Pitch affects cost in two plain ways. A steeper roof has more surface to cover than a shallower one over the same house, so it needs more tiles, more battens and more underlay. It is also taller and harder to work on, which adds scaffold and time. On those two counts a low pitch is the cheaper roof to build.
That is not the whole story, because pitch limits what you can put on the roof. Each tile and slate has a minimum angle, and a covering laid below it will let water in. A low roof can only take the tiles rated for a low roof, so the economy of the pitch depends on whether a good covering exists for it, and on how long that covering lasts.
This post is the cost post in a small group with our definitions of standard roof pitch and the usable-space discussion in best roof pitch for a loft. It shows the geometry of area, the published minimum pitches, the published costs and lives, and the checks that keep a low-cost roof from becoming an expensive repair. We give typical UK figures from named sources, not Fortis Roofing Farnborough prices.
How pitch changes the area you pay to cover
The surface of a pitched roof is larger than the footprint of the house beneath it. Each square metre of plan area becomes more than a square metre of roof, and the steeper the slope, the bigger the factor. The factor is one divided by the cosine of the pitch angle, which is a matter of geometry and not of opinion.
| Pitch | Roof surface |
|---|---|
| 15 degrees | about 104 m² |
| 25 degrees | about 110 m² |
| 30 degrees | about 115 m² |
| 35 degrees | about 122 m² |
| 40 degrees | about 131 m² |
| 45 degrees | about 141 m² |
What the table means
Moving from 25 to 40 degrees adds about a fifth to the surface that must be covered, before counting hips, valleys and waste. Materials and labour both follow the area, so the extra surface feeds straight into the price. A low pitch holds the area close to the footprint of the house.
The edge effects
Area is not the only thing that grows with the angle. A steeper roof has longer rafters, longer valley runs and taller gables, and each of those lifts the cost of the lead, the ridge pieces and the verge work.
Scaffold
A taller roof needs more scaffold and more days. Scaffold is priced on the job and not read from a table, so find out what access is planned for your roof and how many days it stays up.
What a low pitch rules out
The saving from a shallow roof only counts if a suitable covering exists for it. This is where the published minimum pitches come in. The limits for the Marley products on its table run from 12.5 degrees to 40 degrees.
| Covering | Minimum pitch |
|---|---|
| Concrete, Mendip 12.5 | 12.5° |
| Clay, Lincoln pantile | 15° |
| Concrete, Wessex | 15° |
| Concrete, Edgemere | 17.5° |
| Natural slate (BS 5534) | 20° |
| Concrete, Double Roman | 22.5° (smooth) |
| Clay, Hawkins plain tile | 30° |
| Concrete, plain tile | 35° |
| Clay, Canterbury plain tile | 40° |
What narrows the choice
Below about 20 degrees you are limited to a handful of low-pitch interlocking tiles and pantiles. Below 12.5 degrees none of Marley's tiles apply, and the covering becomes a membrane or metal. Plain tiles and many clay products need 30 degrees or more. Cupa, the slate supplier, rules out hooks on slate below 25 degrees, which means a slate roof laid at 22 degrees has to be nailed.
The consequence
A shallow pitch widens the choice of low-pitch tiles and narrows the choice of everything else, so the shortlist is short before cost enters. If your roof is already shallow, the sensible approach is to treat the minimum as a hard limit. Our answer on the minimum pitch for roof tiles shows how to check a data sheet.
Published costs and lives side by side
A cheap roof is not the same as an economical one, because a roof that lasts twice as long costs half as much per year. The published figures let us put cost and life next to each other for the coverings where both exist.
| Covering | Supply per m² | Published life | Per m² per year, supply only |
|---|---|---|---|
| Felt | £65 | 10 to 15 years | about £4.30 to £6.50 |
| EPDM | £105 | 25 to 30 years | about £3.50 to £4.20 |
| GRP | £110 | 25 to 30 years | about £3.70 to £4.40 |
| Lead | £170 | 60 to 100 years | about £1.70 to £2.80 |
Reading it
The figures are the material only, laid out to show how life changes the picture. They exclude fitting, access and the deck, which add to any roof. On that basis the felt, the lowest cost to buy, becomes the dearest per year, and lead, the highest to buy, comes out lowest.
For pitched coverings
HomeBuilding gives supply-only slate prices of £72 per m² for Spanish natural slate, £90 for reclaimed Welsh and £185 for Welsh slate, against published lives of 75 to 100 years, 50 to 80 years and over 100 years. Its worked example, a three-bedroom semi with 65 m² of roof, puts plain concrete tiles at £10,000 to £15,000 including labour, scaffolding and insulation.
Figures like these come from named guides and give only a yardstick. The written price for your roof arrives after the survey, and it covers the whole job.
Why the lowest pitch is not always the saving
A shallow pitch looks economical on the day the roof goes up. Several points can reverse that over the life of the building.
Less margin against weather
A tile laid close to its minimum pitch has little in reserve. In driving rain, or with leaves and debris building up, water can climb back under the laps. A roof built at the limit must be laid exactly right, and it has no allowance for movement or poor workmanship.
A narrower product range
If the original covering is discontinued, a replacement for a shallow roof may be hard to find in the same look. You may end up having to change the covering or the pitch.
Ventilation
Marley's guidance, following BS 5250, asks for more eaves ventilation on shallow pitches: 25 mm for pitches of 15 degrees or less with HR, non-breathable underlay, against 10 mm above 15 degrees. A shallow roof can therefore need more care with its ventilation.
Flat roofs are not an escape
At the bottom of the range, a roof of 10 degrees or less falls under BS 6229:2025, the flat roof standard for membranes. Membranes have shorter published lives than tile and slate, which is why a flat roof is not automatically the economical choice. Which? (November 2025) gives £1,400 to £3,500, ex VAT, for a new felt roof over a 6 m by 3 m garage, and felt will need replacing sooner than a tiled roof would.
Structure and fire
A change of covering that is 15 per cent or more heavier, or that behaves differently in a fire, brings a Building Regulations check under the Planning Portal test.
When the pitch is fixed already
An owner is rarely choosing a pitch at all. The house has a roof, and the choice is what to put on it. In that case the economy lies in matching the covering to the roof.
Keeping the existing pitch
A re-roof keeps the rafters, so it keeps the pitch. The only way to change it is to rebuild the frame, which is Building Regulations work and a much larger job. For nearly every re-roof, the pitch is a given.
Choosing within the limit
Measure the pitch of each slope and shortlist coverings whose published minimum sits below it. Then compare the supply cost, the laying cost and the published life, as in the tables above. Our pitched roofing work includes re-roofing in tile and slate.
Repair instead of replace
The most economical roof is sometimes the one you already have. If the tiles themselves are intact and the fault lies in a slipped tile, a failed ridge or a worn valley, a repair is the better buy. Which? (November 2025) gives £75 to £400, ex VAT, to replace anything from one to six broken or absent tiles, and MyJobQuote gives around £215 for five tiles (October 2026).
Scaffold and access
A roof that is easy to reach costs less to work on. If the scaffold must be set up on the footway, waiting for the highway authority's licence adds lead time. Find out who makes the application and whether the scaffold and VAT sit inside the quoted total.
How to compare two roof quotes on cost
Quotes for one roof can land far apart, and the gap often comes from what each of them assumes. A short list of checks makes them comparable.
Does each name the covering and the pitch?
A quote that says "new tiles" without naming the product leaves the minimum pitch unchecked. Ask for the make, the model and the pitch it assumes.
Does each say what happens to the structure?
Battens, underlay and timber repairs are where a roof quote can grow. Ask what is included and what happens if rotten timber is found.
Is the scaffold in?
Access takes a large part of any roofing price, so a price without it is a different offer from a price with it.
Is VAT in?
At the standard rate of 20% the difference between a quote with VAT and one without is large, and Which? publishes its figures without it. Have the VAT position stated in writing.
Who is sending it, and what did they look at?
A figure given without a visit is a guess. We measure, photograph and explain, then give one written price. Citizens Advice recommends at least 3 written quotes, and they compare fairly only when each roofer has seen your roof.
If you want a fuller picture of how the pitch of your own roof affects the choice, the measuring steps are in our standard roof pitch post.
