Cost to build a flat roof extension in SY23

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Extend your SY23 with an extension

A flat roof extension is a great way to add extra space to your home without splashing out on the costs of a pitched roof extension. Often exempt from planning permission rules, you can build a flat roof extension up to 3 metres in height as long as it's not visible from a road. But how much do they cost in SY23?

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Build a flat roof extension cost in SY23

Flat roof extension cost in SY23

Estimates for build a flat roof extension near SY23

A flat roof extension ranges from the cheapest of £21,608 (SP Coupland Ltd based in SY25) to the dearest of £21,616 (DRAGON CONSTRUCTION T/A based in SY25), but these are just estimates. While they give you an idea of who will be better value, the best way to compare costs is to get real quotes.

Find out how much your flat roof extension will cost in SY23 by posting a job with HaMuch. We'll send it to extension builders in SY23.

Estimates for common extension builder jobs in SY23;

Whether you’re looking to extend your kitchen with a side return extension or you want to convert your basement into a liveable space, read our cost guides to get an idea of how much each project costs before getting a more accurate quote from our database of reliable tradespeople.

Underpin a building

Underpin a building - £17,112

Two storey extension

Two storey extension - £87,418

Build a timber frame extension

Build a timber frame extension - £25,612

Build a swimming pool

Build a swimming pool - £80,612

Single storey extension

Single storey extension - £47,240

Side return extension

Side return extension - £37,135

Install an RSJ

Install an RSJ - £1,812

Outbuilding

Outbuilding - £9,612

Build a Mansard loft conversion

Build a Mansard loft conversion - £51,612

Loft conversion

Loft conversion - £30,113

Build a kitchen extension

Build a kitchen extension - £41,612

Hip to gable loft conversion

Hip to gable loft conversion - £41,612

Granny annexe

Granny annexe - £86,612

Garden office

Garden office - £9,612

Convert a Garage

Convert a Garage - £15,612

Garage

Garage - £18,112

Build a flat roof extension

Build a flat roof extension - £21,612

Build a dormer loft conversion

Build a dormer loft conversion - £41,612

Concrete foundations

Concrete foundations - £5,862

Convert a bungalow loft

Convert a bungalow loft - £28,612

Convert a basement

Convert a basement - £33,135

More extensions & conversions cost guides...