Loft Conversion Cost UK 2026: Complete Guide

Real figures by conversion type, size and region — plus what most quotes leave out

Buildcostr.ai · July 2026 · 8 min read

How much does a loft conversion cost in 2026?

A loft conversion in the UK costs between £25,000 and £75,000 depending on the type of conversion, the size of your roof space, your specification choices and where you live. The figures below are for materials and labour only — professional fees, VAT and furniture are additional.

These are Q2 2026 UK national averages. London and the South East typically run 20–35% higher than these figures. The North of England and Wales tend to sit toward the lower end.

Cost by conversion type

Velux loft conversion

The most affordable option. Velux conversions add roof windows to the existing roof slope without changing its shape — meaning no structural alterations to the roofline, less scaffolding and a faster build programme. Typical cost: £25,000–£35,000.

The catch: your existing loft must already have adequate headroom (typically 2.2m at the ridge minimum) for the finished space to be usable as a bedroom. Many older terraced houses don't have sufficient height for this without dormer works.

Dormer loft conversion

The most common type in the UK. A dormer extends vertically from the roof slope, creating a box-like structure that significantly increases both floor area and headroom. Rear dormers are generally permitted development (no planning permission needed). Typical cost: £35,000–£55,000.

L-shaped dormers — combining a rear and side return — are popular on Victorian terraced houses and add considerably more usable floor area. Expect to pay £45,000–£65,000 for a well-specified L-shaped dormer.

Hip-to-gable conversion

Common on semi-detached and detached houses with a hipped roof. The sloping hip end of the roof is replaced with a vertical gable wall, creating a much larger loft void. Usually combined with a rear dormer to maximise the space. Typical combined cost: £45,000–£65,000.

Mansard loft conversion

The most extensive option. A mansard conversion alters the entire rear roof slope to near-vertical, maximising headroom across the full floor area. Almost always requires planning permission. Typical cost: £55,000–£75,000 — and significantly more in London. Common in terraced townhouses where maximum space is the priority.

What affects the cost of a loft conversion?

Existing roof structure

Older cut-rafter roofs (pre-1960s houses) are generally easier and cheaper to convert than modern trussed rafter roofs, which require structural engineers to design a new support system before the conversion can begin. If your house was built after 1965, budget for structural engineer fees and potentially higher build costs.

En-suite bathroom

Adding a bathroom to a loft conversion is one of the biggest cost variables. A basic shower room adds £4,000–£8,000 to the build cost. A full en-suite with freestanding bath, quality tiling and premium sanitaryware can add £10,000–£15,000. Most valuers agree the addition of a bathroom significantly increases the uplift in property value.

Staircase

Building regulations require a fixed staircase with adequate headroom clearance. A standard staircase costs £3,000–£6,000 installed. Bespoke joinery — folding stairs, glass balustrades, feature staircases — adds considerably more and often requires specialist trades.

Specification and finishes

The gap between a basic-spec loft conversion and a premium-spec one is significant. Budget flooring, off-the-shelf built-ins and standard sanitaryware will land you near the bottom of the cost range. Underfloor heating, Velux cabrio balcony windows, bespoke storage and premium bathrooms push you well past the top.

Regional cost differences

Labour costs are the primary driver of regional variation. Here's how costs typically compare across the UK relative to the national averages above:

• London: 25–40% above national average
• South East (Essex, Kent, Surrey, Herts): 10–20% above average
• South West: 5–10% above average
• Midlands: At or near national average
• North of England: 5–15% below average
• Wales and Scotland: 5–15% below average

What's not included in most loft conversion quotes

Most builder quotes for loft conversions are materials-and-labour only. These items are frequently excluded and should be budgeted separately:

• Architect or architectural technician fees (typically £2,000–£5,000)
• Structural engineer fees (typically £500–£1,500)
• Planning application fee (£258 in England, if required)
• Building regulations application and inspection fees (£600–£1,200)
• Party wall surveyor fees if applicable (£700–£2,000 per neighbour)
• VAT at 20% — loft conversions are not zero-rated
• Furniture, lighting, window dressings and loose fittings
• Redecoration to the floors below (staircase works often affect existing landing)

Do I need planning permission for a loft conversion?

Most loft conversions in England fall under permitted development rights, meaning no planning application is required, provided the additional roof space created does not exceed 40m³ for terraced houses or 50m³ for detached and semi-detached properties.

Exceptions include: properties in conservation areas or Areas of Outstanding Natural Beauty, listed buildings, mansard conversions (which by definition alter the roofline significantly), and any conversion that extends beyond the highest point of the existing roof. Always check with your local planning authority before assuming permitted development applies.

Does a loft conversion add value?

Yes — consistently. A well-executed loft conversion that adds a bedroom and bathroom typically increases a UK property's value by 15–20%. In London and high-demand suburban areas, the uplift can exceed 20%, particularly where the conversion transforms a 3-bedroom property into a 4-bedroom one, crossing a key pricing threshold for family buyers.

The key word is "well-executed". A loft conversion that lacks proper headroom, has awkward access or has been completed without building regulations sign-off can actually make a property harder to sell.

How to get an accurate cost for your loft conversion

The only reliable way to know what your specific loft conversion should cost is a professional cost plan based on your actual drawings. Generic online calculators give ballpark figures; a proper cost plan gives you the detail you need to manage a builder's quote, challenge inflated figures and make informed decisions.

Buildcostr.ai produces a full QS-methodology cost plan from your architectural drawings in 30 minutes. It covers all 15 cost sections including labour, materials, preliminaries and professional fees — so you know the complete picture before you approach a single builder. See a sample report or order yours from £99.

Also worth reading: single vs double storey extension costs and how to read a builder's quote.