Loft Conversion Cost UK 2026

How much does a loft conversion cost? Dormer, Velux, hip-to-gable, and mansard pricing with a full breakdown of structural work, staircase, electrics, plumbing, and finishing.

Last updated: April 2026

A loft conversion is one of the most cost-effective ways to add a bedroom and bathroom to a UK home without losing any garden space. In most cases it adds more value to a property than it costs — a well-executed loft conversion on a three-bedroom semi typically adds 15–20% to the property value, turning a £300,000 house into a four-bedroom home worth £345,000–£360,000.

This guide covers the realistic cost of loft conversions across the UK in 2026, from a simple Velux rooflight conversion through to a full mansard reconstruction. Whether you are a homeowner exploring options or a builder pricing a job, these figures provide a reliable benchmark for all major loft conversion types.

Summary Cost Table

Prices include all structural work, insulation, plastering, electrics, staircase, flooring, and decoration. London and the South East are typically 20–30% higher than the national average. Scotland, Wales, and the North of England sit at the lower end of each range.

Detailed Cost Breakdown

Scaffolding

Scaffolding is required for all loft conversions and is usually the first item on the quote. The extent depends on the conversion type.

• Velux conversion (rear only) — £400 – £800
• Rear dormer — £600 – £1,200
• Hip-to-gable + dormer — £800 – £1,500
• Full mansard (both elevations) — £1,000 – £2,000

Structural Steel and Timber

Most loft conversions require steel beams to support the new floor and redistribute loads from the modified roof structure. A structural engineer's design is essential.

• Structural engineer calculations — £400 – £800
• Steel beams (RSJs, typically 2–4 beams) — £600 – £1,500 supply and fit
• Floor joists (new or reinforced) — £500 – £1,200
• Timber for dormer or roof structure — £1,500 – £4,000
• Party wall work (semi-detached or terraced) — £800 – £2,000 per neighbour

If you live in a semi-detached or terraced house, the Party Wall Act 1996 requires you to serve notice on your neighbours before structural work begins. A party wall surveyor costs £800–£1,500 per neighbour, though many neighbours agree to a shared surveyor which reduces the cost.

Dormer Construction

A rear dormer is the most popular conversion type because it maximises usable floor space with full-height headroom across the width of the house.

• Small box dormer (single room width) — £8,000 – £15,000
• Full-width rear dormer — £12,000 – £22,000
• Dormer cladding — GRP fibreglass — included in above
• Dormer cladding — lead or zinc (premium) — add £2,000 – £5,000
• Dormer windows (typically 2–3) — £1,500 – £3,500 supply and fit

Most rear dormers are clad in GRP (glass-reinforced plastic) which is lightweight, watertight, and maintenance-free. Lead and zinc cladding are premium options that look better and last longer but add significant cost. Planning departments in conservation areas may require specific cladding materials.

Hip-to-Gable

A hip-to-gable conversion extends the sloping side wall of a hipped roof to create a vertical gable wall, significantly increasing the internal floor area. This is the most popular option for semi-detached houses with hipped roofs.

• Hip-to-gable structural work — £5,000 – £10,000
• New gable wall (blockwork, insulation, render) — £3,000 – £6,000
• Combined with rear dormer (most common) — £45,000 – £70,000 total

Staircase

The staircase is a critical element — it must comply with Building Regulations Part K (minimum 2-metre headroom, maximum 42-degree pitch) and its position often dictates the layout of the conversion.

• Standard softwood staircase — £2,000 – £3,500
• Space-saving staircase (alternate tread) — £1,500 – £2,500
• Premium hardwood or bespoke design — £3,500 – £6,000
• Balustrade and handrail — included in above

The staircase typically rises from the existing landing, taking space from the bedroom below. Most loft conversion specialists can position the stair to minimise the impact on the floor below, but you should expect to lose approximately 2–3 m² from the room directly beneath.

Insulation

Loft conversions must meet current Building Regulations for thermal performance. The roof, walls, and floor all require insulation to achieve compliant U-values.

• Roof insulation (between and under rafters) — £1,000 – £2,500
• Dormer wall insulation — £400 – £800
• Floor insulation (acoustic, between joists) — £500 – £1,000
• Typical total insulation cost — £1,500 – £3,500

Electrics

A loft conversion requires a new electrical circuit run from the consumer unit, including lighting, sockets, smoke detection, and potentially a heated towel rail circuit for the en-suite.

• New circuit from consumer unit — £300 – £500
• Lighting (downlights, pendant, bedside) — £400 – £800
• Sockets (typically 6–10 double sockets) — £400 – £700
• Smoke and heat detectors (Building Regs requirement) — £200 – £400
• Typical total electrical cost — £1,200 – £2,500

Building Regulations require interconnected smoke detectors on every level of the house when a loft conversion is carried out. This often means adding detectors to the ground and first floors as well as the new loft floor.

Plumbing and En-Suite

Most loft conversions include an en-suite shower room. Plumbing in a loft is more complex than at ground level because waste runs need to drop through the floor below to reach the main soil stack.

• En-suite — budget (shower, basin, WC) — £3,000 – £5,000
• En-suite — mid-range (quality sanitaryware, tiling) — £5,000 – £8,000
• En-suite — premium (walk-in shower, underfloor heating) — £8,000 – £12,000
• Waste pipe and soil stack connection — £500 – £1,000
• Hot and cold supply (from existing system) — £300 – £600

If your existing boiler cannot handle the additional demand, you may need a boiler upgrade or an unvented hot water cylinder. See our new boiler cost guide for pricing.

Plastering and Finishing

• Plasterboarding (walls and ceiling) — £1,000 – £2,500
• Skim plastering — £800 – £1,800
• Painting and decoration — £500 – £1,200
• Flooring (carpet, engineered wood, or LVT) — £600 – £1,500
• Skirting boards and architraves — £200 – £400

Windows and Rooflights

• Velux rooflight (centre-pivot, 78 x 98 cm) — £400 – £700 supply and fit
• Velux rooflight (top-hung, larger sizes) — £600 – £1,000 supply and fit
• Juliet balcony Velux (Cabrio style) — £2,000 – £3,500 supply and fit
• Dormer window (standard casement) — £500 – £900 each

All windows in a loft conversion must meet current Building Regulations for thermal performance and fire escape. At least one window must be an approved fire escape window (minimum 450 mm clear opening) unless the loft has a protected staircase with fire doors throughout.

Factors That Affect Cost

• Conversion type — a Velux conversion is the cheapest option; a mansard is the most expensive but adds the most space and value
• Roof structure — modern trussed roofs (built after the 1960s) are harder and more expensive to convert than traditional cut roofs with purlins and rafters
• Head height — you need a minimum of 2.2 metres at the ridge to make a conversion viable. Lower ridges may require a dormer or raising the ridge (both add cost)
• Party wall agreements — semi-detached and terraced houses require party wall notices, adding £800–£2,000 per neighbour
• En-suite specification — a basic shower room adds £3,000–£5,000; a premium en-suite with walk-in shower and underfloor heating can add £8,000–£12,000
• Staircase position — if the staircase cannot rise from the existing landing, structural alterations to the floor below add cost
• Location — London and the South East are 20–30% above the national average; the North, Wales, and Scotland are at the lower end

How Long Does It Take?

These timescales cover the full build from scaffolding erection to final decoration. Most of the work takes place from the outside during the first two weeks (structural steel, dormer construction, roofing) before moving inside for insulation, plumbing, electrics, plastering, and finishing. You can live in the house throughout the build, though there will be noise and dust.

How to Save Money

• Choose a Velux conversion — if your roof has sufficient head height, a rooflight-only conversion is £15,000–£20,000 cheaper than a dormer and often does not require planning permission.
• Skip the en-suite — omitting the en-suite saves £4,000–£8,000. You can always add plumbing later if you run waste and supply pipes during the initial build.
• Agree party wall quickly — serve party wall notices early. If your neighbours consent in writing, you may not need a formal surveyor, saving £800–£1,500 per neighbour.
• Handle decoration yourself — painting, carpeting, and fitting skirting boards are straightforward tasks that save £1,000–£2,000 in labour.
• Get multiple quotes — loft conversion prices vary more than almost any other building trade. Get at least three detailed, itemised quotes and compare like for like.
• Plan during winter — loft conversion specialists are quietest from November to February. Some offer discounts of 5–10% during this period.

Common Questions