Loft conversion cost: A breakdown of costs

Loft conversion costs 2025

Thinking about a loft conversion for your home, but unsure of the cost? A well-planned loft project turns underused roof space into a bright new bedroom, office or playroom without the upheaval of moving. It can also boost resale appeal by up to 25%. Recent surveys found 18% of homeowners were considering a loft conversion as their next space-creating project. 

Beyond space and value, a conversion offers an opportunity to enhance comfort and efficiency – consider improved insulation, smarter lighting, and ventilation. While every home is unique, many lofts can be converted under permitted development, making the path from idea to build more straightforward. 

In this guide, we’ll explain the factors that shape loft conversion cost so you can plan with confidence. For a deeper dive into types, rules and timelines, see our ultimate guide to loft conversions.

 

Costs to create a simple loft room 

There are several types of loft conversions to consider, based on your budget, house style, and what you want to achieve. These include:

• Rooflight or Velux: Adds roof windows to the existing roofline with minimal structural change. Great for light and ventilation, but doesn’t increase headroom.
• Dormer: A box-like extension projecting from the roof to create extra headroom and floor area.
• Hip-to-gable: Converts a sloping hip end into a vertical gable wall, unlocking space on hipped roofs (semis, end-terraces, detached). Often paired with a rear dormer.
• Mansard: Rebuilds one side of the roof with a steep lower slope and shallow upper slope, maximising usable space and a near-vertical rear wall. Typically needs planning permission.

*These prices are dependent on factors such as property location, project complexity, and the materials chosen. 

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Loft conversion cost breakdown

When calculating your loft extension costs, it helps to have an idea of the breakdown for each element. 

Floor build-up

You’ll need a solid, hard-wearing floor for a usable loft space. Many existing roof spaces already have insulation between the joists, but this is a good opportunity to check if it needs replacing. Our comprehensive guide to home insulation will help you decide.

• Timber joists: Around £10 per metre for C24 treated, kiln-dried timber
• Flooring deck: From £9.00 per m² for 18mm tongue-and-groove chipboard
• Between-joist quilt: From £2.90 per m² for a 100mm roll of glass mineral wool*
• Vapour control layer: Around £2.20 per m² for reinforced vapour membrane

Lining the sloping ceilings

The type and required amount of lining depends on the style of your chosen conversion, but the most commonly used linings include:

• PIR rigid insulation: Around £16.60 per m² for 100mm PIR
• Plasterboard lining: Around £4.50 per m² for standard 12.5mm board
• Skim finish: Between £1 – £2 per m² for a multifinsih product

Your builder should provide a breakdown for each element of the project, but may only give prices for materials upon request – for instance, if you want to compare prices. However, most have preferred suppliers that offer the best cost-effective prices. 

Electrical compliance 

Loft conversions nearly always involve new circuits and sockets, so budget for professional testing alongside labour costs of around £40 per hour.

Structural changes

Many loft conversions include roof retiling, new windows, adding a permanent staircase, or the addition of an en-suite bathroom.  

Retiling a roof 

You might need to retile if structural changes disturb the current roof covering, the existing tiles are at end-of-life, or updated weatherproofing or insulation details require a new roof skin. You could expect to pay in the region of £30 per m² for concrete tiles, with labour costing an average of £200 per m² for stripping and retiling. 

Velux windows

A Velux window introduces natural light and fresh air into the new loft room – often helping meet daylight and ventilation requirements without significant structural changes. Plan to spend around £980 – £1,200 per standard unit.

Small dormer window

Including a small dormer window offers extra light, outlook, and headroom, and usable floorspace at the eaves without the cost and structural impact of a full-width dormer. Allow upwards of £9,000 for incorporating a small, straightforward UPVC dormer in your loft conversion. 

Permanent staircase

A habitable loft must have safe, permanent access and a protected escape route under Building Regulations. Loft ladders aren’t acceptable as the main access, so a fixed staircase is required. For a simple, straight softwood flight, expect to pay from £1,200; however, this can rise to £10,000 or more for more complex, hardwood designs. 

En-suite bathroom

Including an en-suite bathroom in your new bedroom increases convenience and privacy. It also boosts the room’s usability and resale appeal as a self-contained suite. A standard en-suite typically costs between £3,000 and £7,000.

Raising the roofline

If your current loft can’t achieve a safe headroom of around two metres, you may need to raise the roofline; lowering the ceiling below is the other common workaround. Any project that increases the ridge height requires planning permission; however, under Permitted Development, you cannot exceed the existing roof’s highest point. 

Roof-lifts sit at the top end of loft conversion costs because they involve major roof reconstruction. As a benchmark, raising the roof for a mansard loft conversion averages about £2,290 per m².

Hidden loft conversion costs

Any building project involves several hidden costs, and a loft conversion is no different. While these are easily overlooked, they impact the overall cost and should be included in your budget from the start. 

Fire safety 

A conversion that creates a new storey typically needs a protected escape route and mains-powered, interlinked smoke alarms on each storey – all of which add materials and labour.

VAT

Remember VAT at 20% on most building labour and materials, unless a specific reduced or zero-rate applies.

Planning applications, certificates, and regulations

• Householder planning application:  Depending on the type of loft conversion you choose, you may not require planning permission. As a guide, an application for a property in England costs £528, but costs in the home nations may vary.
• Permitted Development certificate: Depending on the proposed changes, the certificate costs around £240 in England. 
• Building control: Your local council charge a fee for checking your plans and for any required site inspections. These vary by area and the size of the loft conversion, but expect to pay around £1,000 for up to 40 m². 
• Party Wall Award: If your conversion affects a party wall, you may need a Party Wall Award. Typical surveyor rates range from £90 to £450 per hour, but this depends on the project’s complexity. 

Work with your trusted builder to ensure your loft conversion complies with all the relevant regulations. 

A well-planned loft conversion turns underused space into a comfortable, valuable part of your home.

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