foundation footer and addition 1

[Arties dig]

I currently have a 20x24 cabin with a 4' foundation on a 16" footer . I am planning an addition next to current foundation where I need to dig 4' below existing footer for new footer, 8' concrete walls and a concrete slab. Can I do an "L" shape foundation bench straight down from outside edge of footer to the 4' depth in 6-8' span lengths in sequence?
Artie

 

[Ron]

Pet peeve....it is not a footer. It is a footing.

Next, you have not given enough information to get reasonable advice on such a specific question. Need to know soil conditions, site slope, etc.

Last...this is not a DIY site and it is not for free engineering advice. If you are an engineer, you are welcome to engage the qualified engineers here on a peer-to-peer basis. If you are a homeowner looking for free engineering, this is not the place.

You need to hire a local geotechnical engineer and a structural engineer for your issues. At the least, you need a local structural engineer who is familiar with your soil conditions.

Good luck.