A loft conversion is one of the best-value ways to add space and value to a UK home. Done well, it can add 20% or more to your property's market value — and you avoid the cost and disruption of moving. But the final price depends heavily on the type of conversion, the condition of your existing loft, and where you live. Here's what you need to know before getting quotes.
Types of Loft Conversion and Typical Costs
There are four main types of loft conversion, each with different structural requirements and price points.
Velux (roof light) conversion: £20,000–£30,000 The simplest and most affordable option. Velux windows are fitted into the existing roofline without changing its shape. It's only suitable if you already have enough headroom (typically 2.2m from floor joist to ridge). No external structural changes means less disruption and lower costs — but the usable space is limited.
Dormer conversion: £35,000–£55,000 The most popular type in the UK. A box-shaped extension is built out from the roof slope, creating a vertical wall and flat (or slightly pitched) roof section. Dormers dramatically increase headroom and floor area, and can usually be built under permitted development rights — no planning permission required in most cases.
Hip-to-gable conversion: £40,000–£60,000 Suited to detached and semi-detached houses with a hipped roof (sloped on all sides). The hip end is replaced with a vertical gable wall, which creates a larger loft footprint. Often combined with a rear dormer for maximum space. More complex structurally, which is reflected in the cost.
Mansard conversion: £45,000–£70,000+ The most substantial and expensive option. One or both roof slopes are rebuilt at a near-vertical angle (typically 72 degrees), maximising usable space. Common in older Victorian and Edwardian properties in London and other cities. Almost always requires full planning permission — and in conservation areas, getting approval can be difficult.
All prices above are for a basic finish (stud walls, insulation, basic flooring, staircase). Add-ons like an en-suite bathroom, fitted storage, or a high-spec finish will increase costs.
Do You Need Planning Permission?
Many loft conversions fall under permitted development rights, which means you don't need to apply for planning permission as long as certain rules are met:
- The additional roof space doesn't exceed 40m³ for terraced houses, or 50m³ for detached and semi-detached houses
- Materials match the existing house
- No extension beyond the existing roof slope on the front elevation
- No balconies or raised platforms
Planning permission is required if your property is in a conservation area, is a listed building, or the conversion exceeds permitted development limits. A planning application costs £258 in England (as of 2025) and typically takes 8 weeks to determine.
You'll also need Building Regulations approval for any loft conversion — this covers structural integrity, fire safety, insulation, and staircases. Your builder should handle this, but confirm it's included in any quote.
What Affects the Final Cost?
Structural work. Most loft conversions require strengthening the floor joists to make them suitable for habitable use. You'll also need a structural engineer's calculations — typically £500–£1,500 — before any work starts.
Stairs. A proper staircase (required by Building Regulations) costs £1,000–£3,500 depending on style. Space-saving staircase designs are an option for tight floor plans but must still meet minimum standards.
Bathroom. Adding an en-suite is one of the most popular additions — and adds £3,000–£7,000 to the bill, including soil stack extension and wet room or shower enclosure.
Location. Labour costs in London and the South East are typically 20–30% higher than the rest of England. The same conversion that costs £45,000 in Birmingham may cost £58,000 in London.
Roof condition. If your roof needs repairs or re-felting as part of the conversion, this adds cost. It's worth knowing the condition of your roof before getting loft conversion quotes.
What Return on Investment Can You Expect?
According to estate agents and property research from Nationwide and Halifax, a well-executed loft conversion adds between 15% and 25% to a property's value. On a £350,000 home, that's £52,500–£87,500 in added value — potentially well above the conversion cost.
The return is highest when:
- The new room is a usable bedroom (ideally with an en-suite)
- The conversion is in proportion with the rest of the house
- The neighbourhood has strong demand for larger family homes
A loft conversion is also more cost-effective than moving — avoiding stamp duty, solicitor fees, and removal costs that can easily run to £25,000+ on a move.
For a comprehensive guide to planning permission rules, building regs requirements and a full breakdown of the different loft conversion types, see our loft conversion UK planning and costs guide.