For decades, the building envelope industry has understood something the broader construction world is only now catching up to: you cannot manage what you do not measure. Air leakage is one of the most consequential, and most invisible, performance failures a building can have. It wastes energy, degrades indoor comfort, invites moisture damage, and quietly erodes long-term durability. Yet for most of LEED’s history, systematic field testing was entirely optional. LEED v5 BD+C changes that.
For the first time, building enclosure commissioning (BECx) of the air barrier is embedded in the EAp3 Fundamental Commissioning prerequisite, incorporated by reference through ANSI/ASHRAE/IES Standard 90.1-2019. Every project pursuing LEED certification must now engage with air leakage testing. This is not a voluntary stretch goal, but a floor requirement.
The prerequisite mandates whole-building pressurization testing by an independent third party under either ASTM E779 or ASTM E1827, with a maximum allowable air leakage rate of 0.40 cfm/ft² at 0.3 inches of water pressure. Projects that cannot achieve whole-building testing may instead implement a continuous air barrier design and installation verification program. The transition is phased. Projects registered before January 1, 2028 follow 90.1-2019. Those registered after must meet the more demanding 90.1-2022.
Not all air leakage tests are created equal. ASTM E779 quantifies how much air is leaking but not where. ASTM E1827 is faster and more adaptable, producing a comparable result. Both satisfy EAp3. The Enhanced Commissioning credit (EAc5) opens a broader menu: ASTM E783 for installed windows and doors, ASTM E1186 for qualitative leak location using smoke, tracer gases, and infrared thermography, and ASTM E3158 for large or multizone buildings where achieving 50–75 Pa is logistically prohibitive.
The two-tiered structure is deliberate. EAp3 sets a predictable compliance floor – for the first time at scale, air leakage performance must be demonstrated, not assumed. EAc5 goes further, requiring a full building enclosure commissioning process under ASTM E2947-21a from design through post-occupancy. The commissioning provider must be engaged during design, not construction, to define protocols and write them into project specifications before a single wall is closed.
This shift is a market signal. Building envelope professionals who understand these standards and can deliver a commissioning process that starts at the design table will be better positioned than those who cannot. It also reinforces what IBE has long advocated: the building envelope is an active, engineered system that must be designed, installed, tested, and verified. Testing is the only way to know if it is doing its job.
The era of treating air leakage testing as optional is over. The standard has been raised, and the building envelope industry is ready to meet it. But this moment is about more than leak testing. The new LEED requirements reflect a broader shift in expectations from regulatory bodies, the design community, and building owners alike: measured performance, not modeled assumptions, is becoming the new baseline. By affirming the design and installation practices that deliver real energy efficiency, quality, and durability, LEED v5 is helping move the entire industry toward a future where building performance is proven, not just promised.