Building an Extension Plan

Building an extension - Designing Buildings Wiki

Anyone who is in the construction industry will tell you that creating extension plans requires a lot of planning before even you lay a single brink. Therefore, you need to consider everything from your budget to the building. In this article, we’ve decided to put together a beginner’s guide which covers everything one needs to know in building an extension plan.

The Cost of the Extension Plan

In the UK, most extension plans start from £1,000/m2 going up. However, the cost of your extension plans will depend on factors such as size, specification, or location. If you are planning to build a single-storey extension, the cost will look like these

  • Basic quality: £1,000 to £1,680
  • Good quality: £1,680 to £1,920
  • Excellent quality: £1,920 to £2,160

If you decide to build a two-storey extension, it won’t cost a lot of money per square metre because, apart from the exterior fixtures, you are just adding walls and floors. Most importantly, the extension will need a roof and foundation whether you want to build a single or two storey.

The Cheap Way To Build An Extension

If you want to build a cheap extension plan, first you need to ensure your design and shape are simple. In other words, whether you decide you want a single-storey square or rectangular shaped, just make sure you don’t have complicated designs and roof structures.

When it comes to materials, you will want to choose concrete subfloor and concrete blockwork because they are cheaper than oak or timber frame. Concrete blockwork is available and most builders know how to work using this material

Concrete blockwork exists in three types. We have dense, lightweight, and aerated blockwork. Their cost ranges from  £10/m2 for cheap dense blocks to around £30/m2 for high-performance aircrew blocks. If you are an expert DIYer, you can always give a little hand to keep the costs down. You can help with plasterboarding, layering the flooring, and tilING.

Lastly, if you are remodelling or extending a property which has been empty for 2 years, most contractors treat that as a conversion. Therefore you will be charged VAT at 5% lower. You can only get VAT concessions if you work with VAT-registered contractors. If you have a project that you want us to look at, you can check out Extension Plans UK.


Building an extension will increase the value of your home. For instance, if you build a large extension, your home could cost a lot. But bear in mind that it will cost a lot of money to build such an extension. What’s more, you need to have a ceiling price in mind to make sure the numbers add at the end of the day. Perhaps the best thing you can do is talk to the local estate agent. They will paint for you a fair picture of the market and what extended homes are selling for. That way, you will know how much you will need to invest in building an extension plan.