Meeting the Airtightness Challenge
This is Part 5 of a blog series describing construction of the Orchards at Orenco project in Oregon. The first installment was titled Building the Largest Passivhaus Building in the U.S.
Every hole must be sealed. Transitions in the plane of airtightness need particular attention and even more focus is needed when those transitions occur at corners. Here Doug is detailing a wall to foundation transition condition at an inside corner. He is taking care to apply the self-adhered membrane with a tool to help work the material into the fold and ensure adhesion to the primed substrate. A small amount of wet sealant will be applied to the membrane at the pinhole corners to minimize air leakage.
Certainly the level of airtightness required to achieve Passive House certification is a high bar. While it’s debatable what level of airtightness is needed from a building science standpoint to achieve efficiency and durability, in our case on Orchards we were pursuing Passive House certification through PHIUS and the requirement was clear and simple: less than or equal to 0.6 ACH50. Going into the project as the builder, we had distinct concerns about our ability to pull it off; concerns founded on the results of whole building testing from ten or so previous projects where we and the design teams had placed a lot of focus on airtight design and construction. So, this was not really equal to taking a moon shot, but anything that significantly exceeds what has been accomplished before would be concerning to a rational group of people.
Architect’s wall section drawing indicating configuration of air barrier system and thermal barrier
Image courtesy of Ankrom Moisan Architects
We forged ahead and needless to say we placed a great deal of emphasis on achieving the airtightness requirements of the standard, working closely with the design team to ensure continuity of the air barrier system – and just as importantly – the constructability of the system and associated detailing. The architects – Michael Bonn and Amanda Lunger with Ankrom Moisan Architects – did a great job with design documentation, clearly indicating the location of the air barrier through all the building section and wall section drawings for the project. This allowed us to understand the plane of airtightness at a more conceptual level, and then we could follow through better at the detail level to ensure air barrier continuity.
Key details for airtightness included the wall to foundation conditions, the wall-to-roof interfaces, and the window-to-wall interfaces. We also had several very tricky details where the passive house enclosure extended through the building interior (at the elevator and fitness/laundry room stacks near the center of the building and at the exit stairways and trash room stacks at each end of the building).
We staggered the construction of the stairway/utility volume at each end of the building relative to the Passive House volume/zone. This allowed us access to the walls so we could air seal the Passive House enclosure with Wigluv tape on the plywood sheathing We also needed to run the foundation insulation through the interface between the two zones . This is an example of non-typical sequencing of the work necessitated by certain aspects of the Passive House design at Orchards.
With proactive coordination of the work, we were able to identify any conditions that weren’t addressed in the initial design drawings and work through those details with Michael and Amanda during construction.
Near the midpoint of construction we planned to conduct a preliminary airtightness test, to assess the relative tightness of the building. We were keen to understand where we would be at that point, since we’ve tested many buildings over the past 5 years but had never achieved a Passive House level of airtightness before. The results from our previous whole building airtightness tests have ranged from 0.17 CFM75/SF to 0.36 CFM75/SF. The Passive House requirement of 0.6 ACH50 is premised on the building’s volume, not the surface area of the enclosure, so we had a difficult time comparing what would be needed for Orchards to what we have achieved on those other buildings. Our best estimate was that something approaching 0.11 CFM75/SF would be needed.
We included several days of downtime in the project schedule to prepare for and conduct the preliminary test, and to allow for any remedial air sealing work at leaks that might be identified during testing. As soon as we topped off the building structure and installed the SAM temp roof / air barrier on the roof deck, we were ready for the test. All windows and balcony doors had been installed and sealed at their perimeters, all joints in the plywood wall sheathing had been taped and the wall sheathing had been sealed to the foundation. Every significant penetration of the Passive House enclosure was installed and complete at this time with the exception of five building entry doors, thirteen interior Passive House doors, and one large dampered vent that would be located at the top of the elevator shaft. At these openings, we installed temporary closures with plywood and tape.
Prior to the actual test – conducted by Ryan Shanahan, PHIUS+ Rater with Earth Advantage (EA) – we ran an internal quality control check on the building. We had a nice cold Friday night in November so were able to fit the building with our blower door and scan the building thoroughly with infrared cameras. We cranked up the temporary heat in the building to create some temperature differential to assist with the scans. Of particular concern for quality control was the top of the elevator shaft where the plane of airtightness was quite convoluted, however we did not find any significant leakage paths in this area. We did identify a few small leakage paths around the bottom of several balcony doors at the first floor but other than that we found the building to be buttoned up pretty nicely. We took a few test runs of the building ourselves and our “pre-prelim” numbers were pretty good but we didn’t want to jinx the “official” prelim test. When Ryan ran his test the following Monday, the result was 0.075 ACH50. The whole team was stoked at the results and we could all rest a little easier, knowing we were solidly where we needed to be to achieve the Passive House airtightness goals.
Prior to the preliminary airtightness test, Marty and Dalan inspected the building for any significant air leaks .Here they are scanning the top of the elevator shaft with infrared cameras.
Infrared scan of the south façade. We turned up the temp heat inside the building to create a temperature differential to aid with the scanning process. The walls appear to be burning quite “hot” since no insulation has yet been installed in the framing cavities. The thermal quality of the triple glazed windows can clearly be seen in the photo.
The quality of tightness achieved at this point allowed the team to consider making several changes to the design. The elevator had been isolated from the Passive House enclosure in the initial design, due to concerns about the amount of air leakage that could occur at the required backdraft damper at the top of the shaft. This design move created considerable additional complexity and expense since the walls and top of the shaft – and the doors into the elevator lobby – had to be air sealed and highly insulated. Given the preliminary airtightness result, the owner’s representative – Craig Kelley with Housing Development Center (HDC) – questioned whether it would be possible to reconfigure the Passive House to include the elevator shaft. This would allow the team to use standard hollow metal doors at the elevator lobby in lieu of the airtight, highly insulated, custom wood doors that had been specified. Additionally Craig wondered if more standard storefront doors could be used at the building entries rather than the airtight, highly insulated doors that had been planned (to be sourced from Schuco, a German window and door manufacturer). The Schuco doors, while exhibiting excellent performance data, were a concern to the team since their standard sill/threshold did not appear to meet ADA accessibility requirements.
Using product air leakage data, and with input from Ryan as well as Dylan Lamar (Passive House consultant with Green Hammer), Craig estimated the net loss in airtightness from these changes would be around 0.055 ACH50. Dylan then studied the impacts of these proposed changes in the PHPP, and found them both to be allowable within the energy limits of the standard. In the case of the Passive House enclosure reconfiguration at the elevator, we needed to install additional insulation at the foundation and exterior walls and do a bit of revised air barrier detailing, however these were relatively easy upgrades to accommodate at this point during construction. These two design changes combined saved $26,000 and, by using storefront doors with standard saddle thresholds, we were able to avoid any issues with meeting accessibility requirements.
Interesting to note that at the time of preliminary testing, no interior drywall and very little water-resistive barrier had been installed. We knew these materials would increase tightness as they were installed; however, we also knew the storefront doors and elevator vent would counteract that increase. In May, as we approached project completion and turnover to REACH, it was time to conduct the final airtightness testing.
This process was relatively straightforward given the building’s design, with very few ventilation penetrations of the enclosure. We cleared out the building so there was no interior trade work on test day. We filled all plumbing traps with water to ensure they were sealed, checked all windows and exterior doors to verify closure, propped open all the interior doors, and sealed off the ventilation intake and exhaust at each of the mechanical penthouses. We took a close look at the storefront doors and noticed we could see daylight through the butt joints in the door framing. Oh well. That’s storefront!
Ryan set up a single blower door in the main entry and the basic testing was completed in less than an hour. Results: 0.12 ACH50 negative, 0.15 ACH50 positive, 0.13 ACH50 average. When figured in terms of the enclosure area, the airtightness is 0.011 CFM50/SF.
One blower door, positioned in the main entry door, was all that Ryan and Sara needed to test our Passive House volume of 380,171 cubic feet.
These results are no doubt a testament to the level of collaboration and teamwork between all the individuals and firms working on the Orchards project. Major credit also goes to the superb efforts of our field crew, for their nearly flawless execution of a very good air barrier design. Our friends at RDH Building Sciences maintain a database of North American building airtightness. They say Orchards is the tightest multi-unit residential building in their database. We think that’s pretty cool!
To add to our understanding of the role that various design measures play in the building’s airtightness, the team commissioned several additional test iterations by Earth Advantage. In one particularly interesting iteration, all 9 interior passive house doors were propped open for the “whole building” test. The trash chute was wide open and the louvers on the trash room doors were left open. The resulting leakage was measured at 2131 CFM at -50 PA. Given the additional building volume, this added about 0.3 ACH50 to the overall building air leakage number.
The crew made all the difference. They were skillful, trained for the tasks and diligently executed the design. Their hard work paid off in a highly airtight building. They sealed the holes large and small. Here Phil applies a peel and stick membrane “dart” over the pinhole at an inside corner of the wall to roof interface condition. It is attention to detail at this level that can make a difference in achieving a high degree of airtightness.
The team found this to be informative and very surprising. To quote Dylan Lamar: “It suggests if we’d known how good a job we’d be doing on the enclosure that we could have afforded cheaper, leakier commercial doors and even some limited open louvers. On the other it shows that this limited number of components alone amounts to the same leakage as the entire building enclosure and all its high quality windows and doors. A few bad apples doesn’t necessarily spoil the bunch, at least when the bunch is a seriously well-executed set of apples.”
A forthcoming blog will discuss the HVAC and other systems at the Orchards at Orenco project.
Unless otherwise noted, all photo credits to Walsh Construction Co.