Loft Conversion Types and Costs UK — Velux, Dormer, Hip-to-Gable and Mansard Pricing Guide (2026)

Why loft conversions are so popular — and so valuable

More than 100,000 loft conversions are carried out in the UK each year, making it the single most popular structural home improvement. The appeal is straightforward: most semi-detached and terraced houses have a largely empty roof void that can be converted into one or two bedrooms, a home office, or a bathroom without touching the garden or footprint of the property.

From a property value perspective, the numbers are compelling. Independent valuations consistently show that a well-executed loft conversion adds 15–25% to a property's market value — often more in London and the South East where the cost of moving to a larger home is prohibitive. A £400,000 semi-detached house in the Midlands might add £60,000–£100,000 in value from a £45,000 dormer conversion, representing a strong return on investment even before accounting for the space gain. This is why homeowners who have lived in a property for several years and are looking to upsize without moving are the core customer for loft conversion companies.

For trade businesses, loft conversions attract clients who have already committed to spending significant money, have realistic budget expectations, and are not simply fishing for the cheapest quote. Winning one well-priced loft conversion can generate three or four more through neighbour referrals — particularly on roads of similar terrace or semi-detached properties where neighbours can see the completed work.

Loft conversion costs at a glance — 2026 UK prices

The figures below are complete project costs for a homeowner: all trades, all materials, structural engineer, scaffolding, building regulations fees, and project management. They exclude bathroom fitting, decoration, furniture, carpets, and VAT where applicable.

UK averages 2026. London and South East typically sit at the upper end of each range or above. Hip-to-gable figures are for the hip-to-gable element alone; when combined with a rear dormer add £8,000–£15,000.

Velux / rooflight conversion — £15,000 to £25,000

A Velux or rooflight conversion is the simplest and most affordable loft conversion type. No structural changes are made to the roofline: existing tiles are removed, the rafters are strengthened, new joists are installed to create a structural floor, insulation is fitted between and below the rafters, and roof windows (typically Velux-brand, though other manufacturers are available) are cut into the existing roof slope.

Because the external profile of the roof is unchanged, a Velux conversion almost never requires planning permission — it falls under permitted development in the vast majority of cases. Construction time is typically 4–8 weeks, making it the fastest conversion type to complete. There is no scaffolding required in most cases beyond a small working platform, which reduces cost further.

The key constraint is head height. The finished floor-to-ceiling height must be at least 2.2m for the space to be habitable and to satisfy building regulations. Because the structural floor raises the internal floor level by approximately 200–300mm, the existing ridge must be high enough to accommodate this. As a rule of thumb, if the distance from the existing ceiling joists to the ridge is less than 2.5m, a Velux conversion is unlikely to produce a comfortable habitable room — though a structural engineer should assess each case individually.

A standard Velux conversion includes two roof windows, a new structural floor with insulation, a staircase, plastered walls and ceiling, first-fix electrics (lighting circuit and sockets), and smoke detection. An en-suite is occasionally included but adds significantly to the cost and may not be feasible depending on the position of the existing soil stack.

Dormer loft conversion — £30,000 to £70,000

The dormer is the most popular loft conversion type in the UK and works on the widest range of properties. A box-shaped structure with a flat or low-pitch roof projects vertically from the rear (and occasionally the side) slope of the existing roof, dramatically increasing both headroom and usable floor area. Unlike a Velux conversion, a dormer creates full-height walls across a substantial portion of the loft, making it possible to fit bedrooms, bathrooms, and home offices comfortably.

All dormer types are usually permitted development on semi-detached and terraced houses (within 40m³ additional volume), and on detached houses (within 50m³). Properties in conservation areas, national parks, areas of outstanding natural beauty, or listed buildings require planning permission regardless of type.

Hip-to-gable conversion — £35,000 to £55,000

A hipped roof slopes inward on all four sides to meet at a central ridge — the side slopes (the “hips”) cut into the available loft space significantly. A hip-to-gable conversion removes the side hip slope and replaces it with a vertical gable wall, squaring off the end of the roof and reclaiming that lost floor area. The result is a substantially larger loft footprint without the need for a full mansard rebuild.

Hip-to-gable conversions are most common on end-of-terrace and detached properties where the hipped end is not shared with a neighbour and faces a garden, driveway, or side access. They are often combined with a rear dormer to maximise the floor area — the hip-to-gable creates more width at the side, while the rear dormer adds height and depth. When combined, budget £45,000–£70,000 for the complete project.

Because the external roof profile is changed on the side elevation, hip-to-gable conversions almost always require planning permission rather than falling under permitted development. Planning applications typically take 8–10 weeks. This adds time to the overall project programme and should be factored into any timeline given to the client. Local planning policies on hip-to-gable conversions vary — some councils are broadly permissive, others apply strict design guidance to preserve neighbourhood character on roads of hipped-roof properties.

Mansard conversion — £45,000 to £75,000+

A mansard conversion rebuilds the rear (and sometimes all) roof slopes at a near-vertical angle — typically 72° from horizontal — with a small flat section at the top. This creates the maximum possible floor area and ceiling height of any conversion type: the near-vertical rear wall means almost the entire loft footprint is usable at full standing height. The front elevation of the property is usually unchanged.

Mansard conversions are the dominant type in central London, particularly on Victorian and Edwardian terraced stock where rows of properties have already been converted and the mansard style has become the accepted norm. Outside London, they are less common, partly because the planning requirement (planning permission is almost always required) and the structural complexity make them significantly more expensive than a rear dormer that might deliver adequate space for many clients.

The structural work on a mansard is intensive: the existing roof structure is largely removed and rebuilt, the rear wall is constructed in blockwork or structural timber frame, and a new structural floor and ridge arrangement is required throughout. In conservation areas — which cover many of the London streets where mansards are most common — planning policies often dictate specific materials and window arrangements. Allow significant contingency on mansard projects and price from a detailed structural engineer's specification rather than from rule of thumb.

What's included and what's excluded

Understanding what a loft conversion quote typically includes — and what it does not — prevents the client expectation disputes that damage reputation and erode margin.

Always define inclusions and exclusions explicitly in the written quote. Disputes over whether bathroom fitting, decoration, or flooring were “included” are among the most common causes of loft conversion final account disagreements.

Planning permission and permitted development

Most loft conversions can proceed under permitted development rights without a formal planning application — but there are important exceptions, and getting this wrong means enforcement action and the cost of undoing the work.

Even where permitted development applies, it is good practice to obtain a lawful development certificate from the local planning authority before starting work. This costs £206 (2026) and provides written confirmation that the works are lawful — protecting the homeowner when they come to sell. Advise all clients to obtain one.

Building regulations — always required

Planning permission and building regulations are separate processes. Building regulations approval is required for all loft conversions, regardless of whether planning permission was needed. There is no exemption. The main areas covered are structural, fire safety, insulation, means of escape, and staircase design.

Building regulations fees vary by local authority and application route. A full plans application (the recommended route for loft conversions) typically costs £400–£900. The completion certificate is issued at the end of the project after the final inspection. This document is required for property sale — ensure it is obtained before releasing your final invoice.

Party wall agreement

Any loft conversion on a semi-detached or terraced property where structural work affects a shared (party) wall triggers the Party Wall etc. Act 1996. This is not planning law — it is separate civil legislation. It applies regardless of whether planning permission or permitted development rights are being used.

The homeowner must serve written notice on adjoining owners at least two months before work begins. If the neighbour consents in writing, work can proceed. If they dissent or do not respond within 14 days, a party wall award must be agreed — typically involving a party wall surveyor appointed by each party (or a single “agreed surveyor” appointed by both). Party wall surveyor fees run to £500–£1,500 per neighbour, paid by the building owner (your client). On a terraced house with two neighbours, this can mean £1,000–£3,000 in additional costs.

Advise clients to serve party wall notices as early as possible — delays here are one of the most common causes of loft conversion programme overruns. The two-month notice period cannot be shortened even with neighbour agreement, so early action is critical.

How to structure a loft conversion quote

Specialist loft companies and builders approach quoting differently, and both approaches can win work — provided the quote is clear, detailed, and professionally presented.

Loft conversion timeline — what to tell your client

The realistic end-to-end timeline from initial enquiry to moving into the completed loft room is 4–9 months, depending on conversion type and whether planning permission is needed. Set this expectation early — clients who expect a 6-week turnaround from enquiry to completion will be disappointed and will blame you for the delay even when it is entirely outside your control.

Total project duration for a permitted development rear dormer (no planning required): typically 4–6 months from survey to completion. For a mansard or hip-to-gable requiring planning permission: 7–9 months is a realistic expectation. Advise clients of this timeline at the first meeting, not after they have signed the contract.

How Trade2Base helps loft conversion companies

Loft conversion companies invest heavily in marketing — Google Ads, Checkatrade, MyBuilder, local SEO, van signage, and referral programmes. The challenge is knowing which channels are actually generating the enquiries that convert into signed contracts — not just the enquiries that come in, but the ones that become real, profitable jobs.

Trade2Base tracks which marketing source each enquiry came from and follows it through to quote, win, and job value. So when you look at your marketing spend, you can see not just how many enquiries each channel produced, but how many of those enquiries became signed loft conversion contracts and what the total project value was. If your Google Ads are generating 20 enquiries a month but only 2 convert, while your referral programme generates 5 enquiries that all convert at high value, Trade2Base shows you that — and you can redirect budget accordingly.

For loft conversion companies that are spending £1,000–£5,000 per month on marketing, knowing which channels produce profitable enquiries rather than time-wasting tyre-kickers is the difference between a marketing budget that grows the business and one that drains it.