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
Your home may be repossessed if you do not keep up repayments on your mortgage. PocketWise provides information and guidance, not financial advice. Seek independent mortgage advice before making decisions about borrowing.