Loft Conversion: Where the Staircase Goes Decides the Whole Job

Most loft conversions are drawn from the top down. A bedroom, a bathroom, a rooflight, and then somebody works out how to get up there. It should be the other way round. The staircase decides the floor below as much as it decides the loft, and once it is fixed most of the other decisions follow.

This is how NU approaches a loft in a West London terrace, and the questions we settle before anyone draws a bed.

Is there enough headroom?

Roof height alone does not establish how useful the finished room will be. A measured section through the roof should test usable standing height, the floor build up, insulation and where the stair arrives. Two lofts with the same ridge height can produce very different rooms once the floor and the insulation are in.

Ask for that section before you ask for a price. It is the single drawing that tells you whether the loft is a bedroom or a store.

Where the staircase goes

Its location affects the floor below as well as the loft. Headroom over the stair, circulation on the landing, the room you lose to it, and the overall escape strategy all need to be considered before the bedrooms and bathrooms are fixed. Put the stair in the wrong place and you gain a room upstairs by spoiling one downstairs.

A loft conversion may also change stairs, ceilings, service routes and the fire strategy on the existing levels. Those changes belong in the scope and the programme from the start, not as extras discovered halfway through.

Dormer or mansard

A dormer and a mansard create roof accommodation in different ways and alter the external form differently. Choose the roof approach through design and planning review, not only by the nominal floor area gained. NU's 2026 cost guide puts a main dormer loft at £90,000 to £140,000 and a mansard loft at £140,000 to £220,000, construction only, before fees, party wall, contingency and VAT. Per square foot, a loft conversion in London is £250 to £300 to build.

The full breakdown of that band is in loft conversion costs in London. If the loft is one part of a bigger plan, how to extend a Victorian London home without destroying its character covers the rest of the house.

A bathroom in the loft, and the summer question

A loft bathroom is possible, but check hot and cold water, pressure, drainage falls, ventilation and structural loads alongside the room layout. Its position may have implications on the floors below. And plan for summer. A loft that is comfortable in July needs insulation, ventilation and shading decided at design stage, not a fan bought in a heatwave.

Architecture, interior design, project management and construction sit under one contract at NU, so the section, the stair and the price come from the same team.

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Thinking about this on your own house? Fill out the contact form or call 020 7731 6841 and let's get you booked in for a free call with Nick.