The city asked in their first rezoning review if we were willing to sign a covenant to seek Passive House certification. Good question and the time has come to answer it!
(Read more about Passive House and other approaches we considered.)
There are a couple of good reasons to pursue Passive House certification:
- Understanding the nuances of the process by going through it.
- Marketability – it’s becoming increasingly recognized and sought out by savvy buyers around here.
Because of what I do for a living, though, I am inclined to remain certification-system-agnostic. If we go for Passive House, it’s because I want to test it out. We’re not doing it because we think it’s the only way to a good building and to a sustainable future. It is a way. Focusing on passive principles, like airtightness, well insulated walls, no thermal bridging, and effective ventilation – is a very straightforward way to dramatically reduce our energy consumption and greenhouse gas emissions, and I do believe this is a critical approach to building better buildings. A house that consumes 20 kWh/m2/yr instead of the 15 required by Passive House at the end of the day is still miles ahead of a typical one that consumes 100.
I’m also very curious about the impact of occupant behavior. Could we build something slightly less than a passive house and use as little energy through conscious consumption? Would we be more uncomfortable? Is there an ideal balance that is something less than Passive House but right in our mild west coast climate? These are difficult questions to answer on a single project, but interesting all the same.
I’ve had in my mind from the beginning what I believed to be a reasonable but very high performing wall assembly: 2×4 wood frame cavity with batt insulation; plywood sheathing, weather barrier, 6” of mineral fibre insulation; rainscreen and cladding. We’re on board for a high-efficiency heat recovery ventilator (Zehnder, Paul or similar) and we’re set on good triple pane windows. We’re committed to renewables with a goal of net zero energy consumption and zero greenhouse gas emissions.
But I was not sure about other pieces like the amount of roof and below slab insulation. And I wasn’t sure how this would all add up in the eyes of Passive House. There was no way of getting around it – I had to model it in PHPP, the Passive House (giant) spreadsheet software.
In early January, I took the 3-day Passive House modeling course as a follow-up to the 5-day design course I took three years ago. I’ve since been chipping away at the model to give us more confidence about what we are prepared to commit to in our re-submission to the city.
I’m relieved to report that I am *almost* finished the model.
The first time going through a whole model for a smaller house takes at least 3 days, assuming you’ve had some training. I’m 24 hours in so far, and this includes a fair bit of head scratching, learning, looking at other examples, going back and fixing mistakes.
I would recommend to anyone who has the luxury to devote 3 whole days in a row to get your head into it; even half days are wonderful. I found two hours at a time is about the minimum to feel productive. And keep moving – if I got stuck and bogged down by something, I moved on to make progress elsewhere, then looped back after I’d had a bit of time to digest the issues, or could ask someone for guidance.
The modeling tool itself is not difficult provided you are comfortable using Excel, but it does take time to understand the intent of each entry and to follow the protocols where they exist. The most frustrating part of the modeling for me was that there are several key entries that require significant work in the background – for example, calculating total floor area, heat loss area, and domestic hot water pipe lengths – but lead to a single number entered into a single excel cell. The progress is significant but can feel small.
Here is the heart of what you get out of the model:
The software is really an energy balancing tool in which your goal is to moderate heat losses (e.g. through your walls and windows), and then balance them with gains (e.g. through people, light bulbs, appliances, as well as solar gains through windows). The remaining imbalance is your heating demand, represented by the red chunk in the ‘gains’ bar above – this is what you have to add to the space, and this is the number that Passive House requires you to keep less than or equal to 15 kWh/m2/year.
I still have a few key inputs to add, but am feeling confident that this is within reach for our project and we are likely to go for it. In the meantime, time to reclaim my personal wellness time and get outside for some fresh pre-spring air! Thanks for reading!
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