We have begun the additional house sealing that is needed to bring the house up to super-insulated levels.
Despite what may appear to be a well sealed structure can often be very leaky when properly investigated. To measure the leakiness of a building a blower door test is performed. A blower door is pretty much what it sounds like. It is a specially calibrated blower (fan) installed into a doorway. The blower is generally positioned to blow air out of the house, which causes the pressure inside the house to be lower than the outside air pressure. The only way for air to get into the house to “makeup” for the air that the blower is expelling is through cracks and leaks in the house envelope. All doors, windows, and other openings must be closed during the test.
There are different blower door tests, but the standard is to create a differential pressure between the inside and outside of the house of 50Pa. This pressure level is roughly equivalent to a continuous 20mph wind blowing over your house. To actually measure how leaky the house is, there is a display connected to the blower that shows the pressure level and the blower’s air flow rate. The blower speed is increased until the pressure reads 50Pa on the display. When 50Pa is reached, the air flow rate displayed correlates to how leaky the house is. It is essentially measuring the rate of the air flowing into the house through its leaks. So a higher air flow reading means a leakier house and a low air flow is a tighter house with less leaks.
Why are we spending extra time and money to make sure the house is well sealed? House sealing has a tremendous impact on a home’s comfort and energy consumption. Conventionally constructed homes have natural ventilation, that is; air enters and exits the home as it pleases without regard for what is best for the home from a conditioning or energy standpoint. A well sealed home has controlled ventilation, which can make use of recovering energy and only ventilating when necessary. This also makes it much easier to control the humidity and temperature of the house.
Improving building efficiency should require all new houses to be certified to a certain infiltration rate.
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Our plan is to use the blower door data to quantify the effort required to bring the house up to a super-insulated level. How much labor is required, materials, and which seams and cracks. Below are plots of initial tests. Each point represents a blower door test after an amount of sealing. The three plots show the air flow rate, labor hours, and number of tubes of caulk plotted versus the length in feet of seams in the house structure that have been sealed.
The first point at 0ft, is the initial reading before any sealing has been done, which showed the house air flow leak rate at about 1380 cfm (cubic feet per minute) at the 50Pa pressure.
From there we started sealing the sill plate with silicone caulk around the inside perimeter of the house. As you can see from the data, as the seams were sealed, the house leakage dropped to about 1000 cfm. The last two points represent blow door tests recorded after vertical SIP panel wall seams were sealed.
So far the data shows that to drop the house leakage from about 1400 to 1000, just over 350ft of seams must be sealed, taking 6 man hours of labor, and requiring 33 tubes of caulk. Sealing is ongoing and the data will be updated.
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