How Hard is it to Pass the Blower Door Test in Maryland?
First, lets go over What a Blower Door is in simpler terms and what it is.
What’s a Blower Door test? Easy, it’s a way to measure leakage within a house in CFM(cubic feet per minute) at a pressure rate of 50 pascals. When we’re talking about a blower door code test in Maryland, the code requires any new house to be at or below 3ACH(air changes per hour).
So, first, we have to figure out what the volume of the area being tested is.
We usually do this with plan sets and verify in person the house is the same size. The reasoning behind this is, we need to figure out how much air we can fit into the space in order to calculate how many times it can pass through the house(ACH).
Why? If we know how much air can fit into the space, we can measure how much will leave it naturally.
Then, we complete the blower door test, which is measured in CFM, and convert the measurement from minutes to hours by multiplying it by 60. Then, we divide the volume by the CFM*60, and we have the ACH number.
See the equation below for a visual.
Lets do an Example of what a good Blower Door Test would be measured at in ACH.
Example #1: Average Baltimore City Row Home or Townhouse
Let’s say we have about 1500sqft(square feet). Lets say that each floor is 500 sqft. From here we’ll figure out volume. The basement is 500sqft and 8ft ceiling height to the drywall, another 1’ to the floor above, which gives us a 9’ ceiling height. Multiply 500sqftx9ft Ceiling Height and we get a volume of 4500CF(cubic feet). The first floor is the same thing 500sqft with a ceiling height of 9’ including the band joist area giving us a CF of 4500. Finally, we’ll do the top floor, where the area is the same, 500sqft, and the ceiling height is now 8ft because we don’t have a floor above it to include the band joist and the insulation would be laying directly on the band drywall.
I’ll put this into a chart below so it’s easier to understand visually(I’m a visual learner)
Blower Door Example 1
What’s a good Blower Door Number for this House?
Code houses in general are meant to pass at a minimum, which isn’t really a good thing when it comes to quality. Personally, the 2-2.5 ACH range is the sweet spot for me. It’s enough to get you to a safe range of passing prior and not have to dig through insulation and bust walls out to get a good number. It will take some preparation though.
How do you get the Blower Door To Pass??
Follow these Steps to make sure you’ll Pass and Pass with ease within the 2-2.5 ACH Range :
Once ALL trades have been through the house- Plumbing, Electrical, HVAC, and Pest. Have the insulation crew come out and seal the house, and make sure these things leading to outside or attic have been sealed/taken care of:
Walls should be picture frame sealed along with the floor leading to the outside
Electrical Penetrations
Plumbing Penetrations
Dead Spaces and Chases(sometimes holding wiring and plumbing), and making sure a barrier is in place leading to the attic if there is one, plywood, skyflex, and foam board will do the trick!
Garage bays are blocked and sealed same materials as above will do the trick!
Bathroom fans have decent backdraft dampers built-in
Basement and first-floor rim board is picture frame sealed
Once the drywall has been installed and mudded/first coat is installed, you should call the insulation company out for the “Second Stage” of air sealing. The same electrical, wall, and plumbing penetrations will now be sealed but in the attic. Along with the tops of the walls within the attic.
If you really wanted to take a step higher, you could spray foam the house fully with either open or closed-cell insulation. This would reassure you pass the blower door test without question. However, I would still have someone come out to inspect prior to closing in, I have had small spray foam companies fail blower door tests before.
With these steps, you could 100% pass the Blower Door test, and now you know how the Blower Door is completed and calculated.
