The choice usually comes up in one of three situations: an extension is being planned, a tired flat roof has begun to leak, or a house with a pitched roof is being weighed against a flat-roofed property to buy. The question sounds like a matter of taste. It is closer to a matter of engineering, because the two designs keep water out in different ways and age in different ways.
A pitched roof is a layered covering of tiles or slates that overlap, so that water runs from one to the next and off the bottom edge. It does not need to be sealed, because gravity is doing the work. A flat roof has no overlap to lean on. Its covering is a continuous skin, joined and sealed, and it has to carry water to an outlet along a very shallow fall. Every joint in that skin is a place a leak can start.
Below we compare the two on the points that matter when you pay for them, and we say where each one is the better answer. Flat roofs on their own terms are covered in our flat roof pros and cons guide. This page is the side-by-side.
How long each type lasts
Lifespans in the guides are typical ranges that move with exposure, how well the roof was built and how it is looked after. Treat them as an expectation, never a promise. On the pitched side they run long. On MyBuilder's figures concrete tiles are replaced at around 30 to 50 years and clay at 40 to 60, while a slate roof laid well can reach 80 to 100 years or more. Marley cites a minimum life expectancy of 60 years for clay and expects concrete to last around 60 years, and adds that the figure is no guarantee.
Flat coverings are shorter-lived, and the sources disagree among themselves. For flat roofs generally MyBuilder gives 15 to 30 years. GreenSpec expects EPDM, a synthetic rubber membrane, to serve for 20 to 30 years, while the cost guide Less puts it higher at 30 to 50 years. Less gives GRP, a glass-reinforced plastic often called fibreglass, at 25 to 40 years, and torch-on felt at 10 to 20 years, adding that a poor felt job can fail in under ten.
| Covering | Typical life as published | Source |
|---|---|---|
| Concrete tile | 30 to 50 years | MyBuilder, 21/08/2026 |
| Clay tile | 40 to 60 years | MyBuilder, 21/08/2026 |
| Natural slate | 80 to 100 years or more | MyBuilder, 21/08/2026 |
| EPDM | 20 to 30 years | GreenSpec |
| GRP | 25 to 40 years | Less, March 2026 |
| Torch-on felt | 10 to 20 years | Less, March 2026 |
The spread inside each material is wide for good reason. The same tile lasts longer on a sheltered Downs lane with clear gutters than on a neglected roof facing the Channel, so use these figures to compare families of covering, not to predict a date.
Drainage: a slope against a fall
On a pitched roof the slope does most of the draining. Rain meets the tile surface, runs down to the gutter and leaves. Even if one tile is cracked, the overlap beneath it and the underlay below that give the water somewhere else to go for a time, which is why a pitched roof tolerates small faults better than a flat one does.
A flat roof still carries a built-in slope, only a gentle one, which steers the water towards an outlet or a gutter. IKO, citing the 2018 edition of BS 6229 (since revised), sets the recommended minimum at 1:80 and says the roof should be designed for 1:40 to allow for tolerances and deflection. In other words, the design aims at 1:40 so that what is built still achieves 1:80.
Why ponding matters
If a flat roof settles, or the fall was marginal to start with, water lies in shallow pools after rain. Standing water finds the weakest seam, adds weight, and encourages algae and debris. On a flat roof survey we check for it early, and it is the drainage difference that most affects which type is the lower-maintenance choice.
Gutters sit at the foot of both. Brett Martin suggests 1mm of fall for every 600mm, and FloPlast recommends 1:350 for its MiniFlo system. A gutter that spills over the back of the fascia wets the wall beneath either type of roof, so good roofing with poor guttering still leaves damp. Check the outlets and joints of whatever gutter you have before blaming the roof covering for a wet wall.
For a pitched house the practical point is straightforward: the steeper the slope and the better the overlap, the less the covering relies on perfect workmanship at each joint. For a flat roof, the practical point is that falls, outlets and seams carry everything.
What each costs to put on
Compare the whole job, not the rate per square metre, because the two roofs are built quite differently. MyBuilder's new roof guide gives these typical UK figures for a semi-detached house: a gable roof at £5,000 to £8,000, a hipped roof at £8,000 to £12,000 and a flat roof at £2,500 to £6,000. The pitched figures are higher partly because a pitched roof has more area, more materials and more labour, plus scaffold to reach the eaves.
Flat roof prices are usually quoted by area. MyBuilder gives a range of £2,800 to £7,500 for a flat roof overall, averaging £75 per m², and breaks the coverings down as felt at £70 to £100 per m², EPDM at £90 to £130, GRP at £95 to £150, PVC at £95 to £140 and lead at £150 to £200 or more. For pitched coverings, the same group of guides gives £100 to £180 per m² for slate.
The lifetime arithmetic
A lower price on the day is only half the picture. A flat roof that lasts 20 years and a tiled roof that lasts 50 are not equal purchases at the same price, so the useful comparison is cost per year of life, with the cost of access, scaffold and disposal counted each time the roof is replaced. We cannot give you that figure without seeing the roof, which is why our quote is written once we have surveyed, as one total price.
For the pitched side, our guide to pitched roof shapes explains why a hip costs more than a gable.
Planning and Building Regulations
Both types are treated the same way for planning when the work is like-for-like. Replacing a roof covering with the same kind does not usually need planning permission, with caveats for listed buildings and Article 4 areas. Swapping a pitched roof for a flat one, or the reverse, changes the look of the house and its outline, so ask the planning team at the council first, before drawings are paid for, particularly if your street falls in a conservation area or within the Park boundary.
Building Regulations are where the two diverge. For a pitched re-cover, the Planning Portal's limits for skipping a building control application are under 25 per cent of the building envelope and under 50 per cent of the roof. A flat roof is often a whole element, so the limit is easy to pass. Under Approved Document L, a flat roof given a fresh waterproof membrane is treated as renovated for thermal purposes, and when the work reaches more than 50 per cent of the roof surface, the entire roof element has to meet the upgraded thermal standard. Table 4.3 gives a threshold U-value of 0.35 W/(m²·K) for roofs in existing dwellings, with 0.16 as the improved figure.
Weight, and the structure underneath
If a heavier covering goes on, the Planning Portal says approval applies where the weight rises by 15 per cent or more. Approved Document A uses the wording "more than 15%". Swapping a light flat roof for a heavy tiled one therefore means a structural check. We explain consent and arrange the Building Regulations notification where the work is notifiable.
Upkeep: what to check on each roof
A pitched roof asks for a look at its details, not its whole surface. The ridge and hip tiles, the verge, the valleys, the flashing round the chimney and the gutters are where age shows first. BS 5534 changed in 2014: ridge and hip tiles can no longer depend on a mortar bed alone and are clipped or screwed down as well. Old capping held only by mortar is therefore a repair candidate even when the tiles look fine. Moss on its own does little harm until it blocks a valley or a gutter.
A flat roof asks for a look at its surface. Pools after rain, blisters, cracking at the edges, lifted laps and loose flashings at the wall are the signs. Leaves and silt in the outlet need clearing from time to time, which is a more regular job than anything a tiled roof needs. A flat roof is also less forgiving to walk on, so access for a maintenance visit is part of the running cost.
Neither type is maintenance-free
The old idea that a flat roof is easier to look after does not stand up. It depends on the covering and the drainage. A well-laid single-ply roof with a clear outlet needs very little, while a tired felt roof needs attention often. Likewise a clean, well-fixed tiled roof can go years without a call-out.
The sea adds to both. Salt air, gales and driven rain test seams and fixings, and a roof near the front deserves a closer look after each winter. Our guide to roof tile types shows which coverings suit the coast, and a survey tells you what yours needs.
Choosing between them for your house
For most existing homes the decision has already been made by the building. A Victorian terrace, a 1930s semi and a Downs cottage were designed with a pitched roof, and removing it would change the character and the structure. In that case the choice is between coverings, and our guide to how a pitched roof is built explains what lies under the tiles. A roof that only needs re-covering is a smaller question than one that needs redesigning, and the survey separates the two before any quote is written. Our pitched roofing hub covers the pitched side in full.
Flat roofs earn their place where the design calls for them: rear and side extensions, dormers, garages and porches, and the roofs of flats, where there is little height to spare. In those situations a pitched roof may not fit under the window line or the neighbour's boundary. A flat roof there is a sound answer when it is laid to a proper fall and detailed well at every upstand and edge.
Questions that decide it
Ask what the roof is for. A roof you walk on, put a terrace on or connect to a wall of a higher building has different needs from one you never visit. Ask how much height the design allows, whether the frame below will take the weight, and whether any planning designation applies to the street. Ask what the survey shows about the existing roof, because repair is sometimes the smallest job that works.
The written quote sets out what the chosen route includes. Send us photographs of the roof you are weighing up and we will say which route we would take and the reasons for it.
