I was at Home Depot getting some fence posts and I asked where their selection of 4x4s were located. All I saw was one stack. It was labeled construction select. I asked if they were rated for ground contact and the answer was yes. So I continued with the same question for 2x4s, 4x6s, etc. I was told all of their PT wood is construction select, 2 or better, and rated for ground contact. How can this be correct? Lowes has several options from 2 and better, 3 and better, ground contact, etc etc. Lowes also states clearly what wood species the PT lumber is, whereas HD does not. Can anyone clarify?

I want to thank everyone in advance for the help and hopefully I don't sound too ridiculous asking the questions I will be asking. I am looking at building a free stand 20'x16' deck. I want it to run 20' along my house and extend out 16'. My first issue is ground clearance. It's good and bad. I don't need a permit since it'll be so low and not connected to my house but I am stumped on where to put the footings and support beams. My plan is to have doubled up 2x10's around the whole deck. Then run a pair of doubled up 2x10's down the middle parallel to the house. My questions are can I use 2x8's for the joists since I will have the beam in the middle and the will only span 8'? Next where and how many footings. I obviously can't do them in the corners next to the house so where should I support the portion next to the house and the rest of the deck with the footings. I know I sound like I don't know a thing but if the deck was a bit higher we wouldn't have any issues but this is really throwing me for a loop. Any help is appreciated. Thank you.