A loft conversion is one of the best investments you can make in a UK property. You’re creating usable living space from what’s essentially dead air — no extension, no planning permission headaches in most cases, and a meaningful uplift in property value. But what does it actually cost in 2026? That’s what this guide covers.
Loft Conversion Cost 2026 UK: The Quick Numbers
Costs vary depending on the type of conversion, the size of your home, and where you are in the UK. Here’s a realistic breakdown:
| Conversion Type | Typical Cost (2026) |
|---|---|
| Velux / Rooflight | £18,000 – £28,000 |
| Dormer (single) | £30,000 – £50,000 |
| Hip-to-gable | £35,000 – £55,000 |
| Mansard | £45,000 – £70,000 |
| L-shaped dormer | £40,000 – £65,000 |
These are build costs only — they don’t include architectural drawings, structural engineering, or planning application fees. More on those below.
What Type of Loft Conversion Do You Need?
Velux (Rooflight) Conversion
The simplest and cheapest option. Velux windows are installed into the existing roofline — no structural changes to the roof shape. Works best when you already have decent headroom (at least 2.2m at the ridge). Because the external appearance doesn’t change, this almost always falls under permitted development, meaning no planning permission required.
Ideal for: terraced houses with a pitched roof where headroom isn’t an issue.
Dormer Conversion
A dormer extends vertically from the slope of the roof, creating a box-shaped structure with vertical walls and a flat (or pitched) roof. This dramatically increases usable floor space and headroom. Most rear dormers on houses fall under permitted development — you don’t need planning permission unless you’re in a conservation area or the dormer faces the street.
Ideal for: semi-detached and terraced properties, adding a master bedroom with en-suite.
Hip-to-Gable Conversion
Detached and some semi-detached houses have hipped roofs — where the sides slope inward as well as the front and back. A hip-to-gable conversion extends the hip end to create a vertical gable wall, maximising internal space. Often combined with a rear dormer for the best result.
Ideal for: detached homes and end-of-terrace properties with hipped roofs.
Mansard Conversion
The most extensive — and expensive — option. The roof slope is replaced with near-vertical walls (typically 72°) and a flat roof on top. This creates the maximum possible internal space, but it almost always requires planning permission due to the scale of the change.
Ideal for: Victorian terraces in cities, where the additional space justifies the investment.
What’s Included in the Cost?
Build quotes from contractors will typically include structural work, insulation, flooring, stairs, and windows. What they often don’t include:
- Architectural drawings — required for building regulations approval regardless of whether you need planning permission
- Structural engineer calculations — needed to confirm floor joists and beam sizes
- Building regulations application fee — typically £500–£900 depending on your local authority
- Party wall agreements — if you share a wall with a neighbour (usually £700–£2,000 per neighbour)
- Electrics and plumbing — sometimes quoted separately, especially for en-suites
- Decorating and furniture
Factor in an extra £3,000–£6,000 on top of your build quote for the above.
Do You Need Planning Permission for a Loft Conversion?
In most cases, no. The majority of loft conversions in England and Wales fall under permitted development rights — meaning you can go ahead without applying to the council. The key rules are:
- The additional volume must not exceed 40m³ (terraced houses) or 50m³ (detached and semi-detached)
- No extension beyond the plane of the existing roof slope on the principal elevation (i.e., the front)
- No raised platforms or balconies
- Materials should match the existing house where reasonably possible
If you’re in a conservation area, an Area of Outstanding Natural Beauty, or a listed building, you’ll need full planning permission. You’ll also need it for mansard conversions.
Building Regulations: Always Required
Even when planning permission isn’t needed, building regulations approval is always required for a loft conversion. This covers:
- Structural integrity (floor joists, steelwork, load-bearing walls)
- Fire safety (escape windows, fire doors, smoke alarms)
- Insulation and energy efficiency
- Staircase width and pitch
- Drainage (if adding a bathroom)
You’ll need accurate architectural drawings to submit your building regulations application. At Arkiplan, we handle this as part of our standard package — see our loft conversion drawings service here.
How Long Does a Loft Conversion Take?
From first enquiry to moving in, you’re typically looking at:
- Architectural drawings: 2–4 weeks
- Building regulations approval: 4–8 weeks (can be done in parallel with finding a builder)
- Build time: 4–8 weeks on site for most conversions
Total: roughly 3–5 months from start to finish in most cases. Mansards and larger projects can take longer.
Will a Loft Conversion Add Value to My Home?
Yes — consistently. Adding a bedroom to a property is one of the highest-return home improvements you can make. According to Nationwide and various estate agent surveys, a well-executed loft conversion typically adds 10–20% to the property value.
On an average UK home worth £280,000, that’s a potential uplift of £28,000–£56,000 — often exceeding the cost of the conversion itself.
How to Get Accurate Drawings and Quotes
The biggest mistake people make is getting build quotes before they have drawings. Builders need to see what they’re actually quoting — without drawings, quotes vary wildly and commitments are meaningless.
The right order is:
- Get your home surveyed (we use LiDAR 3D scanning — accurate to millimetres)
- Get architectural drawings produced
- Submit building regulations (and planning if needed)
- Get competitive builder quotes based on approved drawings
- Start build
At Arkiplan, we handle steps 1–3 with a fixed-price package, no hidden fees. You’ll know the full cost upfront. Find out more about our loft conversion drawings service — or get an instant quote below.