Can you turn a flat garage roof into a pitched one?

The usual reasons are easy to follow. A flat felt roof has leaked twice, the garage looks out of place next to a pitched house, or there is a wish for storage space in the roof. A pitched roof sheds water without relying on a membrane, and the right covering lasts a long time.

Set against that, the change costs far more than re-covering the flat roof. National figures from MyBuilder's garage roof guide, updated August 2026, put a flat single garage at £700 to £1,000 and a double at £900 to £1,400, while a pitched garage roof comes out at £2,500 to £4,500. That gap buys a new structure rather than a new skin, and it buys a different building from the street.

If the problem is a leaking membrane, the lightest cure is often a repair or a re-felt rather than a conversion. Our page on repairing a felt garage roof shows how to tell which situation you have. For a full cost picture, read garage roof replacement cost.

This decides everything. A flat garage roof is a horizontal deck resting on the wall tops. A pitched roof pushes outwards as well as down, and the walls and any tie arrangement have to resist that spread. Single-skin brick garage walls, and especially tall unbraced gable walls, may not be able to do it without strengthening.

A proper conversion adds a wall plate fixed to the brickwork, rafters tied across the span by ceiling joists or collars, and bracing against wind. Piers or padstones may be needed under concentrated loads. Foundations that were adequate for a flat roof can need checking too, and this is where a structural engineer or the building control body earns their fee.

The covering also counts. Marley gives its concrete plain tile at 73.8 kg/m² laid, a lot heavier than felt on boards. Lighter coverings such as metal sheet or fibre-cement are kinder to an old garage wall.

Everything starts with a survey of the walls, the foundations, the span and the joists, with photographs of your own building.

Two sets of rules apply, and neither can be assumed away.

On Building Regulations, the Planning Portal lists structural alterations as one of the things that mean you need approval. Building a new roof structure on a garage falls into that category, so expect a building control application and inspections, with the council's building control team or a registered building control approver. Swindon Borough Council runs its own building control service. Our guide to garage roofs and Building Regulations sets out when rules apply.

Planning is a separate question. A pitched roof is taller than a flat one, and a change to the shape and height of an outbuilding may need planning permission, particularly near a boundary, in a conservation area or on a listed property. No roofer can give you a legal ruling from a doorstep. Put the question to Swindon Borough Council's planners, or to whichever authority covers your postcode, before any work begins.

A garage built hard against a neighbour's wall may also bring party wall rules into play, so raise that early too.

Pitch and covering go hand in hand, because each product has a minimum slope. These are figures from manufacturers and the BS 5534 route, and the data sheet for the actual product has the final say.

A low pitch keeps the ridge height down, which helps with planning and with neighbours, and suits sheets or interlocking tiles. A steeper pitch gives loft space but raises the building. Sheet coverings on a pitched garage roof are covered in our guide to pitched garage roofs. Light tiles may need a new look at the eaves, verge and ridge, with the ridge mechanically fixed under BS 5534:2014 rather than bedded on mortar alone.

The old covering comes off first. On a garage built before 2000, corrugated sheeting is presumed to be asbestos until a test shows otherwise, and the soffits and fascias deserve a look as well. HSE's non-licensed category covers asbestos cement that comes off carefully and intact. Our page on how asbestos waste is disposed of explains the consignment-note side.

For a flat felt roof, the old layers and boards are stripped and taken away. Some of the existing deck can stay if it is sound and can act as a ceiling, but a new roof structure is normally built above it, so the old deck often becomes the ceiling lining.

Insulation is a design point as well. If the garage is likely to be converted later, the new roof is the easiest moment to provide for it, and an insulated roof brings its own Building Regulations considerations for the thermal element.

Because a conversion has so many unknowns, we begin with a survey. It covers the walls, the span, the existing deck, the eaves and the neighbouring structures, with photographs of your own garage. If re-covering the flat roof cures your problem, you will hear that from us, because a conversion is a big spend for a small gain in that case.

One written total arrives after the survey. Should the project go ahead, we explain which consents it needs and handle the Building Regulations notification where the work is notifiable. A decade-long written guarantee covers the workmanship, and we haul away what we strip. Ask whether VAT and scaffolding feature in any price you are given. For a first conversation, send photographs of the garage from the front, the side walls and inside the roof space if there is one, by WhatsApp, or call 01793 626096. See also our garage roof replacement overview.