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.
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:
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.
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)
Floor size (metres)
With Velux or similar windows
4 x 5
6 x 5
12 x 7
With dormer and Velux windows
4 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.
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.