Quick Answer
A loft conversion in the UK costs £15,000–£25,000 for a basic Velux conversion, £30,000–£50,000 for a dormer, and £50,000–£75,000 for a Mansard conversion. Most homeowners spend around £35,000–£45,000 for a mid-range dormer loft in 2026.
A loft conversion is one of the most cost-effective ways to add living space and value to your home. By converting an unused roof space into a bedroom, bathroom, or office, you can add 20–25% to your property's value — often for less than the cost of moving house. In 2026, with high property prices and stamp duty costs, more UK homeowners are choosing to extend upward rather than move.
The cost of a loft conversion depends primarily on the type of conversion, the size of the space, your location, and whether you need planning permission or simply fall under permitted development rights. This guide covers all the main loft conversion types, typical costs, and what affects the final price.
All prices are based on 2026 UK market rates and assume a typical semi-detached or detached house unless otherwise stated. Want to compare quotes? Post your loft conversion job on GetQuickHelp for free.
In this guide
Loft Conversion Types and Costs
There are four main types of loft conversion in the UK, each with different structural requirements, planning implications, and price points:
| Type | Typical Cost | Planning Needed? | Best For |
|---|---|---|---|
| Velux / rooflight | £15,000 – £25,000 | Usually no (PD) | Homes with high ridge height, simple use |
| Dormer | £30,000 – £50,000 | Often no (rear dormers PD) | Most common — adds standing room and floor area |
| Hip-to-gable | £35,000 – £55,000 | Often yes | Detached/semi-detached with hipped roof |
| Mansard | £50,000 – £75,000 | Yes (major works) | Maximum space gain, typically end-of-terrace or London |
| L-shaped dormer | £45,000 – £65,000 | Often no (rear PD) | Victorian terraces — combines rear and side dormers |
Velux conversions are the most affordable because they don't change the roof shape — they simply add roof windows and convert the existing loft space. The catch is that your loft needs to have sufficient headroom already (at least 2.2m from floor joist to ridge). Many UK homes, particularly post-war semis, don't have enough height for a usable Velux conversion.
Dormer conversions are by far the most popular type in the UK. A rear dormer creates a box-like structure projecting from the rear slope of the roof, dramatically increasing both floor area and headroom. Most rear dormers fall under permitted development, meaning no planning permission is required.
Mansard conversions are common in London, especially on Victorian and Edwardian terraces. They change the roof profile almost entirely — the rear slope becomes near-vertical, creating a near-full-height room. They require planning permission and are the most expensive option, but they add the most usable space.
Stages of a Loft Conversion
A loft conversion involves multiple trades working in sequence. Here's a typical breakdown:
| Stage | Typical Cost | Notes |
|---|---|---|
| Structural engineer / drawings | £800 – £2,000 | Required for Building Regulations application |
| Planning application (if needed) | £206 – £462 | Householder planning fee (England 2026) |
| Building Regulations application | £500 – £1,200 | Includes inspections |
| Structural steelwork and beams | £2,000 – £5,000 | Steel beam installation for floor support |
| Roof works (dormer structure) | £5,000 – £15,000 | Largest single cost item |
| Insulation and fireboarding | £2,000 – £4,000 | Required for Building Regs compliance |
| Windows and roof lights | £1,500 – £4,000 | Depends on number and glazing type |
| Electrics | £1,500 – £3,000 | Lighting, sockets, potentially new consumer unit |
| Plumbing (if en suite) | £2,500 – £5,000 | Full en-suite addition |
| Staircase | £2,000 – £6,000 | New staircase access — major variable |
| Plastering and finishing | £2,000 – £4,000 | Skimming, boarding, decoration |
The staircase is one of the biggest variables in loft conversion costs. Building Regulations require the new staircase to meet specific headroom requirements (minimum 2m headroom), which often means reconfiguring the landing below or stealing space from an existing bedroom. A bespoke oak staircase can add £5,000–£8,000 alone.
What Affects the Cost of a Loft Conversion
| Factor | Impact | Details |
|---|---|---|
| Conversion type | Very high | Velux vs Mansard — £30,000+ difference in cost |
| En-suite bathroom | High | Adding a bathroom adds £5,000–£10,000 |
| Location | High | London adds 25–40% to labour costs |
| Property type | Medium | Mid-terrace more complex than detached |
| Roof structure | Medium-high | Cut roof vs trussed rafter (trusses cost more to alter) |
| Staircase requirements | High | Simple loft ladder vs full compliant staircase |
| Specification level | High | Budget finishes vs premium — £5,000–£15,000 range |
💡 Tip
Check whether your loft has a "cut roof" (traditional rafters) or "trussed rafter" construction before getting quotes. Trussed rafters (common in homes built after 1960) need to be altered or reinforced, which adds cost. A loft specialist can assess this during a free survey.
Planning Permission and Building Regulations
Most loft conversions in England can be built under permitted development (PD) rights, meaning no planning permission is required. The key permitted development rules for loft conversions are:
- Volume added must not exceed 40m³ (terraced houses) or 50m³ (detached/semi-detached)
- No extension beyond the existing plane of the roof slope at the front (facing the highway)
- No higher than the highest part of the existing roof
- Side-facing windows must be obscure-glazed and non-opening below 1.7m
- Must not be in a conservation area, AONB, or National Park (where different rules apply)
Even when planning permission isn't needed, Building Regulations approval is always required for a loft conversion. This covers structural safety, fire escape requirements, insulation, and staircase design. For a full overview of what's covered by PD, read our guide on permitted development rules in the UK.
For homes where PD rights have been removed (conservation areas, some new developments), you'll need full planning permission. Read our guide on planning permission for home extensions for more detail on the process.
Does a Loft Conversion Add Value?
A loft conversion typically adds 20–25% to the value of a property, according to Nationwide and Savills research. In practical terms, if your home is worth £400,000, a well-executed dormer loft conversion could add £80,000–£100,000 in value — significantly more than the conversion cost of £35,000–£50,000.
The return on investment is strongest in higher-value areas (London, South East) where adding a bedroom has a significant impact on the asking price. In lower-value areas, the value uplift may be smaller but the conversion is still usually worthwhile for the additional living space.
To understand how the project fits into a wider home renovation plan, see our guide on how to hire a builder in the UK and our article on how long a loft conversion takes.
Frequently Asked Questions
How long does a loft conversion take?+
A simple Velux conversion takes 3–5 weeks. A dormer conversion typically takes 6–10 weeks from start to completion. Mansard conversions, which involve more complex structural work, can take 12–16 weeks. These timelines assume no planning delays.
Do I need planning permission for a loft conversion?+
Most loft conversions in England fall under permitted development rights and do not require planning permission, as long as they meet the size and design rules. However, Building Regulations approval is always required. You always need planning permission for a Mansard, for properties in conservation areas, or where PD rights have been removed.
Can any house have a loft conversion?+
Not every house is suitable. You need a minimum head height of approximately 2.2m from the floor joist to the ridge beam for a usable conversion. Many post-war bungalows and some 1970s–1990s houses have very low roof pitches that make conversion impractical without significant (and expensive) roof alteration.
How much does a loft conversion add to house value?+
Typically 20–25%, depending on location and property type. Adding a bedroom (particularly a master bedroom with en suite) has the greatest impact. In London and the South East, the return is often higher. Always get a local estate agent's view before committing.
What is the cheapest type of loft conversion?+
A Velux (rooflight) loft conversion is the cheapest, typically costing £15,000–£25,000. It doesn't change the roof shape — just adds roof windows and converts the existing space. However, it requires your existing loft to already have sufficient headroom.
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