What kind of “pressure treated”?

[Henry in MI]

Tim, there are 3 levels of pressure treatment. The least amount of the pressure treating chemical is called “treated to rejection”, next if .4 pounds per cubic foot, then .6 pounds per cubic foot. If you used the first category of PT wood, it will rot quickly in ground contact. Resistance goes up from there and you can get creosote at a home center that will protect the most succeptible part of a timber, the end grain, from rot for a longer time. Creosote is normally put on just where the wood is in ground contact or concrete contact. One thing that is used many places it to put gravel in the bottom of the hole before you put in the concrete. This gives a route for any water that comes down the wood or next to it to get out of the hole.

That said, you should not listen to me or almost anyone else who posts here. Your local conditions determine what steps you need to take. What you need to do in the swampy country of south Louisiana, in the dry southwest of Arizona and on the rocky shores of Maine are totally different. We don’t know where you are and what precipitation and temperature conditions exist. Personally, I would go to your building inspector, since you will have to meet code, and or a local lumber yard. You may or may not talk to the right person at a home center. You may be far enough out in the country where zoning and building codes are not enforced but I doubt it. If you do not follow the code, they CAN make you tear down your bathroom and do it over. If you don’t build per code and you have a problem, such as a fire or major leak, insurance that otherwise would have covered you will not cover the damage. Is it worth the risk??

Henry in MI