takes in the existing gutter, the fascia, the brackets and the roof area it drains, and the options come with the reasons for each and a plain recommendation. Access is named in the written total.
The gutters, soffits and fascias hub sets out the other parts of the eaves.
