If you can raise a larger budget, you can afford to undertake a more substantial loft conversion, a double garage or a cellar conversion, or add a large single-storey, or a small two-storey, extensions to your home.

Five cost effective extension ideas

1. Orangery-style extensions

A traditional-style option, designed to be in keeping with a period house and measuring 30m², would cost £1,250-1,450 per m² depending on location. A room measuring 4x7m would be ideal for a dining or sitting room and, in many instances, would fall within permitted development rights and so not require planning permission.


Thinking of extending? Find out whether you’ll need planning permission using our FREE, interactive tool. Simply select your house type, the kind of extension you’d like, and get an instant result. Click here to try it out.


2. Garage conversions

An attached double garage measuring 28m² could be turned into extra living space at a basic cost of £850-1,050 per m². To then integrate this space into the existing house by removing the partition wall – replacing it with an RSJ – add £4-5,000 to the cost.

If the space were to become a new kitchen, the cost of new units must also be added at around £5,000 upwards, depending on the kitchen supplier chosen. Your permitted development rights mean a garage conversion will not usually require planning permission, but it must comply with Building Regs as the project would constitute a ‘material change of use’.


3. Cellar conversions

An existing cellar measuring around 35m² could be converted into an additional living room or home office at a cost of around £850-1,050 per m², including dampproofing (a tanking membrane) and insulation.

Adding a new lightwell and window would cost an additional £4,000-5,000. Cellar conversions come under permitted development rights but, as above, this is a ‘material change of use’. For details of specialist cellar-conversion firms, try basements.org.uk


4. Single-storey extensions

This level of outlay could be sufficient to create a substantial extension, 30-40m² — budget for £1,050-1,450 per m². This might be enough to extend by around 4m right across the back of a typical semi or detached house, with either a flat or low-pitched sloping roof — ideal for creating a large open-plan kitchen-diner.

£40,000 rear extensions (pictured above)

Pippa Tunnell extended across the back of her semi-detached home in Glasgow to create a spacious open-plan kitchen/dining space. Her former dining room was also remodelled into a music room, which does still open onto the kitchen but can be separated as required.

The contemporary-style build cost £40,000 and incorporates large areas of glazing round the dining area, with garden access, and an overhanging flat roof. This reduces solar gain to prevent the room from overheating in hot weather.
Architect: William Tunnell Architects – 0131 331 2813

A contemporary design with folding-sliding doors, glazed roof lanterns and large floor-to-ceiling glazing units would cost £1,800-2,200 per m², so on the same budget the scale of the space may need to be reduced to around 23m². Many single-storey side and rear extensions will fall within your permitted development rights, but always check. And Building Regs will apply.


5. Two-storey extensions

More cost-effective than a single storey because they double-up on the use of the foundations and roof – two of the most expensive parts of a build – a two-storey extension on this budget could measure up to 30-40m² (both floors). At the rear of a property, this would typically extend the kitchen with a new bedroom above.

Many such extensions projecting no more than 4m from the rear of the original house are covered by permitted development rights, but a two-storey side extension will require planning consent – and don’t forget Building Regs.

Ready made kitchen feature in which the extension is lifted into position complete. Kirsty and Peter Turner and their children Amy,5, and Ted, 2. 19/5/06 pic lynn hilton

£30,000 rear extensions

Kirsty and Peter Turner extended the rear of their Edwardian end-terrace home (pictured above) in Ealing, west London, at a cost of £30,000. The 17.5m² project cost £1,715 per m² — typical for a small contemporary-style extension.

The couple then spent a further £10,000 remodelling and upgrading the rest of their ground floor, so the new space is integral to their open-plan kitchen/dining room.

Those with a smaller budget might wish to see what you can do for between £20,000 and £30,000. Or if you have a little more to spend, take a look at extensions between £50,000 and £90,000.

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