Should I go for passivhaus cert?
I’m building a very low budget, below net zero house. It is a 1.5 story on a 40’x28′ footprint. It will have 1920 sf of conditioned space. its close to Dallas TX (2800 cdd 65, 2500 hdd65)
I’ve run some numbers. With slightly above average insulation and high seer wall mount mini splits I can easily hit under 4.5kbtu/sf for heating.
It will have an ERV installed.
the only other metric I am aware of is the ach 50 of under 0.6
my current house (self-built) has 33 operable windows!! and I hit an ach50 of 1.48
this new house will have maybe 4 operable windows so I’m thinking, why not push myself a little on the air sealing and get under 0.6 ach 50? I think I could easily do this.
it wont save me any money. The solar system that will go on this house will ensure a negative bill every single month. so this would only be for bragging rights.
Should I do it?
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We built passive some years ago (flatrock passive house). We were able to get to 0.36ach50 and we have 15 or more operable windows and a wood stove so it's totally doable to reach sub 0.6ach50 with less and the right air sealing details. We decided against it for several reasons. Our remote location made it hard to access passive house certified raters. Also, I was the owner/contractor/builder (certified at the time) and to be honest I didn't see the point of adding all the "paperwork" to what might already be a headache given that there was no one here to consult with onsite other than myself. So I think it's all context but if you can follow the guidelines and meet the metrics that's all the matters really. The bragging rights may have been nice but, to be honest, it is still the case that most people in my province don't know what a passive house is! Do it if you want to but it's not necessary.
David,
Good to see you posting. Really enjoyed following your build.
Thanks Malcom! From time to time I visit the site! Saw this question and thought “I’ve been in this situation, I should answer” . We enjoy or house as much as the first day we moved in. So much has changed. We have a productive backyard farm now with chickens, a cellar, a 4 season greenhouse, and several years ago added areas of food forest. We also added a 16 kW microinverter system and an electric vehicle. We now have rainwater collection capacity of 12000 L in place for annual and perennial production spaces. Last year we produced our first apples and this year our first plums and there’s food literally taking up almost every square foot of open space. It’s amazing being surrounded by the results of choices made to live a different lifestyle. Such abundance.
David,
Great to hear!
David,
Thanks so much for the insight. I didn't realize it was that much paperwork. Maybe I'll just build it to the standard and not worry about the cert. I can do what a lot of people do and say it "meets the passivhaus standard".
btw, love your build series. VERY informative.
Good luck with everything and thanks! It seems that people are still gaining some insights into building from my documentation which is good to see.
The Passive house Idea is good but the last time I looked dollars weren’t part of the BTU divided square footage equation that the program is based on. Often the equation has people buying insulation that has zero chance of ever saving enough energy to recover its cost.
Consider the PGH (Pretty Good House) idea. No certification fees. No paid consultants. No award plaque. You design and build the home with the lowest cost to build and operate over the next 20 years in your climate with your barrowing cost and your guess at future inflation rates for fuel. Learn about the free BEopt software program to optimize your design.
https://www.nlr.gov/buildings/beopt
If you are truly on a budget the only real way to cut it is to reduce the number of square feet and or the window area nothing else moves the numbers. Note having window area exceed 20% of the wall area is a mistake. Windows are great but they make terrible walls If you throw money at then you might get over R5. Consider the largest single line in your budget is generally the window and door line.
Seems to me heating in Dallas is not the big energy user it would be cooling. I do like the idea of eliminating you HVAC from the attic with wall mounted minis. Note avoid milt splits with several heads connected to an outdoor unit and stick with mini splits that have one indoor unit for each outdoor unit.
.6 ACH50 is an achievable goal finding someone in Texas with a blower door may not be easy.
The idea of a negative electric bill is cute but pretty much impossible with the net metering contracts available today if you can even get net metering. Generally the most they will allow is 80% of projected usage. If you somehow get an inflated projection and go into negative kWhs they pay credits at about 10% of retail. So do your local research before you buy an oversized system.
Walta
Hi Walta, thanks for the input. Is very informative.
I do like the pretty good house idea and I'm sure the house will meet all the criteria.
I actually used beopt to give me the idea that I could get under the 4.5k btu/sf requirement.
I agree with you about window area but it almost seems like it's easier to achieve passivhause with more square footage not less, since bigger houses tend to have less envelope per sq ft of living area.
I'm putting 800 sf of the 1920 sf in the attic and making use of space we normally waste here in Texas. That helps maximize the square footage for the envelope area.
I 100% agree with you on not using multi zone mini splits. I've read that they can be terribly inefficient. One head per outdoor unit for me.
I actually happen to own a blower door so finding one won't be a problem :)
I picked it up inexpensively when I was building my current house.
I chose to talk about the solar separately as I'm very passionate about it. All your points are correct.
It's difficult to have a negative bill with the new buyback rates but not impossible.
A self installed system is incredibly inexpensive and batteries have gotten extremely affordable.
I can purchase 12kw worth of pv for under $5k. The inverter is $2k and the mounting is $1500. This system will produce more than 2x what the house will use annually. My utility is currently at a 68% buyback rate so there is no need for batteries but if they drop the buyback rate to say 20% I could inexpensively add batteries to keep the monthly bill below zero.
I haven't paid an electricity bill in over a year and all last year I spent $60 on electricity. My current system cost me about 23k but prices have dropped (especially batteries) since then
I was in the same boat as well. I was the GC on my project. I used the German PassivHaus targets and calculated what I would need in insulation to hit that. I used Salamander European windows from Debesto. 14 operable and 19 fixed glass. My blower door ended up around 0.5 (remember to fill your P-traps, I did not!). I used a double stud wall, so making it 11.25" was easy, and allowed me to use 2x12 top/bottom plates on some tall walls with staggered studs instead of double stud.
I decided not to pursue any passivehaus certifications, I didn't see the point. This house is for me, and acheiving that goal was a pet project. I used the targets because I wanted a comfortable house that had more stable energy bills over time.
I also installed a solar system. I have a 12.9kw ground mounted array along with 30kwh of battery and whole home backup through that system. Super happy with it. DIY install, so it cost about the same as my neighbors generators... The batteries died overnight on my last power outage though, so I guess it's not perfect. I don't have a way to disable my EV charger when grid power is out yet... Grid went down at 1am, about the same time my car is scheduled to start charging. System switched over to batteries and the car sucked every watt out of them in a hurry. Oops. Working on integrating all this a little smarter with Home Assistant.
Tim O , you are so right. the money I save not pursuing the certification will buy more solar panels (•‿•)
I think its enough to know that I hit the standard.
If youre willing to share, I'm curious about your pv system. how did you achieve whole home backup? I have 12kw of inverter but my house can sometimes go above 14kw so I had to do a critical loads panel.
what type of ev charger do you use? does it interface with home assistant? if you are already using home assistant hopefully its really easy to create an automation that keeps it from charging if the grid is down. I wouldnt know how to do this though as I dont think I have any system in place to know tell when the grid is down.