Loft conversion cost UK: 2026 price guide
- Velux rooflight: £22,000 to £32,000
- Rear dormer: £40,000 to £60,000
- Hip to gable with dormer: £55,000 to £75,000
- Mansard: £60,000 to £85,000
- Structural engineer fee: £395 to £1,200 (fixed fee, Building Control-ready)
Costs depend on the type of conversion, the number of steel beams required, property size, location and specification. All loft conversions need Building Regulations approval and structural calculations.
A loft conversion is one of the most cost-effective ways to add an extra bedroom, bathroom or office to a UK home. The cost varies significantly by type: a simple rooflight conversion and a full mansard are both "loft conversions" but they involve very different amounts of work.
This guide gives clear 2026 price ranges for every type of conversion, explains what drives the cost up or down, and covers the structural engineer fees that every loft conversion must include.
Loft conversion cost by type (2026)
| Conversion type | Typical total cost | Structural engineer fee |
|---|---|---|
| Velux rooflight | £22,000 to £32,000 | £395 to £600 |
| Rear dormer (terraced) | £40,000 to £55,000 | £450 to £700 |
| Rear dormer (semi-detached) | £45,000 to £60,000 | £450 to £700 |
| Hip to gable only | £45,000 to £65,000 | £600 to £900 |
| Hip to gable with rear dormer | £55,000 to £75,000 | £650 to £1,100 |
| Mansard | £60,000 to £85,000 | £700 to £1,200 |
| Trussed rafter roof conversion | £50,000 to £75,000 | £600 to £1,100 |
These are total project costs including builder, steelwork, insulation, windows, plastering, structural engineer and Building Control fees. They do not include an en-suite bathroom, which adds £8,000 to £15,000 depending on specification.
What makes loft conversion costs go up or down?
Four things drive most of the cost variation between loft conversions.
1. How much of the roof you remove
A velux conversion barely touches the roof structure. A dormer cuts out a section of the rear. A hip to gable removes the entire end hip. A mansard rebuilds almost the whole roof. The more roof you remove, the more steel you need, the more structural engineering is involved, and the more the builder charges for labour.
2. Number and size of steel beams
A velux conversion typically needs two floor beams and a ridge beam. A hip to gable needs three or four floor beams, an upgraded ridge, purlin support and a structural gable wall frame. Steel supply alone costs £1,500 to £4,000 per conversion, and each beam also needs installation, padstones and Building Control inspection. For a full breakdown see our loft conversion steel beams guide.
3. Whether the roof is cut or trussed
A traditional cut roof, with individual rafters and purlins, is easier and cheaper to convert because individual timbers can be modified. A trussed rafter roof (common from the 1960s onwards) uses prefabricated triangular frames. Every truss must be removed and replaced with a new structural system, which adds significant cost and steelwork.
4. Location and specification
London and South East builders charge 20 to 30 per cent more than the Midlands and North for comparable work. Bespoke windows, high-spec finishes and full-width Juliet balconies add cost quickly. A standard finish with off-the-shelf windows is consistently cheaper.
Full cost breakdown: where the money goes
Here is a typical breakdown for a rear dormer on a terraced house, as an example of how the total cost is made up.
| Item | Typical cost |
|---|---|
| Builder (labour, materials, scaffolding) | £28,000 to £42,000 |
| Steel beams (supply and installation) | £3,000 to £6,000 |
| Structural engineer calculations | £450 to £700 |
| Architectural drawings | £1,200 to £2,500 |
| Building Control fees | £500 to £900 |
| Windows and rooflights | £1,500 to £4,000 |
| Stairs | £2,500 to £5,000 |
| Insulation and plasterboard | £2,000 to £3,500 |
| Electrical first fix and sockets | £1,500 to £3,000 |
| Plastering and decoration | £2,500 to £5,000 |
The structural engineer fee is a small percentage of the total project cost, but it is the document that unlocks Building Control approval. Without it, the project cannot legally be signed off and cannot be sold or remortgaged with confidence.
Loft conversion cost by property type
Terraced house loft conversion cost
Rear dormer: £40,000 to £55,000. Terraced houses have the simplest roof structure for conversion and the most competitive builder market. The party walls on both sides affect the structural design.
Semi-detached house loft conversion cost
Rear dormer: £45,000 to £60,000. Hip to gable: £55,000 to £75,000. The 1930s semi-detached house is the most common candidate for a hip to gable conversion. If the hip rafter sits close to the party wall, a Party Wall Notice may be required.
Detached house loft conversion cost
Rear dormer: £50,000 to £70,000. Hip to gable: £60,000 to £80,000. Detached houses with hipped roofs can be converted on either end. No party wall issues.
Bungalow loft conversion cost
£55,000 to £85,000. Bungalow roofs have larger spans, which means bigger beams, more steelwork, and higher structural engineer fees. Many bungalows also have trussed roofs, which adds further structural complexity and cost.
Structural engineer fees for loft conversions
Every loft conversion in the UK requires a structural engineer's calculation pack for Building Control. This is not optional and cannot be skipped. Here is what the fee covers and what the different conversion types cost.
| Conversion type | SE fee range | What is included |
|---|---|---|
| Velux conversion | £395 to £600 | Floor beams, ridge assessment, trimmer around stair, padstones |
| Rear dormer | £450 to £700 | Above plus dormer steelwork, dormer wall frame |
| Hip to gable | £600 to £1,100 | Ridge beam upgrade, floor beams, gable wall frame, purlin support, party wall notes |
| Mansard | £700 to £1,200 | Full roof structural redesign, new beams at every level, load transfer calculations |
All fees are fixed and confirmed in writing before we start. The fee includes the full calculation pack, a structural drawing your builder uses on site, and answers to any Building Control inspector queries. Turnaround is typically 5 to 7 working days.
Regional cost differences across the UK
Builder day rates and subcontractor costs vary significantly by location. As a rough guide for a rear dormer loft conversion:
| Region | Typical rear dormer cost |
|---|---|
| London and South East | £50,000 to £65,000 |
| South West and East of England | £45,000 to £58,000 |
| Midlands | £40,000 to £52,000 |
| North West and Yorkshire | £38,000 to £50,000 |
| Scotland and Wales | £36,000 to £48,000 |
The structural engineer fee is broadly consistent across the UK because it is a design service, not a physical build. Our fixed fees apply nationwide.
Planning permission and Building Regulations
Most loft conversions in England do not need planning permission under permitted development rights, provided certain limits are not exceeded. However, all loft conversions need Building Regulations approval regardless of whether planning is required.
Permitted development limits for loft conversions
- Maximum 50 cubic metres of additional roof space for detached and semi-detached houses
- Maximum 40 cubic metres for terraced houses
- No extension above the highest part of the existing roof
- No verandas, balconies or raised platforms
- Side-facing windows must be obscure-glazed and non-opening below 1.7 metres
What Building Control covers
Building Control approves the structural calculations, fire safety, insulation, escape windows, stair design and overall compliance with Building Regulations. A Building Control inspector visits at key stages during the build, and issues a completion certificate when the work is signed off. This certificate is essential for resale and remortgaging.
Hip to gable loft conversion cost: why it costs more
A hip to gable loft conversion costs more than a simple rear dormer because it involves significantly more steelwork. The hip rafter on a hipped roof carries a substantial portion of the roof loads. When it is removed, those loads must be redistributed through a new ridge beam, purlin support and gable wall structural frame, in addition to the floor beams every conversion needs.
For a 1930s semi-detached house, a hip to gable conversion typically needs three or four steel beams compared to two for a rear dormer. The structural engineer fee reflects this additional design work, starting from £600 rather than £450.
If your property is a 1930s semi with a hipped roof in an area like Didsbury, Harborne, Solihull, Childwall or Sale, a hip to gable conversion is almost certainly the best use of your loft space. The additional cost over a simple dormer is typically £10,000 to £15,000, but the usable floor area gained is 30 to 50 per cent larger.
Ways to reduce loft conversion costs without cutting corners
- Choose a simpler conversion type if your headroom allows it. A velux conversion at £22,000 to £32,000 is far cheaper than a dormer and perfectly adequate if the ridge height is sufficient
- Keep the bathroom simple or leave it out entirely. An en-suite adds £8,000 to £15,000 and can always be added later
- Use standard windows rather than bespoke or aluminium-framed options. A standard casement rooflight costs a fraction of a full-width aluminium dormer window
- Get your structural calculations done first before approaching builders for quotes. A fixed-fee calculation pack lets builders price accurately and avoids the contingency uplift they add when the structural spec is unknown
- Get three builder quotes with the same structural drawings and specification. Builder prices for identical work can vary by 20 to 30 per cent
Frequently asked questions
How much does a loft conversion cost in 2026?
Between £22,000 for a simple velux conversion and £85,000 for a full mansard, depending on type, size, location and specification. A rear dormer on a terraced house is the most common type and typically costs £40,000 to £55,000.
What is the cheapest loft conversion?
A velux rooflight conversion, starting from £22,000, is the cheapest type. It works by using the existing roof shape and adding rooflights for light and ventilation. It is only suitable where there is already enough headroom in the loft, typically where the ridge height is at least 2.2 metres above the ceiling joists.
Do I need a structural engineer?
Yes, for every type of loft conversion. Building Control requires a structural engineer's calculation pack covering the floor beams, ridge beam and any dormer or gable wall structural elements. The fee starts from £395 for a simple conversion and is confirmed as a fixed price before work starts.
How long does a loft conversion take?
A velux conversion takes 4 to 6 weeks. A rear dormer takes 6 to 10 weeks. A hip to gable takes 10 to 14 weeks. Allow two to three months before that for drawings, structural calculations and Building Control applications.
Does a loft conversion add value?
Most loft conversions add 15 to 20 per cent to a property's value. An extra bedroom and bathroom is the single highest-value addition for most UK houses. The conversion must have a Building Control completion certificate for the value to be realised at sale.
Get structural calculations for your loft conversion
If you are planning a loft conversion and need structural calculations for Building Control, here is how we work:
- Send your architectural drawings, estate agent plans or a sketch with dimensions
- We confirm a fixed fee in writing before any work begins
- We produce the full calculation pack, structural drawings and Building Control submission documents
- Ready in 5 to 7 working days
- Inspector queries answered as part of the fixed fee
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