Why Passive House Buildings Create a Healthier Interior Environment

Date Published July 21, 2020
Category Sustainable Design & Passive House
Author Deborah Moelis; Ryan Lobello; Louis Koehl of Handel Architects
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Passive House buildings are undoubtedly better for the environment because they use less energy than a typical building. But how does the interior experience in a Passive House building compare to a typical building? Here's an explanation of why Passive House buildings provide superior indoor air quality, thermal comfort, and acoustics.


Indoor Air Quality

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Handel Architects has conducted post-occupancy surveys at “The House” at Cornell Tech in order to better understand how residents are experiencing the building. This allows us to understand what is working and what can be improved upon, with a goal of designing better Passive House buildings in the future. One of the most frequent comments we received from residents at The House was that the air quality in their unit was noticeably better than what they were accustomed to. One resident commented that their hay fever allergy, typically bad in springtime in New York City, was much improved once they moved into The House. Another commented on less frequent asthma attacks.

Passive House buildings like The House require that filtered fresh air be delivered to all habitable spaces 24/7.

This means little to no stagnant air. The air filters in a Passive House building typically have a MERV of 13. MERV stands for Minimum Efficiency Reporting Value, which is a measurement of a filter's ability to capture larger particles between 0.3 and 10 microns. Hospitals use 13-16 MERV filters.

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Passive House buildings require a tight facade.

In many older buildings, if you stand near the facade, you can actually feel the air leaking through around the windows, vents, etc. In Passive House Buildings, air infiltration must be less than 0.6 of the total building volume per hour under 50 pascals of pressure. This is extremely tight - 7-10 times tighter than the facade of a typical New York City building (NYCECC 2020 requires a maximum of 3.0 ACH, meaning a Passive House building is 5 times tighter). In addition to protection from cold or warm air, this "buttoned up" facade effectively eliminates the infiltration of pollutants into the interior spaces, pollutants that would typically pass through a “leaky” facade.

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Interior view of the sealed facade panels at The House at Cornell Tech

The humidity of the interior air is controlled, which leads to healthier bodies.

Correct indoor humidity levels help prevent the spread of infections and respiratory diseases. If spaces are too humid, mold can grow; spaces that are too dry lead to cracked skin and weakened immune systems.

Passive House building systems control the overall interior climate, leading to better health. The airtight facade keeps moisture from being pulled through, preventing condensation from forming within the building facade. This can help prevent mold and moisture buildup that, if present, can contaminate the air that we breathe within the building. Smart vapor and humidification control reduces condensation and mold growth over time.

Indoor odors are flushed out quickly.

Lastly, those of us who have lived in multifamily buildings have all experienced smelling our next-door neighbor's fish dinner being cooked, or the daily special of the restaurant downstairs. Stagnant air inside a poorly ventilation multifamily residential building means that odors linger. By moving and filtering air, Passive House buildings flush out indoor odors quickly.


A Comfortable Interior Temperature

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Passive House buildings have criteria for certification that are driven by a need to protect the environment by reducing carbon emissions, as well as a need to provide a comfortable interior experience.

Since these buildings are tightly constructed, there isn't a temperature difference when standing along a perimeter wall, or when touching a window frame. The exterior walls of a Passive House building have a 25 to 30 R-Value, compared to 13 to 14 R-Value which is currently the code minimum in New York City. In addition, the windows - often a weak point in a building's thermal envelope - have an extremely low U-Value and are not cold to the touch in a Passive House building. These windows are usually triple-glazed and have a U-value of 0.14 to 0.18 as opposed to a U-value of 0.30 to 0.40 for a New York City code minimum residential building.

Cooling and heating loads are extremely low due to the performance of the facade and windows, thus the conditioning system can be downsized in comparison to a typical building. The systems also don't have to run as much, saving money and the environment.


Outstanding Sound Control

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The House at Cornell Tech is adjacent to the Queensboro Bridge.

Excessive noise is a common complaint in both cities and suburbs. In New York City, noise complaints make up nearly 10% of calls to the city's 311 hotline. Mitigating audible outside noise within a living space can have a significant positive impact on productivity and overall quality of life.

The high performance walls and windows in a Passive House building mean an exceptionally quiet interior acoustic experience. Outdoor/Indoor Transmission Class, or OITC, is a system developed specifically for measuring sound transmission of low- and mid-frequency noises through exterior walls. While the window in a typical multifamily residential building has a OITC of 28, Handel Architects' newest Passive House project, Sendero Verde, has windows with an OITC of 31 and 35, reflecting a significant improvement as OITC is an exponential rating.


Conclusion

Covid is clearly causing people to rethink the “business as usual” aspects of their lives. The places we live and the air we breathe must be better than “business as usual." Passive house design provides a clear pathway to the future of healthier buildings.