Stand a tape measure from the top of the ceiling joist to the underside of the ridge. Get close to 2.3 metres and a straightforward rooflight conversion is realistic. Fall short of that and the honest choices are a dormer, lowering the ceilings on the floor below, or raising the roof itself, and each carries its own cost and disruption.
A traditional roof built with rafters and purlins gives you open space to work with, and converting it is comparatively straightforward. A modern trussed roof is built from prefabricated W shaped trusses that hold the roof up and cannot simply be cut out, so the whole structure needs replacing with steels or new rafters before any room can go in.
Permitted development allows a loft conversion without planning permission in most cases, up to 40 cubic metres on a terraced house and 50 cubic metres on a detached or semi detached house, with no material beyond the existing roof plane on the side facing the street and no balconies beyond a small Juliet balcony. Those rights disappear entirely in a conservation area or in an AONB. Bury St Edmunds has two conservation areas carrying Article 4 Directions, the Town Centre and Victoria Street, so a full planning application is often needed there. Even where permitted development applies, we recommend a lawful development certificate so there is no argument later.
A rooflight or Velux conversion works when the head height is already there. A dormer adds headroom and floor space to a sloping roof. Hip to gable squares off the end of a hipped roof, and an L-shaped dormer or mansard suits a Victorian terrace with a rear closet wing that gives you more room to build into.
Whatever the planning position, building regulations always apply. You need a protected escape route with fire doors, a staircase that meets the rules on pitch and headroom, floor joists strong enough to carry a bedroom load, and proper insulation. On a terraced or semi detached house, work on the party wall also needs a formal notice to your neighbour before it starts.
We start with a proper survey of the roof structure and the head height, and a straight conversation about whether the house sits in a conservation area. Once the paperwork is settled, scaffold goes up and tiles come off the section being worked on. Steels go in for a dormer or hip to gable, the new structure is made watertight, and only then does first fix wiring and plumbing start inside. Insulation goes in to current regulations, the staircase is built into the space that has been planned for it from day one, and building control signs off the structural work, the fire escape and the insulation before second fix and decoration finish the room.
Head height from ceiling joist to ridge underside, measured honestly before any plan gets drawn up.
Roof structure, cut roof or trussed roof, which changes the scope of the job completely.
Staircase position, because building regulations require one, and it very often decides where the whole conversion can go.
