Explaining the Air Leakage Testing Update in the 2021 IECC

Date Published: February 14, 2024

Blower door testing (or air leakage testing) is an important part of the building process, as it determines the overall air tightness of a building, and helps to identify problematic leaks that may be present. As a result, it has been required for all new construction and additions since the 2015 IECC was released. Most CO municipalities have adopted the 2015 IECC by now. And many have moved on to the 2018 IECC and 2021 IECC.

When comparing the three different IECC iterations, their air leakage rules are fairly similar. However, the 2021 version of the IECC implemented a very important update with regards to attached single family, multi-family and small dwelling units.

Since more and more counties are moving toward the 2021 IECC standard, it’s a good idea to get acquainted with this update. As blower door testing specialists, it’s our job to stay on top of these things. So we decided to release an article, specifically about the air leakage section. Let’s dive in!

Image sourced from: https://www.iccsafe.org

2021 IECC Air Leakage Testing Rules

As stated above, most of the of the air leakage testing rules have remained the same since the 2015 IECC. We have touched on these rules in a past blog. So if you need to get to up to speed, check out this article.

To summarize, a blower door test must be performed in any new construction or addition. All the windows, exterior doors, flues, and vents (where applicable) must be closed or sealed off during the test. The test must be conducted at a pressure of 50 Pascals; and the result must not exceed 3.0 air changes per hour (ACH) or 0.28 cubic feet per minute (CFM) in order to pass. These are tests that our energy services team has been performing throughout the CO Front Range for several years now.

So What’s the Update?

If you take a look at section R402.4.1.2, you will see that an exception has been added for air leakage testing. It reads:

Exception: When testing individual dwelling units, an air leakage rate not exceeding 0.30 cubic feet per minute per square foot of the dwelling unit enclosure area, tested in accordance with ANSI/RESNET/ICC 380, ASTM E779 or ASTM E1827 and reported at a pressure of 0.2 inch w.g. (50 Pa), shall be an accepted alternative permitted in all climate zones for:

  1. Attached single-family and multiple-family building dwelling units.
  2. Buildings or dwelling units that are 1,500 square feet or smaller.

This new update essentially allows you to utilize a different metric for attached single-family and multiple-family units or buildings that are under 1,500 square feet when testing each unit individually.

When conducting this test, the blower door specialist must measure the area of all floors, ceilings, and walls to the exterior of the dwelling to calculate its surface area. This means that walls/ceilings/floors shared with adjoining units do not need to be included in the surface area calculation. Next, they perform the blower door test at a pressure of 50 Pascals. We then take our total CFM reading, and divide it by the square feet of enclosure area. If the resulting number is at 0.30 CFM/sq ft or lower, the structure has passed the test.

Blower door testing Air Leakage test. Required in the 2021 IECC

What’s The Difference?

The main difference between the two air leakage tests is dimensions used for each respective formula and how the results are calculated.

For the original test:

The CFM/sq ft is calculated at 50 Pascals, then multiplied by 60 to yield the air changes per hour (ACH). Next, the square footage of the dwelling is multiplied by its ceiling height to calculate the volume of the space. Finally, the ACH is divided by the volume. The answer to this equation must equal 5 ACH or less in order to pass.

For the updated test:

The CFM/ sq ft is calculated at 50 Pascals. Then, the surface area of all floors, ceilings, and walls to the exterior are summed up (remember this excludes walls/ceilings/floors shared with other units). Then the CFM/sq ft is divided by the overall surface area of the dwelling. The resulting number must be 0.30 CFM/sq ft or lower in order to pass.

Is This Update a Good Thing?

Yes it is! This update has proven to be quite helpful for smaller dwellings. Most homes have similar components, regardless of size (i.e. doors, windows, ventilation penetrations, etc.). This means that whether the home is 5,000 sq ft or 1,200 sq ft, it will have to same potential areas for air leakage.

So during the traditional blower door test, a smaller home with the same amount of air leakage as a larger home is going to yield a higher ACH. For this reason small units have a difficult time yielding a passing test score. The updated test has made a passing score more attainable for small homes.

Multi-family and attached single dwellings (such as duplexes) especially benefit from this new exception. In the past, these types of buildings have had difficulty passing due to leakage occurring into adjacent apartments.

However, this type of leakage is not actually occurring to the exterior, and thus not actually an energy loss from the building as a whole. So that type of air leakage is not as big of a concern, from an energy stand point. As a result, the the new air leakage test allows the tester to omit these shared surfaces when calculating surface area.

Learn more about how to best prepare your multi-family building for blower door testing. Check out our article: 7 Tips For Multi-Family Blower Door Testing.

Blower Door Testing Services

Let’s face it, energy codes are strict. And as time passes by, they will probably continue to get stricter. That’s why it helps to have energy pros on your side to help you reach compliance each step of the way. At Scott Energy Services, a division of Scott Home Services, blower door testing is one of our flagship services. With a team of highly trained, experienced and professional energy specialists, we are equipped to help meet your project deadlines.

If you need an air leakage test or any other energy services, we encourage you visit us online or contact our energy service team today!

Blower Door Test set up. required in the 2021 IECC

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About the Author: Chris Kimmel

Chris Kimmel worked as an Associate Home Inspector for two years, handling numerous services including sewer scope inspections, pest inspections, mold air sample testing, radon testing, and water quality testing. Chris now works with Scott Home Inspection as a Content Writing Specialist.

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