An ICF wall (2.5" EPS x 6" concrete x 2.5" EPS) gives one a R-21/23 wall. Passive House walls are usually in the R-30+ arena.

Is it possible to attain PH certification in a Zone 4 climate with an ICF wall? Does PH calcs even take into account the thermal mass or the diurnal swings of a SW desert climate?

Well, here's a Passive House with a R-70 ICF based wall system:

In the Woods

As we discussed in another thread, this one also uses a very boxy design to assist with high efficiently. However, I still prefer a ranch style ICF house with a full hip metal roof with massive overhangs (for passive solar and reduced siding weathering), which I believe is a reasonable compromise between aesthetics and efficiency, and which I believe will have significantly less maintenance issues/expense and a much longer life.

There are many ways to achieve to net-zero, so I question why one would feel compelled to pursue a relatively rigid standard just to achieve some certification with the associated additional expense. Seems like minimizing acquisition cost and eliminating/minimizing operation and maintenance cost would be a better objective.

Posted By sailawayrb on 14 Oct 2013 10:31 PM
Well, here's a Passive House with a R-70 ICF based wall system:

In the Woods

Wow, that house has 11” Insulated Concrete Forms (ICF) for structure, and an 11” Exterior Insulation and Finish System (EIFS) facade with an overall R-value of 70. That's an insane 22" inch wall thickness. I don't think $$$ was an issue for this builder.

I believe R70 walls would be overkill for a Zone 4B climate.

I was just curious to see if PH in Zone4B is even possible with R21/R23 ICF walls. In other words, what is the minimum R-Value for a PH wall in Zone 4?

 

It's possible to place too much emphasis on raw R-value in PassiveHouse designs especially in temperate climates that see a lot of sun, since the solar gain & INTERIOR thermal mass (far more so than the wall-mass of an ICF) make it or break it.

Rather than asking open ended questions with minimal context, tool up and just DESIGN the thing. (BeOpt / DOE2 model the mass effects reasonably well. ) Start here:

http://www.passivehouse.us/passiveHouse/DesignTools.html

Just like framed construction, extra corners reduce the thermal efficiency of the envelope, so at R22-ish whole wall it probably won't tolerate a whole lot of bump-outs & complex shapes without corresponding increases in R, but it should be possible to hit PHIUS energy use levels at R22 mass walls with something more akin to the "shoe-box with gable" look that PassiveHouse critics are so fond of taking to task, if you take the right balance of interior mass, high-performance/low-loss windows and design for the solar gain.

R70 walls might be overkill even for a woodsy location in US zone 6 (where the ICF example was located), but may have been cost trade-offs for more or lossier windows area to keep the place from feeling like a cave. In the desert SW you have more opportunities for taking advantage of the sun and far less extreme temperatures than Hudson WI (Minneapolis area, toward the cooler edge of zone 6), but it'll still take high-performance windows, and not TOO much solar gain to get there.

I don't think specific R-value is a requirement. I found the following document online about the process of PHIUS certification.

http://www.passivehouse.us/passiveHouse/PHIUSPlusDocs/PHIUS+CertificationPacket8.21.13.pdf

It looks like the main requirements are 4,705 BTU/sq. ft./year each for cooling and heating, 11.1 kWh/sq. ft. /year of energy usage, and then of course 0.6 ACH @ 50 Pa. I think it should be pretty easy to achieve these requirements in Zone 4 even with R22 walls. I think once you achieve the ACH requirement the rest should be cake.

Dana - why would corner reduce the thermal efficiency in an ICF building?

what is the minimum R-Value for a PH wall in Zone 4?
In Passive House certification, the R values are determined as part of the calculation, they are not a fixed number. So the R value required for any particular location will vary based on many factors including the window area & values, the wall and roof areas and planned R values, foundation & floor R values, direction of the house, thermal bridging, etc, etc. PH also has it's own way of determining the R values of products. With dense packed cellulose, for example, the manufacturer's R value is different from the value Building Science uses, and from numerous other sources. So it's complicated. You could see if there are existing PH's in your area - that will give you a rough approximation, but you need to use the PHPP or hire someone to do that before you can assume anything. And if you do your own calculations, they will be checked by the certifying organization, and the house will need to be verified during construction by an approved PH certifier. It is a complicated, involved process, which is why it is so important.

Posted By FBBP on 15 Oct 2013 12:51 PM
Dana - why would corner reduce the thermal efficiency in an ICF building?

Adding corners increases the exterior surface area per square foot of conditioned space, and thus more heat gain/loss per square foot of conditioned space.  Though the PassiveHouse measurement of square footage is different from the way real estate brokers do it, at the bottom line one of the stringent specifications is annual energy use per unit area of conditioned space.