“Doveryai, no proveryai” is a well known Russian proverb translating to “trust but verify,” and is a common saying in various circles: cold war history, cybersecurity, leadership self help books, and…(drumroll)...building envelope code compliance!
Yep, building envelope performance verification is now an energy code requirement in several states who have adopted ASHRAE Standard 90.1 – particularly for air barrier systems (if this is news to you, start here, and circle back to this article). A hot topic on this code adoption is the continuous air barrier requirements, particularly with how these requirements are confirmed in design and construction – aka verified.
You Have Two Choices in Life…
At least for air barrier compliance. ASHRAE 90.1 gives you two air barrier verification options:
- Option #1: 3rd party whole building air tightness test (WBAT)
- Option #2: 3rd party design and installation review
Seems relatively straight forward, right? Yes, but in typical slow-motion code fashion, it took about a year for the AHJ Gods to start flagging and enforcing compliance discrepancies. Which brings us to today, in the year 2026, where we get several calls every month from some poor confused architect, contractor, or owner saying “Our permit application was denied because of some air barrier thing? Can you help us with that??” (The answer is yes we can).
Option #1 is relatively straightforward. Design your building, build your building, and then hire your testing-agency-of-choice to run a WBAT via blower doors and cross your fingers and toes that it passes. Option #2 is a little more complicated and requires a sprinkle of forethought, as it spans from design through active construction and relies on specific documentation, team collaboration, and schedule coordination. In either case, the design and construction team is still expected (aka trusted) to design and construct a continuous air barrier for the building. The only 3rd party responsibility is for the verification piece of things.
Which option is better, you may ask? Well, it really just depends.
The pros of the whole building airtightness test (Option #1) is that you get a quantifiable air leakage rate, which may be necessary for owner requirements or various sustainability certification programs. It’s also just super satisfying and great for morale to finish up a project with a killer air leakage rate. The cons of this pathway is that, if you fail, you have a wild goose chase air sealing mission in front of you – which may require deconstruction of building envelope components and some ugly sealant application all over the place by a pissed off contractor. You also might need to shell out another $20k+ for a retest, in addition to the remediation costs. Depending on this size of this project, this option might be cheaper than Option #2, but only if you only have to do the WBAT once – so cost can be unpredictable.
The pros of the design and installation review path (Option #2) is that this approach has more opportunity for proactive quality assurance. Since verification starts in design, Option #2 sets the building up for success in construction by confirming that the appropriate air sealing materials and details are conveyed in the drawings and specifications before the project is even permitted. Additional verification then occurs while the air barrier installation is in progress, confirming that the construction-phase workmanship is in accordance with the drawings. Material adhesion testing and/or window air leakage testing is also often recommended during construction to confirm that the various air barrier system components were installed up to snuff. The cons of Option #2 is that there is no final, quantitative cherry on top (whole building air tightness testing) to prove that the proactive design and construction review actually resulted in an airtight building.
Ideally, we would have the best of both worlds (or however the Russian proverb equivalent puts it), resulting in a program that combines the assurance of 3rd party design and construction review with the confirmation of the whole building air leakage result. But apparently money matters and projects can’t pay for all the things. I personally lean towards Option #2, and I promise that’s not just because it makes me money. As an engineer-ish with a chronic inclination towards risk aversion, waiting to evaluate success until the very end of a project gives me the bad kind of butterflies. That’s like your entire grade hinging on a final cumulative exam. No thank you. I’m traumatized enough as it is by my Physics 2 final from undergrad, which was only worth 40% of my final grade. Give me weekly quizzes, study guides, open book notes, and retake opportunities, thank you very much!
Tips for Success with Option #2 — Continuous Air Barrier Design & Verification Program
So, assuming you intend to design and build a code compliant building, and prefer not to risk the last ditch blower door situation, here’s some tips to implementing Option #2 – or as the code kids like to call it, “Exception 3 to Section 5.4.3.1.1; ‘Continuous air barrier design and installation verification program in accordance with Section 5.9.1.2’ (Verification of the Design and Installation of the Continuous Air Barrier)”. We know, it’s a mouthful.
So…Dear Architects,
⭐ Actually read the air barrier requirements in Chapter 5 of the code. Like, in full. But in particular, note Section 5.4.3.1.2, which says (and I quote):
- Components designed to provide the continuous air barrier, and the component's position within each of the building envelope assemblies, shall be clearly identified on construction documents.
- The joints, interconnections, and penetrations of the continuous air barrier components shall be detailed in the construction documents.
- The continuous air barrier shall extend over all surfaces of the building envelope and be identified in the construction documents to be continuous.
…and then, make sure your drawings and specifications actually convey the above requirements! Use the word continuous. Make sure your line weights are legible and distinguishable. Go crazy and use a color. Stop using the term “weather barrier,” I literally have no idea what that means. If you don’t have a dedicated air barrier membrane (e.g., precast walls), think about what functions as the air barrier and indicate it accordingly.
⭐ When sharing the drawings and specs with your 3rd party reviewer, make sure all of the above is adequately developed. When we’re engaged as the 3rd party reviewer, we find the documents passed off to us are usually about 50% CD. Don’t make me have to professionally tell you it’s not compliant because you didn’t even try to read the code. It’s awkward and I don’t want to.
⭐ The design team needs to be prepared to participate in the verification process. This might require revisions to drawings and specifications to incorporate the verifier's recommendations. This takes time and money. Account for it in your fee and schedule.
⭐ Clearly identify the air barrier verification pathway the project intends to follow on your construction documents. To clarify, Option #1 and Option #2 are not official terms you can slap on there. But “air barrier verification via 5.4.3.1.1 – Whole-Building Air Leakage” and “air barrier verification via Exception 3 of Section 5.4.3.1.1 in accordance with Section 5.9.1.1” are. This is flagged on pretty much every permit review that makes its way to us.
⭐ Consider developing a standardized air barrier verification spec section that includes construction-phase requirements for air barrier continuity and verification activities to better convey compliance with code intent (or pay me for mine). This can include:
- who the designated air barrier verification provider is
- the roles and responsibilities for the entire project team as related to air barrier verification
- a field verification plan for the air barrier
⭐ And finally, don't wait until permitting to reach out for design-phase air barrier verification. A retroactive review really helps nobody. Late stage design changes are unlikely and tedious, the budget is probably already shot, and what’s intended to be a proactive, valuable exercise gets reduced to nothing more than a compliance check box. Help us help you, and bring on your verifier early enough to actually make a difference.
…and, Dearest Contractors,
⭐ You should also actually read and understand the code requirements, specifically Section 5.4.3.1.2, which is titled “Continuous Air Barrier Design and Installation”. Compliance for air barrier continuity is absolutely not just the burden of the Architect. At a high level, it is paramount that builders understand that air barrier continuity is especially emphasized in the code, and that you will probably get tattled on if you’re not installing air barrier components to spec.
⭐ The construction team needs to be aware of the verification requirements at bid prepared to participate in the verification process. This will include coordinating verification site visits with the appropriate milestones, facilitating site access, responding to air barrier deficiencies raised by the verifier, and confirming resolution of said deficiencies. This takes time and money. Account for it in your fee and schedule.
⭐ Be aware of any specific contractor-requirements related to air barrier verification, which should be relayed in the project manual. This could include responsibilities for carrying the costs associated with any rework, retests, and additional verification site visits.
And, we have not forgotten you…Dear Owners,
⭐ Don’t assume that air barrier verification is the same thing as building envelope commissioning (gasp). It is not. There may be other commissioning-y things you need to do to comply with the code in addition to your air barrier verification. Also, do not assume that opting out of blower door testing = no field testing of any kind; assembly and material tests may still be necessary to evaluate air barrier continuity.
⭐ Lastly, yes, all of this costs money. However, fee alone should not determine which compliance path you take for air barrier verification (easier said than done, I know I know). While code is indeed inherently prescriptive, there is no “one size fits all” approach to 3rd party QA/QC programs. Meeting code is the bare minimum. If building performance is particularly important to you, you’ll want to 1) talk to someone who speaks BECx, and 2) exceed the bare minimum code reqs for envelope verification. Buildings cost a lot of money, there’s no way about it. At least get your money's worth!
So, Trust but Verify, and Make Your Buildings Suck Less (Air)
And that’s a wrap (an airtight one – ba-dum-tss). If we want high performance buildings that stand the test of time and don’t leak air and money, trust just isn’t enough. Read the code, understand the code, make a good effort to comply with it, and make room for other experts at the table to help you with the particulars.