Ask five builders what a loft conversion costs and you will get five different answers. Ask five homeowners and the spread gets wider still. Round numbers are still useful, though. £30,000, £50,000 and £70,000 are the three budgets people most often arrive with, and each one buys something noticeably different: in space, in specification, and in how much awkward structural work the job can absorb.

What every loft conversion pays for first

A sizeable chunk of any quote goes on work you will never see. Strengthening the floor joists, adding steel where a wall is coming out, forming a proper stair opening, running a compliant staircase, upgrading the smoke alarm system, insulating to current standards, and getting building control to sign it off — none of that is optional, and none of it shrinks just because you have chosen a cheaper bathroom.

Head height is the first thing to check. You generally want roughly 2.2 metres of clear height at the top of the stairs, and if the existing roof pitch is shallow you may need a dormer or a full roof alteration to get it. Older houses with traditional cut roofs are usually easier to convert than newer ones built with factory-made trussed rafters, which often need cutting and re-supporting with structural calculations. The cheapest staircase is the one that sits directly above the existing one. Move it, and you are often sacrificing part of a first-floor bedroom to make the whole thing work.

£30,000: a rooflight conversion, done properly

This budget is the classic rooflight conversion — sometimes called a Velux conversion. The roofline does not change: windows go into the existing slope, and the usable floor area is more or less the footprint you already have. It is the most cost-effective way to add habitable space, provided the bones of the house co-operate.

Realistically, you are looking at one good-sized bedroom, study or playroom. A small shower room can sometimes be squeezed in if a soil pipe is within reasonable reach, but that is not guaranteed at this price. In lower-cost parts of the UK, £30,000 can cover a tidy rooflight conversion including a modest en-suite. In London and much of the South East, it is tight and may not stretch past a straightforward room with rooflights. If your roof needs raising, or the stairs need rethinking, this is not the budget for it.

£50,000: the rear dormer and a real bedroom

The rear dormer is the workhorse of British loft conversions. It adds genuine floor area, gives you full-height headroom across most of the new room, and allows for proper windows rather than just roof windows. At this level you can usually expect a comfortable double bedroom with an en-suite, finished to a decent standard.

Typical specification at £50,000 might include uPVC or mid-range aluminium windows, a well-made bathroom with branded fittings, engineered flooring, a plastered and painted finish, and reasonable lighting design. A few extras often slip in too: built-in wardrobes, a desk nook under the eaves, better-than-basic insulation for a quieter room.

Where this budget gets squeezed is in the awkward details. An L-shaped or wrap-around dormer costs more than a simple rectangular one. Moving a boiler or hot water cylinder, running a new soil stack, or dealing with a chimney breast in the wrong place all eat into the figure. The same £50,000 will go considerably further in Newcastle than it will in Surrey.

£70,000: bigger footprints and difficult roofs

At this level you are usually paying for complexity as much as for space. Hip-to-gable conversions, L-shaped dormers and mansard roof alterations all involve far more structural work than a simple rear dormer, and mansards in particular tend to come with leadwork, bespoke joinery and planning involvement.

What £70,000 typically buys is two rooms and a bathroom, or one large principal bedroom with an en-suite and dressing area. It also opens up a higher specification: underfloor heating, a mix of rooflights and dormer windows, bespoke cabinetry, higher-end sanitaryware, and sometimes mechanical ventilation or air conditioning for a room that gets hot in summer.

Even a generous budget can be swallowed by a listed building, a conservation area, or an Article 4 direction that removes your permitted development rights. Check planning constraints before you fall in love with a design.

VAT, fees and the costs that surprise people

Most loft conversions are standard-rated for VAT at 20%, and builders’ quotes are not always clear about whether VAT is included. A quote of £50,000 could mean £60,000 by the time it is paid. There are reduced rates in specific circumstances — for example, renovating a property that has stood empty for a long period — but the rules are narrow and specific, so confirm your position with an accountant or with HMRC rather than assuming.

Beyond the headline figure, these are the items that most often push a project over budget:

  • Structural engineer’s calculations, steel beams and roof alterations
  • Party wall notices, plus the neighbour’s surveyor’s fees if they appoint one
  • Planning application fees where permitted development does not cover the design
  • Building control fees and the final completion certificate
  • Scaffolding, skips and waste removal — scaffolding hire often runs longer than planned
  • Electrical work, a possible consumer unit upgrade and certification
  • Plumbing: a new soil stack, or relocating a boiler or cylinder
  • Deeper insulation and ventilation to meet current standards
  • Plastering, decoration, flooring and the furniture the new room demands
  • A contingency of at least 10–15% held back for the unexpected

If your builder is not VAT-registered, you will not pay VAT on their labour, but they also cannot reclaim VAT on materials, so the saving is rarely as large as it first appears.

Why identical budgets behave differently across the UK

Regional labour rates are the obvious factor, but they are not the only one. Access matters: a terraced house with a shared alley is harder to scaffold than a detached property with a driveway. Local housing stock matters too, since Victorian and Edwardian terraces often convert more easily than newer homes with shallow trussed roofs. Where quotes differ wildly, the reason is usually exclusions rather than day rates. One builder may have priced the electrics, the skip and the building control fees; another may have left all three for you to arrange.

Setting a budget you can actually live with

Start by deciding what the room is for, then get three itemised quotes against exactly the same specification. Ask each builder what is excluded, who handles building control, how long scaffolding will be up, and how variations are priced.

  1. Fix your specification before you ask for prices, not after.
  2. Compare like for like, line by line, including VAT.
  3. Hold back 10–15% of the total as contingency, and treat it as spent.
  4. Agree any changes in writing before the work starts.

It also pays to check your mortgage lender’s position, confirm your buildings insurance covers the works, and take proper advice on the contract you are signing. A conversion is a significant financial commitment, and the paperwork is worth getting right before the scaffolding arrives.

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