5 tips for extending your house for under £100,000

Industry experts offer advice for planning dilemmas and keeping your project on budget

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If you're planning an extension, our guide is here to help you make the most of your money while increasing your living space with clever and stylish design. Industry experts offer advice on everything from planning dilemmas to design limitations, while managing your expectations of what a £100,000 extension budget can offer.

£100,000 a little out of your budget? Take a look at our tips for designing an extension under £50,000.

1. Understand what can you expect from a £100,000 budget

Marta De Sousa of property developer Lux Reality suggests that with a budget of £100,000 you needn’t restrict yourself to a single storey extension. ‘With this budget you can create a double-storey extension at the back or on the side of your home.'

‘Outside of London, overheads are less expensive for experts, tradespeople and builders, allowing you to use more of your budget on a creative project with potentially more windows or openings,’ Marta adds. 

‘In London, there are many more controls, from what can be delivered to the outside of your home, to noise, parking and traffic restrictions. Your project will be more expensive as your builder will have to take more time and effort to work around them.

‘Structural work, excavation and creating the foundations will make up the bulk of your building and material costs. But it’s the point of access that makes a massive difference here. If your property is in London, it is likely to be terraced, which means you won’t necessarily be able to get any structural beams into the back garden area as easily, or place a digger there – all the digging would have to be done by hand and the rubble taken out through your home, which is very expensive.’

2. Stick to a simple design

Simplicity is key. ‘The more complicated the design for your extension, the more expensive it will be,’ says Marta De Sousa. ‘Adding curved walls, various light wells or very large openings will increase the cost substantially. Putting in two windows is cheaper than one of their combined size, but the more glazing or windows you include, the higher your final cost will be.

‘For this budget, I would keep it simple by choosing ready-made windows of standard sizes and asking your architect to incorporate them into the design. You may also have room to include bi-fold doors.’

3. Be upfront about your budget

Be upfront from the beginning about your budget. ‘If you are employing an architect, you should definitely tell them what the total budget is at the outset so that an appropriate design solution can be found,’ says Alan Cronshaw of Acronym Architecture & Design.

‘Always have at least 10 per cent of your budget set aside as a contingency fund. This will help you if you have to pay for any unforeseen difficulties unearthed once you start building, or allow you to make small design changes during the main construction phase. You will also need to deduct fees for having the architectural and structural drawings drawn up, council planning (if planning permission is needed) and building control,’ Alan continues.

‘If your scheme contains a lot of glass, it may be necessary to employ a thermal consultant to prove that the design is energy efficient. If you are in close proximity to other properties, you may also have to employ a party wall surveyor. Then, when you get prices back from builders, you will know if they are within your budget.’

4. Explore the possibilities under permitted development

As well as addressing the design of your extension, you can maximise your spend in other ways. ‘Explore the possibility of building under your permitted development rights,’ says Alan Cronshaw. ‘Rear extensions that meet certain criteria can be added to houses without needing planning permission, even in Conservation Areas. This may have the added benefit of saving you time as well as money.

‘Consider having the extension finished in painted render rather than facing brickwork, then the construction can be of concrete blocks, which are cheaper and quicker to erect than bricks. Tender the project to four or five builders – you might be surprised at the difference in the prices that you are quoted.’

5. Consider the budget you're setting aside for interior finishes

The cost of interiors will vary widely depending on the room or rooms that you want to create in your extension. ‘Estimate £5,000-£10,000 for a bathroom, £7,000-£10,000 for complete decoration and fully furnishing a living room, and £5,000-£7,000 for complete decoration and fully furnishing a bedroom. Kitchens are expensive, so estimate £15,000-£30,000,’ says interior designer Phoebe Oldrey, founder of Smartstyle Interiors.

‘I like to balance the budget by buying anything run of the mill at the best price possible and saving the big bucks for a one-off showpiece that will make the design truly individual.’

Budget less than £100,000? Find advice and inspiration here...