On 07/12/2012 20:36, Bill Wright wrote:
QuackDuck wrote:
Hi everyone, I hope you don't mind my first post being a request for
help, but I've been trawling the internet for days and read about every
website/forum post there is about gas smells in buildings.

I live in a 140 year-old(ish) granite building that at some point has
been converted into four flats. Because it was all one big house before,
we do get noise and cooking smells etc travelling between floors.
Natural gas has the smell added to it artificially. It doesn't smell
like coal gas at all. Which type of gas does yours smell like?
The smell added to natural gas is like rotten eggs. Could there be
something rotting away under the floor or behind the fridge or in a
void? I had a problem with a smell like that. Eventually it stopped.
That must have been when all the flesh had gone. I found the cat's
skeleton a few years later.
I dimly remember the tapwater in a college hall of residence smelling
slightly of hydrogen sulphide. Maybe that was sulphur.
If you have sewage pipes behind boxing-in they might be leaking a bit. I
had this problem in the basement. The smell was only there now and then.
I only found out what was happening when the sewer blocked outside and
that caused it to block inside, so the plywood had to come off, and the
outside of the stack was damp.

Bill

You are right about the smell being added, but it isn't like hydrogen
sulphide at all. I think it might be methyl mercaptan. Something similar
was added to coal gas too (although I agree, coal gas had a sort of
"gas-works" smell, for those old enough to remember gas works!)

The normal sewer or drains smell is hydrogen sulphide: it's formed by
bacteria in the black slimy sludge which you find in ditches and other
places with stagnant water.

My money would be on it either being from a sewer or soil pipe with some
sort of fault or a sink / washing machine drain without a functioning
trap, or something dead and decaying. Rat under the floorboards? Pigeon
in the loft?