Passive Houses - I took the course so you do not have to ;)

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peakbagger

Minister of Fire
Jul 11, 2008
7,450
Northern NH
As a Professional Engineer I have to take 30 Hours of official Continuing Education Courses (CEU)s in order to renew my license. I attend a lot of webinars but not all of them give official CEUs. My state, NH, gives us a lot of flexibility on course content so my choices are eclectic. I had done a lot of Onsite generation course this past two years and a somewhat low quality electric distribution course but still needed some CEUs. I am mulling over building a new house so I took a Heatspring.com course on Passive Houses in the Real World. It was $190 for 10 hours of CEUs. I have taken courses from them in the past,some paid, some free and in general they are usually good quality interesting courses. There are CEU mills that churn out courses (like the electric distribution course turned into) but I actually like learning something. Note the Heat Spring courses require putting in the hours so if someone just needs the hours there are better spots to go to.

So Passive House (occasionally referred to as Passivhaus) is one of the gold standards for home construction. A certified Passive House is built to require minimal heating and cooling while maintaining healthy air quality with the majority of the heat coming from direst solar heating. The concept originally was formalized in Germany and the US followed the German Passive House Institute rules but at some point the US broke off with its own version. The types of construction differ in the US with a lot more climate variation in the US than in Germany with a different approach to construction, so it's tuned a bit better to the US. Both have formal certification rules that start long before the start of construction. It's a complex process with cost and schedule increases but in the end the house really can almost run by itself with no supplemental heating even in cold climate areas. The course has several examples of homes without power that run through a week of winter weather with no power.

Passive Houses sometimes gets linked to LEED certification (Leadership in Energy and Environmental Design) There are some similarities but there are differences in that LEED takes into account sustainability for the entire construction process and materials while Passive House sticks to ultra low energy requirements and high indoor air quality. LEED tends to be a bit "flashier"while Passive House tends to ensure that the techniques used to build the house ensures its going to be low energy high air quality structure. There have been a few media articles about poorly performing LEED buildings that worked when they were built but very rapidly the complexity of the building meant that the savings were not sustained.

Build a certified Passive House and your days of being a wood burner are probably over. Wood stoves are problematical at best as the methods used for post construction certification would not deal well with a wood stove. My speculation is if you really wanted one it would have to be truly sealed total combustion air and flue system and its probably best an off the record design component installed after the certification plaque is screwed on the wall ;) These builds get most of their heat from the sun using very high-performance windows (mostly European) they make a typical Anderson window look like bargain basement windows. Just as important as the windows is house orientation and window orientation. If someone does not have control of their southern solar horizon for possible shading they will have tough time getting a Passive House certified. In the case of shading, the homeowner may need to settle for Zero Net Energy home and use solar and net metering to make up the loss of heat from the sun in the building. Note they also appear to skip some active measures of energy savings that a dedicated homeowner may consider as they require the homeowner to actively manage a system like cellular blinds with side tracks. Yes they do need to be opened when the sun it out and closed when its not but that means the windows just need to be even more expensive.

The construction of these homes is not something a typical tract home builder is going to pop out. It just requires way too much detailing during construction and specialty subs that can perform to high standard. A case of caulk and spray foam will probably never be able to meet the standard. In order to use the sun in cold climates the minimal net energy received from the sun in winter means the insulation has to be deep in the walls floors and ceilings. Some numbers were R50 walls, R 96 ceilings and 8 to 12 inches of foam in the slabs. The R values are calculated actual values and thermal bridging of structural components has to be avoided. This can get quite complex in framing, and moisture management in the walls and ceilings can be a big issue. Do it wrong and it could be time bomb in the walls that may not appear for years. Previous low energy construction in the 80s and 90s had many of these time bombs that unfortunate folks have had to deal with. One thing that was not a surprise to me was some photos of spray foam insulation failures as my house has some areas where it was applied in an energy retrofit where it pulled off of the joists. My stuff is not covered but these failures occurred over months and seasons so with a typical home, the owner would be unaware that they had defects that could lead to the house having internal rotting issues over the long term.

A very interesting course that made me think but up front I do not think a certified Passive House is in my future or many other's futures. These are mostly one off buildings backed up by architects, certified Passive House Consultants, third party certifiers both off site and on site and final performance testing. Great if someone is a lottery winner or just is willing to pay a premium but my guess is I will use Passive house inspired techniques especially for air sealing and air quality but living up in rural area assembling a team of experts is just not viable unless I want to pay a lot of travel time and mileage. There will be a big portion of DIY on my new home and I would be in no rush so I could take my time to air seal and use advanced framing and probably buy some very expensive windows. I would use a blower door test to test its airtightness before the drywall goes up and integrate heat recovery ducting and a HRV unit into the house design. In my case I would probably take a bit more heat loss and net metered ground mounted solar panels to make it a zero net energy home and maybe even move one of my solar hot water heaters onto the new house. I am unsure I would go with wood heat for the house which means my Tarm boiler would at best be a shop heater for what I believe will be a very large shop.
 
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EbS-P

Minister of Fire
Jan 19, 2019
2,978
SE North Carolina
Thanks. I’ve had similar feelings on the topic. I don’t see how the extra cost of the the last 10-15% could ever be justified for the real person. I get it as show piece and demonstration of emerging tech. I think we do need to encourage advancements and I do think this is one way to push the cutting edge.
 

peakbagger

Minister of Fire
Jul 11, 2008
7,450
Northern NH
Yes I was aware of the pretty good house concept but not in detail. As noted, I needed some CEUs and figured I would check on the pros and cons of Passive House. I learned a lot. As I mentioned, I will probably have a somewhat more "active" house.
 
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blades

Minister of Fire
Nov 23, 2008
3,769
WI, Leroy
for nothern climates i think a envelope type construction might have merit. for those not aware it is a building within a building to put it simply. the outer shell creates a dead air space around the inner if done correctly. with minimal thermal bridging outer to inner.
 

DBoon

Minister of Fire
Jan 14, 2009
1,292
Central NY
Hi peakbagger, I am in agreement with you on this topic. I'm (finally) nearing the end of a five-year remodel of a 1750 square foot arts and crafts house. I used passive house standards as a great goal, but not as a hard requirement.

I aimed for 0.6 ACH50 infiltration and achieved 1.0 ACH50 pre-drywall, when there were still some leaks in the house that I later fixed, and before I weatherstripped the old (remaining) wood windows. I am expecting to hit or get close to 0.6 ACH50 during final test in the spring. Of course, I have an HRV installed.

I got my heat loss down to 18,000 BTU/hour at 0 degree F - low enough to make a radiant floor heating system practical. That is paired with a geothermal heat pump that will use about 4 MWh of electricity a year. This will be easily powered by an extra 5 kW solar PV array that was installed (as part of a 10 kW array upgrade - now 15 kW total). Of course, there is still a backup wood stove - will ultimately be a Woodstock Fireview that has 100% combustion air from outside (if I connect it to outside air, which I will).

For me, it's all about costs and aesthetics on the remodel. If I renovated that house to passive house standards, I would have had to wrap it with 4" or more of foam insulation (goodbye to all of the nice, architectural details), replace all of the perfectly good wood windows with tilt-turn windows that don't match the style of the house, and who knows what else. I think this would have penciled out to about $125-150k of extra expense. Instead, I spent about $22k on the geothermal heat pump, about $10k on more solar, and probably would have spent $10k on the radiant floor heating install if I hadn't done most of that myself. I have a lot of sweat equity in the air-sealing and insulation details (2" spray foam in the walls, rock wool custom cut and fit over that, 1/2" foam strips over framing to - I would not and cannot trust a contractor to do that stuff. So I saved ~$125k and spent ~$42k and achieved the same net result - a net zero energy home that is still pretty resilient (5 degree temperature drop in 24 hours on average winter day), even without a wood stove backup fire going. And if I get a backup battery installed (not even a very big one), I'll be able to run my radiant floor pump during a power outage and circulate the 180 gallons of heated water that will keep the house warm for another 3 or 4 hours after an outage. If the incentives were there for not exporting or exporting my solar PV excess kWh, I might even build a several hundred gallon heat storage tank to make low-grade heat when I have the solar PV production or overnight when there is surplus wind or nuclear power. Lots of possibilities with the right rate structures or incentives.

If I was building a new home, I'd be happy to build to even better standards than I did on this one, but probably not passive house standards. This is the whole concept behind the "pretty good house" informal standard.

Solar PV has really changed the thinking on Passive House standards - this standard originated before really economical solar PV and I think it will remain a super niche. Why build 3000 perfect houses a year instead of 1 million pretty good houses?
 

peakbagger

Minister of Fire
Jul 11, 2008
7,450
Northern NH
Great numbers for a retrofit!

There is definite feeling of pushing the envelope from the Passive house folks and one section of the course was how to market the concept. There are also a lot of folks who have invested their careers into the concept. I got the same vibe off the Timberframers guild and Ted Benson. Years ago I was helping erect a scratch built timber frame at the same time that This Old House had Ted Benson building a Timberframe house (after conning a couple that their old barn was salvageable). The barn I worked on is still standing and far more representative of the craftmanship used to build a barn instead of the overkill exhibited by the Timberframers Guild. Yes the Passive House approach works for a one off but my guess is certain standard designs could be developed a short form could be done with the proof being some intermediate testing. I guess I dont need to have Rolls Royce when a Toyota will do.

It is real hard to justify going to nth degree on thermal loss when PV is so cheap. Add in battery technology and even if the grid goes down, a house can run off PV and battery for the typical duration of an outage. The Pretty Good House bunch seem to have it right and in general seem to have a far better approach. There is definitely some correlation to the German Stereotype and American Stereotype. One is engineer it to death and bury the process in rules while the other is get together a knowledgeable team and build on what worked in the past.
 

begreen

Mooderator
Staff member
Nov 18, 2005
94,478
South Puget Sound, WA
Sounds like it was a good class. I recall the passive home experiments of the 70s and 80s going awry. Often the trombe wall house were ok in winter and ovens in summer. But some things did work out ok.
Can we assume that the perfect passive house design was for NH climate zone? I suspect that a house built like that in our relatively mild climate would get overheated just with lighting, refrigeration, and body heat. Turn on a toaster or the oven and you'd have to open up some windows.
 

peakbagger

Minister of Fire
Jul 11, 2008
7,450
Northern NH
The teacher and a lot of his examples were from Mass and one from RI. The entire structure is modeled based on location, location relative to true south, and exposure using monthly runs at minimum, there is a more sophisticated model that goes hourly. In an area with more sun they could go with lower R value walls and possibly install overhangs over south facing windows to reduce hot weather solar gain. They may just reorient the house.

Comments are occasionally made about early Passive experiments and "crutches" like trombe walls as not the way to go. The Society for Protection of NH Forests (SPNHF) has a cluster of high efficiency buildings built starting in the seventies. The early building is quite intrusive solar elements, the last building built 15 years ago barely looks like its low energy.

In general, every Passive House is a custom design to match the specific site. Keep in mind with heavy insulation and overhangs it will take a long time for hot weather to enter the house and minimal AC once it gets inside.
 

SpaceBus

Minister of Fire
Nov 18, 2018
7,018
Downeast Maine
Our house had a Trombe wall, complete with ducts down from the slab that ran up the trombe wall and opened into the bedrooms. The duct was fed by a register under the steps on the north side of the house, down under the slab, and then up into the rooms. I suspect the ducts and blower were an attempt at AC or heat distribution. We took the whole thing off the house when we repaired the first floor framing and siding. It took me a solid week to remove all of it, and I still have a bunch of the corrugated stippled aluminum hanging around. Some of the fiberglass glazing made it onto the gable ends of the alpaca shelter.