Loft Conversion Cost Calculator
Find out what a loft conversion would cost for your property. Choose your conversion type, floor area, and extras, and we will give you a full breakdown including professional fees and an estimate of the value it could add to your home. No email needed.
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How this calculator works
Our loft conversion calculator estimates the total project cost based on your conversion type (Velux, rear dormer, hip-to-gable, L-shaped dormer, or mansard), the usable floor area, and whether you want to include extras like an en suite bathroom, staircase upgrade, or additional windows. Each conversion type has a different cost per square metre reflecting the structural work involved.
The tool also calculates professional fees separately, including architect or designer costs, structural engineer fees, Building Regulations, and planning permission where applicable. It provides an estimate of the value the conversion could add to your property, based on typical UK property uplift percentages for each conversion type.
Loft conversion costs depend heavily on your existing roof structure, head height, and the condition of the property. These estimates are a reliable starting point for budgeting, but your actual cost will be influenced by factors like access, the need for steel beams, and the complexity of the staircase installation. Get at least three quotes from specialist loft conversion companies before committing.
Common questions
How much does a loft conversion cost in the UK in 2026?
A loft conversion costs between £22,000 and £80,000 in 2026, depending on the type. A simple Velux conversion starts at around £22,000, a rear dormer costs £32,000 to £55,000, and a mansard conversion can reach £80,000. Prices vary by region - London is typically 20% more expensive than the Midlands.
Do I need planning permission for a loft conversion?
Most Velux and rear dormer conversions on houses fall under permitted development, so planning permission is not required. However, hip-to-gable, L-shaped dormer, and mansard conversions usually need planning permission because they change the roofline. Properties in conservation areas, listed buildings, and flats always need planning permission. Building Regulations approval is required for all loft conversions.
How long does a loft conversion take?
A Velux conversion takes 5 to 7 weeks, a rear dormer takes 8 to 12 weeks, and more complex conversions like mansard or hip-to-gable take 10 to 16 weeks. Allow an additional 4 to 12 weeks beforehand for planning permission (if needed) and Building Regulations approval.
Does a loft conversion add value to your home?
Yes. A loft conversion typically adds 10 to 25% to a property's value, depending on the type. A rear dormer adding a bedroom and en suite can increase a £290,000 home's value by £43,000 to £58,000. Conversions that add a full extra bedroom with a bathroom tend to deliver the best return on investment.
What is the cheapest type of loft conversion?
A Velux (rooflight) conversion is the cheapest at £22,000 to £38,000. It involves fitting roof windows without changing the roof shape, so there is no need for structural alterations to the exterior. The main limitation is that usable floor space depends on the existing roof height and pitch - you need at least 2.2 metres of head height at the ridge.