The short answer
A rooflight loft conversion, often called a Velux conversion after one of the best-known window makers, turns the loft into a room without changing the shape of the roof. Windows are fitted into the existing roof slopes, a new floor is laid, the roof is insulated and a proper staircase is added. It is usually the least disruptive type of loft conversion, but it only works when the loft already has enough height and a reasonably steep roof pitch.
Is there enough headroom?
The key measurement is from the top of the existing ceiling joists to the underside of the ridge. The new floor structure and insulation will take some of that height, and the room still needs comfortable standing space in the middle and over the stairs. Shallow roofs, common on many modern houses, often do not have enough height for a rooflight conversion, and a dormer or raising the roof becomes the realistic option.
Planning and Building Regulations
Because the roof shape does not change, rooflight conversions often fall within permitted development, provided the windows do not project too far above the roof plane and the house is not in a conservation area or otherwise restricted. Building Regulations approval is always needed, covering the floor structure, fire safety and escape, the staircase, insulation and ventilation.
The staircase and fire safety
The stairs are often the hardest part of the design. They need enough headroom and a safe pitch, and they take space from the floor below, usually from a bedroom or the landing. On a typical two-storey house, the stairway must also be protected so people can escape in a fire, which usually means fire-rated doors to the rooms off the stairs and linked smoke alarms.
Floor, insulation and windows
Existing ceiling joists were designed to hold up plaster, not people, so new floor joists are normally added alongside them, sometimes with a steel beam where the span is large. The roof is insulated between and under the rafters while keeping a ventilation gap where needed. Rooflights are placed to suit the room layout, with at least one large enough for escape where required, and blinds help with summer heat on sunny slopes.
Rooflight or dormer?
A rooflight conversion keeps the roof shape and is quicker and less disruptive, but the usable floor area is limited by the slope. A dormer adds a box-shaped section with vertical walls, creating much more standing room and space for a bathroom, at the cost of more structural work and a bigger visual change. Some conversions mix the two, with a dormer at the back and rooflights at the front.
Common mistakes
Measuring headroom from the loft floor boards rather than the top of the joists. Leaving the stair position until late. Forgetting the fire-safety upgrade to the floors below. Placing rooflights where they look neat from outside but give awkward head height inside.
About us
D & A Brickwork & Building is a family-run firm based in Bidwell, Dunstable, with more than 26 years of building experience. Our bricklaying is NVQ Level 2 qualified, we are Federation of Master Builders members and fully insured, and estimates are free after a visit.
Loft conversions are part of the conversion work we carry out alongside garage and outbuilding conversions.
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Questions people ask
What is a Velux loft conversion?
It is a loft conversion that uses windows set into the existing roof slope instead of changing the roof shape. Velux is a brand name that has become shorthand for rooflights.
Do I need planning permission for a rooflight conversion?
Often not, as the roof shape stays the same, but limits apply and conservation areas are different. Building Regulations approval is always required.
How much headroom do I need?
It depends on the roof, but there must be comfortable standing height once the new floor and insulation are in. Measure from the top of the ceiling joists to the ridge and have the design checked.
Is a rooflight conversion cheaper than a dormer?
It usually involves less structural work, but the cost depends on the house. A dormer gives more usable space, so compare what each option gives you, not just the build.