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10 Apr 2021
Loft Conversion Types: Which Suits Your Roof Space
Before you fall for photographs of a sleek glass box or a Parisian-style mansard, spend ten minutes in your loft with a torch and a tape measure. The conversion that suits your home depends on the roof structure you already have, the head height at the ridge, the position of the existing staircase, and how much space you are willing to lose below. Most UK lofts fall into three broad categories: a trussed roof with shallow pitch, a traditional cut roof with purlins and rafters, and a hipped roof where the slope runs down on three or four sides. Each points you towards a different design.
A dormer projects from the rear or side slope, creating a vertical wall for windows and a flat roof above. A typical rear dormer adds 2.2 to 2.4 metres of head height across the new floor — enough for a bedroom, bathroom or study. Because it sits within the existing roof plane, it often falls under permitted development, provided volume limits are not exceeded: usually 40 cubic metres for a terraced house and 50 cubic metres for a semi or detached. You will still need building regulations approval, and flats often have no permitted development rights.
The new staircase usually rises directly above the existing one, turning once at the top. That is efficient, but the stairwell dictates where the landing and bathroom can go. Structurally, a dormer is relatively straightforward: the builder removes part of the roof slope, cuts back rafters, and builds a new timber frame. Most lofts still need steel beams to support the new floor and carry loads where rafters have been removed. Older cut roofs may need extra strengthening to ceiling joists or a ridge beam.
If your roof slopes down on the side as well as the rear, you have a hipped roof. A hip-to-gable conversion replaces that sloping side with a vertical gable wall, extending the main roof to the side of the house. It is popular on semi-detached and end-of-terrace homes because it creates a full-height wall, often used for an en-suite or wardrobes. Head height is usually excellent — often the full height of the new gable — because you are no longer constrained by the inward slope. It can be combined with a rear dormer to form an L-shaped room.
Stair placement is similar to a dormer: most builders stack the new stair over the existing one, though the extra space sometimes allows the stair to move to the side. Structurally, this is a bigger job. You are building a new gable wall, which may need its own foundations, and the roof must be reworked with a steel frame. Party wall agreements are almost always required for semi-detached and terraced homes. Planning permission is more likely than with a simple rear dormer, especially if the gable faces a road or sits in a conservation area.
A mansard steepens the roof slope — usually to about 70 degrees — to create a nearly vertical wall, often on the front, rear, or both, with a flat section at the top. This is the classic Parisian look, and in UK cities it suits Victorian terraces where a dormer would be too small or the roof pitch is shallow. Head height is the best of the three: a mansard can create a full storey with 2.4 to 2.6 metres of ceiling height across the whole footprint.
Stair placement is flexible. Because the new floor is a complete storey, the staircase can often sit centrally or over the existing stair without awkward compromises. The trade-off is structural work. A mansard usually requires removing much of the existing roof, building a new steel frame, and sometimes rebuilding the top of the front or rear wall. Party wall agreements are standard, and planning permission is almost always needed, particularly in conservation areas. It is the most expensive option, but it can add the most usable space.
A dormer gives good head height in the centre and lower ceilings at the edges. A hip-to-gable gives a full-height wall on one side, ideal for showers, basins and storage. A mansard gives full head height across the whole floor, which is why it suits a principal bedroom or large bathroom. Stair placement is least disruptive in a dormer or hip-to-gable, where the new stair usually sits over the old one. A mansard gives more freedom but often requires more reconfiguration below.
Measure the head height at the ridge from the top of the ceiling joists. If you have less than 2.2 metres, a dormer or mansard may be needed to make the space usable. Trace the existing staircase and check whether the new stair can rise above it without clashing with a bedroom door or chimney breast. Look at your roof pitch: shallow roofs often suit a mansard, while steeper roofs take a dormer more easily. Check your title deeds and local planning policies, especially in a conservation area, listed building or flat. Finally, ask a structural engineer to survey the rafters, purlins and party wall before you commit. The roof space, not the brochure, should decide which type you choose.
Gm Building Design No rushing, no fuss — just thoughtful notes and practical help, written by people who care.
April 25, 2019 at 10:46 am
Take in the iconic skyline and visit the neighbourhood hangouts that you've only ever seen on TV. Take in the iconic skyline and visit the neighbourhood.
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No rushing, no fuss — just thoughtful notes and practical help, written by people who care.
Soldman Kell
April 25, 2019 at 10:46 am
Take in the iconic skyline and visit the neighbourhood hangouts that you've only ever seen on TV. Take in the iconic skyline and visit the neighbourhood.