Loft Conversion Cost Calculator (UK, 2026)
Get an instant, itemised estimate for your loft conversion — velux, dormer, hip-to-gable, L-shaped dormer or mansard. Built around real UK loft conversion cost per m² data, adjusted for your region.
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Loft Conversion Cost Calculator
Answer four short steps to get an itemised UK loft conversion estimate, including regional adjustment, bathroom, staircase and planning costs.
Step 1 — Loft type & size
Step 2 — Specification level
Step 3 — Region & extras All optional
Step 4 — Review & calculate
| Line item | Cost |
|---|
Estimates only — actual loft conversion costs vary by contractor, roof structure and site access. Always get 3 local quotes before budgeting.
How This Loft Conversion Cost Calculator Works
The calculator applies a UK-specific formula: floor area × base rate per m² (set by conversion type) × specification multiplier × regional multiplier, then adds bathroom, staircase, structural and planning costs on top.
- Pick your conversion type. Velux/rooflight loft conversions need no roof alteration and carry the lowest base rate. Dormer, hip-to-gable, L-shaped dormer and mansard conversions each add progressively more structural work.
- Set your floor area in m². UK loft conversions typically run 20–45 m². Larger lofts cost more in total but slightly less per m² due to fixed costs like scaffolding and skips being spread further.
- Choose a specification level. Basic drops the rate by around 18%; high-end adds up to 35% for bespoke joinery, engineered flooring and feature lighting.
- Apply your region. London loft conversions run roughly 40% above the Midlands baseline; Scotland, Wales and Northern Ireland typically run 15–22% below it.
Loft Conversion Cost Formula (Per m²)
This mirrors how UK loft conversion companies structure their quotes: a per-m² rate for the shell and structural work, then fixed-price add-ons for bathroom, staircase and professional fees layered on top.
Base Cost = Area (m²) × Base Rate (£/m²) × Spec Multiplier Regional Cost = Base Cost × Regional Multiplier Total = Regional Cost + Bathroom + Staircase + Structural Steel + Party Wall + Planning Fee Example: 30m² dormer, standard spec, Midlands, with staircase: 30 × £1,950 × 1.0 = £58,500 base + £3,200 staircase + £1,500 building regs = ≈£63,200
Loft Conversion Cost Per m² by Type
| Conversion type | Basic (£/m²) | Standard (£/m²) | High-end (£/m²) |
|---|---|---|---|
| Velux / Rooflight | £1,350 | £1,650 | £2,230 |
| Dormer (single, rear) | £1,600 | £1,950 | £2,630 |
| Hip-to-Gable | £1,760 | £2,150 | £2,900 |
| L-Shaped Dormer | £1,970 | £2,400 | £3,240 |
| Mansard | £2,130 | £2,600 | £3,510 |
These figures cover structural work, insulation, plastering, electrics and a standard fit-out. They exclude bathroom, staircase, structural steel, party wall and planning fees, all of which are priced separately in the calculator above.
Loft Conversion Cost by Type — Whole Project (UK)
| Type | Typical low | Typical mid | Typical high | Best for |
|---|---|---|---|---|
| Velux / Rooflight | £20,000 | £28,000 | £38,000 | Homes with 2.2m+ ridge height already |
| Dormer | £35,000 | £48,000 | £65,000 | Most semi-detached & detached homes |
| Hip-to-Gable | £40,000 | £54,000 | £72,000 | Detached & semi-detached hipped roofs |
| L-Shaped Dormer | £50,000 | £68,000 | £92,000 | Victorian/Edwardian terraces |
| Mansard | £55,000 | £75,000 | £105,000 | Maximum headroom & floor area |
A basic loft conversion cost for a small velux conversion under 20m² can come in near the bottom of the range above. A 2 bedroom loft conversion cost calculator estimate should sit toward the mid-to-high end of the dormer or L-shaped dormer rows, since two bedrooms usually need an additional partition wall, second rooflight and extra electrical circuits.
Loft Conversion Cost by Region — Is It Different in London?
| Region | Multiplier | Dormer loft conversion (mid, 30m²) |
|---|---|---|
| London | 1.40× | ≈£81,900 |
| South East England | 1.15× | ≈£67,275 |
| Midlands / East England | 1.00× | ≈£58,500 |
| North England | 0.90× | ≈£52,650 |
| Scotland / Wales | 0.85× | ≈£49,725 |
| Northern Ireland | 0.78× | ≈£45,630 |
The multiplier reflects labour day-rates and material delivery costs, which are consistently higher inside the M25 and lower in rural or lower-cost-of-living regions. Use the region selector in the calculator to apply the correct adjustment to your estimate.
What Affects Loft Conversion Cost — 7 Key Variables
Conversion type
Velux is cheapest; mansard is most expensive because it rebuilds the entire rear roof slope.
+35–60% dormer→mansardRoof structure
Modern trussed roofs (post-1960s) need structural steel and joist strengthening; older cut-rafter roofs convert more easily.
+£3,000–£8,000Ensuite bathroom
Routing new plumbing, waste and ventilation to the loft is the most popular — and most expensive — single add-on.
+£4,500–£11,000Staircase
Building Regulations require a fixed compliant staircase for any habitable loft room, which also consumes floor space below.
+£2,500–£4,500Party Wall Act
Most terraced and semi-detached lofts need a Party Wall agreement with neighbours before structural work starts.
+£700–£1,500Planning route
Permitted Development needs Building Regulations only; exceeding volume or height limits triggers full planning permission and fees.
+£1,500–£3,500Location
London and the South East carry the highest labour rates in the UK; the same spec costs notably less in the North or Scotland.
±15–40%Cheap Loft Conversion UK — Can You Do It for £10k?
For a true small loft conversion that meets Building Regulations, £20,000–£28,000 is the realistic entry point in most of the UK for a basic velux conversion with no ensuite. Ways to keep costs down without cutting corners on safety:
- Choose velux/rooflight over dormer — no roof structure alteration needed.
- Skip the ensuite; use the existing family bathroom instead.
- Reuse the existing staircase location to avoid losing space downstairs.
- Pick a basic specification: painted plasterboard, carpet, and standard joinery.
- Get 3+ local quotes — regional variation alone can be a 20–40% swing.
If your budget is genuinely close to £10,000, a loft boarding-and-ladder storage conversion (not a habitable room) is the realistic option — see our Attic Conversion Cost Calculator for storage-only conversion pricing.
Loft Conversion Planning Permission & the 10-Year Rule
Most UK loft conversions fall under Permitted Development and never need full planning permission at all — but every loft conversion, regardless of planning route, must satisfy Building Regulations covering structural safety, fire escape, insulation and staircase design.
When do you need full planning permission?
- The extension exceeds 40m³ (terraced) or 50m³ (detached/semi-detached) additional roof volume.
- A dormer faces the front of the house (front dormers virtually always need permission).
- The property is a flat, maisonette, listed building, or sits in a conservation area.
- The roof shape or materials would look significantly different from the existing house.
What the 10-year rule actually protects
If a loft conversion was built without required planning permission and the council took no enforcement action for 10 continuous years, the development generally becomes immune from enforcement and can be formally confirmed with a Certificate of Lawfulness. It does not retroactively grant Building Regulations approval — an unsafe or non-compliant loft can still cause problems when selling, insuring or remortgaging the property, regardless of how long it has stood.
How to Compare Loft Conversion Quotes
Once you have this calculator's estimate, use it as a sanity check against contractor quotes — not a replacement for them. A good quote breaks down:
| Line item | Should be itemised? | Typical range |
|---|---|---|
| Scaffolding & skip hire | Yes | £1,500–£3,500 |
| Structural steel / joists | Yes | £3,000–£8,000 |
| Roof windows / dormer structure | Yes | £4,000–£20,000 |
| Insulation & plasterboard | Yes | £2,500–£6,000 |
| Electrics & heating | Yes | £1,800–£4,500 |
| Staircase | Yes | £2,500–£4,500 |
| Ensuite bathroom | Yes | £4,500–£11,000 |
| Building Regs / Planning fees | Yes | £1,500–£3,500 |
Avoid any quote that bundles everything into a single lump sum with no line items — this makes it impossible to spot where the budget is actually going, and to compare quotes on a like-for-like basis. Use our Raw Material Cost Calculator if you're sourcing and pricing materials separately from labour.
Frequently Asked Questions
How much should I expect to pay for a loft conversion?
Expect to pay £20,000–£38,000 for a basic velux/rooflight conversion, £35,000–£65,000 for a standard dormer, and £55,000–£105,000 for a mansard, at UK average (Midlands) pricing. London and the South East typically run 15–40% higher; Scotland, Wales and the North typically run 10–22% lower. Use the calculator above for a figure tailored to your area, size and specification.
How to convert a loft cheaply?
Choose a velux/rooflight conversion over a dormer, skip the ensuite bathroom, reuse the existing staircase position, pick a basic specification (painted plasterboard, carpet, standard joinery), and get at least three local contractor quotes. Together these choices can reduce total cost by 30–45% compared with a full dormer conversion with ensuite at high-end spec.
Can you do a loft conversion for £10k?
Not a genuine habitable-room loft conversion — £10,000 typically only covers boarding the loft floor, adding a loft ladder, insulation and basic lighting for storage use, which does not require a staircase or full Building Regulations sign-off. A true loft conversion that meets Building Regs starts from roughly £20,000 for a basic velux conversion in most of the UK.
What is the 10-year rule for loft conversion?
The 10-year rule means a local council generally cannot force you to reverse an unauthorised loft conversion once it has existed, unchanged, for 10 continuous years — this replaced the previous 4-year rule in England from April 2024. It only removes the risk of planning enforcement; it does not grant Building Regulations approval, which remains a separate, non-expiring requirement for structural safety and fire escape.
What is the loft conversion cost per m²?
UK loft conversion cost per m² ranges from around £1,350–£2,230 for a velux/rooflight conversion up to £2,130–£3,510 for a mansard, depending on specification level. These per-m² rates cover structural work, insulation, electrics and a standard fit-out, but exclude bathroom, staircase and planning fees.
How much does a dormer loft conversion cost calculator estimate typically show?
For a standard-specification single rear dormer at 30m² in the Midlands, expect a total around £58,000–£63,000 including a new staircase and Building Regs fee. London pricing for the same project typically lands closer to £80,000–£86,000. Enter your own area, region and add-ons into the calculator above for an exact figure.
Do I need planning permission for a loft conversion?
Most UK loft conversions fall under Permitted Development and don't need planning permission, provided the extra roof volume stays under 40m³ (terraced) or 50m³ (detached/semi-detached), the dormer isn't on the front elevation, and the property isn't listed or in a conservation area. Building Regulations approval is always required regardless of the planning route.
How much does a 2 bedroom loft conversion cost?
A 2-bedroom loft conversion typically needs a larger floor area (35–50m²), an internal partition wall, a second rooflight or dormer window, and extra electrical circuits — pushing cost to the mid-to-high end of the dormer or L-shaped dormer ranges, roughly £65,000–£100,000 depending on region and specification.
Is a loft conversion worth it?
A well-executed loft conversion typically adds 15–20% to a property's value in the UK, often the highest return of any home improvement per pound spent, provided the work is fully compliant with Building Regulations and, where required, planning permission.