Loft Conversion Cost at a Glance
In 2026, a loft conversion in the UK typically costs between £20,000 and £70,000, depending on the type of conversion, the structural work involved, the finish, and your location. The figure that applies to your home depends mostly on which type of conversion your roof can take.
As a broad benchmark, expect to pay in the region of £1,500 to £2,500 per square metre for a standard conversion, rising for high-spec finishes, bathrooms and complex structural work. London and the South East sit towards the upper end of every range below. The most reliable way to know your true cost is an itemised quote against a proper specification — not a rough rate per square metre.
Loft Conversion Cost by Type
The single biggest factor in your cost is the type of conversion your roof and property allow. Here are the four main types, what they involve, when they suit, and the planning implications of each.
Velux / Rooflight Conversion
£20,000 – £30,000The simplest and most affordable option. Velux (rooflight) conversions add windows into the existing roof slope without altering the roof structure or footprint. They suit roofs that already have generous headroom — typically older homes with a steep pitch.
When it suits: Best for lofts that already meet the minimum 2.2m head height. No change to the roofline.
Planning: Almost always falls under permitted development, as nothing protrudes beyond the existing roof. Building Control approval is still required.
Dormer Conversion
£30,000 – £50,000The most common type in the UK. A dormer extends vertically from the roof slope to create a box-shaped structure, adding usable floor area and full-height headroom. A rear dormer is the standard choice for terraced and semi-detached homes.
When it suits: Ideal where the existing roof lacks headroom or floor space. Adds the most usable room per pound on most properties.
Planning: Rear dormers often fall under permitted development within volume limits (40m³ terraced, 50m³ detached/semi). Front or side dormers usually need planning permission.
Hip-to-Gable Conversion
£40,000 – £65,000Suitable for properties with a hipped (sloping) side roof — common on semi-detached and detached houses. The sloping side is extended outwards and up to form a vertical gable wall, dramatically increasing internal volume. Often combined with a rear dormer.
When it suits: Detached and semi-detached homes with a hipped roof and no usable space at the side of the loft.
Planning: Can fall under permitted development on many detached and semi-detached homes, but the combined volume increase frequently pushes it into requiring planning permission.
Mansard Conversion
£45,000 – £70,000The most extensive — and most expensive — option. A mansard alters one or both slopes of the roof to create an almost-vertical rear wall and a near-flat top, maximising headroom and floor space across the whole footprint. Common on period and London townhouses.
When it suits: Properties where you want to maximise space, and period or terraced homes in conservation areas where a mansard matches the streetscape.
Planning: Almost always requires planning permission because of the significant change to the roof shape. Party wall agreements are common given shared walls.
What Affects the Cost of a Loft Conversion
Two conversions of the same type can differ by £15,000 or more. These are the factors that move the number within — and sometimes beyond — the ranges above.
Size and complexity
A larger loft costs more in materials and labour, but complexity matters more than raw square metres. A simple rectangular dormer is cheaper per square metre than a multi-level layout, an awkward roof shape, or a conversion that involves rerouting services.
Structural work
New steel beams to support the roof and floor, plus reinforcement of the existing ceiling joists into a proper structural floor, are among the biggest cost drivers. The number and span of steels needed depends on the original construction.
Staircase position
Fitting a compliant new staircase — with adequate headroom over it and a landing — can force changes to the floor below. A straightforward run over an existing stair is cheap; sacrificing a bedroom or reconfiguring a landing adds cost.
En-suite or bathroom
Adding a bathroom means new soil pipes, hot and cold feeds, waterproofing, ventilation and tiling. An en-suite typically adds £5,000–£10,000 depending on specification and how far the new drainage has to run.
Roof structure
A traditional cut roof (rafters and purlins, common pre-1960s) is far easier and cheaper to convert. A modern trussed roof — with a web of timber W-trusses — must be substantially restructured with new steels, which adds materially to the cost.
Location
London and the South East carry a premium of 10–20% over national averages due to higher labour rates, parking and access restrictions, and tighter planning. RCB works across London, Kent and Essex and prices honestly for each location.
Specification and finish level
Standard plaster, painted finishes and mid-range fittings sit at the lower end of each range. Bespoke joinery, underfloor heating, high-end bathrooms, rooflights to premium brands and feature staircases push costs towards — and beyond — the top of the range.
Access
How materials reach the loft affects labour. Properties with no rear access, a narrow plot, or restricted street parking need more manual handling and sometimes craneage or roof hoists, all of which add to the preliminaries.
Party wall
Terraced and semi-detached conversions almost always require a Party Wall Agreement with neighbours. Surveyor fees (typically £1,000–£2,000 per neighbour where an award is needed) are usually a client cost, not part of the build quote.
What's Included vs What's Excluded
One of the most common reasons a loft conversion costs more than expected is a misunderstanding about what the build quote covers. A headline price that excludes design fees, party wall costs and decoration is not comparable to one that includes them. Here is what a typical RCB build quote includes — and what usually sits outside it.
Typically Included
- Structural works — steel beams, floor reinforcement and load-bearing alterations
- The full build — roof alterations, dormer construction, walls and roof covering
- Insulation to current Building Regulations thermal standards
- Plastering and plasterboard throughout the new space
- First-fix and second-fix electrics — wiring, sockets, switches and lighting points
- New staircase installation to the loft
- Internal doors, skirting and architraves (at the specified standard)
- Building Control liaison and inspections during the build
Commonly Excluded
- Planning permission and Building Control application fees
- Architectural drawings and structural engineer's design and calculations
- Party wall surveyor fees and any party wall award
- Furnishings, fitted wardrobes and free-standing furniture
- Final decoration in some quotes (always confirm whether painting is included)
- Specialist finishes — premium flooring, bespoke joinery or high-end sanitaryware upgrades
When comparing quotes from different builders, always check these exclusions line by line. A £35,000 quote that excludes decoration, design and party wall fees can end up costing more than a £40,000 quote that includes them. Our guide on how to compare builder quotes explains how to do this properly.
Cost Per Square Metre — A Word of Caution
Many homeowners search for a simple rate per square metre. As a rough benchmark, a standard UK loft conversion works out at around £1,500 to £2,500 per square metre, with London and the South East at the higher end and bespoke or structurally complex projects exceeding it.
But a square-metre rate is only a starting point. Two lofts of identical floor area can cost very differently depending on the roof structure, the steelwork needed, whether you add a bathroom, and the staircase solution. Use the per-square-metre figure for an early budget sanity check — then rely on an itemised quote for the real number.
RCB's Approach to Loft Conversion Pricing
At RCB Design & Build, we quote loft conversions with a fully itemised, transparent breakdown — never a single lump sum. You see exactly what each element costs: the structural steelwork, the build, the staircase, the electrics, the finishes. The scope is fixed and the exclusions are stated in writing, so there are no surprise variations mid-build.
That means the price we agree is the price you pay, provided the scope does not change. If you do choose to add or alter something, it is priced and agreed before any work starts — never discovered on the invoice afterwards.
- Fully insured — public liability and contractor's all-risk cover
- Building Control sign-off managed and documented for every project
- Written, itemised quotes with a fixed scope and stated exclusions
- No hidden variations — changes are quoted and agreed before work begins
Planning Your Budget and Timeline
Cost is only half the picture — knowing how long the work takes helps you plan around it. Most loft conversions take 6–10 weeks on site, separate from the design and approval stage beforehand.
Read: how long does a loft conversion take?