You must have had it set to Moscow, OH, because Moscow RS (UUEE), at 56°N, had 8805 HDD (ref 65°F) last year. That reconciles nicely with the 20" of wall thickness.

56°N... that's awfully close to the arctic circle. It has to be tough to be passive when the sun is 10° above the horizon at noon on the solstice.

This is the data set I used:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> >>>
Description:,"Fahrenheit-based 5-year-average (2006 to 2010) heating degree days for a base temperature of 65F"
Source:,"www.degreedays.net (using temperature data from www.wunderground.com)"
Accuracy:,"No problems detected"
Station:,"Airport: Moscow Vnukovo, RS (37.27E,55.65N)"
Station ID:,"UUWW"

,HDD
Jan,1517
Feb,1376
Mar,1072
Apr,663
May,325
Jun,160
Jul,97
Aug,134
Sep,353
Oct,694
Nov,979
Dec,1253
Total,8623 <===============
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> >>>

...try something else.

-AC

The second-last data point here, the one that does not fit the curve, corresponds to Moscow and should have around 9000HDD, not 4500. I bet your correlation coefficient would go from "meh" to "aha!" if you were to correct that. That's all I'm getting at here.

NOTE: data error in post # 26 has been repaired

-AC_Hacker

The angle at which the sun's rays hit the window is much closer to perpendicular. But yes, the sun is above the horizon for no more than 6-7 hours, plus the rays of sunlight have to travel through a thicker layer of atmosphere. Here in Warsaw (52°N) the amount of energy from the sun in the winter is 4 times less than in the summer (~350 W/m2 vs ~1300 W/m2). I believe that passivhaus design for locations close to the polar circle is geared towards thermal mass, to hold as much of summer's/autumn's heat for as long as possible, and towards using heat produced by the inhabitants, cooking, and waste heat from electronics. "Don't unplug that wall wart or we'll freeze!"

Aha! An r-value (the correlation coefficient, not the insulation value) like that proves that Passivhaus wall thickness is in fact linear with annual HDD.

Looking at the third plot, I see I fall in with most of the rest of the EcoRenovators, around 6000HDD/yr. This suggests an insulation thickness of 14". Hmm, that's an awful lot.

AC_Hacker, you mentioned that you would do cellulose instead of foam if you could do it over again. Would you recommend cellulose over a CFC-free (e.g. CO2) blown foam as well?

Hah... I've been there.



Viceroy have sent me a pricelist and specification sheet for their houses... they also mentioned that their houses are well sealed, and many customers install a ventilation heat recovery system. I like everything I've seen about them so far, except the fact that new construction is a fair bit more expensive than buying used. But the opportunity to get the house I want, in the right location, sited correctly, is pretty compelling.

Just putting this out there:

You seem to be looking for something particular.

You give the word and I'll be there in 3 days with a 16 man framing crew to do your job for less than what you are looking at. And it will be done right.

PM me if you want.

There may be an increased cost in spray foam insulation if you use it but if you go with Structural Insulated Panels with new construction, you avoid the framing labor, get a thinner wall than using fiberglass or cellulose. Since it is rigid foam inside, you have a built-in vapor barrier and air sealing that is hard to mess up too. Doing a little reading to see if these can be bought thick and it seems Wikipedia mentions that they can be 12" thick. If the stuff is polystyrene, which I think is R-5 per inch, it would be about R-60, right? Since there is no framing members, no thermal bridge, you would just need to worry about the air sealing and thermal bridging of penetrations like doors and windows.

It was my impression after watching a television show on prefab houses about 5 years ago, Build one place, ship somewhere else and assemble. The show I was watching explained how instead of using nails and screws, attaching components with adhesives were used instead to speed up the process. I thought it was fascinating. I thought they used SIPs in the construction.

http://www.ecosteel.com/tech/insulatedpanels.pdf

EcoSteel offer a 4" structural insulated panel with R-14, and a 3" insulated panel with R-24. A 10" stack of SIP + IP + IP would have R-62, and a 13" stack would have R-86. As EcoSteel are happy to remind you, these are "whole wall performance" figures, including thermal bridging effects. So a 12" SIP would be a serious performer, perhaps even overkill for any application other than a northern Passivhaus.

Yes.

Fine Homebuilding mag from the early part of this year, has an article on foam + cellulose, and they even talk about the minimum foam thickness required to prevent condensation.

-AC_Hacker