Rooflight / Velux conversion
Usually the simplest option because the roof shape is mostly retained. It suits lofts that already have enough head height and need light, insulation, access and internal finish more than major structural change.
Loft conversion costs
Loft Conversion Cost Calculator UK
Estimate the cost of converting unused roof space into a bedroom, office or en-suite room. This calculator uses conversion type, usable floor area, room plan, finish level and region to produce a realistic UK cost range.
This calculator is part of the extensions cost section. If you are comparing a loft conversion with building new space, use the single storey extension cost calculator or double storey extension cost calculator.
Use this estimate before speaking with loft specialists
A loft conversion reuses existing roof space, so the cost is shaped by the structure already in the property. The key question is not just how large the loft is, but how much of it can become comfortable, legal and usable room space. This estimate gives you a planning range before you arrange site visits.
What type of loft conversion are you pricing?
The conversion type sets the tone for the whole budget. A rooflight conversion keeps the roof shape mostly intact. A mansard conversion changes the roof much more heavily and usually needs a larger allowance.
Dormer loft conversion
A common choice where the existing roof has limited usable headroom. A dormer creates more vertical wall space and makes the room easier to furnish, but it adds structure and external detailing.
Hip-to-gable conversion
Often relevant for semi-detached or end-of-terrace homes with a hipped roof. It extends the sloping side roof into a gable wall, creating a more usable room shape.
Mansard conversion
Usually the most involved option. It changes the roof shape more heavily and can create a larger room, but it normally needs more design work and external construction.
Typical UK loft conversion cost ranges
These ranges are a planning guide. They are most useful when compared with the calculator result for your likely conversion type and usable floor area.
| Loft type | Typical usable area | Estimated range | Why the cost moves |
|---|---|---|---|
| Rooflight / Velux conversion | 15–30 m² | £25,000–£55,000 | Lower structural change if the roof already has enough usable head height. |
| Dormer loft conversion | 20–40 m² | £45,000–£85,000 | Adds headroom, roof works, weatherproofing and external detailing. |
| Hip-to-gable conversion | 25–45 m² | £55,000–£100,000 | More structural roof change and external wall work than a basic dormer. |
| Mansard conversion | 30–50 m² | £70,000–£140,000+ | Larger roof alteration, design complexity and wider finish spread. |
Loft suitability: what the calculator cannot see
The calculator can estimate cost, but loft conversions depend on whether the roof space can become practical living space. A cheap-looking conversion is not good value if the staircase eats too much floor area, the ceiling height feels cramped or the new room is hard to furnish.
The main checks are head height, staircase position, existing roof structure, fire safety route, insulation, ventilation and bathroom drainage if an en-suite is planned. These details explain why two lofts with the same floor area can receive very different quotes.
What affects loft conversion cost?
Loft pricing behaves differently from ground-floor extensions. The existing roof shape and structure can help keep costs down, or they can force a more involved design.
Existing roof structure
Some traditional cut roofs are easier to adapt than modern trussed roofs. When the structure needs major alteration, design and labour costs increase.
Access and stairs
A staircase takes real space from the loft and the floor below. A difficult stair position can reduce usable area or add design complexity.
Bathroom and en-suite services
An en-suite adds plumbing, drainage, ventilation, waterproofing, tiling and fixtures. The cost depends on how easily services can connect.
Insulation and fire safety
A loft room needs proper insulation, escape planning, smoke alarms and fire protection measures. These are not optional extras in a habitable room.
If your loft includes an en-suite, compare related costs using the bathroom renovation cost calculator and bathroom plumbing cost calculator.
Real-world pricing scenarios
These scenarios show how conversion type and room plan change the result. The floor area matters, but the roof shape and use of the room often matter more.
22m² rooflight conversion
A rooflight conversion used as an office or occasional bedroom may sit in the lower range if the loft already has usable head height and the roof shape stays mostly unchanged.
30m² dormer with en-suite
A dormer bedroom with en-suite often moves into the middle or upper range because the project adds headroom, plumbing, drainage, waterproofing and more internal finish.
40m² hip-to-gable conversion
A hip-to-gable conversion can create a more usable room shape on a hipped roof, but structural design and external changes make it more involved than a simple rooflight option.
Loft conversion vs extension
A loft conversion uses space that already exists inside the roof. An extension creates new space by building outward or upward. The right choice depends on the room you need, the property shape and whether the roof has enough usable volume.
| Factor | Loft conversion | Single/double storey extension |
|---|---|---|
| Uses existing space | Yes | Usually no |
| Adds footprint | No | Yes |
| Best for | Bedrooms, office, en-suite | Kitchen, living space, whole-home expansion |
| Main constraint | Roof suitability | Site footprint and structure |
| Cost pressure | Stairs, roof, head height | Foundations, groundworks, external walls |
Compare outward-building options with the single storey extension cost calculator and double storey extension cost calculator.
Cost per square metre needs extra care for lofts
Loft cost per m² can be misleading because not every part of the loft becomes equally usable. Sloped ceilings, staircase space and low eaves can reduce the practical room area even when the measured floor area looks generous.
Use cost per m² as a rough comparison, then judge the room by usable layout. For a broader floor-area comparison across extension types, use the extension cost per m² calculator.
Loft area can be misleading
Total loft floorNot enough
Usable standing areaMore useful
Staircase spaceReduces area
What to prepare before getting quotes
Before requesting quotes, try to estimate usable floor area rather than total loft floor area. Take note of where the staircase may go, whether you want an en-suite and whether the roof needs a dormer or other structural change.
A quote becomes clearer when the room plan is specific. A simple office, a main bedroom and a bedroom with en-suite are different projects even if the floor area looks similar.
Quote-ready summary
Example brief: 25 m² rooflight loft conversion, bedroom / office only, standard finish, Rest of England pricing, VAT included and 10% contingency.
Alternative projects worth comparing
If the loft is cramped, awkward to access or expensive to adapt, another project may produce better usable space. The right comparison depends on whether you need bedrooms, living space, work space or storage.
Garage conversion
Compare this if suitable existing ground-floor structure could become living or work space.
Basement conversion
Relevant where below-ground space is possible, but structure and waterproofing need careful allowance.
Single storey extension
Useful when the main goal is a larger kitchen, dining area or ground-floor living space.
Double storey extension
Compare this when you need both downstairs space and additional upstairs rooms.
Related extension cost calculators
Use these calculators to compare loft conversion costs with nearby project types inside the extensions cost cluster.
Home extension
Broad estimate across common UK extension types.
Single storey extension
Estimate one-level rear, side and kitchen extension costs.
Double storey extension
Estimate two-floor extensions and compare cost per m².
Extension cost per m²
Compare extension costs by floor area and total budget.
Garage conversion
Estimate costs where existing structure can be reused.
Basement conversion
Estimate below-ground conversion costs and structural allowances.
Loft conversion cost FAQs
How much does a loft conversion cost in the UK?
A simple rooflight conversion may start around £25,000. Dormer projects often sit between £45,000 and £85,000, while larger mansard or high-specification conversions can exceed £140,000.
What is the cheapest type of loft conversion?
A rooflight or Velux-style conversion is usually the cheapest because it keeps the existing roof shape mostly intact. It works best when the loft already has enough head height.
Is a dormer loft conversion worth it?
A dormer can be worth it when the existing roof has limited usable headroom. It creates more vertical wall space and makes the room easier to furnish.
Does an en-suite increase the cost?
Yes. An en-suite adds plumbing, drainage, ventilation, waterproofing, tiling, fixtures and extra labour.
Is a loft conversion cheaper than an extension?
It can be cheaper because it uses existing roof space and does not usually need new foundations or external walls. Suitability depends on head height, stairs and roof structure.
Why is cost per m² tricky for loft conversions?
Sloped ceilings, low eaves and staircase space can reduce usable floor area. A low cost per m² is less helpful if the room feels cramped or awkward to furnish.