When David Arnott of STARK Architecture contacted us about certification, I jumped at the chance to review the Tantrum. I had reviewed only single-family homes, so I was eager to work on a retail and office building. I secured PHI’s promise to assist and got started.
I appreciated the fact that Tantrum was a classic Passive House, in the sense that its envelope did almost all of the work to ensure the building’s comfort. I’m not a mechanical engineer, so I prefer reviewing buildings with simple mechanical systems. For this building, only a bit of electric-resistance heat would be needed in winter. And in Revelstoke’s dry summer climate, the righteous envelope meant no mechanical refrigeration was needed for the small cooling load.
I’m also deeply in love with wood in all of its forms. Tantrum incorporated wood-fiber insulation not only in the exterior walls and roof, but even within the panelized floor and roof system.
Unfortunately, although the building was exemplary, the process wasn’t. Certifiers much prefer to work with the designer from the start, when their experience can prove most valuable to the project, helping to inform the design, if needed. With Tantrum, construction was almost complete when I started. At that stage, certifiers are not necessarily part of the solution, but can be more like a judge or even worse, the IRS!
The designer and builder want to hear “Yes” as soon as possible, even when “No” is a distinct possibility throughout the review process. And understandably, most teams don’t want to pay for a full review only to find out they missed certification. So we started with a limited-scope initial review. Once that review was completed, both Susanne Theumer of PHI and I felt certification was likely, but not assured. Tantrum was close enough to the limits that it could have gone either way.
Then we started the deep dive. I quickly discovered the many differences between single-family and commercial buildings, starting with density. For single-family homes, occupant density is based on default densities; for a commercial building, you need the precise occupancy number not only for the high internal heat gains from higher density, but also because those warm bodies come with computers, printers, and servers that can easily push a project past the PER (primary energy renewable) limit.
Estimating occupancy is particularly difficult with retail operations, where you must estimate average customers in addition to staff, and both staffing and customer counts may change seasonally. Fortunately, because the bike shop had opened already and the office tenants were moving in, we were able to calculate the number of occupants (including customers) precisely, ultimately settling on a much lower density than had been assumed in the initial planning PHPP.
On the other hand, estimating domestic hot water consumption was easier with only office and retail uses and less important to the building’s energy balance than it is in residential buildings. However, thermal bridges caused by roof-vented drainpipes had to be addressed. The design PHPP had not included these, even though they can cause significant heat loss. Once I explained how these would be included in the PHPP, Tree Construction was able to minimize the heat loss by strategically installing one-way valves and insulating the pipes in the basement.
In another important distinction from a single-family home, retail lighting energy demand, even with 100% LED fixtures, can be substantial. And in this case, the bike repair area required intense illumination. Fortunately, Tantrum’s office space is naturally lighted by the combination of its open floor plan and generous windows at both ends of the building that brighten the private offices. Sensors and automatic controls not only turn lighting off when occupants are not present, but also dim it when daylight contributes illumination.
The effect of ventilation was another surprise. Large-volume buildings usually require the Additional Ventilation sheet with its tricks, and ventilation heat losses can be a much larger fraction of total heat loss. Tantrum’s certification depended on precise entry of both ventilation times and flow rates, which change depending on the use; the bike shop’s retail hours are longer than those of the offices.
Although Arnott and Hoffart successfully overcame Tantrum’s slouching, encroaching neighbor, the solution came at substantial thermal cost and only after much thermal bridge modeling. The subslab grade beams under the basement floor supporting the heavy concrete SEP sidewalls result in four different combinations of concrete and the EPS insulation under it. Each change in thickness is a thermal bridge, as heat moves both perpendicularly through the floor and laterally through the concrete to where the foam under it is thinner. And the thickness of the polyiso foam in the concrete SEP sidewalls also varies. The design PHPP did not include these thermal bridges. Fortunately, the outside corners, particularly the junction of the long SEP sidewalls and the superbly insulated roof, were negative thermal bridges and offset the positive thermal bridges.
Most teams legitimately worry that the certifier’s closer look will reveal only problems, but certification can also reveal unexpected energy savings. While reviewing construction photo documentation, I realized that Hoffart was not kidding when he told me they pushed the encroaching building back across the property line with their SEP sidewalls. You could not see light between the buildings in the photos. So a small area of one sidewall is adiabatic—an unexpected but welcome correction of the planning PHPP.
Certification is a team sport that depends on numerous players. Upon my request, STARK Architecture produced numerous diagrams, photos, and marked-up versions of its plans to graphically document the U‑values, areas, shading, volumes, and so forth. Tree Construction also provided a constant stream of photos to document the construction and helpfully explained the parts of the building that were difficult to understand from the plans alone. If STARK and Tree learned as much as I did, they will have an easier time creating their next Passive House office/retail building.
Finally, PHI is always part of the team as well. Susanne Theumer and Elena Reyes patiently provided feedback and advice so that I was able to certify the Tantrum as a Passive House.
Matthew Cutler-Welsh speaks with Ken Levenson about his journey to Passive House and his co-founding of both 475 and NAPHN.
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