old foundation, new garage - help please!

[eurobound]

Need some help. Plan to build an extension off the east side of the house - garage below and bedrooms on top. I am getting an architect and engineers help however I like to research things on my own. I have attached my sketch and the house plans. it is a 1979 bi-level with a basement below grade.

I did a little digging to see what the structure of my foundation/footing was and I drew a little sketch. Can anyone chime in and let me know if it makes sense? I found it odd that the footing was stepped? Is this normal? After the step I dug a bit more and it didn't seem to go straight down it was jagged and I could dig under the footing a bit... it was kinda jagged...

Because the footing is not 18" below the slab I have less options. I will be sloping the garage to get an 8' door/9' ceiling at the opening which will then slope up to an 8' ceiling. The garage will be heated with radiant flooring.

Any comments would be appreciated.

Also, wondering if anyone has any suggestions for the layout of the inside of the garage? I will need a workstation to take apart my dirt bike and suspension. Need to fit lots of bench space, compressor, nitrogen tank, 36" wide parts washer, sink, etc. I was thinking of putting in an island on wheels too? HRV, wall mounted heater with 6 pumps, central vacuum, and water distribution manifold have to fit in there somewhere too! Only 1 Ford Escape will be parked in their daily... but would like to be able to drive my GMC full-size pickup inside (without the Ford) and close the garage door to do general maintenance and cleaning when necessary.

 

[wssix99]

Where is this being built? I assume someplace warm since you were able to dig. (Where I live, we currently need explosives to make a hole in the ground.)

After the step I dug a bit more and it didn't seem to go straight down it was jagged and I could dig under the footing a bit... it was kinda jagged...

What do you mean by stepped? The different width at the bottom? If so, that's the "foot" of your "footing." It spreads the bearing force over a wider surface area of the soil. A stepped footing is something different, which you may have in other places.

Typically, contractors don't take the time to make the footing trench perfect (and you wouldn't want to pay them to do so) so the concrete is just poured in the hole. That will give you the jagged edges on the bottom and sides. You can think of it as bonus material.

Because the footing is not 18" below the slab I have less options. I will be sloping the garage to get an 8' door/9' ceiling at the opening which will then slope up to an 8' ceiling. The garage will be heated with radiant flooring.

Did you dig the hole behind the garage? Your footing (since your house is on a slope) is likely "stepped" and a different relative depth at different spots around your house.