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Home & garden.

Updated: 30 Jun 2021

Loft conversion costs

Find out how much you can expect to pay for your loft conversion and read our money-saving tips so you can get the best-value conversion.
Which?Editorial team
Attic under constuction 436692

Loft conversions can be a cost-effective way to add value and living space to your home, but they don't come cheap.

The cost of your loft conversion will vary depending on many factors. Some - such as the age of your house, the type of roof you have or the area you live in - are not within your control.

However, clever planning of other elements, such as where to position a bathroom, for instance, could save you a small fortune.

We've spoken to dozens of Which? members who have had their loft converted, as well as industry experts, to find out the inside track on loft conversions and money-saving tips.

How much will a loft conversion cost?

The cost of a loft extension predominantly depends on the type of conversion you have, where in the country you live, and whether you need planning permission. 

To help you work out what you might need to budget for a loft conversion, we've worked with the Royal Institution of Chartered Surveyors* (RICS) , which publishes average building work and repair costs, to bring you the average price of a loft conversion. 

The costs below are based on two different types of loft conversion:

  • a simple conversion that doesn't require the outer structure of the building to be altered
  • a more complex conversion with a dormer - an extension to the original loft space that protrudes from the slope of the roof. 

It also includes average costs for three different room sizes, for more than one dormer and for one, two or four windows in the roof, also known as skylights or rooflights.

Loft conversion costs table

Comprising clearing loft, relocating existing tanks, insulation, softwood framing and plasterboard to walls, insulation and plasterboard to ceiling, softwood floor, new straight-flight staircase, new electrics and heating, openings in roof for windows (excludes internal partitions, WC suite, vanity units, shower enclosure and electric shower)

Log in to unlock the table and to learn what factors you should watch out for and which could drive up the cost of your conversion, from experts and people who have had their loft converted.

If you're not a Which? member, joining Which? now will give you instant access to this and our insider tips page, where we reveal how you can avoid costly mistakes.

TypeFloor size (metres)Two windowsFour windows
With Velux or similar windows4 x 5
 6 x 5
 12 x 7
With dormer and Velux windows4 x 5 -
 6 x 5
 12 x 7

These costs include labour and materials. They also include clearing of materials from the loft space, relocating existing water tanks (if any), insulation of walls and ceiling, softwood framing (where wood is placed to make new structures), plasterboard on walls and ceiling, new straight flight of stairs, new electrics and heating.

The costs don't cover internal partition walls, a shower-room/bathroom or painting and final decoration.

RICS calculations

To arrive at these average prices, RICS uses cost data from its Building Cost Information Service (BCIS) database, where costs are collated from a variety of sources and analysed. 

Materials costs are based on the best trade prices from a range of suppliers across the UK, which are then benchmarked to reveal the best national average. Labour rates are based on the current Building and Allied Trades Joint Industrial Council wage agreement. RICS then uses this data in a standardised model of the average loft conversions. Prices correct October 2020.