How to Quote a Loft Conversion: Pricing Guide for UK Builders

How to Quote a Loft Conversion

Loft conversions are one of the most profitable jobs for UK builders — but they are also one of the hardest to quote accurately. The scope can vary enormously between a simple Velux conversion and a full dormer with en-suite. This guide walks through how to price a loft conversion properly, covering all the key cost areas and common mistakes.

Types of Loft Conversion

The type of conversion dictates the price. Make sure you and the customer are aligned on what is being quoted:

• Velux / rooflight conversion: The simplest type. No changes to the roof structure — just windows, insulation, floor strengthening, stairs, and finishing. Suitable where there is already adequate head height.
• Dormer conversion: A flat-roof or pitched-roof dormer extends the usable floor area. Requires structural steel, new roof construction, and more complex finishing.
• Hip-to-gable: Converts a hipped roof end into a vertical gable wall. Common on semi-detached and detached houses. Significant structural work.
• Mansard: The most extensive type. Changes the roof profile entirely. Almost always requires planning permission.

Step 1: Survey and Feasibility

Before quoting, check:

• Head height: Minimum 2.2m at the highest point for a usable conversion
• Roof structure: Traditional cut roof (easier) or trussed roof (requires more structural work)
• Party wall: Semi-detached or terraced properties trigger Party Wall Act requirements
• Planning permission: Dormers to the rear are usually permitted development; front dormers, mansards, and conservation areas typically require full planning
• Building regulations: All loft conversions require Building Control approval — fire safety, structural calculations, insulation, staircase design
• Services: Where will plumbing, heating, and electrics be routed?

Step 2: Break Down the Work Packages

A loft conversion typically involves these work packages:

Structural Work

• Steel beams (RSJs) — typically 2–4 beams depending on the span
• Floor joists — strengthening or new joists to take domestic loading
• Dormer construction (if applicable) — cheeks, flat roof, fascia
• Roof alterations — cutting rafters, new ridge, valley gutters

Staircase

• New staircase from first floor to loft — custom-made or off-the-shelf
• Opening up the first-floor landing — structural trimming
• Fire door upgrades to existing rooms (Building Regs requirement)

First Fix

• Plumbing first fix — if en-suite or radiators
• Electrical first fix — lighting, sockets, smoke/heat detectors
• Insulation — between and over rafters, meeting Part L requirements
• Plasterboarding — walls and ceilings (including fire-rated board)

Windows and Ventilation

• Velux or dormer windows
• Fire escape window (must meet minimum opening size for Building Regs)
• Mechanical ventilation to en-suite (if applicable)

Second Fix and Finishing

• Plastering
• Second fix electrics — sockets, switches, light fittings
• Second fix plumbing — en-suite, radiators
• Flooring
• Skirting, architrave, door hanging
• Decoration

Step 3: Cost Ranges for 2026

These are typical all-in costs (labour + materials) for standard-specification loft conversions:

• Velux conversion: £25,000–£40,000
• Rear dormer: £35,000–£55,000
• Hip-to-gable + rear dormer: £45,000–£65,000
• Mansard: £55,000–£80,000+

London and the South East typically sit at the higher end. Regional variations of 15–25% are normal.

Key Cost Items

• Structural steels (supply and fit): £2,000–£5,000
• Staircase: £1,500–£4,000
• Velux windows (per window): £500–£1,500 fitted
• Dormer construction: £8,000–£15,000
• En-suite bathroom: £3,000–£6,000
• Scaffolding: £1,500–£3,000 (often for 8–12 weeks)
• Building Control fees: £400–£800
• Structural engineer: £500–£1,200
• Party wall surveyor: £700–£1,500 per neighbour

Step 4: Labour Planning

A typical rear dormer loft conversion takes 6–10 weeks with a team of 2–3. Labour breakdown:

• Structural/carpentry: 15–25 days
• Roofing: 3–5 days
• Plumbing first and second fix: 3–5 days
• Electrical first and second fix: 3–5 days
• Plastering: 3–5 days
• Tiling (en-suite): 2–3 days
• Decoration: 3–5 days
• Flooring and finishing: 2–3 days

Step 5: Present the Quote

Loft conversion quotes should be broken down by work package so the customer can see where the money goes. Include provisional sums for any items that are not yet finalised (bathroom suite, flooring finish, etc.).

Tools like MyQS can help you produce itemised loft conversion quotes quickly. Upload photos of the existing loft space, specify the conversion type, and the AI generates a detailed pricing breakdown covering all trades. You can then adjust rates and add bespoke items before sending a branded PDF to the customer.

Common Pricing Mistakes

• Forgetting scaffolding hire duration — loft conversions can take 8–12 weeks; scaffold hire adds up
• Not allowing for Building Control and structural engineer fees
• Underpricing the staircase — especially if the existing layout is tight and needs a custom design
• Ignoring fire safety upgrades — fire doors, interlocked smoke detectors, and fire-rated boarding to the staircase enclosure are all Building Regs requirements
• Not checking Party Wall Act requirements — this can add £1,500+ per neighbour and cause delays if not started early

Frequently Asked Questions

Do loft conversions need planning permission?

Most rear dormer conversions on detached and semi-detached houses fall under permitted development and do not need planning permission. Front dormers, mansard conversions, properties in conservation areas, and flats almost always need full planning. Always check with your local authority before quoting.

How much profit should I make on a loft conversion?

Most builders aim for a net profit margin of 15–20% on loft conversions after all labour, materials, and subcontractor costs. On a £45,000 job, that is £6,750–£9,000 profit. Make sure your margin accounts for the project duration — tying up your team for 8–10 weeks is a significant commitment.

Should I quote a loft conversion as a fixed price or day rate?

Fixed price is standard for loft conversions. Customers want certainty on cost. Use provisional sums for items that depend on the customer's choices (sanitaryware, flooring, etc.) and include a clear exclusions list to protect yourself.

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