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Question DetailsAsked on 10/5/2016

Will natural gas permanently permeate sheet rock/drywall/plywood and/or insulation or will it eventually dissipate?

I bought a 4 year old home in March. Beginning in April, a smell developed in only one of my second story closets. This smell is only in the closet, and is very, very unpleasant. The back of this closet butts up to a bedroom closet and no other rooms. I removed the carpet, pad, and plywood floor to the exposed joists, but it still persisted. A few days ago, we were in the attic to remove insulation from the ceiling of the closet (we were going to remove all the drywall) and we discovered the natural gas line which the manifold and regulator were right above the closet ceiling!! We had no idea the gas line regulator was in the attic!!! I could smell gas so we called our gas company, they determined there was a leak between the manifold and the regulator and they turned gas off. We had leak repaired. I have no experience with gas or smells related to it. I am only assuming the smell in the closet is due to the gas leak. (it is definitely not decaying animal matter:)

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3 Answers


First - I would get a scratch-and-sniff test sheet from the gas utility - or maybe just stick your nose adt the open outlet of the regulator, to smell what your gas odorant smells like - just to be sure what you smell in actually the gas and not seepage from a toilet or leaking pipe rotting a wall or subfloor or such.

To some extent yes it will dissipate - but I would expect that with a good drywall cleaning with TSP, then a bit of judicious use of lemon scented cleaner or pot pouri and leaving the closet door open as much as possible (like all the time you are out of house) it should drop to non-objectionable within a month or so. This assumes the carpet and pad is disposed of - unlikely to be able to get the smell out of them - though if you live in a sunny area you might try draping them over a deck railing or fence for several days - sunlight works wonders on odors in carpets and padding.

Gas regulator in the attic - that is a new one on me - I can't imagine that is legal now (though gas company should have told you if it was not), and might be it was installed prior to current code. Though you said 4 year old house - something sounds hokey to me. Normally the regulator is outside the house where the gasline comes into the house - vented to ouside atmosphere. Sometimes in so-called "medium pressure" supply areas (mostly older areas) each appliance would have a regulator on it, but each generally (under the National Fuel Code and INernational Fire Code) has to have a vent pipe leading outside the house to a safe dissipation area (certain requirements on distance from flame sources, doors and windows, etc.)

I would certainly make an effort to get that vented outside to prevent another occurrence and also for fire safety - because the regulators are designed to vent excess pressure, and commonly do so to a limited amount on a daily or weekly basis. If the propoer type of regulator was put in your house, should have a threaded fitting on the vent (usually 1/4 or 3/8" for residential sized regulators) to put in a vent tube.

Depending on local practice - in some northeast states a Pipefitter has to do this (many Plumbing outfits have one on staff), in other a Plumber, in others Heating and A/C would be the Search the List category for this. Presumably since you had a line leak repaired, you have a guy to call - call and ask about the regulator. Assuming this is a gasline regulator (not the individual regulator on each appliance) I would get a vent line on it regardless of whether required by code or not - because if the diaphragm regulator fails it will leak gas. When mine failed a few years back (about 30 years old at the time) it put out a very substantial amount of gas at the back of the house - had it been indoors in garaqge or attic or such it would have certainly blown up or caught fire before I noticed the smell - and of course if you are out of the house at the time it fails ...

Answered 4 years ago by LCD


Oh - two other thoughts -

1) if in doubt on the drywall as a smell source in the future, coating it with Kilz (oil based only) primer AFTER TSP washing, then repainting should certainly go a long ways towards stopping any smell coming out of the drywall.

2) since the smell only accumulated in that closet, I would look to see if there is a wiring penetration or such in the top of the walls in the attic which let the smell into that closet - might be an idea to plug it up as it is a vermin entry point risk and also likely has household air passing inot the attic during the heating season - and possibly hot air coming in during the A/C season.

Answered 4 years ago by LCD


BTW - in case you are worried about the gas trapped in the walls. The combustible gas itself is primarily methane with odd amounts of propane, ethane, butane - etc - the gases used for barbecues and lighter fluid and such. They are very "light" (low molecular weight) and have high vapor pressures (which is why they transition from liquid storage to gas so easy) so they dissipate quite rapidly - so with a few days (or most likely just a couple of hours) of the closet standing open and natural ventilation in the attic after the pipe repair at the most the gas concentration should be negligable and of no risk. Even a house that is totally saturated with natural gas from a gas leak only takes an hour or two of ventilation by the fire department to be safe.

The smell itself is an odorant added to the gas so you can smell it strongly because natural gas from transmission lines (which has had the very noticeable natural hydrogen sulfide removed from it to reduce corrosion) is nearly odorless and the nose very quickly becomes acclimated to it, so after a very short exposure you do not smell it at all). The odorant - mercaptin or similar chemical - which is added before transmission and distribution to customers is use because it is highly detectable to the nose and is very persistent - so while its odor may linger and be detectable in the closet for some months in diminishing amounts (especially if not thoroughly washed off surfaces and sealed in with new primer and paint), its presence (after you have removed the leak source) is not indicative of any gas presence or danger of explosion or such once the immediate area has been aired out.

It is likely that anything stored in the closet will need cleaning or washing to remove the odorant smell. Washable fabrics you should wash normally for the material, but except for exotic fabrics also use Borax powder (NOT Boraxo hand soap - I mean regular laundry borax like 20 Mule Team Borax) per instructions on the box to help remove the smell. Can also be added to detergent and water used to wash wall and ceiling in the closet and the outsides of "hard" items that were in there. If items were heavily exposed they may need a couple of washings to remove the smell because it is a very tenacious chemical - bonds to surfaces well and is by design highly odiferous at low concentrations.

It is also possible for the first month or few tha the odor will come back weakly but detectable during wet weather, as higher humidity causes it to smell stronger. If you do smell it during that time period, be sure to check around in other rooms and the attic to be sure that you are just smelling the residual odorant and not a new gas leak somewhere.


One final thought which I may not have fully discussed regarding your original post - you said you are only assuming the smell in the closet is from the natural gas leak - logical if the leak was above it. However, before painting and putting everything back, you might get on hands and knees (after washing the surfaces to mitigate any gas odorant there) and sniff around at all the drywall seams with doorframe and flooring, and possibly even drill an inch hole or so in the subfloor to smell there (and plug with a glued in wood plug afterward), just to be sure that what you smell IS the natural gas odorant, not some rot or fungal growth in the subfloor or wall form a water or sewer pipe leak. Good way to check is use a cardboard tube like the core from wrapping paper or paper towels held to the opening or crack, use vacuum to pull a suction on the tube, then move the vacuum hose aside and smell the tube while the air is still flowing out of it from the suction, because otherwise you do not know that you are smelling air from the hidden area rather than air just flowing down through the tube to it. Simpler and more effectiver but a lot more uncomfortable to get on handas and knees and get your nose up close and personal with the baseboard and subfloor exploratory hole and such.

Answered 4 years ago by LCD

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