Can You Build On Top Of A Single Storey Extension

Posted by Tim Foster on Jan 16, 2020 10:38:00 AM

Can You Build On Top Of A Single Storey Extension

If you’ve already added a single-storey extension to your home, you might be wondering whether it’s legally or logistically possible to convert it to a double-storey extension. In many cases, it’s perfectly fine, but before you start budgeting or discussing plans with a builder or architect, there are several things you’ll need to consider. Click here to download our FREE essential guide to extending your home!

Why Convert To A Double-Storey Extension?

There are lots of reasons why homeowners might want to add an extra floor to their existing extension. New additions to the family, the need for a home office, the desire to add a gym or games room or simply wanting to increase the value of the property are all solid arguments for constructing a double extension.

Whatever your reasons, you will likely need to consult several specialists before going ahead with construction. You may also need to apply for planning permission, and depending on the location of your home, this could be a stumbling block.

The First Step

The most important step is to understand exactly what you’re working with from a safety perspective. The addition of an extra storey can put a significant increase on the load bearing of the existing foundations of your extension. You’ll need to consult a qualified surveyor and structural engineer to assess whether your current foundations will be enough for an additional storey. If they are deemed to be insufficient, the existing foundations will need to be dug deeper to handle the load.

Conducting An Examination

The process of checking your foundations involves the digging of a trial pit which will allow your structural engineer to look at what you’ve got to work with. If your foundations are deemed to be adequate, you can progress to the next stage. If your foundations aren’t sufficient, they will need to be replaced or reinforced.


Gaining planning permission can often be a problem when it comes to adding another storey to your existing extension. Whether planning permission is granted largely depends on the type of property. For example, building two storeys up to the boundary line of two semi-detached houses is usually not allowed by local authorities. However, planning regulations can vary from authority to authority. If you’ve got at least 2 metres of space from the boundary line, you may not even require planning permission – although it’s always worth clarifying this with your local planning department for clarity before starting a renovation project.


If you want to develop your existing extension but don’t know where to start, give BDS Architecture a call today and we’ll be happy to talk you through the process!

The Essential Guide To Extending Your Living Space

Topics: Extensions, Two Storey Extension

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