Musings on Passive House Standards and the Costs of New Home Construction, Part 3

If you have not yet read my posts (rants) in Part 1 and Part 2, maybe check those out first.

Have you heard of the Pareto Rule 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 (PH) follows this rule to a T. It has certainly been our experience in building an extremely energy efficient home and following the principles of PH. I believe that 80% of the benefits of PH come from about 20% of the cost and effort (from Part 1 of these posts, I noted that our financial cost was about 8% more than a standard house construction). Whereas to get that last 20% to the hit the PH certified 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 software (PHPP) to predict our values.

As you may recall, we were never pursing PH certification, right from the beginning we were told the cost-effectiveness (80/20 rule) was just not there. Maybe if there was 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.

I decided to ask around and see who could put our house through the PHPP for us. Or at least get a price quote for it. Maybe it would be too costly and so I wouldn’t bother if it was. After a few emails, I was eventually referred to a very well-respected PH 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 lead to some interesting points of discussion.

Based the three criteria for PH certification, recall:

  1. Space Heat Demand: max. 15 kWh/m2a  OR  Heating load max. 10 W/m2
  2. Pressurization Test Result @ 50 Pa: max. 0.6 ACH
  3. Total Primary Energy Demand: max. 120 kWh/m2a

Our results were as follows:

  1. Space Heat Demand: 37 kWh/m2a
  2. Heating load: 22 kWh/m2a
  3. Pressurization test result (assumed 0.6 ACH, prior to testing)
  4. Total Primary Energy Demand: 116 kWh/m2a

So, you can see that the only criteria we met was the Total Primary Energy Demand. The blower door test we did later came back at 0.72 ACH (we’d run the software assuming 0.6 ACH as a target). As a result of the actual pressurization value, this would correspondingly increase the other values, but, for argument’s sake, let’s simply say that the Total Primary Energy Demand we either met, or were very close to meeting, while for the Heat Demand and Heat Load, we were WAY above the German PH maximum values.

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 PH consultant:

“If we were still in the planning stages of the house, what would be your recommendations to try and 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?”

​The ways to reduce the heating load & 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 one to build multi-family dwellings… but the result in North America has been a lot of larger single family homes getting certified).
​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 ​solar PV generation than to add more insulation.​

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?”

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’d 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 maximise your return on investment. For example, adding 1″ of cellulose in the attic is much cheaper than 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 R10, 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<VE> as a energy modelling tool because of its ability to accurately predict overheating.
“Did you have any thoughts or considerations you would have given us had we run these numbers off the bat with the house planning? “
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 unjustifiably cost. The PHIUS criteria is 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.​
All of this was very interesting and at the same time reassuring to me. Like many others, I had put a lot of credence on the PH standards as the be all and end all (even still 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 PH in Saskatchewan.
Even still there was one last thing that I just had to know… it kept coming up again and again. It was 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.
It is regarded that the German (or Polish and Lithuanian) Passive House certified windows are the creme de la creme of windows. They are attractive, heavy, thick (6″ 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 PH-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 back. I was actually surprised that the cost of the PH windows was only $17,000 CDN more than the windows we purchased from Duxton Windows. Although they would have been certainly way outside our budget anyway – 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 fibreglass, triple pane windows we got? The U-factors and solar heat gain coefficients were not that big a difference. Maybe the 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 bottomline, of course, though 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.
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4 thoughts on “Musings on Passive House Standards and the Costs of New Home Construction, Part 3

  1. Hello Kent:

    I found your website after reading one of your articles at the Green Building Advisor. I then spent the rest of the morning reading your very interesting blog and found many parallels with the house we are building. Although we didn’t make the walls 12 inches thick, we did orient the house to the south for passive gain, have lots of glass on the south, made the overhang wide to block out the summer heat and have extra insulation. We also have infloor heating and plan to have supplementary heat with a woodstove as we have lots of wood on our property We had considered the shou sugi ban technique for siding too but decided against it. The information you provided on painting siding was very helpful. We were going to use cedar as we had a local person make some board and batten siding for our barn from cedar telephone poles. However, he no longer does this so pine might be another option for our house. Did your siding come from Saskatchewan? Does pine stand up well if painted? We are also got quotes for our windows from Duxton and Accurate Dorwin for the same reasons you mentioned but have not decided which to go with yet. Are you pleased with the windows you have. I was surprised at the price you mentioned in your recent posting as it seems low. I don’t like standard eaves trough either and was considering a different solution, however, I really like the look of yours. Is it possible to provide the name of the company that made them? I was also looking at cedar soffit vents but the price is quite high. Your solution is a great idea. Is the venting done on the rake as well as the eaves and if so how did you establish the amount of venting on the rakes?

    Thank you for any information you can provide.

    Carole Jeninga

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    1. Hi Carole,
      It sounds like we might be living parallel lives! Thanks for your comment and I’ll do my best to answer:
      – siding – we found cedar to just be too expensive. At 1/3 the cost you can do pine and stain it with the pine tar and linseed oil. The pine was milled in Saskatchewan at Hy Grade Millwork in Saskatoon (they supplied all of our woodwork and have a beautiful selection of wood). They can also do whatever type of siding you want. We wanted 1×8 ship lap reveal which they’d never done, but they made up the blades for it special for us. They will definitely of above and beyond. As for the stain on the pine, it hasn’t been a year yet, but it still looks like we just stained it yesterday. There is no fading or discoloration. They say the pine tar and linseed oil shouldn’t need to be redone for 15-20 years.
      – I really like the fiberglass Windows. They are beautiful and having such a big viewing area. They hardware is heavy duty and locks tight. I have not been overly happy with the customer service from duxton though. We had a problem with a door closing properly due to the door being bowed. It took several months and a few angry emails to finally get them to come fix the problem. Which they did. But still it was very frustrating. I found accurate dorwin to be really good to deal with so if I was doing it again I might try them. The windows are essentially identical from either company. But go with your gut and who you got a better feel from.
      – eaves trough – Ug yes , standard eaves are so ugly. We had them custom fabricated by a sheet metal work company in Saskatoon called “Tex Klassen”. Though I’m sure a sheet metal company could do it in your area.
      – soffit venting – I really like the solution we came up for this. There is a standard calculation for how much Minnie venting you need based on the volume of space of your attic (I can’t remember it, but it comes up on google really easy). Ours was somewhere in the range of 10-15 sq.ft. For the the venting at the peak of the roof there was a filter that they installed with the metal roof so this was not a problem. For the soffits, we calculated the required area then figured out the width and length and number for vents needed in the soffits (we did 3/4″ x 36″ every 4th board) which gave us what we needed and a little extra. For the rakes, you actually don’t need venting- it really does not make any difference. What matter is the soffits and peak. However, we still did it at the rakes, more for aesthetics. And remember, you are always better to have extra venting then to not have enough.

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  2. I just came across your blog and it is really helpful as we are just starting the process toward building and thinking along these same lines regarding Passive design but not to full certification since we are in Northern Minnesota and the cost-benefit is similar to what you found in your area. Your house looks beautiful on the outside and love the simple lines. Do you have any pictures of the floor plan indoors? We will likely be doing a walkout basement with added living space since we have a family of 6, but I’m interested in the layout on your main floor.

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    1. Hey Ryan, I’m glad you’re finding the blog to be helpful. I’m planning to post a few interior your pictures soon. I’ll also make note to post the floor plan in another post as well.

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