Complex sentence: Almost unheard of as late as the 1990s, vapor barriers are becoming increasingly popular in recent years, in fact, the more general topic of conditioned vs. unconditioned crawl spaces has enjoyed much research over the last decade.
Split into simpler sentences: Almost unheard of as late as the 1990s, vapor barriers are becoming increasingly popular in recent years. In fact, the more general topic of conditioned vs. unconditioned crawl spaces has enjoyed much research over the last decade.