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How Much Does a Loft Conversion Cost in 2025?
Please Note
The figures presented are for guidance only and are rough estimates. Since every loft conversion is unique, its final cost is subject to major variables, including your location, design complexity, and specific structural requirements.
| Loft Type | Typical Cost per m² (excl. VAT) | Example Size | Estimated Build Cost |
|---|---|---|---|
| Velux (Rooflight) | £1,600 – £2,200 | 25 m² | £40,000 – £55,000 |
| Dormer | £2,000 – £2,800 | 30 m² | £60,000 – £84,000 |
| Hip-to-Gable | £2,200 – £2,900 | 35 m² | £77,000 – £102,000 |
| Mansard | £2,500 – £3,200 | 40 m² | £100,000 – £128,000 |
Additional Costs to Consider
| Item | Allow for ~ |
|---|---|
| VAT | +20% |
| Professional Fees | +10–15% |
| Bathroom or Fit-Out | £5,000 – £15,000 |
| Contingency | +10–15% |
A dormer loft conversion at £2,400/m² for 30 m² ≈ £72,000 build cost (around £90k total with fees & VAT).
To receive a clear, stage-by-stage cost breakdown tailored to your loft conversion, simply today and get up to 5 free quotes from local specialists.
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The Loft Conversion Journey — Step-by-Step
| Stage | What Happens | Who’s Involved | Typical Time |
|---|---|---|---|
1Survey & Design | Measured survey, feasibility checks, and concept plans for your loft space. | 1–2 weeks | |
2Planning | Permitted Development or planning application prepared and submitted. | ArchitectLocal Council | 6–8 weeks |
3Structural Design | Structural engineer calculates beams, joists, and load paths to support the new space. | 1–2 weeks | |
4Construction | Floor structure, dormers, insulation, stairs, glazing, and internal fit-out delivered on site. | 8–14 weeks | |
5Completion | Snagging, testing, and Building Control sign-off prior to handover. | BuilderClient | 1–2 weeks |
Survey & Design
What Happens
Measured survey, feasibility checks, and concept plans for your loft space.
Who’s Involved
Typical Time
1–2 weeks
Planning
What Happens
Permitted Development or planning application prepared and submitted.
Who’s Involved
Typical Time
6–8 weeks
Structural Design
What Happens
Structural engineer calculates beams, joists, and load paths to support the new space.
Who’s Involved
Typical Time
1–2 weeks
Construction
What Happens
Floor structure, dormers, insulation, stairs, glazing, and internal fit-out delivered on site.
Who’s Involved
Typical Time
8–14 weeks
Completion
What Happens
Snagging, testing, and Building Control sign-off prior to handover.
Who’s Involved
Typical Time
1–2 weeks
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Loft Conversion Project FAQs
Get Answers to All Your Loft Conversion Project Questions
Please Note: The figures & stages presented are for guidance only and are rough estimates. Since every loft conversion is unique, its final cost is subject to major variables, including your location, design complexity, and specific structural requirements.
To get a clear loft conversion cost breakdown of each stage please and get up to 5 free quotes in your area.
What Are Architect Fees for a Loft Conversion?+
Typical Fees
Architect fees for a loft conversion usually range between £2,000 – £5,000, or around 6–10% of the total build cost depending on complexity and service level.
Client tip: Check if your architect includes structural coordination — this can save time and cost later.
What’s Included
- Initial feasibility assessment and measured survey
- Design drawings and layout options
- Planning or lawful development application (if required)
- Building Regulation and structural coordination drawings
- Optional tender and on-site support
Client tip: Ask which deliverables are included at each stage so you have clarity before committing.
Read more →What Does a Loft Conversion Architect Do?+
Main Responsibilities
- Assess roof height, access, and structure to confirm feasibility
- Design the best layout, dormer configuration, and staircase position
- Prepare and submit planning or lawful development certificates
- Coordinate with a structural engineer on beams and load paths
- Produce detailed construction drawings for your builder
Client tip: Choose an architect who has completed local loft conversions — it helps navigate council approvals faster.
Explore loft design support →What Are Loft Conversion Builder Costs?+
Typical Costs per m²
| Loft Type | Typical Cost per m² (excl. VAT) | Example Size | Estimated Build Cost |
|---|---|---|---|
| Rooflight (Velux) Loft | £1,500 – £2,000 | 25 m² | £37,500 – £50,000 |
| Dormer Loft | £1,800 – £2,500 | 30 m² | £54,000 – £75,000 |
| Hip-to-Gable Loft | £2,000 – £2,800 | 35 m² | £70,000 – £98,000 |
| Mansard Loft | £2,500 – £3,200 | 40 m² | £100,000 – £128,000 |
Loft Type
Rooflight (Velux) Loft
Typical cost per m² (excl. VAT)
£1,500 – £2,000
Example size
25 m²
Estimated build cost
£37,500 – £50,000
Loft Type
Dormer Loft
Typical cost per m² (excl. VAT)
£1,800 – £2,500
Example size
30 m²
Estimated build cost
£54,000 – £75,000
Loft Type
Hip-to-Gable Loft
Typical cost per m² (excl. VAT)
£2,000 – £2,800
Example size
35 m²
Estimated build cost
£70,000 – £98,000
Loft Type
Mansard Loft
Typical cost per m² (excl. VAT)
£2,500 – £3,200
Example size
40 m²
Estimated build cost
£100,000 – £128,000
What Affects the Price
- Roof structure and access
- Plumbing and bathroom fittings
- Windows, dormers, and finishes
- Structural steelwork requirements
Client tip: Allow a 10–15% contingency for hidden roof or structural issues uncovered during construction.
What Is the Builder’s Role on a Loft Conversion?+
Key Tasks
The builder takes your approved drawings and safely delivers the project on-site. Their responsibilities include:
- Installing steel beams, joists, and floor structure
- Building dormer extensions or altering the roof
- Adding insulation, windows, and stairs
- Completing electrics, plumbing, and plastering
- Ensuring Building Control approval and finishing details
Project Timeline
Most loft conversions take 6–10 weeks from start to finish, depending on complexity and weather.
Client tip: Stay in touch with your builder through weekly progress updates to manage timing and quality.
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