Photograph of - damaged vinyl siding A Procedural Checklist for Odor Source Diagnosis

  • ODOR DIAGNOSIS CHECKLIST, PROCEDURE - CONTENTS: Checklist aids in finding the source of building smells or odors: a procedural checklist & an odor event log can diagnose and track down the source of building odors. Does your home have "BO" - building odor that is hard to track down? Here we suggest step by step procedures to help find the source of a building odor complaint. Here we list possible odor sources and we discuss using a time and event log to help track down odor sources, explaining how to find the source of and then eliminate sewer gas or other smells anywhere in buildings, including the living area, basements, bathrooms, kitchens; how to remove septic smells or other odors of any kind from buildings; Links to articles on diagnosing and curing smells in buildings
  • POST a QUESTION or READ FAQs on procedures used to identify the source of smells or odors in buildings - an odor source checklist

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Building odor & smell diagnosis & cure procedure:

This article provides a methodology useful for tracking down the sources of odors in buildings. When you can't seem to find the source of an annoying building smell, we suggest using these investigation methods that include noting the time, weather, area, operation of equipment and similar conditions that will help track a building odor problem to its source.

How to find the cause of odors, odor sources, and how to find and cure the source of smells in building air, water, heating and cooling systems, or other sources.

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Procedure Checklist for Diagnosing the Source of Odors or Smells in Buildings

Stuffed animals were hiding building damage (C) Daniel FriedmanWe offer below a list of smell and odor diagnosis clues that any home owner, home inspector, or other investigator can follow in seeking to pinpoint the source of an annoying or obnoxious odor in buildings. Readers are asked to contact us to suggest additions or corrections to this list.

Often people's perception of odors varies with time and exposure or with a number of other site factors that make it hard to track down just where a smell is coming from.

But if we think carefully about when, and under what conditions we notice odors, often that information is instrumental in tracking down an odor to its source and thus in helping us decide if an odor refers to a potentially dangerous or unhealthy condition.

This odor diagnostic checklist is in simple alphabetic order, not in order of probable cause, importance, or health risk, all of which can vary widely. A printer-friendly abbreviated PDF version of this smell diagnostic checklist is at
Odor Diagnosis Checklist-PDF
, thanks to reader Kathleen Black

Odors That Have Specific Events as Sources

  • Gulf Oil Spill & Odors from similar events: The New York Times reported in May 2010 that residents in New Orleans, Louisiana and as far as 100 miles inland from the coast have been observing a strange chemical odor that comes and goes, but also it is described as a "kind of sewage smell". The odor is speculated to be associated with the offshore Gulf oil spill.

    The Times article added that "More than 800 air samples are being tested by the state's scientists, the federal EPA, and private contractors hired by BP [British Petroleum] from the shoreland to ... population centers farther inland". To May 15 2010 these sources had declared the air "safe". Readers should also
    see Gulf Oil Spill & Air Quality.

  • Relating building odors to specific events such as: housekeeping, use of new or different cleaning products, installation of new products or materials (such as carpeting or cabinets or glued tiles)

Keep an Odor or Smell Log to Track Down Odor Sources

Sanitizer used as a deodorant - OdoBan displayed at a building supply store (C) InspectApediaOdors Related to Time, Weather, Events, Mechanical Systems - how to Keep an Odor or Smell Time & Data Log to Help Diagnose the Cause or Source of an Odor

Photo at left: OdoBan™ is a dilutable-liquid product advertised for use in "elimninating odors" in buildings. This product was on display at a building supply store and is widely available. The container labeling advertises the product for use as a deodorizer that "eliminates unpleaseant odors on washable surfaces", as a sanitizer, a disinfectant, a mildewstat
(MILDEW PHOTOGRAPHS BUILDINGS ? ), and as a viricide.

We could not find the product ingredients on its label but the product's MSDS is readily available and indicates that principal ingredients (other than water) include isopropanol and Alkyl (C12-16) dimethyl benzyl ammonium chloride.[7] There the product is described as including a floral alcohol - its source of a more pleasant scent than the odor it is intended to ban. Indeed, killing bacteria (if that is the odor source) or washing a contaminated surface with a sanitizer or disinfect is likely to significantly reduce the contribution of that specific surface area as an odor source.

But as we comment at CHEMICAL ODOR SOURCES, because an odor reservoir can provide effectively a continuous source of smell, in our opinion the most effective means of odor removal in buildings is to find and remove the odor source. For this reason this article series focuses on methods to find the source of smells or odors in and around buildings.

Keeping a log sheet that records date, time, weather, operation of building mechanical conditions, sun, wind, etc. can help track down otherwise mysterious smells in or around buildings.

  • Odor or Smell diagnosis log: using the possible odor sources or odor and smell causes in building air, water, or mechanical systems listed below, and elaborated in more detail in articles listed at ODORS GASES SMELLS, DIAGNOSIS & CURE [link given below], if you are having trouble diagnosing an odor problem in a building, try keeping a detailed record or log, by date and time, of your observations of the conditions and factors listed below.

    Often data from just a few days or a week will provide a strong suggestion about where to look more closely to find and fix an odor problem in buildings, water, mechanical systems, or other building components. Your odor log can be just an informal set of notes, or you can use an organized spreadsheet or form.

    Keep an Odor or Smell Diagnostic Log: Use either of the three files listed below to record various data that can help figure out the source of a mystery odor or smell - we recommend the first Odor Checklist Form listed below as it is the most detailed version. When using the Odor Checklist Form, also review our Checklist of Possible Causes/Sources of Odor or Smell Complaints that begins in this article, just below, and to prepare yourself also review our home page for this topic:

    • ODOR EVENT LOG & CHECKLIST FORM printer-friendly PDF file to record odor observations such as time of day, weather, temperature, sunlight, & possible sources as an aid in finding the actual source of odors & smells in or around buildings

    • ODOR LOG EXCEL Spreadsheet to record your observations for further analysis for those who perfer to work with spreadsheets to enter odor observation data

    • ODOR LOG abbreviated form "short list" printer-friendly PDF file lists observations that can help track down an odor source.

Checklist of Possible Causes/Sources of Odor or Smell Complaints At or In Buildings

  • Odors from Animals: are there animals present outside or inside the building?

  • Odors from Air Conditioning systems: see HVAC system odor notes below; Also

    and DUCT SYSTEM & DUCT DEFECTS (animals, mold, debris or water in ductwork),


  • Biological sources of odors: in addition to animals, above:
    • is there visible mold or a mold/"mildew" or musty odor in the building, in the complaint area, below the complaint area, or in HVAC equipment serving the complaint area?
    • is there condensation in or near the complaint area, such as on windows or on other cool surfaces? Are there exhaust fans in bathrooms or kitchens that are not being uses? Is the indoor relative humidity high (60% or more?)

    • Is there standing water in the building, crawl spaces below the building, or in HVAC systems or ductwork serving the complaint area?
    • are there humans or animals in or near the complaint area who are ill or suffering digestive problems or flatulence?
  • Odors in boats, cars, campers, trucks: how to find and remove smells from vehicles, including moldy cars, dead animals, exhaust gas, burning smells, etc.
  • Odors & Building Structure: does the odor relate to presence of a nearby air movement pathway such as a building stairwell, elevator shaft, or heating and cooling duct system?
  • Odors & Building height, use, occupancy: does the odor relate to the level in the building (convection currents are very powerful updrafts in high-rise buildings), to use of elevators, windows open or shut, stairwell or parking garage doors open or shut; condition of air shafts, cooking.
  • Odor Character: Describe the odor and its strength: chemical, flue gases, fuel gas, heating oil, sewer gas, rotten egg, mold, musty, plastic, food, cigarette, smoke, other. Also see Odors & Paints, below.
  • Odors from carpeting or rugs: see Carpeting odors: diagnose & cure

    carpet smells due to mold, mildew
    , pet urine,

    and carpet stains - thermal tracking,

    and carpet testing advice and

    CARPET PADDING ASBESTOS, MOLD, ODORS - odors in carpeting or carpet cushions and padding may be from mold or other sources.


    see CARPETING & INDOOR AIR QUALITY for a discussion of chemical like odors associated with certain carpets or carpet pads.
  • Odors from chemicals: look for chemical spills, chemicals stored near the complaint area or near HVAC systems serving the complaint area; look for recently-installed products that include glues, roofing materials, mastics and solvents, paints, coatings; have pesticides been sprayed on or around the building?

    See CHEMICAL ODOR SOURCES for more detailed suggestions.
  • Odors from Chinese Drywall:
    discusses indoor air quality concerns that may involve sulphur or "sewer gas" odors in buildings due to the use of corrosive sulphur and other outgassing from Chinese drywall used in some structures. These gases are also corrosive and can damage HVAC equipment as well as other building components including safety devices like smoke alarms and CO detectors.
  • Odors from Concrete: while concrete itself is not normally much of an odor source once it has cured, people may observe or complain of "concrete dust" odors in buildings where concrete dust is present, especially when combined with moisture. Reports of concrete dust odors are particularly likely near concrete cutting operations - a situation that may present an airborne particle hazard. Details are
  • Odors & Electrical Wiring: a smell of burning plastic may be associated with potentially dangerous overheating of electrical components, wire insulation, plastic receptacles or light switches.

    Watch out: If you smell "burning plastic" or or smoke similar odors indoors or even outside of a building, a dangerous electrical failure could be present and there is risk of a building fire.

    Following the explosion of an electrical transformer in a New York City sidewalk vault, the The New York Times reported that an employee of a nearby store and others in the area had observed an increasing "smoky odor that was growing stronger ... it smelled like burning plastic." Inside residential buildings, aluminum electrical wiring can overheat sufficiently to start a building fire without tripping a circuit breaker, or any electrical wiring can overheat if the circuit is overloaded, improperly used, or damaged. The risk is still greater if the circuit breaker such as FPE Stab-Lok or an improperly installed fuse have made circuit protection unreliable.

    Turn off any suspicious or malfunctioning electrical circuits immediately, install smoke detectors, call your fire department, and hire an electrician familiar with aluminum wiring.
  • Odors & Fans: while exhaust fans are often used to move odors out of a building, a little thinking and investigating may be in order: does the exhaust fan or whole house fan or attic roof vent fan cause odors, dust, or even mold to move upwards through the building? (Be careful that your whole house fan or other exhaust fans do not overpower and cause improper operation of your radon mitigation system if you have one installed).
  • Odors & Fireplaces: Type of fireplaces (gas, wood, coal), fire place door (glass vs screen), damper open/shut, in use, frequency of use.
  • Odors from furnishings: some fabrics, upholstery treatments, and glues used in some furnishings (and cabinets) may be the source of odor and IAQ complaints; do odor complaints correlate with installation of new furnishings or building material?
  • Odors & Glues or Adhesives: many adhesives use a solvent that can produce very strong odors, especially when the adhesive is recently applied. We suspect that adhesives used over wide areas are more likely to be noticeable in buildings, such as carpet or flooring adhesives. Also
  • Odors & Heating Equipment or other Appliances: does the odor appear only when certain appliances are running: cook stove, air conditioner, heater, aquarium pump, fans, clothes dryers, clothes washers, dishwashers, or electrical devices such as TV's?

    Heating Oil fired equipment: If the odor appears to be related to oil burning appliances such as an oil fired furnace, boiler, or water heater,

    If the odor appears due to a leaky oil tank or a heating oil spill,

    LP or Natural Gas fired equipment: If the odor appears related to gas burning heating appliances, see chimney
    backdrafting, leaks, and odors from flues.

    Separately we discuss CARBON MONOXIDE hazards in buildings. Readers concerned with LP gas or natural gas combustion flue gas products and hazards should also


    Also see CHIMNEY INSPECTION DIAGNOSIS REPAIR if odors appear related to any heating appliance that vents through a chimney.
  • ODOR HISTORY: when was the odor first noticed? What date? For how long has it been observed? Who first observed it? Does the first occurrence of a smell relate to an event, change, or modification in the building? If so, what exactly? Examples of events to which odors might be traced include:
    • Building occupancy: an event that involved an unusual number of occupants
    • Change, service, or replacement of HVAC equipment, change to duct work, filters
    • Events, such as a fire or flood, building cleaning, mold remediation, painting, use of deodorizers, pesticides, paints, coatings, insulating products
    • Modifications: additions, construction, window replacements, installation of insulation or change in building ventilation system or plumbing system or fixtures
    • Pets added to the building (see Odors & Pets below)
    • Purchases: of new furnishings, carpeting, draperies, blinds
    • Use of equipment such as an ozone generator following mold "cleanup" -
    • Weather, heavy snowstorms, other weather related events, possibly recurrent or cyclical. Also see Odors & time of occurrence, below.
  • Odors & HVAC systems & Ductwork: odors may be picked up from a source near a return air inlet and odors may travel through a building's air duct system from a variety of sources, not only when the blower fan is on but by convection even when the fan is not operating.

    See HEATING SYSTEM ODORS about odors from combustion products, and

    see BACKDRAFTING HEATING EQUIPMENT for a discussion of dangers of improper venting of oil or gas fired heating equipment.

    Check for adequate fresh-air supply to the building and to its combustion appliances (15 cfm per person); check that the air supply vents are actually open and unblocked, and that the duct system is not leaky or contaminated. Also
  • Odors & indirect odor sources: a smell or odor that is perceived to be in a particular building area, in water, or even in individual items in a building may actually originate indirectly in another source. The New York Times reported an example of indirect odor causation in describing a Johnson & Johnson product recall of "several hundred batches of popular over-the-counter medicines, including Benadryl, Motrin, Rolaids, Simply Sleep, St. Joseph Aspirin and Tylenol".

    The Times reported a statement by Johnson & Johnson subsidiary McNeil Consumer Healthcare that "... the breakdown of a chemical used to treat wood pallets that transport and store product packaging was the source of the moldy smell in some products."

    OPINION: a diagnostic clue that the company might have used in tracking down this odor source would have been the appearance of a similar odor across multiple products whose contents are produced at different times, possibly on different fabrication lines, even possibly in different locations. What did these products share in common: perhaps the production of their containers.

    An additional example of indirect sources of building smells is the ability of heating and cooling ducts to pick up odors from one location and transport them to another in the building, through the ductwork.
  • Odors from building insulation: Insulation Odors: may be caused by contamination of the insulation by rodents or other animals (urine, feces, nesting materials), or mold (INSULATION MOLD TEST). Some cellulose insulation may emit an odd odor if the cellulose manufacturer used an ammonium sulfate/borate mix. Details are
    at Cellulose Insulation Odors, Smells.
  • ODOR LOCATION: does the odor appear throughout a building or only on certain floors, in certain rooms, or at certain walls?
    • What is different about the room where an odor appears:
      • What side of the building is the room on? What conditions are different there such as sun exposure, wind exposure, nearby trees, prevalent wind direction, outdoor possible odor sources?
      • What side of the room, what wall, has the strongest odor: is it an exterior or interior wall?
      • What materials are unique to the odor-source room, such as carpets, carpet padding, drapes, window shades, kind and type and age of windows, screens, heat, air conditioning, pet occupancy, people occupancy, laundry storage, proximity to baths, kitchens, laundry, openings between floors?
    • What is different about the floor or level in a building where odors occur? Proximity to basements, attics, leaks, rodents, pests, animals, heating equipment, pesticide treatments

      See SMELL PATCH TEST to FIND ODOR SOURCE This article describes a procedure that assists in pinpointing odor sources to a particular surface or piece of furniture or carpeting, using aluminum foil, paper towels, and simple masking tape.
    • Does the odor appear related to specific equipment such as heating or cooling system ductwork or air handlers? Does it occur only when certain equipment is operating?
  • Odors & Medical Conditions: consult with your physician to rule out illness, neurological disorder, or to ask about possible relationship between the odor complaint and medical condition or individual sensitivity. For example, pregnant women often have an increased sensitivity to odors.

    Some tumors or other illnesses are associated with changes in perception of odors.
  • Odors & Mold: moldy smells or odors present? visible mold in the building, history of building leaks? Mold odors are generally MVOCs - these gases are produced inconsistently, not by all molds, and not under all conditions; MVOC production may vary by indoor conditions such as temperature, humidity, light, darkness, even season or mechanical disturbance of moldy materials.
  • Odors & neighbors: does the odor correlate with activities by building occupants or building neighbors? What about trash burning, level of septic system usage, use of woodstoves, coal stoves, home improvements, building projects, cooking, wine making.
  • Odors & occupants: does the odor occur when the building is occupied by large number of people, visitors, or specific individuals who may have brought something new into the building?
  • Odors from other outdoor sources: in addition to neighbors and septic systems cited above, look for industrial activity nearby and especially that are upwind (wind blowing from the source towards the complaint area) including also construction activity (painting, roofing, paving), highways and traffic areas, truck terminals, fueling stations, loading docks, areas where vehicles may be left idling, spraying of pesticides
  • Odors & Ozone Treatments:
  • Odors & paints: paints, both exterior and interior are odor sources. Paint odors are strongest when the paint is being applied and during the paint drying process. But some high VOC paints may continue to outgas VOCs at low levels for years after initial application.

    Newer low-VOC interior paints and no-VOC interior paints were described in a New York Times article (Feb. 2010) in an application, odor, and durability test. After a manufacturer-recommended 6-week drying time, the low-VOC and zero-VOC paints were considered equivalent to higher VOC coatings in quality, and were described as low in odors during application when none of the paints was odor free, and odors "disappeared in an hour or so."

    Low-VOC and zero-VOC paints tested were described as temporarily producing odors such as wet cement, mild-ammonia (common), fruit, and sour smell. Also
  • Odor perceivers: who notices the smells? Is the odor perceived only by certain occupants? Is the odor more noticeable to building occupants or to occasional visitors. People's sensitivity to many odors tends to diminish over longer exposure times as the odor-sensing neurons and brain response become desensitized.

    Such individuals may notice an odor only upon entry to a building and not after being indoors for a time; people can also become desensitized to an odor such that even after leaving and returning to the building they do not notice the odor as much as is noticed by visitors. This seems especially true with animal and pet odors for people who live with pets.
  • Odors & Pets or other Animals in Buildings: what is the history of animals and pets occupying the building? What about prior owners and their pets. What about animal pests such as rodents: mice, squirrels, raccoons, insects, who may be responsible for smelly insulation, animal urine or fecal waste on building surfaces, dead animals in walls or ceilings.
    See Pet Odor Removal and

    see Building Inspection & Test Procedures for Pet Allergens.
  • Odors & Plumbing: does the odor presence relate to the use or dis-use of plumbing fixtures in the building? Does heavy usage bring out the odor problem? Problems with the building drain-waste-vent piping, leaks, and even loose toilets are common sources of sewer gases, septic odors, and even "rotten egg" odors in buildings.
  • Odor strength: is the odor perceived as strong or mild? Does the level of smell vary? Under what conditions?

  • ODORS & TIME OF OCCURRENCE: does the odor appear all of the time or only at certain times. For odors that come and go, does the time of the odor correlate with:
    • Activities: Cooking activities may be an odor source
    • Time of day, sunlight, operation of heating or cooling equipment
    • Time of year, season, foliage, outdoor or indoor activities including activities of neighbors or industrial facilities that can produce odors, chemicals, gases, that move towards the subject property
    • Heating or cooling season: does the odor appear when the heating system comes on? Check immediately to assure that there are no carbon monoxide hazards or flue gas hazards.
    • Odors in high-rise buildings: use of elevators, use of stairwells, doorways left open or shut during different periods
    • Use of equipment: operation of a vehicle in an attached garage, use of an ozone generator, electric motors that may be overheating
  • ODORS & TEMPERATURE: does the odor appear or disappear in relation to changes in building temperature?
    • Sunlight striking plastic window screens may make a distinctive odor only on the sunlit side of the building
    • Plumbing system drains or vent systems may release odors when a private septic system is under heavy use or in certain weather conditions -
    • Flooding conditions: Also, if odors appear at drains or fixtures only in times of area flooding, odors at a basement floor drain (for example) may be due to backing up sewer or septic drain lines.
  • Odors & trash or garbage: are there refuse or garbage containers stored in or near the building? Are they improperly covered? Can you trace odor by strength to these locations? Don't rule out indoor trash and garbage containers and/or areas around them that need cleaning
  • Odors and VOCs or MVOCs, volatile organic compounds or mold volatile organic compounds.


  • ODORS & WEATHER conditions: does the odor correlate with weather conditions such as humidity, temperature, rain, snow, wind? Does the odor or smell correlate with heavy snow-cover?
  • Odorless chemicals or gases in buildings? See ODORLESS CHEMICALS / GASES: CHECK FOR? for a strategy
  • Weird hard-to-identify odors are also discussed in the FAQs of this article, from peaches to a Chinese laundry to sauerkraut smells.

Odor Diagnosis Strategies:

You can start tracking down the cause or source of an odor in one or more of several ways:

  1. ODOR DIAGNOSIS SIX STEPS - taking an orderly approach to odor source tracking
  2. ODOR DIAGNOSIS CHECKLIST - an easy checklist of stuff to examine or test - this article
  3. ODORS GASES SMELLS, DIAGNOSIS & CURE - includes a catalog of places to look when tracking down an odor source
  4. SMELL PATCH TEST to FIND ODOR SOURCE - procedure for testing specific surfaces or items to see if an odor souirce of if they have absorbed and are re-emitting an odor


Continue reading at ODOR DIAGNOSIS SIX STEPS or select a topic from the More Reading links shown below.

Or see ODOR EVENT LOG & CHECKLIST FORM printer-friendly PDF file to record odor observations


Suggested citation for this web page

ODOR DIAGNOSIS CHECKLIST, PROCEDURE at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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