How Much Does a Loft Conversion Cost in the UK? (2026 Prices)

A loft conversion transforms unused roof space into a habitable room — typically a bedroom, office, or bathroom. In the UK in 2026, loft conversions range from £20,000 for a basic Velux conversion to £65,000+ for a mansard, with the most popular dormer conversions costing £35,000–£55,000.

Whether you're a homeowner planning the project or a builder pricing one up, this guide breaks down loft conversion costs by type, explains what's included and what isn't, and covers the planning and building regulations you need to know about.

1 Cost by Conversion Type

The type of loft conversion is the single biggest factor in the final price. Here's what each type typically costs in 2026, including labour and materials but excluding VAT:

• Velux / rooflight conversion: £20,000–£30,000. The simplest and cheapest option. Roof windows are installed into the existing roof slope with no structural changes to the roof shape. Works well when you already have enough head height.
• Rear dormer conversion: £35,000–£55,000. The most popular type. A flat-roofed box extension is built out from the rear slope, creating full standing height across most of the room. This is the sweet spot for most semi-detached and terraced houses.
• L-shaped dormer conversion: £40,000–£60,000. Two dormers joined in an L-shape, typically on Victorian or Edwardian terraces with a rear outrigger. Provides significantly more floor space than a single rear dormer.
• Hip-to-gable conversion: £40,000–£55,000. The sloped side wall (hip) of the roof is extended vertically to create a gable end, adding usable floor area. Common on 1930s semi-detached houses.
• Mansard conversion: £50,000–£70,000. The most extensive type. The entire roof slope is rebuilt at a near-vertical angle (72 degrees is standard), maximising internal space. Often the only option for flats and properties in conservation areas, but almost always requires planning permission.

These figures are national averages. In London and the South East, expect to add 15–25% to every price above. Conversely, costs in the Midlands, North, and Wales tend to sit at the lower end of each range.

2 What's Typically Included

A reputable loft conversion company or builder should include the following in their quote. If any of these are listed as extras, ask why:

• Structural steel — steel beams (RSJs) to support the new floor and any load-bearing wall modifications
• Floor strengthening — upgrading ceiling joists to proper floor joists that meet building regulations
• Staircase — a building-regs-compliant staircase from the landing below up to the new loft room
• Dormer construction — if applicable, the full dormer structure including cheeks, flat roof, lead or GRP covering, and fascia
• Windows — Velux roof windows and/or dormer windows, including any required fire escape windows
• Insulation — between and over rafters to meet current building regulations (typically 0.18 U-value)
• Plasterboard and plastering — walls and ceilings finished to a standard ready for decoration
• Electrics — lighting, sockets, smoke/heat detectors, and consumer unit upgrades as required
• Plumbing — if an en-suite bathroom is included, the supply and waste plumbing for basin, WC, and shower

3 What's Usually NOT Included

These items are almost always excluded from loft conversion quotes and need to be budgeted separately:

• Decorating — painting, wallpapering, and any finish coats are typically left to the homeowner or a separate decorator
• Flooring finish — the structural floor will be in place, but carpet, laminate, or engineered wood is extra
• Furniture and fitted wardrobes — built-in storage in the eaves is sometimes offered as an add-on but rarely included in the base price
• Bathroom fixtures and tiling — the plumbing connections will be in place, but the actual shower enclosure, tiles, basin, and WC are usually supplied by the homeowner or quoted separately

Tip: When comparing quotes, check whether scaffolding, skip hire, and building regulations fees are included or extra. These three items alone can add £2,500–£4,000 to the project if they're not in the headline price.

4 Example Quote Breakdown

Here's what an itemised quote for a typical rear dormer loft conversion with en-suite might look like. This is a realistic mid-range example for a three-bedroom semi-detached house outside London:

If you're a builder quoting loft conversions, presenting this level of detail wins trust. Homeowners who see a single-line quote for "£40,000" with no breakdown will nearly always choose the contractor who itemises the work — even if the total is slightly higher. For tips on structuring quotes that convert, see our guide on how to quote a building job.

5 Factors That Affect the Final Price

Even within the same conversion type, costs can vary significantly depending on:

• Roof type and head height. A roof with a steep pitch and plenty of ridge height is easier and cheaper to convert than a shallow-pitched roof that needs more structural intervention to achieve usable head height.
• Party wall agreements. If you share a wall with a neighbour (terraced or semi-detached), you may need a Party Wall Agreement under the Party Wall etc. Act 1996. This typically costs £700–£1,500 per neighbour for the surveyor fees.
• Structural requirements. Some properties need more steel than others. If existing timbers are undersized, rotten, or affected by woodworm, additional structural work will add to the cost.
• London premium. Labour rates, material delivery costs, parking permits, and congestion charges all push London loft conversion prices 15–25% above the national average. A rear dormer that costs £40,000 in Manchester might cost £50,000–£55,000 in South London.
• Access and logistics. Tight terraced streets with no rear access mean materials have to come through the house. This adds time and cost. Properties with easy scaffold access and space for a skip keep costs down.

Understanding these variables is essential for protecting your profit margins if you're a builder, or for setting a realistic budget if you're a homeowner.

6 Planning Permission & Building Regulations

Planning permission

Most dormer loft conversions fall under permitted development rights and do not require planning permission, provided they stay within certain limits. The key rules for England are:

• No more than 40 cubic metres of additional space for terraced houses, or 50 cubic metres for detached and semi-detached houses
• The dormer does not extend beyond the plane of the existing roof slope facing a highway
• No part of the extension is higher than the highest part of the existing roof
• Materials are similar in appearance to the existing house

Mansard conversions almost always require full planning permission because they fundamentally change the roof shape. Properties in conservation areas, listed buildings, and flats also typically need planning approval regardless of the conversion type. Planning applications currently cost £258 for householder applications in England and take 8–12 weeks for a decision.

Building regulations

Every loft conversion requires building regulations approval — this is non-negotiable, regardless of whether planning permission is needed. Building control will inspect the structural design, fire safety (including escape windows and fire doors), insulation, staircase design, and electrical work. Budget £500–£1,000 for building regulations fees, and make sure your builder factors this into the programme — inspections need to happen at specific stages and can cause delays if not scheduled in advance.

7 How Much Value Does a Loft Conversion Add?

A well-executed loft conversion typically adds 20–25% to the value of a property, making it one of the best returns on investment of any home improvement project. Adding a bedroom and en-suite to a three-bedroom semi-detached house effectively turns it into a four-bedroom property — a significant jump in market value.

For context, if your home is worth £350,000 and you spend £40,000 on a dormer loft conversion, you could expect to add £70,000–£87,500 to the property value. That's a strong return, and one reason loft conversions remain so popular even as construction costs rise. For a detailed look at extension costs that also add value, see our house extension cost guide.

Wrapping Up

Loft conversions remain one of the smartest ways to add space and value to a UK home. The key to getting it right — whether you're the homeowner or the builder — is understanding what each type costs, what's included in the price, and what the regulatory requirements are before work begins.

For builders, presenting clear, itemised loft conversion quotes is the fastest way to win work and justify your price. Tools like VoxTrade let you walk through a loft space, describe the work by voice, and generate a professional, priced quote on site — no more going home to type it up. The more detail you give the customer upfront, the fewer disputes you'll have later.