Interactive calculator with real prices adjusted by UK region. Select your scope, pick your region, get your instant estimate.
1. Choose Scope of Work
2. Select Your Region
What Affects the Cost?
Type of conversion
Roof structure and height
Staircase design
En-suite bathroom
Insulation and fire safety
Planning permission requirements
Party wall agreements
Frequently Asked Questions
How much does a loft conversion cost UK 2026?
A loft conversion costs £18,000-£70,000+ depending on type. Velux conversions start at £18,000-£30,000. Dormer conversions cost £30,000-£55,000. Mansard conversions cost £45,000-£70,000.
Do I need planning permission for a loft conversion?
Most loft conversions fall under permitted development and do not need planning permission. However, mansard conversions, conversions in conservation areas, or those exceeding 40-50 cubic metres usually require planning approval.
How much value does a loft conversion add?
A loft conversion typically adds 20-25% to your property value. On a £300,000 home, that is £60,000-£75,000 — often more than the cost of the conversion itself.