Loft conversions: an essential guide to planning, designing and costing when converting your loft

A loft conversion is one of the easiest ways to extend – and add value to – your property, whether you’re dreaming of adding a master suite, a guest bedroom or a home cinema

Loft conversion: If you have space up top, use it to create extra rooms, or a stunning master suite
(Image credit: Clear Architects)

Loft conversions provide one of the best returns on investment you can get when it comes to extending, with experts suggesting they add the most value to your home in comparison to the cost. And, of course, they offer valuable extra living space, that's really flexible and versatile – you can use it as a master suite, an extra bedroom, a space for kids to hang out or even a gym, home office or home cinema. 

Plus, since most loft conversions are generally allowed under permitted development rights, there’s no need to go through the lengthy process of obtaining planning permission. 

Another bonus? You'll get the extra room you need, without having to sacrifice garden space, as is the case a conventional rear or side extension. 

Find out all you need to know about converting your loft in this three page feature, and check our guide to extending a house for more practical advice and inspiration.

How much will a loft conversion cost?

Loft conversion costs will vary depending on size, whether you'll need to alter its structure for staircase access, the type of conversion you're going for and where you live in the country, but as an average, loft conversion will usually cost between £30,000 and £50,000

To break loft conversion costs down further, identify the type you are going for:

A basic, room in the roof conversion: the simplest of loft conversions, usually involving floor reinforcement, skylight(s), insulation, a staircase, electrics, lighting and heating plus fire safety measures can start from around £15,000 (or around £1,150-£1,350 per square metre). 

A dormer loft extension: including all the provisions above, plus a dormer window. This might be your next best option if the basic rooflight conversion doesn't offer enough head height or floor space. Expect to pay from £20,000 for a basic conversion; for the inclusion of an en suite and a finish suited to a master suite, you're more likely to pay £35,000 upwards (or around £1,250-£1,450 per square metre).

A mansard extension (see page two for more on this roof type): expect to pay £35,000 to £45,000 upwards (from £1,500-£2,500 per square metre).

A hip-to-gable extension (see page two for more on this roof type): expect to pay £25,000 to £30,000 upwards (costs range from £1,500-£2,500 per square metre).

Ready-made loft conversions, made off-site and craned into position are quick and will reduce labour costs, which can be beneficial if you live in an area where labour costs are highter. Expect to pay around £55,000.

A conversion that requires change of roof structure: this is obviously the most costly of options, since removing and rebuilding the roof will require an experienced designer and increase labour and material costs. This type of conversion is likely to cost upwards of £40,000 (or from £1,350-£1,550 per square metre).

You can find a more accurate estimation for your loft conversion with the help of our extension cost calculator.

bed in a converted chapel with storage built around it

(Image credit: Chris Humphreys)

Loft conversion costs: planning and professional fees

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Loft extensions can usually be completed under permitted development rights, but it is worth obtaining a Certificate of Lawfulness (£86) from your local council for the work. 

Should planning be required, expect planning permission fees (£172); these may be included in your agreed contract with the loft company, but do check. 

If you live in an attached house, you will need a party wall agreement with your neighbour(s). These typically costs from £700 to £1,000 per neighbour.

Building control fees (around £500, plus VAT) are also payable by the homeowner to the local authority or a government-approved, independent inspection company, to check that the work is as contracted and to issue building regulation certificates to prove that it has been carried out in accordance.

Find out more about planning permission, permitted development, party wall agreements and building regulations on page two.

You’ll find small companies will usually charge 10-15 per cent less than large companies.

Home office storage with blue cupboards and open shelves

(Image credit: Neville Johnson)

Loft conversion costs: design fees

It's likely that design fees are included within your loft company's quote, but if you've appointed an architect to design your loft conversion, expect design fees from three to seven per cent of the construction cost, with a minimum of around £2,700 to £4,000 for the planning drawings, with construction drawings costing a similar. If you need a structural engineer to size roof joists, budget for £500 to £1,000.

If you have asked your architect to put the contract out to tender, appoint the builder and administer the contract, budget for a further three to seven per cent of the build cost. Or, you can agree a day or hourly rate for ad hoc site attendance.

The interior fittings of your loft extension will usually include the basics: sanitaryware; electric points and basic light fittings; door and window furniture; skirting and woodwork; possibly flooring. The price may also include basic decoration – often an all-over spray-paint with a white finish for walls and woodwork. For anything extra, you will need to ask for quotes on top of the original price.

How much is a loft conversion – and what should you spend?

Given that a loft extension costs upwards of £30,000 (but often much more, particularly in large cities and in larger properties), there is a limit to how much you should spend on your loft conversion. 

If you plan on eventually selling the house, you will need to consider the ceiling price of your street – an estate agent can advise on this. Essentially, you want the value of your house to increase by at least the cost of your entire loft conversion, but by spending too much, you may over-value your own house, making it difficult to sell for an appropriate profit.

Comparing the quoted cost of your loft conversion, plus the value of your home, with the cost of moving to a larger house in the same area is a worthwhile practice in assessing the benefits of converting the space.

For example:

Your house is valued at £270,000.

The loft conversion costs £50,000, making the projected cost of the home £320,000.

However, the ceiling price of your street is £300,000, making it impossible to recoup the £20,000 excess spent on a loft conversion.

If there is a house in your area with the space you require for less than £320,000, it is worth considering a move, rather than investing in the loft conversion.

Planning a loft conversion >>

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