Hello, I'm new to this forum, but not to DIY. I currently have a narrow breezeway connecting my garage to my house. I'd like to widen it, close it in, and create a mud room. Widening the roof and building the walls is no problem, but I'm not 100% sure of what to do with the foundation.

I was thinking of digging down below the frost line and pouring concrete foundation about the width of a cinder block. I would reinforce the concrete with rebar. I'd have it run from the garage to the house and it would stick up about 1-2 feet above the ground. I would use this to build my wall on top of. See attached drawing.

Do I have the right idea? Am I using the right materials? Would you do anything different?

Well Here's how us mason do this. Dig a trench 2' wide and how ever deep you need to go to get below frost. Now pour min 8" concrete in the trench for the footers. In the footer put 2 pieces of steel rebar in the footer. Now where it goes to the house if there is a block wall there drill to holes for the rebar to pin the footer into the other block house wall. Now lat your block. Remember To figure a 4" cap solid block as your last course to cap the block. You will need 1/2" anchor bolts for the plate. In my area its required to set your steel anchor bolts within 1' of the corners and every 6'. The block gets parged/stucco below grade and the foundation coating. Above ground its either bare block showing or two coats of parging with a sponge finish or a brush finish.
Check your local buildings on footer depth / anchor bolts ect.

For what I see in the picture I would use min 8" concrete block But check your codes.

It looks like you might be thinking pouring the below grade part all in concrete. That's to expensive and not practical in application for what you are doing.

Signed 21 Boat

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Thanks for the help. I will definitely take your advice and use blocks instead of poured concrete to place on top of the footer. The "4" cap of solid block," is a solid stone block that the wood framing will sit on...right? And what do you mean when you say "lat the block?"

Thanks again for the help... Logan