How to write a quote for a loft conversion (with a real worked example)

A mate of mine, a carpenter in Leeds, quoted £38,000 for a dormer loft conversion on a 1930s semi. One line, one number, a handshake. Three weeks in, the engineer's final calculations came back with a bigger steel than the sketch had shown, the scaffold had to stay up a fortnight longer than he'd allowed, and the customer wanted the en-suite tiled floor to ceiling. He ate about £3,200 and spent a month not speaking to the customer's other half.

Nobody was dishonest. The quote just didn't say what the price covered, what was provisional, and who paid for the bits that come from other people. This guide shows how to write a loft conversion quote so those lines are in writing before the scaffold goes up.

Before you price anything, check what the loft will allow

Loft quotes go wrong at the front end more than the back. Before you open a calculator, get these written down:

• Headroom and roof type. Measure from the top of the ceiling joists to the underside of the ridge. Around 2.2m is the number people work to for a usable room. Less than that and you're into lowering ceilings below, which is a different job at a different price. Trussed roofs from the 1960s onwards need far more steel than a traditional cut roof, so find out which you have.
• Where the stairs land. The staircase takes a chunk out of the floor below and needs headroom of its own. If the only place it fits is through a bedroom, the customer needs to know before you start, not after.
• Planning. Many loft conversions fall under permitted development, with volume limits of 40 cubic metres for terraced houses and 50 for semi-detached and detached. Dormers can't extend beyond the roof plane on the front, and the rules are tighter in conservation areas and on flats. Either the customer has the right paperwork or they don't. Say whose job it is. Check the gov.uk guidance if you're unsure.
• Building Regulations. They apply to every loft conversion, permitted development or not. Structure, fire escape, stairs and insulation all get inspected by local authority building control or a registered approved inspector.
• The neighbours. If a steel bears on a party wall or you're cutting into it, the Party Wall etc. Act 1996 can apply. The notices and any surveyors are normally the building owner's cost, not yours. Say so on the quote.
• Bats. If you find droppings or signs of roosting in the roof space, stop. Bats and their roosts are protected, and disturbing them is an offence. Natural England and the Bat Conservation Trust can tell you what happens next.

Then go up and have a proper look. Check the condition of the rafters and purlins, the position of the chimney breast, the water tank, any wiring and the location of soil stacks that might need boxing in. These turn into variations, and you want them on the quote as exclusions or provisional sums, not as surprises.

Split the quote the way the job is built

One figure at the bottom is an invitation to argue. A quote split into stages shows the customer you've thought it through, and it gives you somewhere to point when they ask for a change. A sensible structure for a dormer loft conversion:

1. Preliminaries, scaffold and fees

Skips, welfare, floor protection and dust sheets on the way up the stairs. Scaffold and a temporary roof covering for the days the roof is open. Engineer's calculations and building control fees, shown at cost.

2. Structure and steel

Steels to the engineer's spec, padstones, strengthening or new floor joists, and the temporary propping that goes with it. This is where the engineer's drawing decides the price, so don't quote it before you've seen it.

3. Dormer shell and roof

Timber frame, roof structure, insulation, the flat roof covering and the cladding or tile hanging. Say what the finish is. "Tile hanging to match" and "grey fibre cement boards" are different invoices.

4. Windows, rooflights and stairs

Dormer window, rooflights to the front slope, and the new staircase with its fire door at the bottom. Supply and fit, with the make or the spec.

5. Insulation, fire protection and finishes

Insulation to the sloping ceilings and knee walls, plasterboard and skim, fire-rated boards where the regs ask for them, internal doors, skirting and flooring boards. Mains-linked smoke alarms go on the electrical line.

6. First fix, second fix and the en-suite

Electrics and plumbing by whoever is doing them, with certificates included. If there's an en-suite, price the fit-out as its own line, with the sanitaryware either supplied by you or listed as a customer allowance.

A worked example: dormer loft conversion, 1930s semi in Leeds

Here's a quote from Adam Wójcik trading as Wójcik Building for a rear dormer loft conversion on a 1930s semi. A double bedroom and an en-suite shower room, about 22 square metres of new floor space, new stairs over the existing stairwell, two rooflights to the front. Cut roof, no trusses. The customer is a homeowner, the work falls within permitted development, and the party wall notice is already served.

Cost build-up (materials, labour and subcontractors):

• Preliminaries: skips, welfare, floor and stair protection = £1,100
• Scaffold and temporary roof cover = £1,900
• Engineer's calculations and building control fees, at cost = £1,350
• Steelwork, padstones and floor strengthening = £4,800
• Dormer shell: timber frame, roof structure, insulation, EPDM roof, cladding = £9,600
• Dormer window and two rooflights, supplied and fitted = £3,200
• New staircase, fire door and partition = £2,700
• Insulation, fire-rated plasterboard and skim = £4,100
• First and second fix electrics and plumbing, certificates included = £5,200
• En-suite fit-out: shower, WC, basin, tiling (customer picks from a £600 allowance for fittings) = £3,400
• Internal doors, skirting, flooring boards = £2,300
• Provisional sum for roof timber repairs and hidden defects, adjusted to actual cost = £1,550

Add those up and you get £41,200. Check it: 1,100 + 1,900 + 1,350 + 4,800 + 9,600 + 3,200 + 2,700 + 4,100 + 5,200 + 3,400 + 2,300 + 1,550 = 41,200.

Overheads and profit at 15% on top: £41,200 x 0.15 = £6,180. That covers insurance, tools, van, admin time and the margin the business needs to stay in business. Total price: £47,380. That's about £2,154 a square metre of new floor space, which sits in the range you'd expect for a dormer conversion outside London, though it moves a lot with the roof type and the spec.

If the firm were VAT-registered, converting a loft in an existing home is standard rated, so you'd add 20% (£9,476) and show the VAT line. The registration threshold at the time of writing is £90,000 of taxable turnover, so one job like this can push a small firm over it quickly. Check gov.uk and talk to your accountant before you quote, not after.

Provisional sums, exclusions and the things the customer pays for

The £1,550 provisional sum covers things you can't see until the old roof is open. Write it in plain words: "Allowance for repairs to existing rafters, purlins and wall plates. Charged at actual cost plus 15%. Any unused amount is deducted from the final invoice." That last sentence is what makes customers trust the number.

Then write what is not included. For a loft conversion, a decent exclusions list looks like this:

• Planning fees, lawful development certificate fees and any party wall surveyors' fees
• Replacement of the existing boiler or hot water cylinder if the system needs upgrading to cope with the extra bathroom
• Decorating, carpets, curtains and furniture
• Making good to rooms below, other than areas disturbed by the new stairs
• Removal of asbestos, if found, and any specialist survey work such as a bat survey
• Upgrading the electrical consumer unit if it doesn't meet current regs

If you're not sure whether a line goes in the quote or the exclusions, put it somewhere. The only wrong place is nowhere.

Payment stages that match the build

On a job this size you can't fund the scaffold, steel and windows out of your own pocket and wait for a final invoice. Tie payments to things the customer can see, and put the schedule on the quote. For the £47,380 job:

• On acceptance, 10%: £4,738. Covers the scaffold booking and the first orders.
• Scaffold up, steels in and dormer frame weathertight, 30%: £14,214.
• Windows in, stairs fitted and first fix complete, 30%: £14,214.
• Plastering done, second fix and en-suite under way, 25%: £11,845.
• Completion, snag list signed off and building control completion certificate, 5%: £2,369.

Check it: 4,738 + 14,214 + 14,214 + 11,845 + 2,369 = 47,380. The last 5% is your carrot for finishing the snags, and the building control certificate matters because the customer needs it when they come to sell. For more on how to structure the schedule, see our guide to stage payments for trades. For the legal side of taking money upfront, see how much deposit a builder can ask for.

What NOT to do

1. Don't price before the engineer has spoken. The steel is the biggest unknown on the job. Quote subject to the engineer's calculations, or make the calculations part of a paid first stage.
2. Don't quote from a sketch and call it fixed. If the drawings aren't final, say the price is subject to final drawings and list what happens when they change.
3. Don't forget the scaffold time. A loft takes longer than the first fortnight you scribbled down. Price the scaffold hire for the real programme, plus a week of slack.
4. Don't leave the en-suite fittings open-ended. "Bathroom suite included" means a £4,000 suite to some customers. Put a figure on it as an allowance.
5. Don't skip the sign-off. If building control hasn't signed it off, you haven't finished. Make the completion certificate part of the last payment trigger.

The short version

Check the loft before you price it. Split the quote by stage, give third-party costs their own lines, use a provisional sum for what you can't see and write the exclusions in plain English. Tie your payments to milestones the customer can see. A quote that does those five things protects your margin and gives the customer fewer reasons to argue about the final invoice.

Frequently asked questions

How much does a loft conversion cost in the UK?

It depends on the loft type and the spec. A simple rooflight conversion can cost noticeably less than a dormer, and a mansard or a full-width dormer with an en-suite costs more. The worked example above, a rear dormer with an en-suite outside London, comes to about £47,380 before VAT. Always price your own job from the drawings, not from a headline figure.

Do I need planning permission for a loft conversion?

Often not, because many loft conversions fall under permitted development. The limits include 40 cubic metres of added volume for terraced houses and 50 for semi-detached and detached houses, and rules on front-facing roof slopes. Conservation areas, flats and homes where permitted development rights have been removed need a planning application. Check gov.uk or the local council.

Does a loft conversion need Building Regulations approval?

Yes, every time. Structure, fire safety, stairs and insulation are all inspected by building control. You'll need a completion certificate at the end, and the customer will need it when they sell.

Who pays for the structural engineer and party wall surveyor?

Usually the building owner pays for the party wall notices and any surveyors. The engineer is normally the owner's cost too, or you pay and pass it on at cost. Whichever applies, put it in writing on the quote.

How should I take payments on a loft conversion?

In stages tied to visible milestones. A deposit on acceptance, payments at weathertight, first fix and second fix, and a final slice after sign-off. Keep the final slice small but real, around 5%, so there is a reason to finish the snags.

What if the existing roof timbers are in worse shape than expected?

That is what the provisional sum is for. Write the allowance, the rate for extra work and the rule that unused money comes off the final invoice. If the repairs go over the allowance, you issue a variation order before doing the work, not after.