How wide do extension footings need to be?

Question

Hello all,

I am planning on some extension work and have not been able to find out how wide the footings for the foundations will need to be. I’ve been told they need to be 1 metre deep, but not how wide. 
Could anyone enlighten me on this, please?
This will be a single storey extension on entirely flat ground.

Jonathan · Accepted Answer

Usually the inner course of block is 100mm then a 100mm cavity then a 100mm outer course plus you need to allow 150mm bearing each side. So in total 600mm. As for being a meter deep, you need to hit good ground, ideally clay!

Hannah · Answer

The rule is 600 mm wide and 1.2m deep but it depends on the ground when you get to the depth.

Ian · Answer

The depth depends on what the ground is like you have to dig to solid ground.
So if you have a solid ground like shallet you might only have to go down 450mm 
For a single storey building strip foundations will typically be 450mm wide and at least 200mm deep, and for two storeys 600mm wide and 200mm deep.

Ben · Answer

When dug out footings should be 1m deep x 500mm wide unless specified larger

Robbie · Answer

Hi,
If it's a double storey extension the footings will need to be 600mm wide. If it's a single storey then in some cases they will only need to be 450mm wide.

Brad · Answer

It's best to make them 1 metre wide and build in the centre. May be overkill to some, but we always go 1 metre on footings width.

James · Answer

Hi,

Almost all building control inspectors will ask for a minimum of 600mm wide and 1 metre depth for any size extension to a property.

Hope this helps.

David · Answer

Hello, In West Oxfordshire we dig our footings 600mm wide.

Gary · Answer

These should be detailed in the engineers/architect drawings.

Allan · Answer

That depends on building control but usually 600mm wide and 1000mm deep.

Sean · Answer

The footings need too be 1metre deep by 450 wide and that should be plenty

How wide do extension footings need to be?

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