At the end of his presentation at last week’s global Passive House Happy Hour, Jesse Thompson of Kaplan Thompson Architects left us with six points to consider. After meditating on these words of wisdom, we decided that we couldn’t let it be and that they deserved to be celebrated in their own post.
These lessons are more for Passive House designers than others within the community, but they stress several issues that are vital to any successful job site: communication, planning, and continuing education.
There’s No Such Thing as Common Knowledge.
Common knowledge is an illusion that arises when you spend too much of your time with people who are experts in one field. In time, everyone in the group begins to assume that the rudiments of their specialized knowledge are commonly known by pretty much everyone—i.e. common knowledge. This is already problematic, but it can lead to very serious problems when it happens on a jobsite because some of the language of Passive House overlaps with the language of typical construction knowledge. However, the meanings of the words in the two languages don’t always line up and this can lead to a two ships passing in the night situation.
Even if it costs a few extra seconds during a meeting or a phone call, always make sure everyone is actually on the same page.
You Just Need Space. More Space.
Something is going to eventually go wrong on any project. It is one of the iron laws of construction. Whether it’s due to your slab’s thermal bridge being bigger than expected or the need to make adjustments to the design of the ventilation system midstream, leave yourself wiggle room to…well…wiggle.
Ventilation Before Insulation.
In a multifamily building it turns out having a heat-recovery or energy-recovery ventilation system can be more critical to high performance than additional insulation. As an example, Jesse examined a handful of different energy models for a senior housing facility in Maine. By switching from an airtightness that would comply with the Passive House standard to one that would only comply with the standard code in Maine, this approximately doubled the heating demand (from to 4.92 kBtu/ft2yr to 9.14 kBtu/ft2yr). By switching out a sophisticated ventilation system with exhaust-only bath fans, the demand doubled again (to 21.12 kBtu/ft2yr).
Surprisingly, additional insulation had very little impact on the demand if the exhaust-only bath fans were left in place. Even if one were to add a huge amount of insulation (R‑54 walls; R‑44 slab; R‑145 attic), the heating demand would only fall to 16.55 kBtu/ft2yr.
The takeaway: Without a high performance ventilation system on these larger buildings, it almost does not matter how much insulation you install; it is not possible to bring the demand back down to Passive House levels.
Air Tightness Is “Cheap”
This shouldn’t be taken to mean that air tightness is something that you can purchase at a discount, but rather that it’s not something that can be clearly itemized. In other words, you can’t remove it from the budget if someone thinks it’s too costly. It’s ethereal and hidden within the costs of labor and materials like tape.
With the right contractor training, Jesse said, this can be a literal secret weapon.
Watch Your Solar
You may learn in your training that one third of your heating comes from the sun, one third comes from internal gains, and one third comes from the heating system, but the easiest way to get all the heat you could ever need is to put all the project’s windows on the south wall. In the continental United States, however, this could backfire. Most places here get as much sun during the year as Spain. (Only Seattle has as little sun as Germany.)
In other words, if you try to maximize your solar gain, you may end up with a solar oven, which is something that no one wants.
“We didn’t make any of this up,” Jesse said at the end of his presentation.
This was not an admission, but rather an acknowledgement that people within the Passive House community have been confronting similar design problems for decades. As those with more experience and knowledge share what they have learned, they provide the ideas and inspiration that makes innovation possible.
“Rooms like this is where it all happens,” he concluded, referring to the virtual gathering of the Global Passive House Happy Hour.
Get the latest passive house news, trends, & insights delivered straight to your email inbox.