Pricing a loft conversion: what to measure and what to allow

Lofts are the job where the money hides above the ceiling line. The floor area looks small, the client's expectations look simple, and then the steels, the stairs and the fire regulations arrive. Here is how to price one so the number survives contact with the building.

Start with the type, because the type sets the price band

Before any measuring, name what kind of conversion this is, because the four common types carry very different cost and complexity:

A client saying "loft conversion" without a type is like a client saying "car". Pin the type down first; everything else in the price hangs off it. Head height decides much of it for you: if the existing ridge gives less than about 2.2 metres clear, a rooflight conversion is off the table and the job climbs the ladder above.

What to measure, in order

With the type fixed, the take-off for a loft is mercifully short but unforgiving. Miss one of these and the price is fiction:

• Clear head height at the ridge and, more usefully, the floor area with 2 metres or more of headroom, because that is the space the client is actually buying.
• Floor area of the new rooms, plus the new floor structure area, which is usually the whole loft footprint, not just the habitable part.
• Dormer dimensions: face area, cheeks, flat roof area, and the length of the junction with the existing roof, which is where the leadwork and the leaks live.
• Roof areas being re-covered, re-felted or insulated, measured on the slope, never off the plan.
• The stair route: where it lands, what it displaces below, and whether a landing window or wall move comes with it.
• Openings: rooflights, dormer windows, and any en-suite that brings soil pipe runs with it.

Measure the stair route on site, physically, with a tape. Drawings are optimistic about stairs more than about anything else, and a stair that steals a chunk of the bedroom below is a scope conversation you want before you price, not after.

The structure hides the money

The single biggest pricing error on lofts is treating the floor as a floor. Existing ceiling joists are almost never adequate to carry a habitable room, so the job includes a new independent floor structure, typically new joists spanning between steels, and the steels themselves, craned or manhandled in, with padstones and connection details from a structural engineer.

Price the engineer's involvement, the steel supply and the installation as their own lines, and read our guide to pricing structural steel on domestic jobs before you rate them. Then remember what surrounds the steel: opening up, temporary propping, and making good ceilings below that crack when the structure goes in. Many firms allow a making-good line for the floor below as a matter of course.

Stairs, fire and the regulation lines people forget

A loft conversion legally changes the house from two storeys to three, and Building Regulations respond accordingly. These items are often missing from cheap loft quotes, and they are not optional:

• A protected stair enclosure, usually meaning fire-rated doors (FD20 or better in practice) along the escape route, sometimes new partitions.
• Mains-interlinked smoke detection on every storey.
• Fire-rated construction in the new floor and any new partitions.
• Escape windows to the new rooms where the design relies on them.
• Insulation to current standards in the slope, dormer and any new gable, which eats more depth and money than most people allow.

Add the professional fees around the work: structural engineer, building control, and a party wall process on any terrace or semi where steels bear on the shared wall. If party wall notices are needed, the programme and the neighbourly goodwill both need managing, and the scaffold on the boundary side needs pricing with care.

Pulling the price together

With quantities in hand, the build-up is the standard one: rate each element from labour, materials and plant; add preliminaries, and note that loft prelims are heavier than the floor area suggests, because scaffold, a possible crane day and beefed-up waste handling all belong there; add contingency for the roof condition you will only truly know once it is opened, with 10 percent being a common allowance on older roofs; then overheads and profit, deliberately.

Sanity check the total against local going rates for the conversion type, and against the simple question of weeks on site times your weekly cost. If you want the arithmetic done for you, QS Quoter builds the full measured bill for a loft conversion, steels, dormer junctions, fire doors and all, from your description or the architect's drawings, priced at your own rates with every line editable. The workflow turns document assembly into a focused review, while the judgement stays with you.