Part of my basement has carpet laid 25 years ago The area is dry: never a water, mold or odor problem. We tested a small area and it was a nightmare to remove the glue from the concrete. We are thinking about installing a sub floor on top of the carpet, constructing a grid of 1 1/2" strapping and 3/4 plywood on top. Will this work?
Edit: Thanks for the replies. I need to add that the house is a back split. The basement lower area basement is split. One half is the traditional basement housing the furnace etc and is 2 1/23 feet lower than the area that I will be making a sub floor for. There are four steps leading to an upper hallway. Off that hallway is the room I wish to install the sub floor. This area consists of the area which is 2 1/2 feet higher than the basement area. That area has been carpet over a cement base. Never had a water problem, no evidence of mold nor any damage to the existing carpet, never any foul order. The area is completely dry.
Pull out the carpets. never put a subfloor over something like old carpet. You may not have any moisture problems now, but any occurrence of water (flood, broken plumbing, spill) getting in that hidden carpet in the future will cause you more grief than you could dream of. This would be a perfect situation to grow mold, mildew, stink and rot the wood subfloor from the bottom up. Don't take the chance, remove it before putting down anything else.
Rather unorthodox but I can't really think of a good reason not to. I'm inclined to want a positive attachment to the slab, but that may not be necessary. Actually, I'm inclined to pull the carpet, leave the glue. Then glue the strapping to the floor/glue residue.
Consider how the floor level changes the height of the last stair riser. Having a riser significantly different than other risers is a significant safety hazard and violates any model code in existence.
ask at your hardware store or flooring specialist about a good scraper for the job. there's no reason why any kind of glue would not come off a flat surface, especially a concrete surface.
my house had an extension built and a room was split in two by a dimwit installing a wall over carpet. i've since removed (all) the dust mite infested carpet and replaced the wall.
you will void any warranty for material and any guarantee from a builder, by (incorrectly) installing a floor on top of carpet.