Planning a loft conversion: what to know

Most lofts can be converted. What varies is the type, the cost and the disruption, and all three are decided by the roof you already have rather than by what you would like.

Which loft conversion suits your roof, the head height you actually need, and the approvals involved. Most lofts can be converted, but the type and the cost are decided by the roof you already have.

The four types, and which roof suits them

A rooflight conversion keeps the roof shape and simply adds windows, which makes it the cheapest and most likely to be permitted development. A dormer extends outwards at the rear to create full-height space. Hip-to-gable squares off a sloping side, which suits semi-detached and end-of-terrace houses. A mansard reshapes the roof almost entirely and usually needs full planning permission.

Your existing roof, not your budget, usually decides which of these is realistic.

Head height, and what eats it

Measure from the top of the existing ceiling joists to the underside of the ridge, in several places, because roofs are rarely uniform. Around 2.2m is the practical benchmark for a comfortable conversion.

• Insulation and the new floor structure can take 200 to 300mm before you start
• Trussed roofs need structural work before any usable space appears
• Water tanks, chimney breasts and old services often have to move
• Dormers and hip-to-gable changes buy height where the ridge is tight

The staircase problem

Stairs are where loft budgets break. Building Regulations require 2m of headroom over the flight, relaxed to 1.9m at the centre and 1.8m at the edge where the ceiling slopes, with a maximum pitch of 42 degrees.

Finding that space almost always means taking a slice from a room below. It is a design decision worth making on a drawing rather than discovering once the roof is open.

Do you need planning permission?

Many rear dormers are permitted development within volume limits of 40 cubic metres on a terraced house and 50 on others, provided the roof shape at the front is unchanged. Front dormers, terraced properties in conservation areas and mansards generally need a full application.

Fire escape and Building Regulations

A loft conversion creates a new storey, which changes the fire strategy for the whole house. Expect a protected stairway, fire doors to habitable rooms off it, mains-wired interlinked alarms and an escape window.

This is not optional and it affects rooms you were not planning to touch, which is why the technical set matters as much as the planning drawings.

Value against cost

Loft conversions are consistently among the strongest returns in UK home improvement, typically adding a bedroom without losing garden. The margin comes from getting the structure and the staircase right first time, rather than redesigning halfway through a build.

Where we come in

We confirm which route applies to your property in writing, free, prepare the drawings, and handle the application with the council. See loft conversion drawings, or get your drawings quoted with no obligation. If any application we submit is refused, you get a 100% refund within 5 days.