Digging near new foundations

[PeterW]

Is there a rule of thumb or calculation about how closely and how deep you can dig to new foundations..?

Contemplating a rainwater system that would need a hole approx 4m x 1.4m x 1.5m deep to be dug to contain the storage. Its not suitable to be driven on, so one thought is that it goes under a patio - the only thing being this would need to dig within 2.2m of the foundations.

Foundation will be around 1100mm deep so its not as though there is a huge depth difference but I can't find any real guidance.

[Ferdinand]

Can't you use the numbers from the Party Wall Act to give you an estimate?

Presumably if you are outside those you are safe.

 

Edited June 18, 2016 by Ferdinand

[ProDave]

I think the basic rule, is take the bottom of your foundation trench, project a line outwards and downwards at 45 degrees from the bottom of that trench. Your excavations should not pass through that line.

If you are digging 2.2 metres away from the foundations, then even with very shallow foundations, you would need to be more than 2.2 metres deep before you would cause concern, so I think your 1.5 metre hole will be fine.

[PeterW]

Thanks ! I thought that would be the case but wanted to check ..!