Vermont Commercial Energy Code

Have You Seen the New Air Barrier Requirements in the 2020 VT CBES?
Part 4: Multi-Family Compartmentalization Testing

To date, our blog series has focused on requirements for whole-building air tightness and continuity. However, depending on your project, there may also be another piece of the 2020 code that you need to pay attention to, and that is the new requirement for compartmentalizing individual dwelling units within a building. That is, making dwelling units themselves airtight, isolated from surrounding units and corridors. This is another requirement entirely separate from that of the whole-building air tightness/commissioning requirements discussed in prior articles of this series. It isn’t a substitute. It is an additional requirement, but only for buildings with multiple dwelling units.

Why Compartmentalize?

Aside from it being a code requirement, compartmentalization of dwelling units is desirable as it reduces odor and sound transmission, as well as fire propagation between units. In high-rise buildings, when thoughtfully designed, compartmentalization can also play a role in reducing whole-building stack effect which, in turn, reduces energy loss and the spread of fire. 

So what are the requirements?

First, there is no alternate compliance path for this requirement. If you have a building with multiple dwelling units, then the following applies:

  1. Dwelling units must have an air leakage less than or equal to 0.35 CFM/SF at a pressure of 75 pascals (1.57psf). This isn’t an overly ambitious target, but it isn’t an automatic slam dunk either. There is an effort required on both the architect and the builder’s part to meet this number.
  2. Compliance is verified via sample blower door testing. Sampling must include 10 percent of all units. Of that 10 percent, there must be at least 1 unit per floor, at least one corner unit, and the tester shall strive to evenly distribute the number of tests on each floor.
  3. If a unit does not pass, that unit must be diagnosed, corrected, and retested, PLUS two ADDITIONAL units must be tested.

Who can perform blower door testing?

Code is clear that testing is to be performed by a 3rd party agency.

As an architect, what should I do about this requirement?

Put simply, make compartmentalization clear for the builder. Make it clear by referencing the code requirements directly in the specifications (perhaps division 01), and make it clear by defining what makes a compartment. Identify in the drawings and/or specifications the following: 1) The compartment boundary outline. What is, or isn’t, considered a part of a compartment? 2) The materials that define the air barrier for the top, bottom, and perimeter boundary of the unit. 3) The details that demonstrate the continuity of these materials where they interface with one another and where they are interrupted by other building components, such as partition framing, and various types of penetrations.

It behooves the architect to pay attention to these things during the design phase of the project. Lack of clarity in compartment design poses a higher risk for missing the mark. If everyone has a different idea about how to make the compartment tight, the team’s efforts become dispersed rather than unified behind a single strategy. I’ve been through it the hard way before and it is a real headache and time waster. Not to mention, with the requirement to perform additional tests in the event of unit failure, testing costs could add up quick, and the architect may have to share in some of those costs if the builder can demonstrate that they haven’t been given proper design instruction.

As a builder, what should I do about this requirement?

As the builder, as soon as you know you’ve got a project with multiple dwelling units, you should be taking a look at the architect’s drawings and specifications to identify three things: 1) The dedicated air barrier materials that define the top, bottom, and perimeter boundary of the unit. 2) The details that demonstrate how each of these materials continuously unite to one another where they interface. Think wall to floor, wall corner, and wall to ceiling transitions. 3) The details that instruct you on how to navigate interruptions at these materials. Think interruptions caused by partition framing, electrical box penetrations, plumbing penetrations, etc. Including those inside of partition cavities. Inevitably, these types of interruptions will be there. As the builder, it is important to review the design immediately because compartmentalization often requires special sequencing and/or air sealing practices above and beyond what is conventional for the materials being utilized, like drywall for example. Catching this detailing as you bid the project is ideal so that you’re carrying these additional costs up front.

Did the architect not define any of the above items? If you’re bidding the project, request this information during the Q&A period. If you’re already on the project, issue an RFI as soon as possible and bring the architect in on sharing some responsibility in this requirement.

Lastly, anticipate the testing. Once you have design clarity, review those details, understand their intent, and pass what you know along to the relevant subcontractors. If you have an envelope commissioning agent on the team, they should be talking about it too. Get everyone on board so that you’re ready come test time. With the requirement to perform additional tests in the event of unit failure, testing costs can start to add up fast, and if the design is otherwise clear, those extra testing costs will likely fall solely on you, the builder.

To revisit our prior articles related to the new VT Code please link through below:

PART I : New Barrier Air Requirements in Vermont

PART II: Taking the Blower Door Compliance Path

PART III: Taking the Air Barrier Commissioning Path to Compliance

Should you have further questions or need any assistance about how to meet these code provisions in your project, please email or call Jon Haehnel, BVH’s Building Envelope Specialist at or 802-522-9713.