Our client, Roy de Vries, asked me to share my perspective on the experience of designing his Damn-Near Passive House. Roy is well into the construction of his new home, and I’m taking a few days off, so I thought it was a good time for reflection. It’s been a long and winding road, to be sure…
Roy first got in touch with us back in 2010. He was retiring in a couple of years to a mountainside property above Kaslo, BC. He wanted to create a home that was inexpensive to heat, durable, low-maintenance, and fireproof. He also wanted to take full advantage of the extraordinary view of the Purcell Mountains and Kootenay Lake. This was to be Roy’s last house, so he was willing to invest time in careful planning, and money in creating an exceptional structure.
Roy emailed us to say that he was looking for “stock plans in the 1000 to 1300 square foot range with virtually every room over-looking the view and the majority of the living space on one floor”. Our “Atlin” plan seemed to fit the bill. We began to modify the design, changing the cross-gabled roof to a shed roof and reconfiguring the foundation, walls and roof to minimize potential energy losses. Our goal was to get as close to the Passive House standard for heating energy intensity (15 kWh/m2/yr) as it made economic sense to go. Early iterations of the model suggested a performance in the 25-28 kWh range. Once the final details and assemblies had been worked out and the windows chosen, we needed an accurate heat-loss and heat load number to size our supplemental radiant heating system.
That’s when things went south. I modelled the design one last time, and to our mutual shock and disappointment it came in at around 50 kWh! I asked Andre Harrmann, a PHPP expert and instructor, to review the numbers. Even making a few optimistic assumptions, we were unable to get it below 38 kWh. This was a significant reduction from the 140 kWh average for that region, but far from our target number of 15. Nevertheless, Roy proceeded to build the house as designed, and I pondered the whole experience from my end.
- There are good and not-so-good Passive House sites. Roy’s site has great views and an impressive solar gain from the east. However, it sits on a 1500m mountain with a prominent shoulder to the south that cuts off the sun by 4:30pm in summer and 2:00pm in winter. This greatly reduces the performance of the home in the heating season. A site chosen primarily for good solar access would yield a significantly better outcome.
- Elevation and climate matter. Accurate climate data is the key to creating a realistic model, but it’s unavailable for smaller Canadian communities. The closest we found was Kelowna, which is hotter than Kaslo in summer, and drier and colder in winter. This resulted in a design that used at least 4-5 kWh/m2 more energy. Also, when we corrected the building site elevation from 300 to 700m, the energy use went up by 5 kWh/m2.
- The design matters too. We started with a basic plan that had living spaces on the main floor facing the view, with a couple of indents into the envelope for covered areas, for a total of 8 corners. In PHPP, more corners = more building envelope area and thus more heat loss. Roy wanted a loft, which increased the envelope considerably. Working from a simpler form would easily give a lower kWh/m2 value. Also, orienting the long side of the house to the south rather than the east would greatly increase the solar gain.
- PHPP penalizes smaller homes, due to their inherently higher ratio of building envelope area and volume to floor area. This fact should encourage people to build multiple-dwelling structures rather than detached single residences. In Roy’s case, he paid the price.
- PHPP is challenging. It is a powerful tool that provides a realistic model of energy use. However, there’s a significant learning curve to use it correctly and accurately, and many hours of data input are needed to calculate expected performance. I spent about 100 hours on various iterations of the model after taking the PH course — an investment of 5 days and $1500. I also sought independent reviews of my work. It became clear that a new SketchUp-based PH modelling software program would help a lot. I’m more inclined now to outsource further PHPP work to a specialist.
- Achieving high energy performance takes extra design time. We started with the idea that this project would be a stock plan modification with a fixed fee. Since I wanted to learn the ropes, I undertook the PHPP training and the modelling of Roy’s home on my own dime. In retrospect, this was naive and optimistic. I estimate that PHPP modelling and envelope design aspects would add $6-8,000 to the basic architectural fees on future projects.
Roy’s home is now under construction. The insulated slab was poured last week, and he hopes to have it to lockup by the end of this summer. (We’ll post more photos as the project progresses.) I don’t regret traveling down this road with Roy, who has been a charming and convivial co-conspirator, maintaining his commitment to the original vision despite disappointing numbers. For my part, I’ve had a chance to experience the business of creating very high building performance from the inside. I hope to use the knowledge gained while it’s still fresh, and to amortize the expensive learning process over many future projects!