Digging out 200mm for laying patio next to shallow footings for extension

[Cellophaneskies]

Hi all.

I would like to lay a new patio next to my garage and extension. I understand the finished level should be about 6 inches (two brick courses) below DPM but the ‘footings’ for my extension (3x3m masonary single skin monstrosity) seems to be only 1 course below DPM, and then itself is very thin.

If I dig 200mm down I’m possibly going to expose the whole footing and leave it ‘floating’ (ie not ground next to it, only directly beneath it’ until I put compacted sub base down.

Do I need to be concerned about this - should I avoid digging too deep, instead having less sub base for the patio? If so, any suggestion on depths? Ie 40mm sub base and then 40mm bedding mortar, saving a couple of cm of digging..

Or perhaps I use some alternative method that’s less long lasting. Go directly onto compacted ground rather than adding type 1 sub base, is that asking for trouble? Patio will only be 3x4m or so.

 

[Wayners]

No. Crack on.

The weight is at the bottom which is why footings go deep. Solid undisturbed ground.

Your just messing with the top layers that were probably levelled and messed with.

 

[lostinthelight]

If your concerned dig out a trial pit to establish the bottom of the foundation and if shallower than you need to dig out come out to depth at 45⁰ from the wall base

 

[Cellophaneskies]

No. Crack on.

The weight is at the bottom which is why footings go deep. Solid undisturbed ground.

Your just messing with the top layers that were probably levelled and messed with.

Thanks for the response!

This is the thing, I don’t think the footings are deep. I can dig underneath that concrete. You can sort of see two little gaps in the photo. It appears the footings are only about a brick thickness, maybe even less - so digging down around them with leave them without anything to sit on (assuming the ground underneath falls away etc)

If your concerned dig out a trial pit to establish the bottom of the foundation and if shallower than you need to dig out come out to depth at 45⁰ from the wall base

Ok sure. So dig as normal but maintain a slip of the ground underneath of 45 degree, so there is earth still butting up against it.

 

[lostinthelight]

This is floor inside the house I dug out below the foundation

 

[Cellophaneskies]

This is floor inside the house I dug out below the foundation

Thanks for sharing, might be awkward laying patio on there but I’ll weigh up my options..!