I'm seeking advice on whether to use footings or concrete blocks for this project. My worry with footings is the depth--the long side of the deck in the attached picture will slightly overlap septic lines. I do plan to attach the grilling deck to the bottom stair and stair support posts (and I've read if it's going to be attached, then use footings). Can I get away with concrete blocks? If I definitely need footings, how deep should the holes be?
You need more than one post before posted pictures show up.
The footing depth is the local frost depth for your area.
If you are attaching to a structure that does have footing. you should have footings.
If it is free standing and you can put up with a little movement from one year to the next the footing aren't so important.