Loft Conversion Cost Calculator
Thinking of extending upwards? Estimate the total cost of a loft conversion in the UK based on the type of roof alteration, finish, and professional fees.
Property Specs
Roughly £2,332 per square metre
A Guide to Loft Conversions
Moving house in the UK has become incredibly expensive. Between stamp duty, estate agent fees, and legal costs, you can easily spend £20,000+ just on the act of moving. That is why extending your current home with a loft conversion is often the smartest financial decision you can make. It unlocks dead space, gives you an exceptional master suite or home office, and significantly increases your property value.
Understanding the Hidden Costs
When builders quote for a loft conversion, their initial figure often excludes vital elements that you are legally required to pay for. Our calculator includes these to give you a realistic final bill.
- Professional Fees: You must hire a structural engineer to ensure the new floor joists and roof alterations are safe. You also need architectural drawings, even for permitted development. (Usually 10% of build cost).
- Building Control: The local council or a private inspector must sign off the work to prove it complies with fire safety and insulation regulations. This costs around £700-£1000.
- Party Wall Agreements: If you share a wall with a neighbour (semi-detached or terraced), you must serve them notice. If they dissent, you pay for their surveyors too (£1,000 - £2,000+).
The 4 Main Types of Loft Conversion
1. Roof Light / Velux Conversion
The most cost-effective solution. You don't alter the shape of the roof; instead, you add skylight windows to the existing slant. This relies entirely on you already having adequate head height in the centre of your loft (at least 2.2m from floor joist to ridge board). Best for adding a simple home office or small spare room.
2. Dormer Conversion
The undisputed most popular choice in the UK. A dormant extends horizontally out of the existing roof slant, creating a box-like structure. This instantly gives you vertical walls and a flat ceiling, massively increasing the usable floor space and head height. You can usually fit a large master bedroom and an en-suite inside a dormer.
3. Hip-to-Gable Conversion
Common on semi-detached houses with a hipped roof (a roof that slopes down on the side as well as the front and back). This conversion involves extending the sloping side wall straight up to form a vertical 'gable' end. This is a massive structural alteration but completely opens up the stairwell and loft space.
4. Mansard Conversion
Often seen in central London and on terraced houses. A mansard essentially replaces one entire side of your roof (usually the rear) with an almost vertical wall (sloping at 72 degrees) and a flat roof across the top. It provides the maximum amount of space possible, practically building a whole new storey, but almost always requires planning permission and is the most expensive option.