An Airtight Presentation

Monday, October 15, 2018

As winter approaches, we start thinking a little more about the drafts in our homes. Now that the warm breezes are slowly changing to biting winds, we are harshly reminded that maybe our homes’ envelopes could be improved.

Early this fall, Building Envelope Specialist Dale Sherman taught KHH staff about some of the basics of the building envelope. He created a presentation for our monthly lunch-n-learn about the four boundaries involved in keeping a building air tight. Surprisingly, most people only focus on the water and thermal boundaries, often completely ignoring the pressure and vapor boundaries.

To be fair, water and thermal are much easier to remember, because they align with our basic need for shelter: keep the warmth in and the rain out. The pressure and vapor boundaries tend to be less noticeable than water and thermal in terms of day to day life.

The pressure boundary limits air flow between the inside and outside of the house. This boundary is what stops our houses from being “drafty.” Usually home owners mistake problems with their pressure boundary for problems with their thermal boundary. The vapor boundary regulates the rate of moisture moving through an assembly such as a wall. If a house’s exterior paint is peeling, there may be an issue with its vapor boundary.

With so much knowledge at our disposal, one would think that these boundary problems would only be found in older houses. However, building envelope specialists are still finding ineffective air barriers in new homes. Many newly constructed homes fail to obtain their Certificate of Occupancy because they do not meet the 2015 Building Code standard for airtightness. This problem is easy to address while a structure is being built, but it becomes much more difficult after the fact.

In other cases, non-continuous boundaries in homes do not make themselves known until long after the structure has received its Certificate of Occupancy. No matter what situation leads to them, poorly constructed boundaries are always problematic. They often result in higher energy bills, building deterioration, discomfort, and even negative health effects.

Luckily for us, non-continuous boundaries can be detected rather easily with the use of the blower door test. This test uses a fan to suck air out of the house. If there is a hole in a barrier – primarily the air barrier – air will leak back into the house. Using this method, specialists can calculate the building’s air leaks and take action to fix the inadequate barrier.

This is just a small sampling of what building envelope specialists know about the boundaries that protect our homes from the elements. During the frigid winters of Central New York, we certainly need their expertise.

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