Indoor Air Quality

and Soffit Ventilation

When your home breathes through healthy soffit, it enhances every breath you take.

Indoor Air Quality

According to the EPA, indoor air quality (IAQ) refers to the “the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants.” Maintaining a healthy IAQ levels is as important as it seems – and maybe easier.

With improved building techniques and modern materials, today’s homes are built tighter than ever, which greatly improves energy efficiency. However, the unintended side effect is that fewer air exchanges take place with outdoor air, resulting in overall poorer indoor air quality. Studies show that indoor air is 2-5 times more contaminated than outdoor air. When you consider that people spend nearly 90% of their time indoors, that is a large opportunity for improving home air quality.

Health problems associated with poor indoor air quality include respiratory ailments, allergies, asthma, certain cancers, and heart disease. Individuals react in different ways to indoor air pollution, depending on age, general health, and other factors. It is also suspected that individuals can develop sensitivity to certain biological or chemical pollutants after repeated exposures.

Pollutants in indoor air include mold spores, volatile organic compounds (VOCs), combustion pollutants, radon, formaldehyde, and house dust mites. Combustion pollutants such as carbon monoxide can be introduced into the home due to an improperly vented or malfunctioning gas appliance, or simply through auto fumes from attached garages. To help with IAQ, we can reduce levels of gaseous pollutants by keeping appliances maintained, changing air filters, allowing new materials to off-gas VOCs before bringing them into the home, and other measures.


Mold is one of the main contributors to poor indoor air quality. Molds fungus exists all around us in outdoor environments, and plays a useful role in decomposing dead organic matter. However, inside the home, mold spores become a problem when moisture allows them to grow on building materials and cause decomposition. They can also release allergens and irritants in the process, which affect individuals who suffer from allergies and asthma, as well as irritating the eyes, skin, throat, and lungs of non-allergic individuals.

Improper ventilation also leads to increased moisture in the attic, which results in mold, mildew, dry rot, and insulation damage. Mold, with its methods of decomposing materials, reproducing via spores, and producing other toxic byproducts, is considered a primary contributor to poor indoor air quality.

Asthma and Allergies

Dramatically rising allergy and asthma rates in the United States also correlate to poor indoor air quality. Americans spend an estimated 90% of each day indoors, so many doctors and health organizations focus on the quality of indoor air for improving symptoms of patients with allergies and asthma.

For asthma sufferers, poor IAQ can either exacerbate the severity of asthma attacks or trigger more frequent asthma attacks, or both. The EPA estimates that 21% of current asthma cases in the United States are related to dampness and mold in homes.

Reports of allergies are also on the rise. “Indoor” allergies that do not seem to change with the seasons are often suspected to be related to indoor air quality. Even people who suffer with “outdoor” allergies such as hay fever may find that remaining indoors when outdoor allergen levels are high does not significantly reduce their symptoms, due to outdoor allergens inside the home.

To improve the health of your home and your loved ones, and avoid issues like asthma, COPD, and lung damage, take some easy steps to make sure your home takes care of you.


The key to improving indoor air quality is ventilation. According to the EPA, ventilation “helps remove or dilute indoor airborne pollutants coming from indoor sources. This reduces the level of contaminants and improves indoor air quality (IAQ).”

There are several simple ways to achieve temporary ventilation improvements. These include spot ventilation like bathroom fans used to draw humid post-shower air outdoors, or kitchen fans that ventilate cooking odors, humidity, and smoke.

The most important type of ventilation scarcely requires another thought when properly designed: Natural ventilation. Natural ventilation cools the attic space and ensures that superheated, stale, and often polluted air is exchanged for fresher outdoor air.

How Soffit Works

Proper ventilation requires adequate air flow through the attic space. Warm air rises; cool air descends. A natural ventilation system takes advantage of this natural convection by allowing cool air to enter the attic under the eaves and warmer air to exit the attic at the ridge. Wind also affects this system by forcing air into the attic under the eaves and drawing air out at the ridge.

Through a thoughtfully engineered combination of air intake and exhaust vents, natural ventilation should be planned into the home design. Intake and exhaust can be achieved in different ways, but according to the U.S. Department of Energy and Habitat for Humanity, a combination of continuous ridge vent along the peak of the roof and continuous soffit vents at the eaves provides the most effective ventilation.

The formula generally used to achieve adequate ventilation requires approximately 50% intake under the eaves and 50% exhaust at or near the peak of the roof. Ideally, the system should allow more intake than exhaust. Both intake and exhaust are measured in Net Free Area (NFA), which refers to ventilation space, or the total amount of unobstructed area through which air can pass through a vent. Most building codes specify NFA for proper ventilation.

The formula for establishing how much ventilation is required on the roof to provide the minimum amount of ventilation is:

1 square foot of ventilation space (NFA) for every 150 square feet of attic floor space

NOTE: In cooler climates, if a vapor barrier is used, the formula for achieving minimum ventilation is 1 square foot of ventilation space (NFA) for every 300 square feet of attic floor space.

The amount of ventilation that is used on the roof then mandates the amount (NFA) of ventilation that is required under the eaves in the soffit. For example, if the average attic requires approximately 22 square feet NFA of exhaust on the roof, a soffit profile with at least 11 NFA on both sides of the house is necessary to achieve a combined NFA of 22.

Soffit ventilation is a dynamic system that has to work in conjunction with your roof vent strategy and system. These specifications should be considered minimum standards and might not be sufficient for healthiest indoor air quality, since they were written before the current trend towards tighter home construction. The presence of vents in soffit can only guarantee proper air flow through the attic if the system is properly engineered. If a home’s vented soffit has less NFA than the roof vent system, it can actually prevent attic air from escaping.

Choosing the Right Soffit

Soffit with superior intake capability is an essential element of a balanced ventilation system. Quality Edge soffit, manufactured from a titanium-enhanced aluminum alloy, is engineered and developed to meet unique strength requirements. The strength of this custom alloy enables Quality Edge soffit designs to achieve a greater number of carefully sculpted small intake vents within each square inch of material. The result is a selection of attractive soffit styles that feature the number of intake vents necessary to achieve the highest intake NFA possible.


Clean, healthy indoor air can be achieved with something as simple and as breath-takingly beautiful as soffit.




source:  U.S. EPA,