New Hampshire Chapter of the Construction Specifications Institute

Odor Infiltration
By  Thomas House, AIA, CSI
Principal, THA Architects

Odor complaints may be filed from people living on the street side of the building exposed to vehicle exhaust, trash receptacles and other businesses. Other odor complaints may be filed that are not associated with an obvious source, however most are from cooking smells.  Identifying the source or sources of these odors can be difficult. Odor mitigation is a challenge not only for odors emitted from unidentified sources but also from those emitted from identified sources.

Odors are of interest to local government agencies concerned with air quality management since the public is concerned about the impact of odiferous substances on health and overall quality of life. The inability of air quality management agencies or any other governmental agencies to consistently identify odiferous substances, trace them back to their sources, and reassure the public that their health is not endangered has been a concern.
Robert Blaisdell, Ph.D., Chief, Exposure Modeling Section, Office of Environmental Health Hazard Assessment, California Environmental Protection Agency gave a presentation titled the "Health Effects of Odors.” Dr. Blaisdell started his presentation pointing out that, in nature, odor sensation is a warning system that prevents animals and humans from consuming toxic materials and spoiled food. To do this, the human nose has evolved sensitivity to very low concentrations of odiferous substances. In many cases, this sensitivity exceeds the measurement capability of available instrumentation.
Dr. Blaisdell stated odors have been associated with health effects in people living in the environs of paper mills and hazardous waste sites. He stated that odor associated health symptoms have been reported for substances present at levels far below those known to otherwise cause non-cancer health effects. He also said odor-related symptoms reported in a number of studies include nervousness, headache, sleeplessness, fatigue, dizziness, nausea, loss of appetite, stomach ache, sinus congestion, eye irritation, nose irritation, runny nose, sore throat, cough, and asthma exacerbation.
He expanded upon this topic by explaining that odor and irritancy are mediated by different mechanisms, but the thresholds can be similar for many chemicals. Thus many symptoms reported as due to odors could be due to irritancy from associated substances. Dr. Blaisdell concluded his presentation by stating that risk assessment is not much help in evaluating the impact of odors on public health due to the high variability in human odor thresholds which make it difficult to apply standard risk assessment techniques to odors.
There are a number of challenges to successful identification of an odor emission source as well as to odor mediation. These challenges include:
  • the fleeting nature of many odors,
  • variation in complainant odor sensitivity,
  • variation in inspector odor sensitivity,
  • complainant and facility perceptions on whether an odor is a nuisance,
  • air sampling issues and
  • analytical instrument sensitivity limitations.
This commentary is not an attempt to mitigate external air quality issues generated from outside sources however it will attempt to minimize outside odors from infiltrating into the individual dwelling units as well as from each adjacent dwelling unit.
Odor Mediation Techniques
Similar to that of air borne noise, odors can permeate into and through the building at any given weak location which allows air infiltration.  Unlike noise-reduction strategies, odor-reduction strategies are not typically discussed and debated at the very beginning of the design process.  Instead, air infiltration is discussed as the building codes have become more stringent in energy efficiency design. In an effort to reduce the odors from travelling into and through the building, the building envelope must be tight therefore; air infiltration and energy efficiency will be discussed briefly. By reducing air and odor infiltration, we can significantly reduce heating and cooling costs, improve building durability, and create a healthier indoor environment.
Air-borne odors can be stopped in the following ways:
  • Closing air-gaps around windows and doors – Odors can carry through the outside wall construction through an improperly seal window and around corridor doors which do not have the proper weather-stripping.
  • Reducing gaps around structural elements – Placing mineral wool around structural elements and applying acoustical sealant reduces air movement and thereby reduces the transmission of odors between the units. 
  • Closing air-holes between spaces – odors can carry through key-holes, around pipes, between a wood floor and a brick wall, through outlets placed back to back, and over-and-under walls which are not thoroughly caulked at the top and bottom.
  • Provide a continuous air infiltration barrier – This is difficult if not impossible t achieve on an existing mill building as the exterior wall consists of brick masonry.  Even water may penetrate the exterior surface as brick is permeable hence a weep hole system is introduced. To minimize air infiltration, care should be taken to be sure that the brick walls are in good condition and that the mortar joints are full.
Professional Assessments:
The air tightness of a building can be determined by using several methods. The PFT (Per Fluorocarbon tracer gas) technique and blower door test both provide information about air leakage and energy loss. To conduct these tests, a professional with the appropriate equipment must be called upon.
The PFT technique uses two pencil-size devices. One, the emitter, gives off a small amount of a colorless, odorless, and harmless perfluorocarbon gas. The other, the receiver, absorbs some of that vapor from the average concentration of the gas in the room. That average concentration is proportional to the building tightness—the tighter the building, the higher the concentration.
A blower door test locates air infiltration by exaggerating the defects in the building shell. However, this type of test only measures air infiltration at the time of the test. It does not take into account changes in atmospheric pressure, weather, wind velocity, or any activities of the occupants that may affect air-infiltration rates over a period of time.
Do-it-yourself Assessments:
You can easily conduct a do-it-yourself assessment. The results will not have professional data however the results may be acceptable to the home owner and the neighbors. With a simple but diligent walk-through, you can spot many problems in any type of home. When assessing your home, keep a checklist of areas you have inspected and problems you found. This list will help you prioritize your upgrades.
Locating Air Leaks:
First, make a list of obvious air leaks (drafts). The potential energy savings from reducing drafts in a home may range from 5% to 30% per year, and the home is generally much more comfortable afterward. Check for indoor air leaks, such as gaps along the baseboard or edge of the flooring and at junctures of the walls and ceiling. Check to see if air can flow through these places using incense sticks. 
  • Electrical outlets
  • Switch plates
  • Window frames
  • Doors frames
  • Baseboards
  • Weather stripping around doors
  • Roof penetrations
  • Wall- or window-mounted air conditioners.
Inspect windows and doors for air leaks. See if you can rattle them, since movement means possible air leaks. If you can see daylight around a door or window frame, then the door or window leaks. You can usually seal these leaks by caulking or weather stripping them. Check the storm windows to see if they fit and are not broken. You may also wish to consider replacing your old windows and doors with newer, high-performance ones. If new factory-made doors or windows are too costly, you can install low-cost plastic sheets over the windows.
If you are having difficulty locating leaks, you may want to conduct a basic building pressurization test:
  • First, close all exterior doors, windows, and any flues that require ventilation.
  • Turn off all combustion appliances such as gas burning furnaces and water heaters.
  • Then turn on all exhaust fans (generally located in the kitchen and bathrooms) or use a large window fan to suck the air out of the rooms.
This test increases infiltration through cracks and leaks, making them easier to detect. You can use incense sticks or your damp hand to locate these leaks. If you use incense sticks, moving air will cause the smoke to waver, and if you use your damp hand, any drafts will feel cool to your hand.
On the outside of your building, inspect all areas where two different building materials meet, including:

  • All exterior corners
  • Where roof and penetrations meet
  • Areas where the foundation and the bottom of exterior brick meet.
You should plug and caulk holes or penetrations for faucets, pipes, electric outlets, and wiring. Look for cracks and holes in the mortar and foundation and seal them with the appropriate material. Check the exterior caulking around doors and windows, and see whether exterior storm doors and primary doors sealed tightly.
When sealing any building, you must always be aware of the danger of indoor air pollution and combustion appliance "back drafts." Back drafting is when the various combustion appliances and exhaust fans in the home compete for air. An exhaust fan may pull the combustion gases back into the living space. This can obviously create a very dangerous and unhealthy situation in the dwelling unit.

In buildings where a fuel is burned (i.e., natural gas, fuel oil, propane, or wood) for heating, be certain the appliance has an adequate air supply. Generally, one square inch of vent opening is required for each 1,000 Btu of appliance input heat. When in doubt, contact your local utility company, energy professional, or HVAC contractor.