Concentration of CO2 in the Atmosphere

The Great Indoors: Creating a More Healthful and Safer Built Environment

Reprinted with permission from Steven Winter Associates, Inc. April 16, 2020 blog at

Steve Winter Associates Team – Jayd Alvarez, Thomas Moore, Lauren Hildebrand, Maureen Mahle, and Peter Stratton

Ventilation on a rooftop. All images courtesy of Steven Winter Associates

As humans, we spend a lot of time indoors. Studies by the U.S. Environmental Protection Agency indicate that under normal circumstances the average American spends over 90% of their life indoors. With the spread of COVID-19 and widespread voluntary and involuntary quarantine, the rise of work from home policies and new direction to social distance has resulted in a further increase to the amount of time we spend indoors. Now more than ever, people are cognizant of the air they’re breathing and the surfaces they’re touching. The buildings that we live, work and play in have impacts on our physical and mental health. With certain building and design considerations, we can make these impacts beneficial.

We recruited some experts at Steve Winter Associates (SWA) to fill us in on the various considerations when it comes to the health and comfort of a building, as well as some certifications that ensure these considerations are met.

Please click on the image to enlarge it.

Filtration and Ventilation

Additional time spent at home is a good time to consider if our living environment is optimized to support our long-term health. One of the keys to a healthy living environment is high quality indoor air and the means by which we maintain the quality of our breathing air is ventilation.

Why do we ventilate buildings? Simply put, ventilation removes contaminants that accumulate in the indoor air and replaces it with outdoor air that is not contaminated. There are several ways to ventilate, but not all techniques are created equal. Most buildings have exhaust-only ventilation systems. This type of system is characterized by local mechanical exhaust fans, operated intermittently, which typically remove air from the kitchen or bathroom. But where does the fresh air that replaces this exhausted air come from? If you have no idea, you’re not entirely alone. In an exhaust-only ventilation system the living environment is likely assumed to operate under some gradient of negative pressure. So, the air that is replacing the exhausted air will be pulled into the living environment from an adjacent corridor, an open window, or your neighbor’s apartment. It might be pulled through the wall assembly, the crawl space, a crack in the foundation, or some combination of the above. I think we can agree that it would be in our best interest to control the quality of the air we breathe; therefore, shouldn’t we know its point of origin? And, if you don’t know where your breathing air comes from, how do you filter it?

There is a better way. Continuous balanced ventilation systems, combined with air sealing and compartmentalization, provide more control over the air we breathe. In a continuous balanced ventilation system, air is constantly exhausted from the kitchen and bathroom at low volumes and is replaced with an equal amount of continuously supplied air from a known origin via a dedicated outdoor air duct. The living environment is pressure-balanced with an equal volume of supply air and exhaust air. As a result, the air in our breathing zone is no longer being pulled from parts unknown. Balanced ventilation systems operate best with the installation of a continuous air barrier system in exterior wall assemblies, and compartmentalization measures between apartments, decreasing the amount of air that is pulled from adjacent apartments and through wall assemblies. There are additional benefits, such as decreasing transmission of odor, smoke, sound, and pests. With a continuous balanced ventilation system, and the appropriate compartmentalization and air sealing measures, we now own the breathing zone. We know the origin of our breathing air, and the inclusion of dedicated ducted supply air offers the opportunity for further quality control through filtration of supply air and the potential for heat and moisture recovery from exhaust air for optimized comfort.

Something else that you should consider, or rather do, is replace your air-handler filter and make use of the minimal efficiency reporting value (MERV) a performance rating, to determine if your system allows installation of a MERV13 filter which can remove particulate matter (PM) 2.5 and less.

-Written by Thomas Moore, Building Systems Analyst

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Thermal comfort – favorable temperature and humidity conditions – is fundamental to wellness and the proper functioning of any occupied space. When indoor environments are too warm, there is evidence of increased sick building syndrome symptoms resulting in occupants’ negative moods, increased heart rate, respiratory symptoms, and overall feelings of fatigue. Relative humidity (RH) that is below 20% can cause dry eyes, skin, and mucous membranes. On the other hand, high relative humidity (above 70%) may lead to stuffiness or mold and fungus growth. Mold and fungi produce allergens (causing allergic reactions), irritants, and in some cases, potentially toxic substances (mycotoxins). In general, I recommend conducting regular inspections of roofing, plumbing, ceilings and HVAC equipment to identify sources of moisture and potential condensation. When moisture or mildew is present, immediately address the source and replace contaminated materials. Limit areas of the building that are routinely wet because of their use (think bathrooms and kitchens) and provide a means for drying them out when they do get wet.

This CDC study details the clear link between damp environments and respiratory illness.

Of particular interest now, viruses survive for longer periods at low humidity so it is even more important to maintain optimal relative humidity between 40% and 60%. If the RH in your home is too low and you have a humidifier, start running it. If someone in your home is self-quarantined, place the humidifier in the isolated person’s room. Provide individual-level thermal control where possible.

-Written by Lauren Hildebrand, Sustainability Director

Building Materials

The current pandemic brings us a renewed awareness of the materials in our homes and our environments. If you are like me, you are constantly tracking what you’re touching. Also, you may be thinking about how a virus to remains viable longer on some materials than others, as some preliminary research indicates. Luckily, thoughtful and responsible choices can help increase our health and wellness as our household spaces become full-time work, education and play spaces.

How can what we are learning affect our materials choices for current and future buildings? First and foremost, think about cleanability. How easy or difficult is it to disinfect a given material with, say, soap and water, or a diluted bleach solution? (Note that while our ‘green’ cleaning protocols would not ordinarily include bleach and the current coronavirus can be destroyed with

simple soap and water, there may be another virus in another time when we need to use something stronger.) How many grout lines or other transition materials are used, how cleanable are those transitions, and can we choose materials that minimize those transitions (such as continuous flooring or larger wall tiles)? We expect to see a renewed focus on cleanable materials that will ultimately improve health and durability under ordinary — and extraordinary – circumstances.

We also foresee a surge in anti-microbial finishes. Be careful with those, because while they are designed to kill or inhibit the growth of microorganisms, many antimicrobials contain triclosan and triclocarban, which have shown to interfere with normal human development and function. For that reason, we advocate such products for targeted use.

Another concept to consider is no-touch building finishes and amenities. It seems to me that in a post-COVID-19 world, we will be choosing touchless automatic door openers and elevator buttons, more lighting occupancy sensors, touchless water-bottle refill stations, and those touchscreens in the lobby or checkout counter will be a thing of the past. Hopefully, we will have a touchless handwashing station in every new building lobby!

-Written by Maureen Mahle, Managing Director, Sustainable Building Services

Universal Design

As the goals of Universal Design suggest, an integral part of designing high performance spaces for all people regardless of age or ability includes incorporating health and wellness into the built environment. Many of the concerns targeted in health and wellness design strategies, such as chronic respiratory disease, diabetes, heart disease, and chronic illness, qualify as disabilities under the Americans with Disabilities Act (ADA). Further, each one of these health concerns is an underlying condition highlighted by the COVID-19 pandemic. Addressing public health issues through design can contribute to promotion of overall health, avoidance of disease, and prevention of injury.

Shared Goals and Design Strategies

There are several shared goals and design strategies among health and Universal Design initiatives — the improvement upon ergonomics, sleep, safety, physical and mental health, among others – not only serve to create healthier environments, but can also contribute to better spaces for all building occupants. Moreover, the inclusion of health strategies in design can assist individuals currently living with disabilities by mitigating chronic symptoms or preventing certain disabilities or injuries from occurring.

For more information about this topic, read the original piece in WBDG (, and the article from WELL Building Institute at .

-Written by Peter Stratton, Senior Vice President, Managing Director, Accessibility Services


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