Air Tightness Requirements in Specifications

The more recent versions of the national energy codes set the performance-based envelope infiltration test limit at 0.40 cfm/SF @ 75 Pa test pressurization.  In reality this is usually tested over a range of pressure differences and a power law relationship is observed between DeltaP and the infiltration rate, and the value at 75 Pa pressure differential can be interpolated or extrapolated.  

The DoD set their goal at 0.25 cfm/sf @ 75Pa, based on some studies of what was acheivable on retrofits of army barracks done back in 2013.  

We have incoroporated this USACE target into our spec for larger projects for the last decade.

Contractors often side-step the 'execution' requirement in our spec that the envelope be tested after the envelope is complete but before the installation of interior gypsum wall board that would impede access to likely leaking points for easy fixes.  They also complain about existing buildngs being "inherently leaky" but we tell them to run the test, look for and fix what leaks they can, and we will be merciful.  When we have done before-and-after renovation testing, we often find 1.5 cfm/sf is common for old existing buildings and 0.5 cfm/sf is routinely achieved even with our least attentive contractors.   

We have a Division 1 Air Barrier Quality Control section for all projects. It establishes QC for air barrier continuity. There's a preconstruction meeting for relevant subs in there. It establishes the cfm/sqft target for the project (whether code max or something lower) It establishes whether blower door testing will be part of the project, and whether the Owner or GC is responsible for it. And then processes if targets are not met. In the Pac NW our projects are required by code to do blower door testing so it's not controversial really. My guess is the basis for this section came from ABAA. Jim Jim Hanford, FAIA, LEED AP BD+C, Principal The Miller Hull Partnership, LLP

Hi Misha, Tomorrow, Friday 12/13/2024 at noon eastern time, engineering firm SGH has a webinar "Understanding IECC Building Enclosure Requirements" that will analyze recent code changes for air barrier design and construction and may be of interest. https://www.sgh.com/events/ In Massachusetts, we have a code requirement for blower door testing, so echoing what Jim said.  Best, Amy

We've also been testing buildings for about a decade, so starting several years before the energy code requirements, and have fairly consistently achieved leakage rates in the 0.12 cfm/sf at 75pa range. Our formula is: * Good detailing. * Preconstruction mockups and testing or early testing on portions of the building. * Persistence during CA to implement details and mockup lessons learned. The hard part can be making sure your mechanical engineer is not sizing equipment based on outdated air leakage assumptions that are much worse than your envelope is providing. Systems cost savings can help support the extra diligence required to deliver an airtight envelope. Mike

Now it's code required here, but we previously had success arguing: * It's worth the expense to rule out excess air leakage as a problem with mechanical system performance. * It keeps the Contractor honest throughout construction, knowing their work will be tested. Other than those two reasons, testing a mockup is almost more important, because this is how you work out all the kinks in detailing and execution. We have not paid for this ourselves, and it has not happened on every project. Happy holidays everyone!! Mike

Agree with everything said here, and I'll add a short anecdote: Sitting in a nerdy ABAA seminar years ago the speaker did the math to demonstrate air leakage rates and had us all visualize the equivalent  amount of "one meter wide cubes of air" (CFM/ft2) flying out of the leaky building every minute (and subsequently the amount moisture laden air heading back in) compared to an airtight one. This experience confirmed my instinct to stop specifying janky storefront for exterior enclosures whenever possible (especially when the product reps say the same). ABAA / DOE has an infiltration calculator showing energy savings and moisture transport for certain project types and regions (including the Northeast). Some quick math (or gallons of water) on a worst case leaky building with no test and a high-performing tested building might help with ROI for some Owners. From my experience, part of the stick with performance testing in the BOD is just setting the right expectations for all the subcontractors on site during construction, from the pre-con to submittals to mock-up and final whole building air test. That ROI might motivate other Owners. https://www.airbarrier.org/technical-information/energy-savings-and-moisture-transport-calculator/

This is required in Washington state for all Commercial buildings, but we have experience outside of WA. We're pleasantly surprised that many of our clients now care about envelope CxA and are willing to pay for it. We see airtightness testing as simply proof that the GC followed the Construction Docs in terms of creating a building that doesn't leak too much. We present it as a check on work that should already be done, as a verification. -Kjell Kjell Anderson FAIA, LEED Fellow Principal, Director of Sustainable Design LMN Architects lmnarchitects.com M 206 812 6546 O 206 682 3460 S Linkedin | X | Instagram