Is a subfloor absolutely needed before carpeting a basement?

I'm no carpet or subfloor expert. Are you saying you will use the basement in the summer with windows open ? And, I assume, no dehumid or A/C.

Personally, I think that's a recipe for disaster. Unless you can guarantee low humidity in the space and no condensation under carpet, it is inviting major mold growth.

YMMV

Jim

Have you considered looking for a carpet designed for basement or patio use? You could also just lay it down in a semi permanent way and check it periodically for problems before making a final decision. My carpet is on concrete with no problems 12 feet underground but it is an absolutely dry basement.

I was told to tape a 2' x 2' piece of solid plastic to the concrete floor and leave it there for at least 3 days. If there is no moisture present after you remove the plastic you should be okay. My carpet was installed over felt padding which I believe had a moisture barrier on one side. The padding was laid right on top the concrete floor.

I know nothing about carpet, so I have no opinion. However....

My basement carpet has been on bare concrete for 21 years. A seam is starting to pucker, but I think that is more from when the dishwasher drain clogged and dumped many gallons through the floor than from the way it is installed.