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7 tips to keep house extension costs down

Last updated Tuesday 21 August 2018

There are only two tips that will always save you money during a building project: don’t cut corners and pay attention.

The fact is: there’s no trick to keeping the cost of your house extension down, but here are 7 things you can do to ensure that you’re making value-adding decisions (without having to settle for less).

1: Make detailed plans

Your extension begins with your design package. Ideally, an architect will produce the floor plans and elevations that will form the foundations of the rest of your project. Plans are more than just a drawing, they’re also used to:

  • Support your planning permission or lawful development certificate application
  • Help your builder provide you with an accurate quote for your extension
  • Form the legal basis of your contract with your suppliers

Ask your architect in advance to specify exactly what output they provide for their fee. If the price seems low, there are probably going to be details which will need to be filled in eventually... for a price. Don’t wait for someone else to charge you double later in the process. Always choose a reliable architect who provides a comprehensive package, as you don't want your beautiful new side extension plans looking like something your child has drawn with crayons now, do you?

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2: Leave time for paperwork

A planning permission application can take anywhere from 8-12 weeks to receive a decision. A lawful development certificate - which protects you if you’re building under permitted development rights, can take about the same.

You should never start building your extension before you have the final go-ahead from the council, as delays in paperwork can hold your entire team up. This also means making sure that your appraisal, building control, surveys and party wall matters are settled before you start. Make sure you leave plenty of time to get everything sorted, and you’ll probably find you’re able to get a more competitive quote.

Luckily, planning permission is valid for two years after approval, so you can get started on your plans first and get the ball rolling on everything else once you’re ready to go.

3: Check your contract and break down your quote

  • Never start building an extension without a tight contract, such as a JCT. If anything changes during your project (and it probably will), this gives you a legal way to keep a handle on inflating costs.
  • Make sure that your builder provides you a fully costed quote, so you understand the price of each element. That way, if you need more of anything, you can reference the original price per unit.
  • Don’t skimp on exploratory work - from CCTV surveys to checking the quality of the roof and foundations. Anything you can do to reduce surprises down the line will help you to budget accurately from the start.

4: Compare suppliers

At every stage of your project - from finding an architect to sourcing a builder - you should be soliciting 4-6 quotes from different suppliers.

However, remember that cheaper isn’t always better: it’s about finding people who are offering you value, quality and trust.

It’s often possible to save money by sourcing your own contractors, rather than allowing one builder to handle the entire contract. However, you’ll need to be extra careful that everyone has a good idea of their responsibilities and how they interact, or mistakes can end up adding time and money in the long run.

5: Consider a project manager

No matter whether you're building a two-storey rear extension with a renovated kitchen or simply removing your conservatory, a project manager is always important to consider.

It’s like the old saying, “you have to spend money to make money”. For a £50k project, it may seem steep to spend £5k on a project manager...but you may make considerable savings as a result of keeping your extension on track.

If there’s anywhere you shouldn’t be cutting corners, it’s on finding experts you can trust.

6: Get to know your materials

On the other hand, there are plenty of places you can save money when it comes to building materials. For example, if your architect suggests a slate roof, the price difference between artificial slate (at 20p per slab) vs. Welsh slate (at £1.50 per slab) can end up in the thousands.

Sometimes this will matter, and sometimes you honestly won’t be able to tell the difference. You don’t always need to go for the best; you just need to find what works for you.

7: Move out

It’s likely that a contractor will charge less for the work if you can vacate the property during your home extension, but make sure to cost out how much this is really going to save you. If you have to pay to live somewhere else, or to travel further to work, it may not make sense in the end.

Pricing everything out as accurately as possible before you make any decisions is the easiest way to stay on top of your spending.

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