Search for loft conversion prices and you will find figures that differ by tens of thousands of pounds. That is not because anyone is wrong: the cost of a loft conversion depends on your roof, your house and what you want the new space to do. This guide explains what moves the price so you can judge a quote sensibly. We do not publish a headline price because no honest figure applies to every home.
What drives the cost
- The type of conversion. A rooflight conversion that keeps the existing roof shape is generally simpler than a rear dormer, a hip-to-gable or a mansard, which change the roof structure.
- Size and headroom. More floor area costs more, and limited headroom may push you towards a conversion that alters the roof.
- Structure. Floors that were never designed to be lived above often need strengthening, and steel or timber beams add cost.
- The staircase. Where the new stairs go, and what has to change on the floors below to fit them, can affect more of the house than people expect.
- Bathrooms and services. An en-suite adds plumbing, drainage and ventilation. New heating and electrics add to the work.
- Windows and finishes. Roof windows, dormer windows, flooring, joinery and decoration all vary with the specification you choose.
- Access and logistics. Narrow streets, limited parking and scaffold or skip licences can add time and cost, particularly in dense parts of London.
Costs that may sit outside the builder’s quote
- Design and drawings from an architect or designer.
- A structural engineer’s calculations, which Building Regulations approval normally needs.
- Planning or lawful development certificate fees, where they apply.
- Building control fees, and party wall surveyors’ fees if a neighbour dissents from a party wall notice.
- VAT. Alterations to an existing home are generally standard-rated, but confirm the position for your project with an accountant.
How to compare quotes like for like
- Give every builder the same drawings and specification, so they are pricing the same job.
- Ask for the quote in writing and itemised, with what is included and what is not.
- Look for provisional sums, which are allowances rather than fixed prices, and ask what they cover and how they are settled.
- Check how variations are handled and when payments fall due.
- Be cautious of a quote that is far below the others. Ask what has been left out before you assume it is a bargain.
Allow for the unexpected
Opening up a roof and floor can reveal things nobody could see beforehand. Many advisers suggest holding back a contingency sum, and a good builder will tell you early if something will affect cost or timing.
This guide is general information for homes in England and is not legal or planning advice. Rules can change and differ between properties and local authorities, so always confirm the position with your council or a qualified professional.
To see how the work is organised, read about our loft conversion service, or request a quote and we will give you a written price once we have looked at the work.