Negotiating the Air Barrier: Consulting on Ohio’s First Multi-Family Passive House

Designing the air barrier for Ohio’s first multi-family Passive House required intensive collaboration between the Passive House Consultants, the architects, and the general contractor in order to meet design goals on budget. Sol provided CPHC, WUFI energy modeling, and testing & verification services for this project—and so we were involved from design through construction. Here’s a peek into that process, and five key takeaways.

The Design: Navigating Special Conditions

The team agreed early in design on the overall approach to the whole building air barrier: taped Zip sheathing on the outside walls and across the underside of the roof truss. This proved to be a practical and cost-effective approach.

But the devil, as the say, is in the details. As design moved along there were a number of special conditions to navigate—some of which required a good bit of back-and-forth between the design team and builders.

Just a few of the special conditions included:

• The elevator shaft, which poked through the top of the ceiling air barrier. Solution: clad the exterior of the CMU shaft with taped sheathing, essentially wrapping the ceiling air barrier over the top of the shaft. 
• The trash chute, which also poked through the air barrier and was originally vented to the exterior. Solution: move to an unvented trash chute within the whole-building air-tight envelope, and provide active exhaust from the trash room. 
• A party wall shared with a commercial space that was not part of the certified Passive House. Solution: isolate the foundation, and sequence construction to enable access to the exterior of the residential wall before the commercial wall was built. 
• Roof access via the attic. Solution: Instead of a stairwell penetrating the ceiling air barrier, we went with an insulated exterior-grade roof hatch, which maintained the integrated of the primary thermal and air barrier.

In the end, the project passed its envelope air barrier test on the first try — thanks in no small part to the care taken by the construction team. But the long design-stage negotiations undoubtedly had a big role to play in creating details that were reliable, buildable, and cost-effective.

The Process: Five Key Takeaways

Here are a few of the “magic ingredients” in the design process that led to a successful result:

1. First off, much of the construction team had attended Passive House training, and were well-versed in the requirements. They were therefore active participants in the conversation, helping to vet solutions and propose alternatives. 
2. The process started in early design and was collaborative throughout. Early-on, the team agreed to the typical wall section & overall approach to the air barrier. As we moved into detailed design, we focused on resolving special conditions. Then, as construction began, we worked with the construction team on questions from the field. 
3. We approached the details (particularly the special conditions) as a collaborative process. On weekly conference calls that included the general contractor, architect, and CPHC, we discussed each special condition, proposed solutions, and reviewed potential problems and alternatives. The GC weighed in on cost and buildability. The architect weighed in on design and code issues. And as CHPC we drew on our previous experience to propose possible approaches, and also evaluated thermal bridging and moisture issues. These weekly team-wide calls were critical in getting everyone on the same page conceptually, above and beyond what was in the drawings. 
4. We made extensive use of “red line” diagrams during design. On building sections and details, we sketched continuous red lines to represent the air barrier (see the image at the top of this post). This simple device got everyone thinking in terms of a continuous air barrier and made the idea concrete. 
5. Finalizing the drawings was an iterative process. The architecture team was happy to adjust their drawings — including updating an extensive set of wall sections and details as the solutions (particularly to the “special conditions”) continued to evolve. This was no small task – but I think it was critical to ensuring success. The result was a consistent, coordinated set that provided clear direction to the construction team. 

So, the simple summary is this: communication + whole-team collaboration. Not rocket science, but effective.