Explaining Denver Blower Door Requirements in 2021
Date Published: July 26, 2021
Now that blower door testing is in full swing in Denver, we’d thought we would write a blog about the different requirements the city has to help clear up common questions our clients have.
The requirements vary from new homes to additions, and Denver’s requirements are slightly different than other counties in Colorado.
While it would be ideal to have a statewide-adopted energy code baseline, that is currently not the case. Each county has adopted a different version of the IECC energy codes, and each one has its own amendments as well.
Not to fear because as energy service providers, we do our best to keep up with the changing energy codes throughout our service areas and pass that info along to our partners.
So let’s dig in! But first….
What is a blower door test?
As a brief refresher, a blower door test is an air leakage test that measures how well sealed the home’s envelope is. This is done by running a sealed fan through a doorway and measuring the amount of air moving through a fan at specific pressures. If you want to learn more about the actual process, read our overview here.
As the HVAC system produces hotter or colder temperatures within a home, the air will want to neutralize itself by moving out of the home’s envelope. If the air leakage in a home is higher, this will cause the HVAC system to run more often as conditioned air escapes.
Although the test itself has its limitations, a blower door test is a great baseline that gives us the ability to compare homes to one another.
Most importantly, a blower door test is required during the building process by most counties in Colorado. This is something you should be aware of throughout the building process as some of the largest air leaks can only be sealed prior to drywalling or insulation.
If you are in need of a blower door test anywhere from Fort Collins to Castlerock including Denver, visit our Blower Door Testing page for more info or contact us now!
Denver Blower Door Requirements on New Construction
Denver has unique air leakage requirements, but they are pretty straightforward. New construction for example follows the IECC 2018 codebook exactly with no amendments.
The IECC 2018 codebook states the following:
R402.4.1.2 Testing: The building or dwelling unit shall be tested and verified as having an air leakage rate not exceeding five air changes per hour in Climate Zones 1 and 2, and three air changes per hour in Climate Zones 3 through 8. Testing shall be conducted in accordance with RESNET/ICC 380, ASTM E779 or ASTM E1827 and reported at a pressure of 0.2 inch w.g. (50 Pascals). Where required by the code official, testing shall be conducted by an approved third party. A written report of the results of the test shall be signed by the party conducting the test and provided to the code official. Testing shall be performed at any time after creation of all penetrations of the building thermal envelope.
Most of Colorado and all of Denver is located in Climate Zone 4, meaning a blower door test has to result in 3 Air Changes Per Hours (ACH) or lower when running the blower door at 50 pascals of pressure.
While that’s a lot of jargon, the important thing to note is that 3 ACH is a fairly well sealed home. Most modern building techniques can achieve this easily, but it is important to ensure this in the back of your mind throughout the project.
Also, when picking materials, high-quality house wraps like zip system and air sealing insulation like spray foam can really help reduce air leakage. If you are interested in common air leaks, we have written a detailed article about that here. Also, if you are building a multi-family building in Denver, we have compiled a list of 7 items to be aware of when buildings have shared walls and accesses.
The only way to know a home’s air leakage is to test it. When blower door tests in Denver do not pass on their first try, our techs do their best to use thermal imaging to find hidden air leaks to seal.
Because of this, builders may choose to do a blower door test prior to drywall to find air leaks within the house wrap and framed walls. This is more common on larger projects.
Denver Blower Door Requirements on Additions
Additions where you are adding square footage to the home are subject to energy code compliance as well according to IECC 2018. The codebook states the following about existing structures:
R502.1.1.1Building envelope: New building envelope assemblies that are part of the addition shall comply with Sections R402.1, R402.2, R402.3.1 through R402.3.5, and R402.4.
Section R402.4 relates back to the blower door testing requirements from the previous section above. However, their wording states that only the new section of the home has to comply with these requirements.
This is a very difficult thing to test with a blower door as you cannot always block off only the new section of the home. Because of this, Denver had released an amendment to the code that states any retrofit or addition that adds 30% or more to the overall square footage of a home is required to do a blower door test on the home. When they do, they have the following options:
Additions larger than 30% of the existing floor area (not including basement area) have two options:
1. Perform a blower door test as a baseline before construction (to be submitted with the construction documents for plan review) and again once construction is complete (to be submitted at final inspection). The final blower door test must demonstrate the same air changes per hour (ACH) or less than the baseline. This path may be optimal for additions on older homes.
2. Or, only perform a final blower door test once construction is complete. The final blower door test must demonstrate five ACH or better. This does not require a baseline blower door test before construction, but could result in costs for improvements to the building envelope at the end of a project in order to meet five ACH.
This is pulled from the City & County Of Denver Community Planning & Development Building Permit Policy document which can be found here.
We always recommend builders opt for option number 1. While it requires an additional test, the chances of passing after construction are much higher, which can save you some headaches.
If you choose to go with option 2, just know that while 5 ACH is a fairly easy Denver blower door requirement to achieve, some older buildings, where the older side of the home is very leaky, can make this very difficult.
Staying Current On Energy Codes
While this article is accurate for 2021, energy codes are constantly changing. Just in July of 2021, Denver City Council voted to passed the 2019 Denver Green Code. This did not affect blower door requirements for residential properties unless you are using the performance pathway (ERI/HERS Rating) to gain compliance.
While HERS ratings and ERI is a different subject from this article, the point is that what is accepted today might not be the same in the future, so it is important to stay up to date. We do our best to keep all our clients informed with the most current energy code information.
Chris Scott is an ASHI certified home inspector with multiple years of experience in home inspections, blower door testing, duct leakage testing, and Boulder Rental License Inspections. Chris is also the Website Coordinator for Scott Home Inspection.