Loft conversion cost calculator: what the job involves and who is registered to do it, and what a cost of loft conversion calculator can and cannot tell you before anyone has seen the roof

How loft conversion cost calculator works

1. Settle whether it is permitted development. A great many loft conversion are permitted development, which means no planning application, but the limits on depth, height, materials and how much of the plot is already built on are specific and a designer should read them against your own house before anybody prices anything.
2. Get drawings and a structural design. Existing and proposed drawings, then a structural engineer's calculations for whatever is being opened up or carried. On a loft conversion this is a small share of the total and it is what turns an idea into something three builders can price identically.
3. Serve the party wall notices in time. Work on or near a shared wall, or excavation within three or six metres of a neighbour's foundations, engages the Party Wall etc. Act and the notice periods are set in months rather than weeks. Serving late is the commonest reason a start date slips.
4. Price it against a specification, not a sketch. Ask each builder to price the same written specification, with provisional sums shown as provisional sums. Two quotes that differ by a third almost always differ in what is included: the kitchen, the flooring, the decoration and the drainage diversion are the usual absentees.
5. Agree stages, retention and building control. A staged payment schedule against completed work, a small retention until sign-off, and a clear statement of who is notifying building control. The completion certificate is what a future buyer's solicitor will ask for.

Insurance and paperwork

Common questions

What area should I measure?

The usable floor area of the finished room, not the footprint of the roof. Space under a low slope does not count as usable, and the difference between those two numbers is exactly what a dormer buys you.

Why does the type change the rate so much?

Because each type adds structure. A rooflight conversion adds none, a dormer adds a framed box with its own roof and walls, a hip to gable rebuilds a wall in masonry, and a mansard is close to rebuilding the roof. The rate follows the structure.

What fixed lines should I add?

Drawings, structural calculations, building control, party wall surveyor fees where notices are served, scaffolding, waste, and the staircase. On a small conversion those are a large share of the total.

Registered contractors by region

• Registered roofers in the East Midlands postcode area
• Registered roofers in the East of England postcode area
• Registered roofers in the London postcode area
• Registered roofers in the North East postcode area
• Registered roofers in the North West postcode area
• Registered roofers in the Scotland postcode area
• Registered roofers in the South East postcode area
• Registered roofers in the South West postcode area
• Registered roofers in the Wales postcode area
• Registered roofers in the West Midlands postcode area
• Registered roofers in the Yorkshire and The Humber postcode area