The short answer
For a tiled house the economical pitch is usually a moderate one, somewhere between the minimum the chosen tile allows and the low thirties of degrees. Shallower roofs use less area, but they limit you to specific tiles or another covering. Steeper roofs cost more to frame, cover and scaffold, though they give more usable loft space and shed water easily.
Pitch in degrees, not ratios
Older articles quote pitch as a ratio of rise to run, such as 5 in 12, and that habit comes from American building. British manufacturers, standards and building control all use degrees, measured up from the horizontal. A flat roof is close to zero. Most British houses sit somewhere between about 20 and 45 degrees, and an older cottage or a pantile roof may be lower or steeper.
Everything else on this page follows from that angle. As the pitch rises, the roof surface gets bigger for the same footprint, the rafters get longer, the walls of the loft get taller, and the choice of covering widens at the top end and narrows at the bottom. The best-value angle is whichever one balances those effects for the house in front of you. To find your own, measure it with a phone app in the loft, or see our note on roof tile types for which coverings suit which range.
What the covering allows
Material comes first, because it sets the floor. Every tile has a minimum pitch, below which water can be driven or pooled under the laps. The figures below come from Marley's published guidance, and the manufacturer's own data sheet always has the last word for the exact product.
| Covering | Minimum pitch |
|---|---|
| Marley clay plain tiles | 30° to 40°, depending on the tile |
| Marley concrete plain tiles | 35° |
| Marley Lincoln clay pantile | 15° |
| Marley interlocking concrete tiles | 12.5° to 25°, depending on the tile |
| Natural slate (moderate exposure, 500 mm slate) | 20° with a 115 mm headlap |
Headlap is the distance by which a tile reaches over the row two rows beneath it, and a shallower roof needs a bigger overlap to stay dry. Plain tiles are the most demanding of the lot. If your design is a low roof, an interlocking tile or pantile gives far more freedom than plain tiles.
Area, framing and labour
Geometry does the rest. The surface of a pitched roof is the plan area divided by the cosine of the pitch, so a bigger angle means more roof to cover for the same house. Roughly, a roof at 20 degrees is about six per cent bigger than the plan, at 30 degrees about 15 per cent, at 40 degrees about 31 per cent and at 45 degrees about 41 per cent. These are straight calculations from the angle, not survey figures.
As a worked example, take a house whose roof covers 50 square metres on plan. The surface to be tiled comes to about 53 m² at 20 degrees, 58 m² at 30 degrees, 65 m² at 40 degrees and 71 m² at 45 degrees. That gap of nearly 20 square metres between the lowest and highest is real tile, real battens and real hours on the roof, which is why a modest pitch is often the economical choice whenever the covering allows it.
More area means more tiles, battens, underlay and labour, and longer rafters. A steeper roof is also slower to work on, and the scaffold and edge protection around it have to be planned with more care. The weight of the covering matters too: a concrete plain tile roof at the standard gauge is listed at about 73.8 kg per square metre, so more surface also means more load on the structure.
Loft space, light and drainage
The case for a steeper roof is mostly inside. A higher pitch gives a taller loft, which can be useful for storage or for a later conversion, and it carries rain and debris off the covering quickly. A low pitch keeps the roof compact and usually looks right on a bungalow or an extension, but headroom is tight and water is slower to clear, so detailing at the laps, flashings and gutters matters more.
If conversion is on your mind, pitch is one of the first things to check, along with roof structure. A modest pitch rarely leaves enough headroom for a room without raising the ridge or adding a dormer, and either is a planning and Building Regulations conversation. Changing the pitch of an existing roof is a bigger decision again, and it is one to take to your council before any work is priced.
Pitch and how long the roof lasts
Pitch shapes lifespan indirectly. A roof that is below the covering's minimum will leak sooner, whatever it is made of. Within the allowed range, a steeper slope sheds water, snow and leaves faster and tends to stay cleaner, while shallower slopes hold moss and debris at the laps and put more strain on flashings. Our guide to pitched roof lifespan sets out how long each covering tends to last, as ranges and never as promises.
Faults that come from pitch, such as tiles lifting or slipping, show up on both extremes. Our page on slipped roof tiles describes the signs you can spot without leaving the garden.
So which pitch should you choose?
For a new build or a replacement roof structure, pick the covering you want first, read its minimum pitch from the data sheet, and then choose an angle comfortably above it. A margin matters because the tile maker's minimum assumes careful workmanship and moderate exposure. Where the house is fixed, as most are, the question is simply whether your existing pitch suits the tile on it, and that is something we check in the survey.
The survey gives you pictures of your slopes and a price on paper, and a 10-year workmanship guarantee comes with the finished job, in writing. Other pitch and tile questions are collected in the pitched roofing hub.