One of the first things we have to do in order to be able to finish our basement is install a sub-floor. We plan to carpet the basement in order to have a rec. room that kids can rumble and tumble in. Since the walls (non-load bearing) will rest on top of the sub-floor, it has to be the first thing installed.

We live in a pretty wet area. Wet, as in, almost once a year a river a few blocks away is higher than the road in front of our house. Since our water table is that high, I have to assume every surface of our basement will be moist once a year. Not much, but enough to rot out wood if it were directly against it over time. With this in mind, the entire sub-floor is elevated using a molded plastic material that is sold under the name Platon at our local hardware store. It is dimpled, allowing any moisture to find its way to the drain, as well as away from the surfaces above it. As a bonus, it acts as a vapor barrier. The product comes in a roll that is close to four feet wide with one side having a 4″ strip without dimples to overlap the previous run. The instructions say to seal the two together with the same type of material you’d use to seal a roof. I used house wrap tape as it is easier and I had it already.

My method was to lay down two runs of the Platon before putting the next sub-floor layer down, which I used OSB for. Considering how unlevel our concrete floor is, I should have used tongue and grove plywood to prevent the seams from being uneven. However, after hauling down some twenty 4×8 sheets of 1/2 OSB down our narrow basement stairs, I was using them regardless. Any unlevelness that occurs should be hidden with the carpet.

Here is the majority of the basement subfloor down:

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The spot on the right