A loft conversion is consistently one of the most cost-effective ways to add living space in the UK. In 2026, you can expect to pay anywhere from £18,000 for a simple Velux conversion to well over £75,000 for a full mansard on a London terrace. The range is wide because “loft conversion” covers fundamentally different structural scopes — some barely touch the roof, others replace it entirely.
This article breaks down what each conversion type actually costs, what that price buys you, how quotes are structured, and where regional variation bites hardest.
Average Cost by Conversion Type
The four main types differ in how much of the roof structure they alter. That single factor drives most of the cost difference.
| Conversion type | Typical cost range | Best suited to | Planning required? |
|---|---|---|---|
| Velux / rooflight | £18,000 – £28,000 | Properties with 2.2m+ ridge height and ample headroom | Usually not (PD) |
| Dormer (rear) | £35,000 – £55,000 | Victorian/Edwardian semis and terraces | Usually not (PD) |
| Hip-to-gable | £45,000 – £65,000 | Semi-detached or detached with hipped roof | Usually not (PD) |
| Mansard | £55,000 – £75,000+ | Terraces and mid-terraces needing maximum space | Planning permission usually required |
| L-shaped dormer | £50,000 – £70,000 | Victorian terraces with rear return | Usually not (PD) |
Figures above are for a standard single-bedroom conversion including structural work, insulation, staircase, electrics, plastering, and decoration. They exclude furniture, fitted wardrobes, and ensuite bathrooms (add £6,000–£14,000 for a modest wet room or shower room).
Velux / Rooflight Conversions
At £18,000–£28,000, a Velux conversion is the most affordable route because the roof pitch and structure remain unchanged. The builder cuts openings, installs proprietary roof windows (typically 780 × 980 mm or 940 × 1,600 mm), insulates between and below the rafters, and fits a staircase. The finished room is usable but limited by the existing slope — expect 50–60% of floor area at standing height. These suits properties where the ridge height already exceeds 2.2 m above the existing ceiling joists.
Rear Dormer Conversions
A dormer extends the rear roof plane vertically, typically adding a flat-roofed box structure that can run the full width of the rear elevation. At £35,000–£55,000, this is the most common conversion in London and south-east England. It typically adds 15–25 m² of full-height usable floor area. The structural work involves removing existing rafters, installing steel beams (typically 178 × 102 × 19 UC or similar), and building the dormer cheeks in timber frame with brick or tile cladding to match.
Hip-to-Gable Conversions
A hipped roof has slopes on all four sides. Converting the hip to a vertical gable wall dramatically increases headroom over the stairwell and upper floor. At £45,000–£65,000, this is often combined with a rear dormer (sometimes called a “hip-to-gable and dormer” conversion), which can push costs toward £60,000–£75,000 but creates a very generous loft room of 30–40 m².
Mansard Conversions
A mansard replaces the roof structure almost entirely, creating near-vertical sides (typically 72° pitch) and a near-flat top. The finished space is maximum use — close to a full storey. Costs start at £55,000 and regularly reach £80,000–£90,000 in London for quality work. They almost always require planning permission, and on conservation area properties, the Local Planning Authority may specify particular materials.
What’s Included in a Typical Quote
A reputable builder’s quote for a loft conversion should itemise or clearly cover:
- Structural design: SE calculations and drawings (£900–£2,500 depending on complexity)
- Building Regulations application: £800–£1,500 (full plans route)
- Scaffolding: £1,200–£2,500 depending on height and duration
- Structural steelwork: £1,500–£5,000 for beams, hangers, and connections
- Roof works: £4,000–£12,000 for dormer framing, weathertightening, flat roof covering
- Insulation: £1,500–£3,000 for spray foam or rigid board to Part L standards
- Staircase: £2,500–£8,000 (bespoke joinery or fabricated steel at the upper end)
- First-fix electrics and lighting: £1,500–£3,000
- Plasterboard, plastering, and decoration: £2,500–£4,500
- Windows (Velux or bespoke): £600–£2,500 per unit
What quotes often exclude: architectural drawings beyond planning stage, party wall surveyor fees (£700–£1,500 per neighbour), and VAT — which is charged at the standard 20% rate on most conversion work. Zero-rating applies only in limited circumstances involving listed buildings or residential conversions from non-residential use.
Regional Variation
London and the south-east consistently run 25–40% above Midlands and northern England pricing for equivalent conversion types. Labour rates are the primary driver; materials vary by only 5–10%.
| Region | Rear dormer typical range |
|---|---|
| London (inner zones) | £48,000 – £65,000 |
| London (outer zones) | £40,000 – £58,000 |
| South East (commuter belt) | £38,000 – £52,000 |
| South West | £36,000 – £48,000 |
| Midlands | £32,000 – £44,000 |
| North West / Yorkshire | £28,000 – £40,000 |
| Scotland | £28,000 – £42,000 |
These are 2026 figures for a standard rear dormer creating one bedroom with no ensuite. They assume a standard Victorian semi in good structural condition.
Hidden Costs to Budget For
Several costs catch homeowners off guard:
Party wall matters: if your dormer or structural work affects a shared wall (most terraces and semis), you need a party wall award under the Party Wall etc. Act 1996. Budget £700–£1,500 per adjoining neighbour for a surveyor acting jointly, or up to £2,500 if each party appoints their own.
Asbestos survey and removal: homes built before 2000 may have asbestos-containing materials in the loft (roof felt, pipe lagging, ceiling tiles). A pre-works asbestos survey costs £200–£400; licensed removal can add £500–£2,000 if materials are found.
Existing structural deficiencies: surveyors occasionally discover that ceiling joists are undersized for the imposed floor load of a habitable room. Strengthening existing joists by sistering new members alongside adds £1,500–£4,000 to the structural package.
Telecoms and meter relocation: aerial cables, satellite dishes, or in rare cases gas or electricity meters located in the loft area may need repositioning. Allow £300–£800.
Temporary accommodation: a full dormer conversion typically takes 8–14 weeks. Most families remain in the property, but noise and dust from the staircase opening phase are significant. Some families choose to stay elsewhere for 1–3 weeks during the most disruptive phase.
How Contractors Build Their Quotes
Understanding quote structure helps you compare tenders fairly. Most loft conversion specialists price on a fixed-price all-inclusive basis for the shell and first fix, with finishes either included or quoted as a separate package. The key variables they assess are:
- Current ridge height and pitch: directly determines how much structural alteration is needed
- Roof type: hipped roofs cost more than simple gabled roofs
- Party walls: terraced properties almost always require party wall notices and add surveyor cost
- Access: narrow side-returns or restricted scaffolding positions increase cost
- Condition of existing structure: any rot, beetle damage, or undersized timbers discovered during works leads to variations
Always obtain at least three quotes and ensure each is based on the same scope of works — ideally a brief specification document you supply rather than each builder’s individual assumptions. A £10,000 difference between quotes can simply mean one builder has included scaffolding and the other hasn’t.
Getting Value
The best-value loft conversions in 2026 tend to be straightforward rear dormers on Victorian semis with good ridge height, managed by an experienced local specialist rather than a national “turnkey” company (which adds a significant management margin). Spending £1,000–£2,000 on proper architectural and structural drawings upfront avoids costly variations during works.
A conversion that adds a proper bedroom with natural light, reasonable headroom, and a compliant staircase will add 10–20% to a property’s market value in most UK locations, making the return on a well-specified conversion genuinely compelling.
