The short answer
Loft conversion cost depends mostly on how much the roof has to change. A rooflight conversion, which works within the existing roof, changes the least. A rear dormer adds a box-shaped extension to one slope and is the most common choice because it gains a lot of headroom. A hip to gable conversion rebuilds a sloping side of the roof as a vertical gable wall, and is often combined with a rear dormer for the most space. Our cost calculator gives a starting range per square metre, and estimates are free after a site visit.
Cost of a loft conversion with a dormer
A dormer needs new roof framing, a flat or pitched dormer roof, cladding or tiling on the face and cheeks, windows and new structure to carry the floor. Full-width rear dormers cost more than small dormers but add far more usable space. A dormer finished in tiles or brick slips to match the house costs more than one clad in a simpler material, and conservation areas may require the matching finish.
Hip to gable loft conversion cost
On a hipped roof, the sloping end leaves little room inside. Rebuilding it as a gable means building a new end wall up from the existing wall, usually in brick or block to match the house, and extending the ridge and roof covering. That brickwork, the scaffold to reach it and the roof work make hip to gable conversions more expensive than a simple rear dormer, but they often turn a loft that was too cramped into a full floor.
Cost of a loft conversion without a dormer
Where the roof is already tall enough, a rooflight conversion keeps the outline of the house the same. It needs a new floor, insulation, rooflights, stairs and finishes but no change to the roof shape, so it is usually the most affordable type. It suits steep roofs and houses where planning restrictions make dormers difficult.
Structure, steel and the floor
Existing ceiling joists are not designed to be a floor. New floor joists are added, often supported on steel beams sized by a structural engineer, and roof timbers that are removed to open the space are replaced with new supports. The amount of steel depends on the roof design and spans, and it is one of the bigger structural costs.
Stairs, ensuite and services
A loft conversion needs a proper staircase, and finding room for it on the floor below can mean losing part of a bedroom or the landing. Adding an ensuite or shower room raises the cost through plumbing, waste pipes and finishes, and the price depends on how far it is from existing pipework. Heating, electrics and lighting are needed in every case.
Building Regulations, planning and party walls
Every loft conversion needs Building Regulations approval, covering structure, insulation, fire safety and escape, including fire doors on the stairs below. Many dormer and hip to gable conversions fall under permitted development, but conservation areas, Article 4 directions and front-facing dormers need planning permission. Semi-detached and terraced homes usually need party wall agreements. Drawings, engineer's calculations and fees all form part of the budget.
Loft conversion and a new roof
If the roof covering is near the end of its life, re-roofing at the same time as the conversion saves scaffolding twice. The extra cost is the roof covering itself, but the access is already paid for.
About us
D & A Brickwork & Building is a family-run firm based in Bidwell, Dunstable, with more than 26 years of building experience. We are FMB members and fully insured, and we give free estimates after a site visit.
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Questions people ask
How much does a loft conversion cost in the UK?
It depends on the type, the roof structure, steelwork, stairs and whether an ensuite is included. Use our cost calculator for a starting range, then get a free estimate.
How much does a loft conversion cost?
Rooflight conversions are usually the most affordable, rear dormers next, and hip to gable conversions, often combined with a dormer, the most involved.
Does a loft conversion need an architect?
You need drawings for Building Regulations and, where required, planning, plus structural calculations. These can come from an architect or a designer.
Is a dormer loft conversion worth it?
For most houses a rear dormer gives the most usable floor space for the work involved, which is why it is the most common type.