The short answer
A flat garage roof can usually be converted to a pitched one if the walls can carry a new timber roof and the extra height is acceptable. The work is a structural alteration, so Building Regulations approval normally applies, and planning may too, so check with the council first. A pitched garage roof costs more than a flat one, and whichever covering you pick fixes the lowest workable pitch.
What changes when a flat roof becomes pitched
A flat garage roof is a deck sloped slightly to drain. A pitched roof is a frame of rafters or trusses rising to a ridge or sloping one way, covered in tiles, slates or sheet. The change replaces the whole structure, not only the covering, so the building has to be assessed as for a small new roof.
The key checks are the walls and the wall tops. A flat roof often rests on a ring beam or just on the top course of brick or block, with little to resist the outward push a pitched roof can exert if it is not tied properly. Wall plates, the timbers laid on the wall head to take the rafters, have to be strapped down, and the walls themselves must be sound and plumb.
If your garage is a precast concrete type, the panels and their fixings need particular attention. We cover those in replacement options for concrete sectional garages.
Building Regulations and planning
The Planning Portal says you will need Building Regulations approval where you carry out structural alterations, or where the replacement covering would add 15 per cent or more to the weight. Turning a flat roof into a pitched one is a structural alteration, so approval is normally needed. In Stroud District, building control runs through the Gloucestershire Building Control Partnership, with a registered building control approver as the private alternative. Where approval is needed we explain the steps, and our team deals with the paperwork.
Planning is a different matter. A straight swap of the covering generally falls outside planning control, but raising the height of a garage or changing its shape alters its appearance, and the answer can differ if the house is listed, if the garage is an outbuilding belonging to a listed house, or if it lies in a conservation area. Stroud District has 41 of them. Put your design to Stroud District Council's planning team early, and keep the reply in writing. Bring the wall heights, the proposed ridge height and a few photographs to that conversation, so the answer you get applies to your actual garage.
Our overview of pitched garage roofs looks at what the finished roof is like to live with.
Choosing a covering and the pitch it needs
The covering controls how steep the roof has to be. Marley's published data gives minimum pitches of 15 degrees for its Wessex and Mendip concrete tiles and 17.5 degrees for Edgemere, while clay plain tiles range from 30 to 40 degrees depending on the type. Natural slate has a minimum of 20 degrees under BS 5534, depending on headlap and exposure. Always check the product's own data sheet.
On a garage with a low parapet and limited wall height, that sets the ridge height. A lean-to shape, rising from the house wall to the front, needs less height than a gable but must be detailed where it meets the house with lead or a similar flashing. Sheet coverings follow the maker's own minimum, so check the data sheet. If the real question is whether the existing flat roof can last a few more years, read can a felt garage roof be patched first.
The weight matters too. Tiles are far heavier than felt or sheet, so we check whether the walls need strengthening before specifying them.
What it costs against staying flat
On MyBuilder's 2026 figures, a single flat garage roof typically runs £700 to £1,000, a double flat one £900 to £1,400, and a pitched one £2,500 to £4,500. The gap is a fair guide to the extra material, timber and labour. It does not include everything a conversion can involve, such as strengthening the walls, forming a gable, new fascias and gutters or insulation.
We have not found a published national figure for a flat-to-pitched conversion, so we will not offer one here. Your written quote is built from a survey and breaks the job into stripping the old deck, new structure, covering, rainwater goods, making good and disposal. Any scaffold is included in the quote.
If the old roof is asbestos cement sheet, removal and disposal come first, and if a shed shares the plot, felt shingles on a shed roof are worth a look at the same time.
Is it worth it? A decision guide
Conversion tends to suit a garage with sound walls, enough clearance and a roof that has failed more than once. It rarely suits a garage already struggling with cracked walls, a shared wall with a neighbour, or a low boundary where extra height will cause a dispute.
Compare the full cost over 20 years. Felt is quoted at 10 to 20 years by the flat roof firm Less, EPDM 20 to 30 years or more and tiles far longer, though sources vary and none is a promise. A pitched roof also gives you a little storage space in the roof and sheds rainwater more readily.
To explore it, send photographs of the garage from each side, or ring 01453 933613. We will survey, photograph the roof and walls, and send a written quote. Our workmanship carries a 10-year guarantee in writing, and the old covering is taken away. The rest of our garage work is under garage roof replacement.