Loft conversion quote looks too high? How to check, UK 2026

A loft conversion is one of the largest jobs a UK homeowner commissions, often £40,000 to £80,000, sometimes more. At those numbers, even a 10% padding adds up to a small car. This guide is a checklist to judge whether the headline price is in the right range for the type of conversion you are getting, and to spot the items most commonly buried or missing.

For ranges and definitions of conversion type, start with the loft conversion cost guide. For the general diagnostic method, see how to tell if a quote is too high.

Typical price by type, so you have a benchmark#

The type of conversion is the biggest single price driver. In 2026:

• Velux (rooflight) conversion, no change to roof shape: £25,000–£45,000. Suitable only where the existing head height already meets the 2.2 m minimum.
• Dormer conversion (the most common type), adding a flat-roof box at the rear to create headroom: £40,000–£70,000.
• Hip-to-gable plus dormer, changing a hipped end into a vertical gable and then adding a dormer: £55,000–£85,000.
• Full mansard, where the roof is rebuilt with near-vertical walls and a shallow top: £65,000–£100,000 or more.

London and the South East sit at the top of these bands. The numbers usually exclude furniture and decoration, and sometimes exclude the en-suite as a separately priced item. If your quote is well outside the band for its type, that is the first thing to ask about.

Build cost versus professional fees#

Most loft quotes separate the build cost from the professional fees. Both need to be visible and the quote needs to be clear about which side it sits on. The professional fees that exist for every loft conversion:

• Architect or designer: drawings for permitted development and building regs. Roughly £1,500–£4,000 for a typical job.
• Structural engineer: calculations for the steel beams and floor joists. Roughly £600–£1,500.
• Building control inspector: the local authority or an approved inspector. Roughly £400–£900.
• Party wall surveyor if a neighbour shares the wall: £700–£2,000 per agreement, often per neighbour.

A "fully inclusive" quote should list which of these are inside it. A build- cost-only quote should make clear they are extra. Either is fine; the ambiguous middle is the problem.

What a fair build cost should itemise#

A reasonable build-cost line set, with a number against each:

• Scaffolding, with duration stated (typically 8 to 16 weeks for a loft).
• Steelwork: supply, lift in, and install. The biggest single structural line.
• Floor: new joists or sistering, deck.
• Dormer or roof extension structure, where applicable.
• Roof covering to match the existing house.
• Staircase: new run, often with a structural opening through the floor below. Position drives cost.
• Insulation to current building regs (U-values for warm or cold roof construction).
• Plasterboarding and skim to walls and ceilings.
• Electrics: lighting, sockets, smoke alarms (mains-wired to the rest of the house under fire regs), any en-suite electrics, with Part P certification.
• Plumbing: if there is an en-suite, hot and cold supply plus waste, often with a pumped soil. Sometimes priced as a separate sub-package.
• Heating extension: a new radiator on each room added.
• Fire regulations: fire-rated doors on the rest of the house's habitable rooms, mains-wired smoke and heat alarms.
• Velux or roof windows: count and size.
• Decoration: walls, ceiling, woodwork, after install.

A single lump sum that says "Loft conversion, £58,000" hides whether any of this is in or out. See how to read a builder's quote for the general format you should expect.

What is typically excluded#

Items that often quietly fall outside the headline price:

• Furniture, fitted wardrobes, blinds, curtains.
• Decoration outside the loft: making good on the stairwell paint, the floor below where the new stair was cut in, hallway disturbance.
• The en-suite, sometimes priced as a separate package of £6,000–£12,000.
• Party wall agreements, professional fees only.
• Soil-stack extension if the existing stack cannot serve a new bathroom.
• Upgrading the consumer unit if the existing one cannot take the new circuits.
• Smoke alarm rewire in the rest of the house, required by fire regs for the new storey.
• Asbestos survey or removal if the property is pre-2000 and the existing roof construction contains it.

For the broader pattern across trades, see hidden costs in builder quotes.

Red flags specific to loft conversions#

• No scaffolding duration stated. Scaffolding is hired by the week. A fixed-price quote needs to bound this; an open arrangement leaves it on you if the build runs over.
• A "structural allowance" with no engineer's calcs referenced. Steel costs depend on span and load. Without calcs the figure is a guess.
• No fire-regs items listed. New mains-wired smoke and heat alarms through the rest of the house, fire-rated doors on habitable rooms, and protected staircase routes are all required and all priced. Their absence is not a saving.
• The staircase position not shown on a drawing. Staircase position often dictates structural openings on the floor below. A loft quote without a clear staircase plan has not been costed properly.
• Provisional sums doing too much work. "PC sum for finishes, £8,000" with no spec means the contractor can substitute downwards or upwards, and the headline price is not a real price.
• Party wall not mentioned at all in a terrace or semi. Either the surveyor fees are excluded and not flagged, or the contractor is planning to skip the Act, which lands on you legally.

For the general pattern, see signs of a rogue builder and hidden costs in builder quotes.

Before you sign#

1. Is the headline price within the band for the type of conversion (Velux, dormer, hip-to-gable, mansard) you are actually getting?
2. Are the professional fees (architect, structural engineer, building control, party wall) clearly in or out, with numbers?
3. Is the build cost itemised down to scaffolding, steelwork, dormer, staircase, insulation, electrics, plumbing, and fire regs?
4. Is the scaffolding duration stated?
5. Is the staircase position on a drawing?
6. Is the en-suite priced in or noted as a separate package?

If three or more are unclear, the quote is not yet in a form where the price can be fairly judged. At £40,000 plus, that matters more than on any other domestic job.

The shortcut#

Running this check by hand means knowing scaffold rates, steelwork prices, loft staircase costs, and fire-regs requirements for your local authority. Check the Quote does that part for you: paste or upload your loft conversion quote and we check every line against current UK rates for your postcode, flag what sits above the fair range, and tell you what is missing. Your first check is free.