Everything to Know About Indoor Air Quality

How Energy Improvement Can Negatively Impact Indoor Air Quality:

Sealing and caulking air leaks in buildings can have unintended consequences for indoor air quality (IAQ) because the rate of natural ventilation decreases. Providing a building with less air leakage will help the building to be more energy-efficient, but it can also trap airborne particles, which include:

  • Paints, cleaning products, and maintenance supplies release VOPs (Volatile Organic Compounds)
  • Particulates and fibers like asbestos and fiberglass
  • Radon, (a naturally occurring radioactive material)
  • Sewer gas
  • Carbon monoxide from combustion appliances
  • Pet borne allergens like pollen, dust mites, cat, and dog hair
  • Microbial organisms like viruses and bacteria and fungi

Modern construction materials also limit the ability of walls to dry to the inside and outside after they get wet and sealed. Walls that get wet but can't dry out are a setup for moisture problems and mold growth in the future.

Modern building materials sometimes make these problems worse by increasing the efficiency of the building. While adding insulation will increase energy efficiency, it's often accompanied by fiberglass, and dust which can all accumulate in air distribution systems. Furthermore, some caulks, sealants, and paints release volatile organic compounds into your home.

Lastly, the building's pressure dynamics can also be affected by certain energy efficiency measures, causing combustion appliances to backdraft, and carbon monoxide levels to increase. As carbon monoxide is colorless and odorless, it is a deadly gas that can be inhaled without anyone realizing it.

Sources of Indoor Air Pollution:

How Can Indoor Air Pollution Affect Your Health?

In addition to moisture-induced problems like mold, dust mites, and bacteria, indoor air pollution can be caused by pollutants like carbon monoxide, volatile organic compounds, radon, and particulates.

Mold grows best in moist, nutrient-rich environments. Several areas in a building can supply the food that molds need to grow if moisture levels are high enough. Aside from wood surfaces, mold also loves to grow on ceiling tiles, insulation, and drywall paper faces. In addition to dirt and pollen, mold can also grow within ductwork, in which case the mold will spread throughout the building.

Air pollution caused by mold can be serious. Several surfaces, such as drywall and oriented strand board, can grow mold when moisture is too high.

Moisture can also lead to an increase in mold, dust mites, and bacteria. Soft surfaces like bedding and carpet are ideal habitats for dust mites, and the higher the relative humidity the more these organisms proliferate.

A building with unvented cooking appliances, a wood burning fireplace, or a fireplace that is connected to a blocked chimney tends to produce more carbon monoxide, which is the byproduct of incomplete combustion of fuel. It is also possible for carbon monoxide to be released from appliances and fireplaces when they are back draughts, which, naturally, can be caused by energy efficiency rules that affect natural ventilation rates and internal pressures.


There are two types of illnesses that can be caused by poor indoor air quality in the building. One of the illnesses that is caused by poor indoor air quality is sick building syndrome, which is a general illness. Symptoms of sick building syndrome can be varied and they can range in severity and duration. A symptom of this disease may be an irritation or a feeling of dryness in the eye, nose, and throat of the patient. Sneezing or nasal stuffiness may accompany these symptoms as well as runny nose. Headaches, dizziness, nausea, irritability, and forgetfulness are possible symptoms. Some people may feel tired and be uninterested in things other than getting better sleep. The symptoms may seem like a set of related symptoms but they may be troublesome or difficult to diagnose.

In addition to indoor air pollution causing the generalized 'Sick Building Syndrome', there are also certain contaminants that may cause illness within a building. Inhalator fever, respiratory allergies, and carbon monoxide poisoning are all examples of asthma - which can be chemically induced or aggravated by mold. It is much easier to diagnose these illnesses since they are caused by specific contaminants.

Those who are more sensitive and those who are ill more quickly will react differently to indoor air pollution. Despite the fact that no one appears to be ill, you still want to ensure that the building has healthy air.


Modern problems require modern solutions! Because of how tight we build modern homes, we need to actually supplement the indoor air with outdoor air. Fortunately, there is a piece of mechanical equipment designed to do this without having to sacrifice energy efficiency - the Heat (Energy) Recovery Ventilator (HRV/ERV). We will talk about the subtle difference between an HRV and and ERV in a later post.
HRV ERV Diagram

As seen in the diagram above, an HRV/ERV will pull in exhaust air (often from a bathroom or kitchen), exchange heat with fresh air from outside and then exhaust that stale air while supplying the fresh air to your air distribution system. These tend to not be perfectly efficient, but most brands exchange heat at a 60-70% efficiency which is pretty good and worth the expense. For this reason, we design all of our house plans to have oversized mechanical rooms that can accommodate an HRV/ERV and pathways for the exhaust and fresh air ducts which must be located sufficiently far from each other on the exterior.

Because most building materials off-gas early in their life cycle, it's important to ventilate as much as possible before you move in. Opening windows and strategically placing box fans can help remove as much of the VOCs as possible before the big move in day. Increasingly, building material manufacturers are offering lower-VOC products which can help as well.

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