ok so I found this quickly: [i]Ground contact wood levels[/i] [list] [*][i][b]UC4A = Ground Contact, General Use[/b][/i] [*][i][b]UC4B = Ground Contact, Heavy Duty[/b][/i] [*][i][b]UC4C = Ground Contact, Extreme Duty[/b][/i] [/list] [i]Yes, not all ground contact is the same. Dry ground requires less treatment. But more importantly is how the wood will be use. The more extreme the use, “duty,” the higher the treatment level it should have[/i] [url]https://decksbye3.com/what-is-the-best-pressure-treated-wood-for-ground-contact/[/url] ----- Didn't I read on tags before some say 'above ground' or 'ground contact' but also 'In-Ground"? Maybe 'In-Ground' I saw was UC4B or UC4C, and at a lumber yard or something already built, because I don't think Lowe's or Depot have anything greater than UC4A. I'm building a shed on 4x4s beams set on 3" tall concrete blocks with fortifier etc in the concrete to make it stronger and the blocks will be about another 3" below grade set on gravel. The area isn't too wet but does get saturated after very heavy rain and has fence close up to 2 sides of the shed and the house on the 3rd side about 10 feet away , so air flow won't be the greatest. I know the foundation and beams are going to kill the shed eventually, that'll be what rots out in IDK maybe 65 years and the shed taken down despite the walls and roof etc should be fine or easily replaced instead of having to knock the whole thing down. Come to think of it worst case scenario maybe I'll just write a note in the shed once the foundation rots to have fun with it and just take it apart and rebuild the foundation, but really I'd like it to last as long as possible. You think it's way overkill and overpriced to source UC4B or UC4C? Keep in mind not only the 4x4s but also all the treated 2x4s which I'm putting about 12" OC for strength and the treated plywood (likely ply would rot first actually), and all these I want to additionally paint on preservative like coppercoat. 16 foot x 8 foot shed , running three 4x4 beams that cost $30 each as 16 footers. So I'll check the price of stronger threaded lumber plus all the 2x4s and plywood so I'll see if it's way too expensive, plus I get %10 off lowes also but not at lumber yard. Plus maybe coppercoat will bring it to a UC4B or C level. I know CCA is stronger but illegal for most uses if you can even find it, but would consider that if possible, but on the other hand I'm not super worried about it now I can write in the shed something like just rebuild it with same materials minus the foundation in 80 years or something, or possibly it could be jacked up and reinforced from below but doubt anyone would do that.

I am putting together a Playhouse with rubber tiles underneath. Plenty of room in my dirt yard. My question is would it help to put anything under the rubber tiles? Such as would rubber mulch make it softer and safer?