Loft conversions are one of the most profitable jobs a builder or contractor can take on. They’re also one of the hardest to quote for. Get the price wrong and you’re either leaving thousands on the table or losing the job to a competitor who priced it better.

This guide breaks down everything you need to know to quote loft conversions accurately in 2026 — from the different types of conversion to a full cost breakdown you can use as a template.

Types of Loft Conversion (And What They Cost)

The type of conversion determines the price more than anything else. Here’s what each type involves and what you should be quoting in 2026:

1. Velux / Roof Light Conversion

The simplest and cheapest option. No structural changes to the roof — just floor strengthening, insulation, staircase, electrics, and Velux windows fitted into the existing roof slope.

  • Typical quote: £20,000 – £35,000
  • Duration: 3–5 weeks
  • Best for: Properties with good existing head height (2.2m+ at the ridge)
  • Planning permission: Usually not required (falls under Permitted Development)

2. Dormer Conversion

The most popular type in the UK. A flat-roofed extension is built out from the rear slope, creating full-height usable space. Much more headroom and floor area than a Velux conversion.

  • Typical quote: £35,000 – £55,000
  • Duration: 5–8 weeks
  • Best for: Most semi-detached and terraced houses
  • Planning permission: Usually Permitted Development (check local restrictions)

3. Hip-to-Gable Conversion

The sloping side of the roof (the hip) is extended vertically to create a flat gable wall. Often combined with a rear dormer for maximum space.

  • Typical quote: £40,000 – £65,000
  • Duration: 6–10 weeks
  • Best for: Detached and semi-detached properties with hipped roofs
  • Planning permission: May be required — check with the local authority

4. Mansard Conversion

The most extensive (and expensive) type. The entire roof structure is altered to create a near-vertical wall with a flat roof on top. Creates the most usable space but requires significant structural work.

  • Typical quote: £50,000 – £75,000+
  • Duration: 8–14 weeks
  • Best for: Terraced properties in London and high-value areas
  • Planning permission: Almost always required

Pro Tip: Always do a site visit before quoting a loft conversion. Photos and measurements from the homeowner are never accurate enough. You need to check head height, roof structure (trussed vs traditional rafters), access, and services (water tanks, wiring) in person.

Cost Breakdown: What Goes Into a Loft Conversion Quote

Here’s a typical breakdown for a rear dormer conversion at £45,000:

Structural Work — £12,000–£15,000

  • Steel beams (RSJs) for floor support
  • Floor joists and boarding
  • Dormer frame construction
  • Load-bearing wall alterations
  • Scaffolding (£1,500–£2,500)

Roofing — £3,000–£5,000

  • Dormer roof (flat roof with GRP/fibreglass or EPDM)
  • Dormer cheeks (lead or tile-hung)
  • Flashing and weatherproofing
  • Roof tiles to match existing

Staircase — £2,500–£4,000

  • Staircase design and construction
  • Balustrade and handrail
  • Landing area modifications
  • Fire door to landing (Building Regs requirement)

Windows & Doors — £2,000–£4,000

  • Velux or dormer windows
  • Window reveals and sills
  • Fire escape window (Building Regs requirement)

Insulation — £1,500–£2,500

  • Roof insulation (between and under rafters)
  • Wall insulation for dormer
  • Floor insulation (soundproofing between floors)

Electrics — £2,000–£3,500

  • Consumer unit upgrade (if needed)
  • Lighting circuits and switches
  • Socket circuits
  • Smoke and heat detectors (Building Regs)
  • Certification (Part P)

Plumbing & Heating — £1,500–£3,000

  • Radiator installation and pipework
  • En-suite plumbing (if applicable — adds £2,000–£4,000)
  • Relocation of water tank (if in loft)

Plastering & Finishing — £3,000–£5,000

  • Plasterboard and skim to all walls and ceiling
  • Skirting boards and architraves
  • Painting and decorating
  • Flooring (carpet, laminate, or engineered wood)

Don’t Forget: Always include the cost of Building Regulations approval (£500–£1,000), structural engineer calculations (£400–£800), and Party Wall agreements if it’s a semi-detached or terraced property (£700–£1,500 per neighbour). These are costs many builders forget to account for.

How to Calculate Your Quote

Here’s a step-by-step approach that works for any loft conversion:

Step 1: Site Survey

Visit the property and assess:

  • Head height at ridge and eaves
  • Roof structure (trussed or traditional)
  • Existing services in the loft (water tank, electrics, aerials)
  • Access for staircase (where it can go without losing a bedroom)
  • Chimney breast (does it go through the loft?)
  • Neighbours and Party Wall considerations

Step 2: Materials Costing

Price up all materials from your suppliers. Don’t guess — get actual quotes for steel, timber, windows, and roofing materials. Add 10% contingency for waste and price increases.

Step 3: Labour Calculation

Estimate the number of days for each trade:

  • Builder/carpenter: 15–25 days
  • Roofer: 3–5 days
  • Electrician: 3–5 days
  • Plumber: 2–4 days
  • Plasterer: 3–5 days
  • Decorator: 2–4 days

Multiply by day rates. If you’re subcontracting, get quotes from each sub.

Step 4: Add Overheads and Profit

Add your overheads (van, insurance, tools, admin time) and your profit margin. For loft conversions, a margin of 15–25% is standard. Don’t feel guilty about this — you’re managing a complex project over 6–12 weeks.

Step 5: Present Professionally

A £45,000 job deserves a professional quote. Break it down into sections so the customer can see exactly where their money goes. Include a timeline, payment schedule, and what’s included/excluded.

Payment Schedule Tip: For loft conversions, a staged payment plan is standard: 10% deposit, then payments at key milestones (steels in, watertight, first fix, second fix, completion). Never take more than 20% upfront.

5 Tips to Win More Loft Conversion Jobs

1. Quote Fast

Homeowners typically get 3 quotes for a loft conversion. The first professional quote they receive sets the benchmark. If yours arrives a week late, the customer has already mentally committed to someone else.

2. Include a 3D Visualisation or Floor Plan

Even a simple sketch showing the layout of the converted space helps the customer visualise the result. It separates you from builders who just send a number.

3. Show Previous Work

Include 3–4 photos of previous loft conversions in your quote pack. Before and after shots are incredibly powerful for jobs this size.

4. Be Clear About What’s Included

The biggest source of disputes on loft conversions is “I thought that was included.” Spell out everything: decorating, flooring, light fittings, door handles. If it’s excluded, say so explicitly.

5. Follow Up

Customers take weeks to decide on a £40,000+ job. Follow up 5–7 days after sending the quote with a polite message: “Just checking you received the quote. Happy to answer any questions or arrange another visit if helpful.”

The Bottom Line

Loft conversions are complex jobs with a lot of moving parts. The tradesmen who win these jobs aren’t always the cheapest — they’re the ones who present clearly, communicate well, and give the homeowner confidence that the project is in safe hands.

Get your pricing right, present it professionally, and follow up promptly. That’s the formula.

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