What do you wish you or the owner knew about a passive house?
chuckac
| Posted in PassivHaus on
Hi all!
I’m moving towards doing passive house development in Massachusetts. I’ve really grown to love the standard and what is required in building quality in order to create the structure.
Really for anyone, I’d love to hear your experience on educating the public and potential buyers.
Alternatively, if you have a passive house, I’d pose the same question to you. What do you wish you would have known about the house or what are your pain points now (if any)?
I’d appreciate the info, and I’m happy to chat offline about this if you prefer, just shoot me a message.
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I would tell any prospective owner that (a) a passive house is likely to cost more than other approaches to building, and that there isn't much evidence that the upcharge will provide cost-effective energy savings, and that (b) if you are pursuing certification of the passive house through PHIUS or the Passivhaus Institut, the costs will be even higher than if the house were not certified.
If you can afford the cost, you'll end up with a comfortable house with low energy bills.
If the cost seems high, you might want to consider the Pretty Good House approach. For more information, see Martin’s Pretty Good House Manifesto.
I would tell the prospective passive house owner:
1. You don't need a central heating system, this house is so energy-efficient. The attic/wall/foundation insulation is double/triple a typical new home. That means the heating needed is only half or a third of a typical new home. A plug in electric heater would be sufficient to heat this home under worst winter conditions. (Electric backup heating is provided just in case inside the HRV/ERV, or radiant panels, or ...)
2. When the electric grid goes down (maybe even for months from an attack), you won't be affected as much. The house will stay reasonably warm in winter and cool in summer. (If you have PV and can run off the PV...you will continue to have some electric power some of the time without a generator needing fuel from somewhere.)
3. You won't care if the price of oil or gas skyrockets. You aren't (or are minimally) dependent upon those fuels.
4. You and your family will be healthier and safer in this home. Continuous, filtered, pre-warmed fresh air is provided with an HRV/ERV. So you can afford to ventilate your house continuously with very little heat loss or heating cost. (If all electric, no burning of fuels that create potentially dangerous by-products or risk of fire.)
5. You will be more comfortable in winter with no drafts and warm windows, even when outdoor temps drop below zero. Look at these triple pane windows...They have half/one-third the heat loss of typical new windows. (If tilt-turn...look you can open the top of the window to ventilate at night without fear that someone can sneak into your home.) The coldest the inside surface gets is ~55 degrees, vs. ~40 degrees for a typical new window. You won't be cold standing or sitting near the window so can sit next to it and enjoy the view.
6. In the future when homes like this are more common (like in Germany), you can resell without buyers considering upgrading energy-efficiency measures, appliances.
7. The home is built with more durable materials. You pay less for maintenance. Notice siding...heating system...etc.
8. (If PHIUS/Passivhaus certified...) These claims are backed up by this home being certified by the most stringent energy-efficient building certification used in Germany, Canada and the USA. Like they say, "German engineering" like Mercedes, BMW, Audi, Porsche. This home is not a Toyota Corroda. :-)
Re: Robert's point #2
"2. When the electric grid goes down (maybe even for months from an attack), you won't be affected as much. The house will stay reasonably warm in winter and cool in summer. (If you have PV and can run off the PV...you will continue to have some electric power some of the time without a generator needing fuel from somewhere.)"
I have sealed and insulated a 1950s Cape Cod. Midwest, cold winters hot humid summers.
I haven't done testing. When I compare it with electric usage in articles on GBA, I use relatively little energy. Last summer, 400kwh to cool 1,500 square feet in a long, hot summer. Cooling via a 5000 btu window unit, running 24/7, to remove humidity.
However, if the power goes out in the winter, I expect it would be close to outdoor temperature within a day. No basis for that, just a guess. I heat it with a portable heat pump and a $10 space heater for extra cold nights. But I would not be comfortable for long on a 0 F night, without power.
Just curious what the real world situation is in a certified Passive House. Will the temperature stay comfortable if the power is out for a week? If the outdoor temperature is around 15 F?
And, a side note, in discussions of energy usage, the indoor temperature is helpful. I prefer around 65 F in the winter. Above 68 it feels stuffy.
A home's indoor temperature would not drop to outdoor temperature unless the home is uninsulated and drafty. Your home's mass and insulation levels would keep the home from losing all of its heat in one day, even if windows were covered, the home was unoccupied, and there was zero energy usage inside the home.
Even after a week, solar heat gain through windows would provide some heat, even if you had no electricity, fossil fuels or wood to heat the place. Solar gains keep the home’s natural set point for the interior temperature warmer than the outdoor temps.
Windows capture some solar gains, depending upon window orientation, size, glazing, cloudiness and latitude. For an average size window, that might range from negligible for a north-facing window on a cloudy day, to about 15k BTUs for an unobstructed south-facing window on a sunny day in January. Each occupant in the home adds about 9k BTUs/day too. You don't notice these gains very much in a typical home, since it might lose something like 500k BTUs per day. But when the total mid-winter heat losses get down to certified PHIUS/Passivhaus levels (let's guess 100 kBTUs/day for a smaller Cape), suddenly the home's indoor temperature stays far above the outdoor temps. The indoor temperature would stabilize far above the outdoor temps, since solar and occupant heat gains might make up a sizable percentage of the total heat losses.
Like the Passivhaus people claim, the heat from a hair dryer would be enough to keep the home warm in winter (with solar gains, heat from appliances and electrical usage, HRV/ERV heat conservation).
I built a passive solar home with far less insulation than certified PHIUS or Passivhaus. More like “pretty good house” levels. It has lots of south-facing glass with a sunny Colorado winter climate (unlike most places in the USA which are cloudier in winter). On the first floor (insulated concrete slab providing thermal mass), the home almost always stayed above 65F without any supplementary winter heating, despite 5500 degree day winters. That would be similar to winter temps in the cloudier mid-west, depending upon your location. However, the upstairs needed heating overnight on about a third of winter days, the coldest or most overcast days. No concrete slab floor upstairs.
I can’t even guess what your home’s natural interior winter temps would be without any electricity or heating. Depends on insulation levels, air-sealing, window orientation, heating degree days, etc. But it wouldn’t reach the outdoor temps if you were there trying to survive.
Robert.
You write: "Like the Passivhaus people claim, the heat from a hair dryer would be enough to keep the home warm in winter (with solar gains, heat from appliances and electrical usage, HRV/ERV heat conservation)."
That part is true. A hair dryer uses 1,000 - 1,500 watts on high. I use less than that to heat my house. My heat pump uses about 800 watts, about 7 kwh per day when the temperature is around 30 F. When it gets to 0 F and below, it takes perhaps twice that capacity, around 1,500 watts, for most of the day. I would not want to be without electricity for a full day.
Your comment about 100k btu per day is remarkable to me. I keep daily track of my electrical use. I am guessing my portable heat pump has a COP under 2, maybe even 1 or just above. But 28 kwh per day (100/3.5) is still my upper historical use limit, during the coldest period. So, a real heat pump might reduce my energy use even more, but a $10 space heater is probably more rational.
As a retrofit, I did not have siting options, and actually preferred to seal and insulate over windows. Perhaps properly sited passive houses can get by with solar heat gain, without electricity.
Erich,
Part of what is heating your house is the use of electricity (or gas) for appliances, lights, etc. The electricity usage generates heat inside the home. Occupants generate heat. Solar heat gain from windows adds to internal heat. That might keep your house interior around 40F on average 30F days in winter without using your heating system. (Just a wild guess, without knowing your home's size and configuration, insulation, air infiltration rate, window glazing info, etc. You estimate it takes double your heating system capacity when outdoor temp is 0F vs. 30F.) Even without the electricity usage, you still have solar gain and occupants to boost interior temperatures above exterior temps.
Certified passive homes seek to reduce heat losses by about 80%. So yes solar gains on sunny days might heat a certified Passive house, along with using electric appliances etc, without using auxiliary space heating. Could easily work in sunny winter climates with the right window configuration and thermal mass, and not heat as well in overcast winter climates or shaded lots. I'm designing for New England winters, moderate sun in January, passive house level insulation/air-sealing, but no certification (keep costs down).
Agree that retrofits have many constraints (and hidden surprises during renovation!), new construction allows much more design freedom.
Great info from everyone, thank you!
Erich, you introduced retrofits into this. When you were doing your retrofit, did you primarily focus on insulation, windows, and systems, or did you remodel any portion of your home (roof/window) to help with solar benefits?
Robert, the pretty good house phrase, I hadn't heard before. Thanks for mentioning it.
Construction cost is definitely the primary struggle-point I'm running up against with clients. Even with numbers in from of them, going with and I quote, "tried and true" building techniques is hard to sway those that aren't already interested in the PH standard.
Erich, a few years ago we had an ice storm in Maine and it was very cold and gray for a couple of weeks. LIke hardly getting above zero cold. I know of a Passive House (Enerphit, actually, iPHA's less-stringent retrofit program) that was without power and unoccupied for 10 days during that event. It's in the woods--not very good solar gain. The house never got below 45-50°F, from what I understand from the owner.
I tell my potential Passive House clients that if they build to that standard, their home will certainly never freeze, and depending on the situation--whether or not it's occupied; what the solar situation is--then it would likely never get below 50° if they never turned the heat on.
Chuck, I'm a fan of both the Pretty Good House approach and the Passive House standards. (Plural for the global standard vs. the U.S. offshoot, which uses different metrics.) In a Pretty Good House you can get away with a few things because there are no hard and fast requirements; I just did one with double-glazed, double-hung windows at the owners' insistence. The energy penalty compared to tilt-turn, triple-glazed windows was affordable, but the comfort and mold-resistance of a Passive House window is a different level of comfort. There is also a perception of quality difference with Passive House-type windows; they are solid, like the door of a fine automobile compared to the ones on my tinny old Subaru.
With a Passive House you know exactly how the house will perform, or very nearly so, because the energy modeling is so intense. Certification provides peace of mind that your Passive House practitioner didn't make any mistakes. Passive House has broad name recognition (though there is still a long way to go) so there is better potential for marketing to certain clientele.
Robert:
"Part of what is heating your house is the use of electricity (or gas) for appliances, lights, etc."
Obviously, in talking about the performance of the house during an electrical outage, there will be no use of electricity. And, it is widely reported that most passive houses use electricity solely, without, gas.
Michael:
"Erich, a few years ago we had an ice storm in Maine and it was very cold and gray for a couple of weeks. LIke hardly getting above zero cold. I know of a Passive House (Enerphit, actually, iPHA's less-stringent retrofit program) that was without power and unoccupied for 10 days during that event. It's in the woods--not very good solar gain. The house never got below 45-50°F, from what I understand from the owner."
My house is also unoccupied. I remain confused how my house can use a similar amount of electricity. If a Passive House stays at 45 F with no energy and no occupancy, it is confusing that it would use so much energy to raise it another 25-30 F.
The Passive House name is a horrible trade name, considering so much of the standard is based on the amount of energy required. The opposite of passive.
Chuck, for a variety of reasons, I prefer an R40 Wall over an R5 window.
Here is another confusing Passive House claim:
"During a five-day power outage last December, we had a chance to really see how our home would perform. Would we need to stay with friends or in a hotel until it passed? Despite below-freezing temperatures and mostly overcast weather throughout, our home lost only a degree per day. When my husband and kids would do jumping jacks, they could warm a room by a couple of degrees!"
http://www.zehnderpassivehouse.co.uk/blog/what-are-the-real-world-cost-savings-of-living-in-a-passive-house.html
Yet somehow it cost $120 per month for utilities, including heat and hot water. Somehow, that equates to a heating cost reduction of 90% less.
The math just doesn't add up.
Erich, the biggest utility cost in a Passive House is for domestic hot water. There are connection fees, appliances, ventilation equipment, lighting, computers and other plug loads. That said, $120 is on the high side for a PH.
Michael, perhaps someone will explain why houses which retain their ambient temperature without any electricity, while outdoor temperatures are at 0 F, still have such a robust need for heat, when the electricity is working.
Hi Chuck, I wanted to see how your building project is coming along. I am in the process and have a ton of information but still looking for land.
Cheers
Todd
RI
Your biggest problem, by far, will come from lack of knowledge and lack of interest in the energy savings associated with really well engineered housing. The financial institutions don't know (and don't want to spend the time and effort necessary to learn) and therefor will not provide any extra cash for the extra quality - the general public is, in general, only interested in the location and appearance of their proposed housing.
I have designed and built and lived in three of these over the years. It has been my experience that the average buyer is only really interested in the aesthetics of the house and the neighborhood. My wife and I were really pleased with all of these
and informed every potential buyer of the fact that they could expect to save more than $1,600 per year on their heat bills, that the house was unbelievably quiet and comfortable compared with others of similar size in our neighborhood - we even provided copies of the last five years utility bills to prove it. Some of the potential buyers told their real estate agents (after they were out of earshot) that we must have faked the documents. This was actually typical buyer behavior for all three houses.
The houses we built and lived in averaged about 2000 square feet, were located in absolutely typical subdivisions for the area and designed to look like any other typical house in the area. There was no discernible difference in exterior appearance and the major difference interior was the width of windowsills due to wall thickness. This was during the high interest rate years (1973 to 2003) in high altitude (7000 feet) locations in the mountain west. Nevertheless, out of all the lookers and sceptics an interested knowledgeable buyer always appeared fairly quickly, and everybody came out happy at the end. Will you be able to come up with enough interested knowledgeable buyers to make a passive house development pay in your area?
The fact that we were able to show a substantial yearly savings on heat bills may or may not prove to apply in Massachusetts but even if it does can you get the public to believe? I sincerely wish you the best of luck!