A loft conversion is one of the most cost-effective ways to add space and value to your home without the expense and upheaval of moving. Here is a detailed breakdown of what it costs, the different options, and how to pay for it.
Loft Conversion Costs by Type
Overview
| Type | Typical cost | What it involves |
|---|---|---|
| Velux / rooflight | £20,000 – £35,000 | Windows fitted into existing roof slope, no structural changes to roof shape |
| Dormer | £35,000 – £65,000 | Extension built out from the roof slope, creating vertical walls and a flat roof section |
| Hip-to-gable | £45,000 – £75,000 | The sloping side of the roof is extended to create a vertical gable wall |
| Mansard | £55,000 – £80,000+ | The roof slope is almost entirely replaced with a near-vertical wall and flat top |
| L-shaped dormer | £50,000 – £80,000+ | Dormer extension over two parts of the roof, common on Victorian terraces |
Regional Price Variation
Costs vary considerably depending on where you live.
| Region | Approximate adjustment |
|---|---|
| London | +20–30% above national average |
| South East | +10–20% |
| South West, East | +5–10% |
| Midlands | National average |
| North West, Yorkshire | –5–10% |
| North East, Wales | –10–15% |
| Scotland | –5–10% |
A dormer conversion costing £50,000 in the Midlands might cost £60,000–£65,000 in London.
What Is Included in the Cost?
Standard Inclusions
| Item | Typical cost |
|---|---|
| Structural work and steels | £3,000 – £8,000 |
| Staircase | £2,000 – £5,000 |
| Roof windows (Velux) or dormer build | £2,000 – £10,000 |
| Insulation | £1,500 – £3,000 |
| Plastering and decoration | £2,000 – £4,000 |
| Electrics | £1,500 – £3,000 |
| Flooring | £1,000 – £3,000 |
| Fire safety (fire door, alarms, escape windows) | £500 – £1,500 |
Common Extras
| Extra | Typical cost |
|---|---|
| En-suite bathroom | £3,000 – £7,000 |
| Fitted wardrobes | £1,500 – £4,000 |
| Juliet balcony | £1,000 – £2,500 |
| Underfloor heating | £1,500 – £3,000 |
| Upgraded windows | £500 – £2,000 per window |
| Structural survey | £400 – £800 |
| Architectural plans | £1,000 – £2,500 |
Planning Permission and Building Regulations
Do You Need Planning Permission?
Most straightforward loft conversions fall under permitted development and do not need planning permission if:
| Rule | Limit |
|---|---|
| Volume added (terraced house) | No more than 40 cubic metres |
| Volume added (detached/semi) | No more than 50 cubic metres |
| Dormer placement | Does not extend beyond the existing roof plane at the front of the house |
| Height | Does not exceed the highest part of the existing roof |
| Materials | Similar in appearance to the existing house |
You will need planning permission if:
- Your home is in a conservation area, National Park, or Area of Outstanding Natural Beauty
- The property is a listed building
- You want a dormer on the front roof slope
- You exceed the permitted development volume limits
- You want a balcony or raised platform
Building Regulations
All loft conversions require Building Regulations approval, regardless of whether planning permission is needed. This covers:
| Requirement | What it covers |
|---|---|
| Structural integrity | Floor joists, steels, load-bearing walls |
| Fire safety | Fire-resistant doors, smoke alarms, escape route |
| Insulation | Thermal performance of walls, roof, and floor |
| Staircase | Minimum dimensions, headroom, handrail |
| Electrics | Wiring to current standards |
| Sound insulation | Between the loft room and rooms below |
Your builder or architect should handle the Building Regulations application. A building control inspector will make several visits during construction.
Does a Loft Conversion Add Value?
Value Added by Property Type
| Property type | Average value added |
|---|---|
| Terraced house | 15–22% |
| Semi-detached house | 15–20% |
| Detached house | 10–15% |
Return on Investment Example
| Scenario | Amount |
|---|---|
| Property value before conversion | £290,000 |
| Dormer loft conversion cost | £50,000 |
| Value added (17%) | £49,300 |
| Net cost | £700 |
| Property value after | £339,300 |
In many cases a loft conversion pays for itself almost entirely. Adding a bedroom and en-suite to take a three-bed to a four-bed home delivers the strongest return, as there is typically a significant price gap between three and four bedroom properties.
Which Type Is Right for You?
Velux / Rooflight Conversion
| Pros | Cons |
|---|---|
| Cheapest option | Limited headroom by the eaves |
| Usually no planning permission needed | No extra floor space created |
| Quickest to complete | May not suit all roof shapes |
| Least disruptive | Less usable space than a dormer |
Best for: Budget-conscious conversions, office or guest room use, homes with good existing head height.
Dormer Conversion
| Pros | Cons |
|---|---|
| Significantly more usable space | More expensive than Velux |
| Vertical walls for furniture placement | Requires scaffolding |
| Most popular option | Can look bulky if poorly designed |
| Usually permitted development at rear | Longer build time |
Best for: Most homes. The most common and practical choice for a bedroom or bedroom with en-suite.
Hip-to-Gable
| Pros | Cons |
|---|---|
| Maximises space on hipped roofs | Only suitable for hipped roofs |
| Can be combined with a dormer | More complex structurally |
| Good value on semi-detached homes | May need planning if it changes street appearance |
Best for: Semi-detached and detached homes with hipped roofs.
Mansard Conversion
| Pros | Cons |
|---|---|
| Creates the most space | Most expensive option |
| Best for period properties | Usually requires planning permission |
| Can create a full additional storey | Longest build time |
| High-quality finish | Most disruptive during build |
Best for: Period properties, homes in London where space is at a premium, or where maximising value is the priority.
How to Pay for a Loft Conversion
| Option | Details |
|---|---|
| Savings | No interest charges, keeps costs down |
| Remortgage | Borrow against your home equity at mortgage rates (typically 4–6%) |
| Home improvement loan | Personal loan of £10,000 – £50,000, unsecured, rates from 3–8% |
| 0% credit card | For smaller purchases (materials), limited period offers |
| Specialist renovation mortgage | Some lenders offer staged release mortgages for major work |
Remortgaging is often the cheapest way to borrow for a loft conversion because mortgage rates are lower than personal loan rates. You will need sufficient equity in your property.
Related: Remortgaging Guide
Choosing a Builder
What to Look For
| Criteria | Why it matters |
|---|---|
| Loft conversion experience | Specialist builders produce better results |
| References and portfolio | Ask to see completed projects |
| Written quote | Itemised, not just a lump sum |
| Insurance | Public liability and professional indemnity |
| Warranties | Insurance-backed guarantees (e.g., QANW, CRL) |
| Payment schedule | Stage payments, never 100% upfront |
| Building control | Should handle the application for you |
Get at least three detailed quotes and compare like for like. The cheapest quote is not always the best value.
Red Flags
- Asking for more than 10–15% upfront
- No written contract
- Vague verbal quotes
- Pressure to commit quickly
- Cannot provide references from recent projects
Timeline
| Stage | Duration |
|---|---|
| Design and planning | 2–6 weeks |
| Building control application | 2–4 weeks |
| Scaffolding and setup | 1–2 days |
| Structural work | 1–2 weeks |
| Roof work and dormer (if applicable) | 1–3 weeks |
| First fix (electrics, plumbing) | 1–2 weeks |
| Insulation and boarding | 1 week |
| Plastering | 1 week |
| Second fix and finishing | 1–2 weeks |
| Staircase installation | 2–3 days |
| Decoration | 1 week |
Total build time: 6–12 weeks depending on the type and complexity.
Summary
| Key point | Details |
|---|---|
| Cheapest option | Velux from £20,000 |
| Most popular | Dormer at £35,000–£65,000 |
| Value added | 15–20% of property value |
| Planning permission | Usually not needed |
| Building regs | Always required |
| Build time | 6–12 weeks |
A loft conversion is usually the best pound-for-pound home improvement you can make. It adds usable space, increases your home’s value, and avoids the costs and stress of moving to a larger property.
Related guides:
- Home Improvements UK 2026 — Costs, Planning Rules, Grants and Adding Value
- Renovating Your Home Guide
- Increase Home Value Guide
- Home Survey Guide
- Cost of Buying a House UK
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- /mortgages/home-improvements/loft-conversion-cost-uk/
Your home may be repossessed if you do not keep up repayments on your mortgage. PocketWise provides information and guidance — we do not offer financial advice. Seek independent mortgage advice before making decisions about borrowing.