People ask what the standard roof pitch is as if one number sat behind every house in the country. It does not. Roofs are built to the angle that suits the covering, the span, the style of the house and the period it was built in, and two houses on the same street can differ by ten degrees or more.
What does exist is a floor. Each tile and slate carries a lowest workable angle, and below it the maker withdraws support, and the rules for flat and low-slope roofs draw their own line near ten degrees. Those are the numbers that matter when you are choosing a covering or checking that an existing one is fit for the slope it sits on.
This post defines pitch, shows how to measure it, sets out the published minimums for the common coverings, and explains where a pitched roof stops and a flat one begins. It is the definition post in a small group: our posts on the most economical roof pitch and the best roof pitch for a loft take up cost and usable space.
What roof pitch means
Pitch is the steepness of a roof slope. It is usually given as an angle in degrees measured up from the horizontal, so a pitch of 30 degrees rises thirty degrees from level. Builders also describe it as a ratio of rise to run, for example one in two, or as the height of the roof compared with the width of the building.
Degrees and ratios
Degrees are the usual unit on manufacturers' data sheets, and they are the unit used in the British Standards for tiles and slates. A ratio such as 1:40 is more often used for flat roofs, where the slope is slight and a degree would be too coarse a measure. A 1:40 slope is about 1.4 degrees and a 1:80 slope is about 0.7 degrees.
Pitch against rafter pitch
You will see two figures on a plan: the pitch of the roof surface, and the pitch of the rafters. On a normal roof they are the same. On a roof with a ceiling sloping to follow the rafters, the line you see from the garden is the true pitch. Where a roof has two slopes on a face, such as a mansard, each slope has its own pitch.
Why it matters
Pitch decides what can go on the roof, how fast water leaves it, how much useful space the loft has and how the roof is ventilated, which makes it among the first things to establish. Tile makers set minimums by it, and the ventilation guidance changes at 15 degrees. A roof whose pitch you do not know is a roof whose covering you cannot check, so measuring it is the first step in any re-roof.
Measuring the pitch of your own roof
You can find the pitch without climbing onto the roof. A few simple methods work from the ground, the loft or a photograph.
From the loft
If you can reach a rafter, hold a spirit level horizontally against its underside and measure the vertical drop over a set distance. A digital angle finder placed along the rafter gives the figure directly. Either way you are measuring the angle of the timber, which is the pitch of the slope above it.
From the garden
Stand square to a gable end, where the roof edge makes a clear triangle against the wall. A phone with an inclinometer app, held level with the edge, gives a good estimate. Take the reading from several spots to check that it agrees, and note the date and the spot so that you can show the surveyor.
From a drawing
If you have the plans for the house or an extension, the roof pitch is normally printed on the elevation. Treat that as a starting point, because builders do not always match the drawings.
Why a surveyor measures it
Pitch is one of the facts a roof quote should state. When pitch decides what covering can go on, a small error matters. On a survey we measure each slope separately, as a roof can have several different pitches, one for the main house and others for a porch, an extension or a dormer cheek. We photograph the measurement so you can see it. Our answer on the minimum pitch for roof tiles shows how to compare your reading with a product's data sheet.
Minimum pitches for common coverings
The best published guide to lowest safe pitches is the table Marley keeps for its own products, supplemented by Cupa for slate. The figures differ product by product, which is why a single standard angle cannot exist.
| Covering | Minimum pitch |
|---|---|
| Clay, Canterbury plain tile | 40° |
| Clay, Ashdowne plain tile | 35° |
| Clay, Hawkins and Acme single camber | 30° |
| Clay, Lincoln pantile | 15° |
| Concrete, plain tile | 35° |
| Concrete, Ludlow Plus and Ashmore | 22.5° |
| Concrete, Anglia (smooth) | 25° |
| Concrete, Edgemere | 17.5° |
| Concrete, Mendip (smooth) | 15° |
| Concrete, Mendip 12.5 | 12.5° |
| Natural slate (BS 5534, via Cupa) | 20° |
The pattern
Plain tiles need the steepest roofs, because their short laps leave little margin against wind-driven rain. Interlocking tiles, with channels that hook into each other, work on far lower slopes. Slate sits in the middle. Cupa adds that hook fixings should not go on any slope below 25 degrees, so the fixing method can narrow the choice as well.
Check the product, not the type
Two concrete tiles from the same maker can have minimums ten degrees apart, and another maker will have different figures again. Always use the data sheet for the tile that is actually going on. The data sheet is also where the fixing method for that tile is set out.
Where a pitched roof becomes a flat one
At the bottom of the range, tiles stop and membranes start. The line between the two is set by the standard for flat roof coverings.
BS 6229:2025
BSI lists BS 6229:2025 as the current standard for flat roofs finished in flexible membranes, and it is written for roofs whose pitch is 10 degrees at most. The older 2018 edition was withdrawn on 16 December 2025. Its scope is the membrane family, meaning EPDM, GRP and felt, and lead sheet falls outside it because lead follows BS 6915.
Falls on a flat roof
A flat roof is never truly level. It is laid to a fall so water runs to the outlet. The finished fall under BS 6229:2025 is at least 1:80, and IKO advises designing the roof for 1:40, which is twice as steep and leaves allowance for the build to settle. Those falls are far shallower than any tile minimum, which is why the two systems are separate.
The gap between
Between about 10 degrees and the lowest tile minimum there is a zone served by profiled sheets, metal and a few low-pitch tiles, and a roofer who works in it needs the product data in hand. The Mendip 12.5, at 12.5 degrees, is the lowest tile on Marley's table. Below that, a roof is a membrane or metal roof, even if it has some slope. The thresholds are not interchangeable, so a manufacturer who supports a tile on 15 degrees has said nothing about 12 degrees.
Why this matters at home
An extension or dormer built too shallow for a tile has to be roofed as a flat. The slopes above the line, in tile and slate, are the work described on our pitched roofing page.
Pitch and the shape of the house
The pitch of a roof is partly a matter of the covering and partly of the design. Older houses and newer ones show different habits.
Older houses
Streets in North Camp and South Farnborough date from the 1860s onwards, and the houses along them went up over many years by many hands. Rushmoor's own history of the area shows how mixed that growth was. A pair of houses from the same terrace may well have been re-covered in different decades, so the pitch and covering you see on one tells you little about its neighbour. Measuring is the only reliable way to find out.
Later estates
Rushmoor's overview names Cove for its 1950s and 1960s housing and Southwood for its 1980s housing. Each phase of building brought its own habits, and the pitch you find on an estate house follows the covering its builder chose, not a rule for the area.
Extensions and garages
Extensions often have lower pitches than the house they join, because the roof must meet the main roof below a window or fit within planning limits. A garage may be flat. A lean-to is a single slope against a wall, normally at a shallow angle.
Gable and hip
Pitch interacts with shape. A hip end falls away on every side, a gable keeps its upright end wall, and in both cases the tile maker's minimum applies to each slope separately. A roof can pass on its main faces and fail on a shallow hip end or a low return over a bay, so each face is read on its own.
Pitch, ventilation and the Building Regulations
Pitch does not only affect the covering. It also changes the ventilation, and some of the rules in the Approved Documents turn on it.
Ventilation openings
Marley's guidance on cold roofs, which follows BS 5250, gives different eaves openings by pitch. With a non-breathable HR underlay, it asks for 25 mm along the eaves on pitches of 15 degrees or less and 10 mm on pitches above 15 degrees. Where the underlay is a breather type and the ceiling is well sealed, it accepts the gap left by ordinary eaves construction, as long as the product is certified by an independent body.
Re-roofing
A change of covering that alters the weight or the fire performance brings a Building Regulations question under the Planning Portal test, and a covering with a higher minimum pitch than your roof offers is a covering you cannot use. Class C of the permitted development rules normally takes in a fresh covering on a house, and the Hart and Rushmoor Building Control Partnership can be reached on 01252 398715.
Loft conversions
The pitch of the roof decides how much headroom a loft has, and so whether a conversion is practical. That is the subject of the loft post linked at the top of this page.
What to do next
If you do not know the pitch of your roof, measure it or have it measured, then use the data sheet for any covering you are considering. A written quote should state the pitch it assumes.
