How to Price a Loft Conversion in the UK (2026 Guide)

Loft conversions are among the highest-value jobs a builder or carpenter can win — and one of the most underpriced. A poorly structured quote on a £35,000 project can wipe out your margin entirely, while a well-presented one can win you the job over a competitor who quoted 10% less. This guide breaks down every cost element, how to price by conversion type, and how to present a loft conversion quote that customers say yes to.

The three main loft conversion types and their price ranges

The conversion type determines structural complexity, material cost, and the amount of planning and building regs work involved. Getting this assessment right before you quote is critical.

• Velux (roof light) conversion — the simplest type. No external structure change; Velux windows are cut into the existing roof slope. Typical cost range: £18,000–£28,000. Usually permitted development, no planning permission needed. Suitable for properties with adequate existing ridge height (minimum 2.2m floor-to-ridge after structural floor).
• Dormer conversion — a box-shaped extension that projects vertically from the roof slope, dramatically increasing usable floor area and headroom. Typical cost range: £30,000–£55,000. Usually permitted development for rear dormers; side dormers typically require planning permission. The most common conversion type for terraced and semi-detached houses.
• Hip-to-gable conversion — the hipped end of the roof is extended to create a vertical gable wall, giving maximum floor area. Often combined with a rear dormer for a full L-shaped conversion. Typical cost range: £40,000–£65,000. Almost always requires planning permission. Most commonly done on end-of-terrace and detached properties.

Mansard conversions (where the entire roof pitch is rebuilt at a near-vertical angle) are the most expensive type at £45,000–£70,000+ and almost always require planning permission. They are common in London and large cities but less frequently quoted by regional builders.

Structural work: what drives the biggest cost variations

The structural floor of a loft conversion is almost always the most variable cost element. Most existing loft joists are designed to support insulation and light storage, not a habitable room — they typically need to be sistered (new joists added alongside existing ones) or replaced entirely. In a typical 30 m² loft, this structural floor work runs to £3,000–£6,000 depending on joist size, span, and access.

Steel RSJs or steel frames are required for hip-to-gable and large dormer conversions to support the new structure. A structural engineer's calculations (£500–£1,500) are required for building regs and will specify the steel sizes. Steel supply and installation typically adds £2,000–£5,000 depending on number of beams and crane or hoist requirements. Do not quote structural steel until you have the engineer's spec — or build in a clear provisional sum with your assumptions stated.

Electrics, plumbing and insulation costs

Electrical work for a loft conversion is almost always a subcontracted element. A first-fix and second-fix for a typical one-bedroom loft with en-suite costs £2,500–£4,500 for an NICEIC-registered electrician. The board upgrade (if the existing consumer unit cannot accommodate the additional circuits) adds £600–£1,200. Get a written subcontractor quote before pricing — do not use a line-item estimate.

Insulation is a major cost and a building regs requirement. Warm roof insulation (rigid PIR boards between and below rafters) is the most effective method for habitable rooms. For a 30 m² conversion, insulation materials run to £1,500–£3,000 depending on specification. Cold roof insulation (mineral wool between joists) is cheaper but rarely achieves the U-values required under current Part L of the Building Regulations. Quote the warm roof method as standard.

If an en-suite bathroom is included, plumbing costs (mains water supply run, soil stack connection, heated towel rail) add £2,000–£4,000 for a basic shower room. Budget en-suites with full sanitaryware supply and fit run to £4,500–£8,000.

Planning permission and building regulations

Many builders leave planning and building regulations as the customer's problem. This is a mistake — customers expect you to know this and will often choose the builder who can navigate it with them. For most rear dormers and Velux conversions on houses that are not listed or in a conservation area, permitted development rights apply and planning permission is not required. The customer only needs a lawful development certificate (optional but recommended at £200–£300 from the council).

Building regulations approval is always required for loft conversions. You can either submit a full plans application (£500–£900, reviewed before work starts) or use a building notice (£400–£700, inspection-based during the build). Full plans gives you approved drawings to build to; a building notice is faster to start but riskier if the inspector raises issues mid-build. For conversions with significant structural elements, full plans is the safer route.

The fire safety requirements for loft conversions are detailed and frequently catch builders out. The new room must be accessible via a protected staircase with fire doors on each floor and a 30-minute fire-rated ceiling below the new stairs. Mains-wired interconnected smoke alarms throughout are required. Factor the correct fire door and intumescent strip specification into your material quote — this is a common area where costs are underestimated.

How to price the staircase

The staircase is one of the most contentious elements of any loft conversion quote because the required space is often taken from an existing bedroom. A standard softwood staircase, supplied and fitted with a fire-rated door at the top, costs £2,500–£4,000. A hardwood or glass-balustrade staircase that the customer has chosen from a showroom can run to £6,000–£12,000 once fitting is included.

If the staircase requires making good to a bedroom ceiling, skimming, and decoration after installation, price this work separately and clearly in your quote. Customers rarely think about the disruption to the floor below when they ask for a loft conversion price — making it explicit builds trust and avoids post-job disputes.

How to present a loft conversion quote professionally

Loft conversion customers are spending £30,000–£60,000 on a project that will take 6–12 weeks and significantly disrupt their home. The quality of your quote directly signals the quality of how you will manage the project. A one-page price with a single figure loses you work. A detailed, itemised quote with a clear project timeline, payment schedule, and written specification wins it.

Structure your quote in sections that mirror the stages of the build: structural floor and steelwork, dormer/roof structure, insulation, first fix (electrics, plumbing, carpentry), plastering, second fix (electrics, plumbing, carpentry, stairs), and decoration. Include provisional sums for any element you cannot price precisely until the structural engineer's spec is confirmed, and explain what a provisional sum means. State what is and is not included — if kitchen extraction, TV aerials, or loft storage are not in scope, say so.

A payment schedule tied to build milestones (deposit, structural complete, first fix complete, practical completion) is standard on loft conversions. State each milestone payment amount in the quote. Trade2Base lets you build a multi-stage quote with milestone payment requests sent automatically as each stage is signed off — keeping your cash flow positive throughout a project that runs for weeks before full payment is due.