Editor’s note: Kent Earle and his wife, Darcie, write a blog called Blue Heron EcoHaus, documenting their journey “from urbanites to ruralites” and the construction of a superinsulated house on the Canadian prairies. The blog below, originally published in April, is the last in GBA’s series documenting the project, but there is still lots to read at their website. A complete list of Kent Earle’s GBA blogs can be found below.
Have you heard of the Pareto principle before? It’s more commonly known as the 80/20 rule. It says that for many events, roughly 80% of the effects come from 20% of the causes.
I think that Passive House follows this rule to a T. It has certainly been our experience in building an extremely energy efficient home and following the principles of Passive House. I believe that 80% of the benefits of Passive House come from about 20% of the cost and effort. (In Part 1 of these posts, I noted that our financial cost was about 8% more than for standard house construction.) Whereas to get that last 20% to hit the Passive House certification requirements, you’re going to have to spend 80% more… At least this was my assumption.
Still, being the curious person I am and because I kept getting asked about it, I just had to know. How close does our house come to the PH standard?
The only way to find out would be to either track the house over the next year or to have someone run the house through the Passive House Planning Package (PHPP) software to predict our performance.
What the test results said
As you may recall, we were never pursing Passive House certification. Right from the beginning we were told the cost-effectiveness (80/20 rule) was just not there. Maybe if there were some incentive or rebate for going full-out, one could justify it. We were also told that there was no need to use the PHPP as it was too expensive. This latter statement, however, is simply not correct.
BLOGS BY KENT EARLE
Adding It All Up, Part 2Adding It All Up, Part 1Blower-Door TestingInsulation, Air-Sealing, and a Solar ArraySoffits and Siding at the Blue Heron EcoHausPlacing the Concrete FloorsAdding Walls and RoofDealing With Really Bad WaterMaking an ICF FoundationLet Construction BeginPicking High-Performance WindowsHow Small Can We Go?Choosing a Superinsulated Wall SystemHeating a Superinsulated House in a Cold ClimateIs Passivhaus Right for a Cold Canadian Climate?
I decided to ask around and see who could put our house through the PHPP — or at least to see if we could get a price quote for it. Maybe it would be too costly and so I wouldn’t bother.
After a few emails, I was eventually referred to a very well-respected Passive House consultant out of Alberta: Stuart Fix at ReNu Building Science. I sent my email explaining that we’d already built the house and so really can’t change anything now, but due to curiosity I was wondering if he could run the house through the software. No problem, he said. The price we were given was entirely reasonable and was actually less than what we had paid to run the house through the inferior HOT2000 software prior to building. Crap!
After a couple weeks we received the results. Not surprisingly, we weren’t a Passive House. But the results on the various aspects of the house were very interesting and might lead to some interesting points of discussion.
Based on the three criteria for PH certification, recall:
Our results were as follows:
You can see that the only criterion we met was the total primary energy demand. The blower door test we did later came back at 0.72 ach50. (We’d run the software assuming 0.6 ach50.) Inputting the actual air leakage value would correspondingly increase the other values, but, for argument’s sake, let’s simply say that we either met, or were very close to meeting,the total primary energy demand, while for the heat demand and heat load, we were way above the German Passivhaus maximum values.
What would have to change
I won’t reiterate why this makes sense given the climatic and heating requirement differences of the Canadian prairies versus Germany (see Part 2). But I had to ask the Passive House consultant: “If we were still in the planning stages of the house, what would be your recommendations to reduce these two values (space heating demand and heating load)? Not that we would change anything at this point, but I’d be curious as to how we would have gotten those values lower — and if it would have been at all possible with our type of house and in our climate to feasibly meet the PH requirements as stated?”
Here was his reply: “â€‹The ways to reduce the heating load and demand are as follows:
“More insulation (you already have great R-values).
“Lower airtightness (dropping from 0.6 to 0.3 has quite an impact, but you’re already doing tremendously well).
“Add more south glazing, reduce all other glazing. (You already have a great balance of glazing).
“Build a larger home. (!?!?… Small homes are the hardest to make meet an intensity based target, as they have the largest surface area to volume ratio. Meaning that a larger building squeezes more floor area into slightly more exterior envelope area, reducing heat loss per unit of floor area. The Germans do this to motivate builders to build multifamily dwellings… but the result in North America has been a lot of larger single-family homes getting certified).
“â€‹Your home is a great example of why you don’t see certified Passive House buildings taking off in Canada. It’s damn near impossible to design a compliant home, without either blowing the bank or ending up with a solar oven. I’ve designed many compliant buildings, and 99% of them end up backing off on insulation and glazing to be around where your home is. You’ll note that local Net Zero Energy homes have similar envelope performance to your home; it’s most cost-effective from that baseline to invest in â€‹solar PV generation than to add more insulation.â€‹”
Under the section of the report on energy balance heating, I asked, “I was surprised by the amount of heat loss through the walls as well as the windows — is that due to the size/number of south windows? Or does that relate to the number of windows on the east/west and north sides more so? How could we have changed that to reduce the heat loss?”
His reply: “Ideally, if the insulation in all areas of the building cost the same, you’d want to balance the R-values so that the heat loss intensity rate is the same through all envelope elements. Your exterior above-grade wall has the highest relative rate of heat loss, so that would be the place to add more insulation first if you want to improve performance. If you want to optimize R-value ratios this way, it’s smartest to add in the cost/ft2 of each insulation type, then you can maximize your return on investment. For example, adding 1 inch of cellulose in the attic is much cheaper than adding an inch of foam outside of a wall.
“The glazing, of course, has the highest rate of heat loss, but that’s just because you max out at around R-10, where your opaque assemblies are R50+.
“Your north, east, and west windows are NET losers of heat, while the south windows offer a net gain. This is as expected, and is really the basis of passive solar design, that a south window can actually HEAT a building throughout the heating season, with the right recipe. If you wanted to optimize the glazing further, you can add more south glazing while removing glazing on the other elevations (north being the biggest drag on efficiency), which will continually reduce the annual heating demand (how much energy is consumed to heat).
“This is a red flag area, though. Following this path of more south glazing will eventually cause overheating throughout the year. Prediction of overheating / discomfort is an area where the PHPP is very poor, and I’ve been burned in the past on some projects where we pushed the passive solar too far in an attempt to reach certification. I now use IES as a energy modeling tool because of its ability to accurately predict overheating.”
Would earlier consulting made a difference?
I also asked, “Did you have any thoughts or considerations you would have given us had we run these numbers off the bat with the house planning?”
He said, “I’d honestly say you’ve done a great job on your home. It’s pretty much impossible to meet the PHI Passive House criteria for a small single-family home in Saskatchewan without significant and typically unjustifiable cost. The PHIUS criteria are based on a more climate-specific analysis, which attempts to stop investment in conservation at the point a little bit beyond where renewable generation is more feasible. Meaning, it’s more realistic to meet the PHIUS+ targets, though we’re not seeing much uptake in the Prairies.â€‹”
All of this was very interesting and at the same time reassuring to me. Like many others, I had put a lot of credence in the Passive House standard as the be-all and end-all (even despite reading and appreciating the issues I’ve previously discussed). It was good to hear that the assumptions we’d made were in the end in line with the reality of trying to build a Passive House in Saskatchewan.
Finally, the question of windows
Even still, there was one last thing that I just had to know. It kept coming up again and again, one of those pesky assumptions we kept getting asked about. And one of my recently reposted blogs on Green Building Advisor brought it back to my mind again: German windows.
Some people say that German (or Polish and Lithuanian) Passivhaus-certified windows are the crème de la crème of windows. They are attractive, heavy, thick (6 inches wide!), and expensive. But if you want to reach Passive House standards, you gotta have ’em! (Or at least that’s what they say).
I felt a little bit guilty asking for quotes on windows that we were never going to buy, but my curiosity just couldn’t be helped. I wanted to know how expensive Passivhaus-certified windows would have been for our place. We’d heard outrageous prices of up to $80,000 for some homes.
We tendered a couple of quotes and received a reply from Optiwin of Lithuania. The salesperson was exceptionally thorough and I was really impressed with his communication (which made me feel more guilty). After a couple of weeks I received the pricing. I was actually surprised that the cost of the Passivhaus windows was only $17,000 CDN more than the windows we had purchased from Duxton Windows.
Although they certainly would have been way outside our budget, they weren’t 400% more than the price we paid by any means (just a measly 75% more). Nonetheless, I really had to pause again and wonder, why? What would make these windows $17,000 better than the fiberglass, triple-pane windows we got? The U-factors and solar heat gain coefficients were not that much different. Maybe the locking mechanisms of the windows could get you a bit lower on your airtightness – but $17,000? How long would it take you to save on heating bills to justify that “investment”?
All this being said, I’m happy to have answered my lingering questions and to confirm some of my assumptions. The bottom line, of course, is that you want to be able to sit back and be happy with what is around you. To know that you did the best you could in building a sustainable home for the future.
I can’t complain.
Get building science and energy efficiency advice, plus special offers, in your inbox.