Loft Conversions: Costs, Planning & Build Stages

Indicative build starting prices are: Velux or rooflight from £30,000; hip-to-gable from £35,000; hip-to-gable with rear dormer from £45,000; rear dormer from £40,000; L-shape dormer from £50,000; double hip-to-gable with dormer from £55,000; and mansard from £70,000. Final construction cost depends on size, specification, structural complexity, access and location. Loft Plans does not carry out the build. Our planning/design stage starts from £950; for full-planning cases the technical stage is a further £550 after approval, making the coordinated package £1,500. Council and statutory fees are separate.

Structural work (steels, joists, dormer framing), insulation to current Part L, plasterboard and skim, electrics, plumbing, central heating extension, staircase, flooring, internal doors, windows or roof lights, decoration and basic fittings. It does not normally include bathroom suites, fitted wardrobes, expensive flooring upgrades, or external scaffolding licences if your local authority charges for them.

A well-designed additional bedroom can add value, but the result depends on the property, location, quality and local market. Obtain local valuation advice rather than relying on a generic percentage or guaranteed return.

Most loft conversions in England don't — they fall under Permitted Development if they stay within 40 m³ for terraces or 50 m³ for semis and detached homes, don't extend forward of the front roof, and don't go above the existing ridge. Flats and listed buildings do not benefit from the same householder loft Permitted Development route and need separate planning and consent checks. Conservation areas and National Landscapes have tighter Permitted Development restrictions, and an Article 4 direction can remove specific Permitted Development rights — so the right route should always be checked for your specific property before submission. Where Permitted Development applies, a Lawful Development Certificate is recommended to provide formal evidence from the local planning authority that the work would be lawful based on the information submitted.

After the survey, we prepare the planning or LDC drawings and submission in approximately 1–2 weeks. For a suitable Permitted Development project, Building Regulations drawings and structural calculations can be prepared within that same design period. For a full-planning case, the standard statutory determination period for a typical householder application is usually 8 weeks, although councils can take longer; after approval we finalise the technical package within a further few working days. Council, building-control and construction times sit outside our preparation period.

Yes — every loft conversion needs structural calculations prepared by a structural engineer covering new floor joists, supporting steel beams, and any changes to the roof framing. Our package includes the engineer's calculations, ready for building-control review, and we answer any queries they raise if needed.

If your home is semi-detached or terraced, you may need to serve notice before work affects a shared wall, including where steel beams bear into it. This is handled separately from Loft Plans' design service; obtain advice and a quote from a party wall surveyor for your property.

Most clients do. The first couple of weeks are noisy and dusty when the roof is opened and the steels are dropped in, but once the loft is weather-tight the noise drops sharply. Expect one or two days without water or power when the heating and electrics are extended. Bathroom-only days at the end are usually fine to live through.