The house is brand new construction and a sour smell, almost like cat urine, was noticed as soon as the insulation and ducting was done, before the HVAC was even used. The ducting is located in the crawl space and is insulated with plastic wrapped insulation. The crawl space is free from moisture and has a vapor barrier. The smell comes through all vents, even when the HVAC unit isn't being used. Also, you can smell the odor emitting from the foundation vents. I have been told it is just the odor of the insulation used or maybe condensation in the ducting creating the smell?
Any input would be greatly appreciated. Even though it isn't unbearable yet, it is enough to drive you crazy!
It could be urine odors from the concrete from before the house was closed in. Some people on construction sites have a strange fasination with urinating in the corners of basements/crawspaces, tubs, shower stalls, you name it.