16 Sep 2014
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United Kingdom
i am replacing my garage door with a door and a window. Under the window, there will be a brick wall.
I am digging a trench. 600mm wide and 1m down...

According to the below image, how deep should (c) be? I would have thought 1m foundation means from ground level to bottom....

Is this correct?

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If you mean the concrete it depends if you go for trench fill. Measure down from your DPC level so it works out in brick or block courses. Before trench fill became popular it was normal to have 9 inches of concrete at the bottom.
sorry i dont understand. the wall i height i need is 1m high and 1.4m wide, it will be a solid brick wall....
Look up Diagram 23 in Part A of the building regs.

In short, the great of 150mm thick or the dimension from the edge of the foundation to the wall.

However, they're usually brought up to be 450mm below DPC as that is two courses of block. That would make dimension (c) 550mm on your diagram.

The thinner the concrete foundation the more blockwork you need to do and concrete is cheaper than labour.
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Trench depth (aka foundation depth) - as deep as the existing foundations either side, or 1m if less.

Concrete strip height - as high as you like up to external ground level. In practice, allow for at least 1 course of bricks below external ground level.

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