We are interested in building a passive solar ranch (1840 sq ft) in Midland, MI (climate zone 5b). Apparently, passive solar works really well in this climate zone. Read somewhere that basement walls account for about 20% of the total heating costs. The builder quoted using superior wall Xi foundation system for the basement. When we asked about using ICF's, he said that using these would cost 3 to 5% more than the superior wall system. We are trying to get the most energy efficient house that we can afford. We've been told it will cost about $155 per sq ft to build this house as close as possible to passive house standards. Does this sound reasonable? Any comments would be appreciated.

Nicky,
I suggest you get a quote or two from both. I would be surprised if this system is less $ than ICF. Also, on review of their website they appear to not consider the conduction of the metal studs within the wall cavity. By far the most important insulation of the system is that which is continuous and not between the studs. If you want to go with metal you need to uncouple the metal that's connecting inside and outside. Heat flow will simply go around the cavity via the metal... In your climate predominately out. Regards.

Hi Nicky, I saw a Superior Wall installation in the late 90's in PA. I thought it went particularly well and the owners haven't had any problems since. Having said that, if passive solar is the path you are taking, I would question if SW is the way you want to go. I believe there is more mass in the ICF system than SW, resulting in better passive solar design/application. I agree with TexasICF regarding the costing of the two systems - get the quotes. Good luck!

While Jake is right that you may need thermal mass to buffer overheating in a passive solar house, ICF is not a good choice. Peak insolation lasts only a few hours in mid to late afternoon. Exposed concrete works quite well in mitigating heat then and carrying it into the evening. I have yet to open windows in my aggressive passive solar house (18 percent glass.) But the concrete in ICF is sandwiched in foam insulation . Most concrete wall systems publish mass-enhanced R-value equivalencies that account for their ability to dampen temperature extremes over 24 hour periods. ICF manufacturers do not, which tells you something.
That said, I am not sure how this matters in a basement unless it has a south-facing walkout. Also,the insulated versions of Superior Walls have continuous insulation and no bridging issues with the steel studs. In a conditioned basement, Superior Walls would make drywall,electric and plumbing easier, and presumably cheaper.

ICF is a great choice and even though the interior portion is covered by 2 5/8" of EPS, the wall still has thermal mass and it does its job quite well. ORNL & other groups did studies and it showed that ICF walls do have a benefit from their concrete thermal mass and the walls are viewed as complex massive wall systems.

For instance, some ICF manufacturers list a Thermal Mass Dynamic R-Value Equivalent and do so in accordance to the ORNL parameters:

Energy Efficiency Data & Performance:
* Thickness of the EPS.………………………………………………… 2.625" / wall panel (5.25" total EPS thickness)
* EPS Steady State R-Value (thermal resistance of the material)…. R - 23 (R - 4.55 / inch @ 40 degrees Fahrenheit)
* CTL Group Thermal Resistance R-Value Calculation Report……. R - 23+ calculated in accordance with ASHRAE 90.1
* EPS K-Factor (thermal conductivity of the material)………………. K - 0.22 / inch @ 40 degrees Fahrenheit
* Air Leakage (infiltration rate).….…….……………………………….. 0.05 to 0.10 ACH (average air changes / hour)
* ORNL Thermal Mass Calculator Dynamic R-Value Equivalent…... Greater than R - 32


Go with the ICF wall system.

In a passive solar home, the question is whether radiant heat in the few hours of peak insolation can penetrate the foam sufficiently to buffer heat. The answer is no.


We have been over this Lbear (and over this.) A quick and dirty calculation is nothing like this report: http://www.rastra.com/ThermalPerformance.html

Posted By toddm on 06 Dec 2012 12:58 PM
In a passive solar home, the question is whether radiant heat in the few hours of peak insolation can penetrate the foam sufficiently to buffer heat. The answer is no.

That's according to you but according to ORNL and other 3rd party and unbiased studies, the answer is yes.

According to BuildingScience and ORNL, the target Phase Displacement is 10 to 12 hours. ICF walls slow temperature penetration of that wall so that the daytime high temperature only reaches the interior when the outside temperature is at a low temperature that the heat can be driven out by ventilation. ICF walls work perfectly in a passive solar home.

Yes, ideally having the interior concrete wall completely exposed works best but then you couldn't even have drywall present. You falsely misrepresent ICF on each and every occasion you can. You openly admitted that you dislike ICF because the workers stalked it incorrectly and you have an axe to grind with ICF ever since.

Posted By toddm on 06 Dec 2012 12:58 PM

We have been over this Lbear (and over this.) A quick and dirty calculation is nothing like this report: http://www.rastra.com/ThermalPerformance.html

Quick and dirty? Please stop with the nonsense.

Dynamic thermal performance of massive walls are a function of the material configuration and the climate:

(2)

where:	: DBMS - Dynamic Benefit for Massive Systems,
	mReqv - R-value equivalent for massive wall, and
	R- steady-state R-value.

Hotbox test by ORNL of the Rastra block showed it to have a RValue of R-8. The 8" Rastra block gets a real R-Value of R-8, the Rastra 12" gets R-15 and the Rastra 14" get R-18. None of the Rastra blocks meet the R-21 minimum code required in most states.

Installing Rastra in a basement with all the moisture is not the wisest choice. Rastra blocks attract & absorb moisture.

NC State says this about decorating a passive solar house: "Wall-to-wall carpeting should not be used on a thermal mass floor. But LBear tells us it is perfectly OK to stick your concrete wall behind 2 inches of foam." Oh wait. I made that last part up. http://ncsc.ncsu.edu/wp-content/uploads/00decor8.pdf (Worth reading, Nicky.)

While your cut and paste skills are admirable LBear, it's that equivalency number that is a bear. Varying by wall and climate, there are literally thousands of such numbers. Most mass-wall manufacturers stick to 6 representative climates ORNL uses.
The only part of Rastra's thermal claims I wanted to note is the column heading "U.S. Department of Energy Oak Ridge National Laboratory Rastra-Specific Tests." Show me "US Department of Energy Oak Ridge National Laboratory ICF-specific Tests" or go away.

No, I wouldn't build a basement out of Rastra. Yes, you can meet code with Rastra by using its R-value equivalency. And no I didn't hijack the thread. I was correcting the misapprehension in an earlier post that passive solar and ICF go together, because they don't.

Perhaps I can assist with this little argument. Portraying Rastra marketing materials as test lab data is not correct. I know each of you have previous posts that emphasize the value of mass walls. AAC and apparently Rastra don't have enough mass (25 Lbs per sqft or so?) to even be classified as massive according to ASHRAE and the US DOE. Thus these reports don't even pertain to AAC or Rastra.

To summarize: Lbear is seeking the truth, ( ICF or not) in his posts even a little (average) 6" wall is three times more massive than AAC or Rastra. One can't take a report that is about mass walls and just add non-massive walls to it.

If ICF is so bad why are the top performing buildings in the US ICF? ... Why is the first net-zero school in the US (likely world) ICF? (Richardsville, KY).

Regards to all.

So then, even if passive solar types to a person tell you to avoid carpet and pad over a concrete floor (R2), 2 inches of foam (R10) over concrete wall has no effect on performance at all. Is that what you are saying?

Yes, TexasICF, we can trust Rastra's published mass-effect claims because the FTC would have their a** if they strayed from ORNL's protocol. I gather that you have not contacted the FCC since we last had this conversation, but here is the online complaint form again: https://www.ftccomplaintassistant.gov/

\T

IMO, if you really want to do passive solar, make the sections of the floor where the sun hits it two feet thick with a concrete slab poured over rocks (with air being able to flow underneath, around the rocks). This will be more effective and less expensive than passive mass elsewhere in the house. Try to make a floor plan that allows the solar soaked rooms to be isolated during peak solar hours (the rock storage is more effective if you let it get really hot in there when you have excess heat available).

Jonr, your rock plan was briefly popular in the 1970s flush of interest in passive solar but quickly abandoned when mold became an issue. It could work in AZ, I guess. I would not try it in MI. Also, a thick concrete floor is surely overkill in MI. I have dark green matte finish ceramic tile over a 4 inch concrete floor. The sun hits it from 9 a.m. to 4:30. If there is a part of it that is even warm to the touch, I haven't found it yet. Your results will vary.

That doesn't mean that overheating won't be an issue in MI. My tile over wonderboard could indeed get hot to the touch. Carpeting and stud walls won't do. The OP wants a basement so concrete floors would take some engineering. A stone fireplace/wall in direct sunlight can be an effective buffer. Or shift the passive solar to an attached greenhouse/sun room that can be closed off from the house.

Nicky, you'll want to spend some time thinking about furniture placement. By mid afternoon, our great room is bright, bright, bright. The windows start at 4 feet in a room that is 10.5 feet tall, so the furniture is tucked under them. There are still spots where the glare and direct radiant heat are issues. And the afternoon soaps are a nonstarter. OTOH, your cats will think they're in heaven.
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In the winter, the rocks are warm (ie, very dry), in the summer, they are in a well insulated area that is part of the conditioned (ie, dehumidified) space with good ventilation. How are they going to get to mold inducing humidity levels?

1000' of 4" slab will only store ~70K btu of heat. That's enough for only about 50 sq ft of windows (ignoring mass elsewhere in the house).

Agreed, over heating, glare, UV damage and heat loss through the windows at night are all things to think about.

Here is the govt on rock bed storage: "Although some early systems passed solar-heated air through a bed of rocks as energy storage, this approach is not recommended because of the inefficiencies involved, the potential problems with condensation and mold in the rock bed, and the effects of that moisture and mold on indoor air quality." http://energy.gov/energysaver/articles/active-solar-heating

Gotta trust my feet over your calculations, Jonr. As I said, there is no part of our slab that feels overly warm, and that's with 240 SF of windows shining on it. Granted we don't have insulated drapes yet so the windows lose as much heat at night as they gain during the day (with a mini split making up the difference.) But the daily swing is ~5 degrees according to the cheapo thermometer I have resting on the slab. Could be you are overestimating how much radiant energy is available in Pa. UCLA's climate consultant recommends passive solar low mass for my climate, and, I'm guessing, ditto for MI. If you add too much mass, passive solar can't budge the needle, too little and you're opening windows. With my amount of glass, which was a design decision, I erred on the side of too much.
As I am sure you realize if the sun isn't overheating my slab there's little reason to build storage of any kind.

As I am sure you realize if the sun isn't overheating my slab there's little reason to build storage of any kind

The criteria is "if you overheat the house". If that's the case, then you have excess heat you could be storing.