We bought a house 14 years ago that had been unheated for several years. The first thing we did was have new carpet installed. Within about 6 months we started to have a soft spot in one area. Unfortunately it was a heavy traffic area so we had the carpet pulled back, replaced that section of subfloor and figured we were done. Within another 6 months we had several more soft spots develop. I ended up removing the carpet in the whole area, ripping up the particle board subfloor and putting down plywood. That was covered with luan and self stick vinyl tiles. We recently had the vinyl taken up as well as more of the original carpet. The whole area was leveled as well as possible and high quality sheet linoleum put down.