Question answered
Can you change the pitch of a roof?
The short answer
Yes, a roof pitch can be changed, but it means altering the structure. Raising the pitch usually lifts the ridge, and permitted development does not allow the alteration to rise above the original ridge, so planning permission is normally needed. Building Regulations apply as well, and the new covering must suit the new angle.
Yes, a roof can be re-pitched, but it is a structural alteration, not a repair. Height limits, Building Regulations and the covering's minimum pitch all decide what is possible on your house.
What changing the pitch involves
Pitch describes how steeply a roof slopes. Changing it means removing the covering and reshaping the timber frame beneath, by raising the rafters on new walls, fitting new trusses or re-forming the structure. Lowering a pitch is less common, and it brings its own trouble, because each covering has a lowest safe angle, and below it rain can be pushed back under the laps.
People ask for headroom for a loft room, for a steeper slope to take a different covering, or as a way to replace a failing flat or shallow roof. Each reason leads to a different design. The survey comes first: we need to see the existing frame, the wall plate and the walls that must carry the new loads before anyone can say what is sensible.
It is a bigger job than most roof work, so be wary of anyone who treats it as a quick swap. Our page on converting a flat roof to pitched covers the nearest alternative, and the wider range of pitched work is on our pitched roofing page.
The height tests that decide planning
Most householders want to know whether the work counts as permitted development, meaning it can go ahead without a planning application. Under Class C of the General Permitted Development Order, an alteration to a roof is not permitted if it stands more than 0.15 metres proud of the original slope, or if it would end up taller than the original roof.
Re-pitching normally fails the second test, because a steeper slope on the same footprint pushes the ridge up. Class B, which covers additions such as dormers, has a matching limit on height, and it requires materials of a similar appearance.
Class B does not apply at all on article 2(3) land, which includes conservation areas and the South Downs National Park. In practice a change of pitch almost always means a planning application. Ask the planning officers at Adur & Worthing first, or the National Park authority where your home lies within the Park, before you pay for design work.
Building Regulations and the structure
Apart from planning, a structural alteration to a roof needs Building Regulations approval. The Planning Portal lists structural alterations among the reasons a re-roofing job goes beyond the usual exemption, and it adds that a covering which makes the roof 15 per cent heavier or more also needs approval. Approved Document A calls an increase in loading of more than 15% a significant change, and strengthening the structure a material alteration.
Where the work is notifiable, our job is to say what is required and to submit the notification, to either the council building control team or a registered building control approver.
Insulation follows. Approved Document L sets 0.15 as the limiting U-value where a roof element in an existing home is new or replaced, so a re-pitched roof is normally insulated to that figure. If the work creates a loft room, escape from the upper floor comes into play as well, and a two-storey house with a new room above may need a protected stair.
How the covering limits the pitch
Even where planning allows it, the covering has to suit the angle. Marley's published minimums run from 12.5 degrees for one interlocking concrete tile up to 35 degrees for concrete plain tiles, and its clay plain tiles need between 30 and 40 degrees depending on the type. For natural slate, BS 5534 indicates 20 degrees at moderate exposure with a 500 mm slate and a 115 mm headlap. Always read the product's own data sheet; slate and clay follow different headlap rules, so the covering is chosen last, once the angle is known.
That is why lowering a pitch often forces a change of covering, and why raising one can widen the choice. Fixing depends on pitch too: Marley points to strong suction across the windward slope when the pitch is under 30 degrees, and a coastal house is the last place to run a covering at its limit. For one detail that changes when roof planes alter, see dry valley troughs.
Cost, and what to ask before you commit
No single price fits a pitch change, because the structure, scaffold, design fees and covering differ from house to house. The covering alone is easier to benchmark, and our page on tiled roof repair cost gives typical UK ranges. For the structural part, a total price is set after the survey and the drawings.
Before you commit, ask whether a structural engineer has looked at the frame and walls, who will handle the planning application and the building control notification, and which tile or slate is proposed with its minimum pitch. See whether the price you are quoted already carries VAT and scaffolding. If a firm cannot say which regulations apply, that tells you what you need to know.
Re-pitching: two more questions
Can I lower the pitch of my roof to keep the ridge down?
Sometimes, but the covering sets the limit. A slope laid below the minimum for its tile or slate can leak when rain is driven under the laps. A lower angle often means a different covering, and the structure and Building Regulations still apply.
Is fitting a roof window the same as changing the pitch?
No. A roof window is a separate alteration under Class C, with its own limits on how far it protrudes and on glazing in side slopes. It leaves the angle of the roof alone, which is why it can be a lighter route to extra daylight.
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