mkr5000 wrote:

I have a room in my house that is above a crawl space and soil.
It's the only room like that. In the winter and most of the time,
everything is fine but sporadically, I have this horrible odor in that room.
Brand new carpet (odor resistant in fact) -- bleached the floors before
putting carpet down -- this has to be from the crawl space.
This odor is always toward the late afternoon, when it happens,
and it's not related to moisture -- if anything, I've noticed it more
often after dry spells. I do notice a similar smell in "some" of my soil
on my land -- any ideas? Not a methane type smell but a strong
putrid "unusual" odor -- more chemical like.

Could be a broken sewer pipe, abandoned dry well, etc. It's difficult
to say without knowing the age of your house and what transpired on
that property prior to your arrival, could be most anything including
buried agri waste, a natural phenomena like an underground spring,
even a long abandoned outhouse... there may even be critters living in
your crawl space. Your house could be built over an ancient cemetery,
it happens more than one thinks. You may want to check the town
records for prior owner's usage. Have a plumber/septic specialist
check your waste lines, might be as simple as an abandoned waste line
that wasn't capped.

Btw, a crawl space should be ventilated to the outdoors,
there are louvered/screened inserts one can install in the
foundation walls... install at least two, on two different walls
if possible for cross ventilation. Ventilators cost very little but
require some labor... a good DIY project. Also a floor over a crawl
space needs to have a vapor barrior installed, a plastic sheet with
insulation between the floor joists.
http://www.doitbest.com/4294967161-F...entilators.dib