Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
ODORS GASES SMELLS, DIAGNOSIS & CURE
AIR CLEANER PURIFIER TYPES
AIR CONDITIONING SYSTEM ODORS
AIR POLLUTANTS, COMMON INDOOR
ANIMAL or URINE ODOR SOURCE DETECTION
BACKDRAFTING HEATING EQUIPMENT
CAR MOLD CONTAMINATION
CARPETING & INDOOR AIR QUALITY
CHINESE DRYWALL HAZARDS
CHEMICAL ODOR SOURCES
COMBUSTION GASES & PARTICLE HAZARDS
DUCT SYSTEM & DUCT DEFECTS
EMERGENCY RESPONSE, IAQ, GAS, MOLD
GASES, EXPOSURE, TESTING
GAS DETECTION INSTRUMENTS
GAS EXPOSURE LIMITS & STANDARDS
GLUES ADHESIVES, EXTERIOR CONSTRUCTION
HEATING SYSTEM ODORS
INDOOR AIR HAZARDS TABLE
INDOOR AIR QUALITY & HOUSE TIGHTNESS
LIGHT, GUIDE to FORENSIC USE
GAS LP & NATURAL GAS SAFETY HAZARDS
METHANE GAS SOURCES
MOTHS, MOTHBALL ODORS
MVOCs & MOLDY MUSTY ODORS
ODORS GASES SMELLS, DIAGNOSIS & CURE
OIL HEAT ODORS & NOISES
OIL TANK LEAK & ODOR CAUSES
OUTHOUSES & LATRINES
OZONE MOLD / ODOR TREATMENT WARNINGS
PAINTS & COATINGS ODORS IN BUILDINGS
PET ALLERGENS / PET DANDER
PLASTIC ODORS-SCREENS, SIDING
PLUMBING SYSTEM ODORS
SEPTIC SYSTEM ODORS
SEWER GAS ODORS
SMELL PATCH TEST to Track Down Odors
STAINS on & in BUILDINGS, CAUSES & CURES
SULPHUR & SEWER GAS SMELL SOURCES
UREA FORMALDEHYDE FOAM INSULATION, UFFI
URETHANE FOAM Deterioration, Outgassing
UV LIGHT BLACK LIGHT USES
VENTILATION in BUILDINGS
VINYL SIDING or WINDOW PLASTIC ODORS
VOCs VOLATILE ORGANIC COMPOUNDS
WATER ODORS, CAUSE CURE
WATER TREATMENT EQUIPMENT CHOICES
This article discusses the role of back drafting in buildings, exhaust fans, or other building air movement in causing sewer gas or septic odors (and other building smells and odors).
This article is part of our series SEWER GAS ODORS that helps track down and cure the source of sewer gas or septic smells in buildings.
Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.
What is "Backdrafting" in buildings?
"Backdrafting" refers to indoor conditions that create sufficient negative air pressure inside a building such that gases may be drawn into the building from a plumbing drain system or such that heating appliances may lack adequate combustion air and may produce dangerous carbon monoxide.
Watch out: backdrafting in a building can be dangerous, causing intake of explosive methane gases from a sewer system, or potentially fatal carbon monoxide gas hazards from heating appliances.
In this article (below) we discuss the causes, effects, and cures for backdrafting in buildings that affects the building plumbing drain vent system. Unsafe heating appliance conditions caused by backdrafting are discussed
What Causes Building Backdrafting Hazards?
Field Report: Example of Rooftop Plumbing Vent Backdrafting Causing Sewer Gases to Enter a Building - and The Cure
Sewer/Storm Drain Flooding: indoor sewer gas odors have been tracked to a combination of wet weather, flooding sewer and storm drains, and backdrafting in the building due to improper bathroom exhaust fan vent installation.
Our photo (left) shows a poorly-installed rooftop bath vent fan outlet, patched to try to stop leaks, and likely to be blocked by snowfall on the roof surface. But you can see the "flapper" that closes this vent opening when the fan is not running.
See CORROSION & MOISTURE SOURCES in PANELS for examples of how backdrafting or negative building air pressure can cause unexpected air and moisture movement, condensation, and moisture-related problems such as rust, corrosion, or odors, or mold.
Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical reviewers are welcome and are listed at REFERENCES.
Continue reading at TRACK SEPTIC / SEWER ODOR to SOURCE or select a topic from the More Reading links shown below.
Suggested citation for this web page
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Question: septic smells in my apartment
(July 21, 2011) ruby douglass said:
Ruby, back in the article starting at SEWER GAS ODORS you'll see some first steps in odor diagnosis.
Second, if the odor is for sure in the water we won't pursue a plumbing drain waste vent problem diagnosis for now.
Third: if the odor is in both cold and hot water than it's likely that it's a water source problem and some treatment may be required for the building's water supply. Do other buildings in the area have smelly water? Is it the incoming water from the city that's smelly or is it local to your building.
An example of a local building water odor source would be bad sacrificial anodes in hot water heaters or bacterial contamination in water heaters both of which can give a sulphur or rotten egg smell to hot water.
Question: horrible sewer smell in the house comes and goes
(Jan 17, 2012) Susie said:
Sounds to me as if there is a plumbing drain waste or vent line leak. If you're pretty confident of the odor's source as you describe, it's worth opening the ceiling below the toilet and drains in the floor above to inspect and repair.
Question: mildewy odor from drains
(Apr 14, 2012) Pam said:
Pam see SEPTIC SYSTEM ODORS for help in tracking down these smells
Question: odors coming from roof vents
(May 29, 2012) Sharon King said:
(Aug 22, 2012) Jon said:
Odors at a roof vent would be normal as the vent is releasing sewer gases from the drain system. On occasion a downdraft or odd site and roof conditions and shapes can send roof vent odors down towards a building window or even to ground level. But odors in an individual bathroom might first be checked by
(July 21, 2012) M Braver said:
(Aug 4, 2012) Laurie Whitaker said:
(Aug 5, 2012) DanJoeFriedman (mod) said:
that will suggest a series of steps useful for tracking down the odor you describe.
Question: more sewer gas smell track-down problems
(Nov 29, 2012) jim said:
(Nov 29, 2012) TAnderson said:
You might want to try the diagnostic link at page left for
Sewer gas odors in cold weather
Also, check that the roofer didn't close off ot modify the plumbing vent
Question: septic odor when use kitchen or bath exhaust fans
(Sept 30, 2014) JBrooker said:
Also, the odor does not appear to be coming from any of the drains in that bathroom and the traps have all been kept wet. If anything, the smell also seemed a bit stronger under the sink where the pipe comes through the wall (which is directly above the pot light). That being said, the smell was also noticeable when standing in that bathroom, which lead me to believe that it was coming from somewhere higher up than the sink (but I couldn't pinpoint where)... The pipe on the roof did not appear to be covered in snow or impeded in any way last winter when the smell was strongest. Thanks
oh, the plumbing vent comes out of the house on the opposite side of this bathroom and is proper diameter. And there is no glub glub or gurgle sound from the drains ever. Thanks again.
I'd be looking for a missing plumbing vent, blocked vent, leaky vent piping that backdraft into the house when there is negative pressure created by a vent fan or any other source.
Question: Georgia septic tank and basement smell when it rains
25 Feb 2015 Tfin said:
There are two articles above at More Reading that should help you diagnose this complaint:
SEWER GAS ODORS
Let me know if questions remain or if you need more help after looking at those guides.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References