We have an old house (1929) which we have been living in for about 9 years. About 5 years ago we had some renovations, and about 2 years later, we noticed odors in the basement during the spring, fall and winter when the temperature is around 50. It seems to go away completely in the summer. The smell sometimes smells septic, and other times like rotting garbage. It sometimes seems to travel up an upstairs bathroom as well. We have had building inspectors, plumbers and septic people over to figure out what it is, but no one has an answer. Most times the smell is intermittent, and only a few people have actually smelled it.