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Replacing a flat roof with a pitched roof is a popular upgrade for homeowners looking for a more durable structure, better drainage, or the option to make use of the roof space. It’s a significant project, but one that carries several benefits. In this guide, we look at the typical cost to replace a flat roof with a pitched roof in the UK, what affects the price, and what to budget for before work begins.

How much does it cost to replace a flat roof with a pitched roof?

As a general guide, the average cost to replace a flat roof with a pitched roof is £3,000–£4,500. Smaller roof conversions with a simple open gable structure tend to sit at the lower end of the range, while larger roofs that need scaffolding or more complex structural work will cost more.

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For an accurate idea of costs in your area, it’s always worth speaking to contractors experienced in roof conversion work.

Enter your postcode to compare checked local roofers and request tailored quotes.

Material costs to replace a flat roof with a pitched roof

When replacing a flat roof with a pitched roof, the type of tiles you choose will have a big impact on the overall cost. The most popular choices for tiles are concrete, clay or slate — each come at a different price.

• Concrete tiles: average cost £1 to £3 per tile

• Clay tiles: average around £1 to £5 per tile

• Slate tiles: expect to pay around £1 to £12 per tile

Labour costs to replace a flat roof with a pitched roof

Roofer

Converting your roof is a major structural job so you’ll need several roofers to carry out the work.

• The average cost of a roofer is £160 to £200 per day

• You can expect the roof conversion to take 2–3 days, depending on the size of the roof and the complexity of the project

Carpenter

There's often a lot of carpentry work needed for roof conversions.

• You can expect to pay around £160 to £200 per day for bespoke carpentry work

Professional fees

Because of the structural change you might also want to get professional designs done by an architect or structural engineer.

They’ll need to assess the project, review plans, check building regulations and then draw the designs. That process should take 2–3 weeks.

• Professional structural designs average around £37.50 per hour

What affects the cost of a roof conversion?

The cost of converting your roof from flat to pitched will depend on a number of key factors, including:

• Style of roof

• Size of roof

• Complexity of the conversion

• Type and quality of materials used

• Any scaffolding needed

• Where you live

Additional costs to budget for

There are a number of other costs you need to factor in when planning your budget to convert a flat roof to a pitched roof:

• A wall plate & fixings need to be included, which cost around £6.78 per metre

• If prefabricated trusses can't be used then you'll need to get bespoke trusses made. Standard trusses cost around £25 to £30 per metre, but having bespoke trusses would increase the cost

• If you're planning to use your new roof space as a living space then plasterboard will be needed for cladding or a ceiling will be required. The cost for materials is around £2.65 per m²

• And don't forget ventilation for the new roof space, which will cost an average of £35.24 per tile vent

How do you convert a flat roof to a pitched roof?

Converting a flat roof to a pitched roof can be done in a number of ways, which an architect or structural engineer can help advise you on.

• Do you want to simply add a shallow pitched roof on top of the existing flat roof?

• Are you planning on adding a brand new floor to your property and then having a pitched roof above that?

These are important questions to think about before you start the project. If in doubt, speak to a local architect or structural engineer for their professional advice.

When it comes to starting the roof conversion, here’s an overview of how it works:

1. Remove the flat roof

All tiles, roof coverings and roof battens need to be removed. The roofing specialists will review the condition of the existing roof structure to check it’s suitable to proceed with the new roof installation. At this point, any rot or roof damage will be dealt with.

2. Joist installation

Once the existing roof structure has been given the all clear then the joist spacing is checked to make sure it can accommodate the pitched roof. If so, trusses are placed over every second joist and attached to the wall.

3. New roof structure added

With trusses in place, wood is attached to the trusses to cover the whole roof. This is when you can see the new shape of the roof. Waterproofing material (usually tarpaper or similar) is then added on top of the wood and finally ridge boards installed.

4. Tiling and finishes

The final step is adding the roof tiles (or other roof coverings) and any final waterproofing to seal the roof completely. Job done.

Benefits of converting a flat roof to pitched roof

• More durable: A well-built pitched roof can last for many years with proper maintenance

• Added space: The roof area may be used for storage or, where suitable, converted into living space

• Better weather protection: The pitched shape helps rainwater drain away more easily

• Energy efficient: The roof space can provide room for ventilation, insulation and, in some cases, solar panels

Do I need planning permission to convert my roof?

In most cases, yes. A roof conversion is a structural change and therefore requires planning permission from your local council.

Planning permission will cost you around £210 in England, or £190 in Wales.

Roof conversion cost checklist

• Decide on the type of roof conversion you want and research your options

• Consider getting professional structural designs drawn up

• Contact your local council to apply for planning permission

• Speak to local roofing specialists for their professional advice and accurate quotes

• Shop around for fair and competitive roof conversion costs

• Look for tradespeople with relevant experience, qualifications and accreditations, such as NFRC membership

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