Loft conversion staircase and headroom

Most loft conversions are drawn from the top down. A bedroom, a bathroom, a rooflight. 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. Once it is fixed, most of the other decisions follow.

This is how NU approaches a loft in a West London terrace. These are 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. It should also test the floor build up, insulation and where the stair arrives. Two lofts with the same ridge height can produce very different rooms. The difference shows once the floor and the insulation are in.

Ask for that section before you ask for a price. This single drawing 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 and circulation on the landing need to be considered. So do the room you lose to it and the overall escape strategy. All of this comes before the bedrooms and bathrooms are fixed. Put the stair in the wrong place. You gain a room upstairs by spoiling one downstairs.

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

Dormer or mansard

A dormer and a mansard create roof accommodation in different ways. They also alter the external form differently. Choose the roof approach through design and planning review. Do not choose only by the nominal floor area gained. NU’s 2026 cost guide puts a main dormer loft at £90,000 to £140,000. It puts a mansard loft at £140,000 to £220,000. These figures are construction only, before fees, party wall, contingency and VAT. The per square foot bands, by tier, are published in the build cost calculator.

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

A bathroom in the loft, and the summer question

A loft bathroom is possible. Check hot and cold water, pressure and drainage falls. Also check 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 three things decided at design stage. They are insulation, ventilation and shading. It does not need 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.

Thinking about this on your own house? Fill out the contact form or call 020 7731 6841. We will then book a call with Nick.