Sniff­ing out source of odour

Winnipeg Free Press - Section F - - HOMES - ARI MARANTZ

QUES­TION: I am writ­ing to you with a ques­tion re­gard­ing an oc­ca­sional strange odour in my house. It smells like sour stag­nant wa­ter or rot­ting wet wood. It doesn’t smell like mould or sewer gas and it’s not com­ing from any drains or the sump pit. I have had some im­prove­ments done in the last few years and hoped they might also elim­i­nate the prob­lem, but noth­ing has helped.

I have had my fur­nace ducts thor­oughly cleaned. I have had a new high-ef­fi­ciency fur­nace in­stalled and the cold air in­take was left in place. The roof has been checked for leaks and has been re-shin­gled. The roof stack has also been checked to see if any­thing is block­ing it. The neigh­bours do not have any­thing nearby that would smell.

I would think if it were any of th­ese things, the smell would be no­tice­able at all times, but the odour is only no­tice­able when it is foggy out­side or if the hu­mid­ity is high and it is not windy. I have also no­ticed it is most preva­lent in the mas­ter-bed­room heat vent, which is the room far­thest from the fur­nace, al­though it is faintly no­tice­able in all of the rooms.

My home is a 26-year-old split-level and the lot backs onto a re­ten­tion pond. The odour started quite a few years ago, and the only thing I can think of is the cold-air in­take is un­der my deck, which is cedar, and there is no air flow when it is foggy and I am get­ting a stag­nant smell. As soon as the wind starts to blow, the odour dis­ap­pears. I’m think­ing I should have this vent ex­tended so it’s above the deck sur­face. If so, who would do this type of work? I would greatly ap­pre­ci­ate your opin­ion and ad­vice re­gard­ing this prob­lem.

Dar­lene Wo­j­cik

AN­SWER: In at­tempt­ing to de­ter­mine the cause of an is­sue in a home, es­pe­cially some­thing as sub­jec­tive as a spe­cific odour, I try to look at all the pos­si­bil­i­ties and then rule them out one at a time.

Your de­scrip­tion of the type of the smell is the nat­u­ral place to be­gin. While I’m quite fa­mil­iar with the odours as­so­ci­ated with rot­ting wood, I’m not sure what a “sour stag­nant wa­ter” smell is. I’m glad you don’t feel it’s waste or sewer gas you’re smelling, but don’t be too quick to rule out mould.

While many moulds can give off what can be de­scribed as a “musty-base­ment” smell, wood rot is also a type of mould, so your de­scrip­tion may in­deed be fun­gus-re­lated. This could be com­ing through the fresh-air in­take un­der your deck if the deck is rot­ting or there are de­com­pos­ing leaves or de­bris.

If the un­der­side of the deck is ac­ces­si­ble, lo­cate the vent hood or screen where the fresh-air in­take duct ter­mi­nates. If not, you may have to re­move a few deck boards. Once found, the vent hood should be cleaned with a damp cloth, brush, or other tool to re­move any dust or de­bris block­ing it. Given its lo­ca­tion un­der your deck, I’d be very sur­prised if the screen on your vent is not partly or com­pletely blocked. If so, the dirt and de­bris may be the source of the smell. This ma­te­rial may be slowly de­com­pos­ing, but may only be no­tice­able on very wet days, or when there is lit­tle wind or air move­ment to dry it out.

Mice, sting­ing in­sects and other pests like to take refuge in ar­eas like this, es­pe­cially if they can come and go with­out be­ing eas­ily de­tected. If they gain ac­cess and cre­ate a nest or per­ish in­side the duct­ing, rot­ting-type odours are likely.

If you find the fresh-air in­take is not plugged or dam­aged and has rea­son­able air­flow, re­lo­cat­ing it may help pre­vent a re­turn of the prob­lem. Be­cause your lot backs onto a re­ten­tion pond, with­out much cover from veg­e­ta­tion or other build­ings, your home is likely more sus­cep­ti­ble to vari­a­tions in wind and weather changes.

Your ob­ser­va­tions about the smells oc­cur­ring on wet or calm days may be another clue to the source. If the odour is due to mois­ture dam­age in the deck or house fram­ing, this may not hap­pen on sunny and windy days, but more likely when it is rainy, calm or foggy. Another pos­si­ble ex­pla­na­tion is our ol­fac­tory sys­tem works much bet­ter when the en­vi­ron­ment is wet or damp, so the smell may al­ways be present but only no­tice­able at th­ese times.

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