How to Quote a Loft Conversion: A Builder's Practical Guide

If there's one job that trips up builders more than any other, it's the loft conversion. It looks straightforward on the surface. Strip out the old storage, put in some beams, fit a staircase, done. But once you start pulling it apart, there are layers on layers of costs that are easy to miss on a first visit.

This guide walks you through exactly how to quote a loft conversion in the UK, from your initial site visit right through to sending the final document. We'll cover the different types, what to check on the day, realistic price ranges, and how to structure your quote so the customer actually reads it and says yes.

First Things First: What Type of Loft Conversion Is It?

Before you can price anything, you need to know what you're actually building. Each conversion type has a very different cost profile.

Velux / Rooflight Conversion

This is the most affordable type. You're not changing the roofline, just cutting in Velux windows, boarding the floor, insulating, and creating a staircase opening. Structural work is minimal. These typically run from £18,000 to £28,000 depending on size and finish level.

Dormer Conversion

A rear dormer is the most common type you'll quote. You're extending part of the roof outward to create a vertical wall and flat or shallow-pitched roof section. It adds serious headroom and usable floor space. Budget range is roughly £35,000 to £60,000 depending on the dormer size, glazing spec, and whether an en-suite is involved.

Hip-to-Gable Conversion

Common on semi-detached and detached houses with a hipped roof. You're converting the sloped hip end into a vertical gable. Often combined with a rear dormer. Typical range: £40,000 to £65,000.

Mansard Conversion

The most extensive option. Changes the slope of the roof significantly, usually 72 degrees or steeper, to create near-vertical walls. Almost always requires planning permission. These are London-heavy projects and typically start at £50,000, often reaching £75,000 or more.

What to Check on Your Site Visit

Your quote is only as good as the information you collect. Rush the site visit and you'll miss things that cost you money later. Here's what to look at:

Head Height

Building regs require a minimum head height of 2.2m for at least 50% of the floor area. Measure the existing ridge height and floor-to-ceiling height. If it's borderline, you may need to lower the ceiling of the room below or raise the ridge, both of which add cost.

Roof Structure

Older cut-roof constructions (pre-1960s roughly) are actually easier to convert than modern trussed rafter roofs. Trussed rafters can't simply be cut away without significant structural work, usually a steel beam across the full width. Factor this in.

Party Wall

If it's a semi or a terrace, you'll need a party wall agreement before any structural work starts. That's the customer's responsibility, not yours, but you need to flag it clearly in your quote and your timeline. Surveyor fees typically run £700 to £1,500 per side.

Structural Load Path

Check the walls below the loft. You'll be adding significant weight. Are they load-bearing masonry or timber frame? If it's a timber frame build, the structural engineering can get complex and expensive fast.

Access and Scaffold

What's the access like? Is there a side passage? Garden access for a skip? Will you need a licence to skip on the road? In tight terrace streets, especially in London, scaffold and skip logistics can add £1,500 to £3,000 to a job.

Existing Services

Are there water tanks in the loft that need relocating? Gas flues passing through? Electrical cables that need moving? Each of these is extra cost. Water tank relocation alone can add £500 to £900.

Breaking Down Your Loft Conversion Costs

Here's a rough cost structure for a standard rear dormer on a 3-bed semi, as a worked example:

• Structural steel and timber frame work: £6,000 to £10,000
• Dormer construction (carpentry, lead flashing, felt, tile/slate to match): £8,000 to £14,000
• Velux windows or dormer glazing: £2,000 to £5,000
• Insulation (floor, walls, roof): £2,500 to £4,000
• Staircase supply and fit: £3,000 to £6,000
• First fix (electrics, plumbing if en-suite): £2,000 to £4,000
• Second fix and finishing (plasterboard, skim, joinery, painting): £4,000 to £7,000
• Scaffold: £1,500 to £3,500
• Building control / structural engineer: £1,200 to £2,500
• Skip hire and waste disposal: £600 to £1,200

Add your labour, your markup, and you can see how a rear dormer lands in that £35,000 to £55,000 range quite comfortably.

What Your Quote Should Actually Include

A lot of builders send over a single-page price. That might work for a small job but for a loft conversion, a vague number is a red flag to any customer who's done their homework. They've had three quotes, they've watched YouTube videos, and they know what questions to ask.

Your quote needs to cover:

• A clear scope of works, broken down by phase (structural, carpentry, first fix, second fix, decoration)
• What's included and, critically, what's excluded (customer-supplied items, other trades not in scope)
• A payment schedule tied to milestones, not arbitrary dates
• Your programme of works with realistic timeframes (a typical rear dormer takes 10 to 14 weeks)
• Planning and building regs responsibilities (who's applying for what)
• Your terms around variations and day works
• Insurance details and any warranties

The more professional your quote looks, the more trust it builds. Customers paying £40,000 to £60,000 want to feel confident they're handing money to someone who knows what they're doing.

Common Pricing Mistakes to Avoid

Underpricing the Staircase Opening

Cutting and trimming an opening in the first floor ceiling is awkward, often disruptive to the rooms below, and almost always takes longer than you expect. Price it properly. Budget at least half a day for the structural work alone, separate from the staircase fit.

Forgetting the Specialist Trades

A loft conversion almost always involves an electrician (new consumer unit circuit or extension, lighting, sockets), a plasterer, and often a plumber if there's an en-suite. If you're supplying and coordinating these, make sure you've got their actual quotes before you price the job, not your back-of-envelope estimates.

Not Allowing for Weather Delays

Roof work stops when it's raining hard. If you're quoting a dormer in autumn or winter, you need a buffer in your programme. Don't promise a tight deadline that bad weather will kill. Overpromise on time and you'll end up either rushing or having very unhappy customers.

Ignoring the VAT Question

A new loft conversion on an existing dwelling is generally standard-rated at 20%. However, if the property has been empty for two or more years, a reduced rate of 5% may apply. Make sure your VAT treatment is correct and clearly stated in your quote.

Not Getting a Structural Engineer Involved Early

Don't price structural steelwork based on a guess. Get a structural engineer's specification before you quote, or at least condition your price on it. A single beam spanning 5m is very different from a 9m span with padstones into the party wall.

How to Handle the Inevitable "Can You Do It Cheaper?" Question

It's coming. Almost every loft conversion enquiry involves a customer who's had a lower quote somewhere. Here's how to handle it without just dropping your price.

First, ask them to compare like for like. A quote that's £10,000 cheaper might not include the structural engineer, the building regs application, or the plaster skim. Ask them to check.

Second, point to your documentation. If your quote is detailed, itemised, and professional and theirs is a one-liner on a scruffy invoice template, that contrast does a lot of the work for you. Customers are spending serious money. They want reassurance.

Third, be willing to value-engineer. If they genuinely need to reduce cost, you can offer alternatives. Simpler staircase. Standard Velux windows instead of premium glazing. Customer-supplied bathroom suite. Give them choices rather than just a lower number.

Presenting Your Quote: Format Matters

A Word doc or email with a bullet list just doesn't cut it for a job this size. You need something that looks like a proper business document. Ideally a PDF with your logo, company details, the customer's address, a reference number, and a clear expiry date on the price.

The expiry date is important. Materials prices move. Labour availability changes. A quote without an expiry is a promise you might not be able to keep six months down the line when the customer finally decides to proceed.

Include a section on next steps. Tell them exactly what happens when they accept. Does a deposit lock in their slot? How far in advance are you currently booking? Create a sense of process and professionalism.

Loft Conversion Timelines to Quote

Setting realistic expectations upfront saves you a lot of grief. Here are typical durations:

• Velux conversion: 4 to 6 weeks on site
• Single rear dormer: 10 to 14 weeks on site
• Hip-to-gable with dormer: 12 to 16 weeks on site
• Mansard conversion: 16 to 24 weeks on site

Add lead time for planning permission if needed (8 weeks typically for a householder application, though it often runs longer) and party wall agreement processing (2 to 8 weeks depending on neighbours).

Pulling It All Together

The best loft conversion quotes are the ones that make a customer feel like the builder already understands their project. Reference specifics from the site visit. Mention the water tank that needs relocating. Note the scaffold licence required. Show that you were paying attention.

That level of detail, combined with a clean, professional document, is what separates the builder who wins at the right price from the builder who either doesn't win or wins and ends up working for nothing.

Take the time to quote properly. On a £45,000 job, an extra two hours putting together a thorough proposal is the best return on investment you'll ever get.