When we were thinking of buying a condominium, we visited several old danchi — apartments built by Japan's former public housing corporation — because they were cheap and, we thought, easy to renovate. One of the units we inspected had bedroom floors made of tatami mats, and we wondered if we could replace them with real wood floors. The realtor told us that we probably couldn't. The tatami was mandated by the condo's management association because it acted as soundproofing. In fact, he didn't think we'd be able to install real wood floors anywhere in the apartment, because other than tatami only a certain type of sound-proofed laminate flooring was allowed in the building.