This is a problem we are having with a few ICF guys ,as I am sure that the Sips industry does as well . But R-values of up to R-90? I've never heard that one. What I here a lot is, if you just even build a ICF basement wall you will save 50% on energy cost. Now that's just plain crazy talk. R-30 to R-40 is actually quite accurate number to use. Unbroken Thermal mass walls with unbroken foam insulation just work differently than Mult structural members with pieced together insulation. . What I'm talking about is a "POINT of BALANCE" or Equilibrium in heat flow. One Btu of heat will travel 20 feet in 6 months time in most types of thermal mass, such as earth or concrete. Now if the soil is insulated on all but one side of the box or earth berm ,then winter arrives the heat flow reverses as there is no summer heat input. And the warmer soil is losing it's heat to what once was the heat input side of the box. This is a annual heat flow or Balance Point. With a thermal mass wall, we are looking at a daily cycle instead of an anual cycle. During the summer months heat travels through the exterior foam insulation and into the cooler concrete of the ICF wall. The concrete absorbs the warmer exterior btu's until the entire wall has warmed to the same temperature as the heat being applied. Each Btu is still seeking to flow into a place of cooler btu's and this would now be the interior of the home. So each BTU is now working to travel through the inner foam. But by this time the day has cooled off outside and now it is cooler outside than the interior of the structure. So rather than the heat flowing into the interior of the structure it instead reverses and starts an outward flow and eventuly gives off all of it's heat gain into the evening air. So a point of Balance has been reached. This is the difference between Icf and other building materials. This cycle is what allows a icf wall to float through the highs and lows temperature swings. Now imagine a Total Concrete Home built in this way. It's works much like radiant heated floors allow you to lower your thermostat a few degrees. The same is true with a Total Concrete Homes. So R-40 is a very fare assessment .

1st of all, good find Mark. I downloaded and tested a portion of the software, and it's accurate. You do need to know how to convert from U-Values to R-Values(1/x), so that you understand how it works.


For the basement alone(if mostly underground) I could believe that! Again, how is it derived? And what if it's a North wall, or it's a cloudy day in the Winter. R-40? I am not speaking from a SIP vs ICF perspective, but rather a common sense perspective.

If on a hot day the heat is making it's way through the outer layer of EPS(warming the concrete), why isn't it making it's way through the inner layer of EPS(knowing that concrete is a thermal conductor and basically has an R-Value of zero)?

Another problem that I have, is trying to combine R-Values & Air Infiltration. These are separate entities, but the ICF world constantly tries to combine them(Apples & Oranges) into an R-Value. Why is that? I have yet to see 1 SIP company trying the same tactic(And I have seen performance exaggerations by SIP companies).

Studies dispute most of the claims by ICF manufacturers, and further more the results vary by climate.

When are the ICF claims going to be supported by neutral study?

I have no interest in bashing ICF's, as they are the superior building method in certain areas. I'd just like to see the truth.

R-value is relative to begin with. products like eps are tested in hot box @ 70 degrees,and then heat flow or resistance to heat flow is measured. .... So yes r-value is relative to climate or more appropriately to temperature difference..... The greater the temperature difference is, the lower the resistance to heat flow will be (lower R). ....So a R-30-R40 wall will have a lower R-value at 32 degrees than it would at 70 degrees per. manufacture specs.. ....Take a wall section on any side"even North" and let's say the outside air is 72 while interior air is 70. That 2 degree difference in temp. will seek and flow to the cooler interior place. No matter what the wall material is made of. .....With icf a thermal mass concrete collector of btu's is placed in the center of the wall cavity to absorb those btus, and it will collect btus as long as it is cooler and the heat input side of the wall. ....This is where the icf datavantage comes in . In most of north america a 6" concrete icf wall is the "balance point to daily heat flow". By the time heat has flowed to the inner icf foam it is now evening and the outside temperature is now lower than the interior air temperature.... It is lower than the concrete temperature and the foam temperature. So....... heat flow reversed and flows outward giving off unwanted heat gain to the cooler night air. ...... If the concrete thickness was only 4" thick the heat flow would be "unbalanced" and would flow into the structure near the end of the day. And once it is inside the structure heat loss back through the wall would be slowed by the interior foam, but only slowed. ..... ICF wall sections have been tested with infrared cameras and do reach those high relative r-values. .... Comsumers know that a higher r is better than a lower r...... Most folks dont know what a K, or U value is, so to be accurate we must us this apples to oranges outdated R-value comparison. Or we would be telling to our prospective customers, that icf only have a R22 . But a icf wall preforms much better than R-22. So what are we to do?

Hi Guys,

I agree with most of your thoughts. On effective R-value: When I use that term, I am referring to the "effective R-value" after taking into acount the total wall system, insulation, framing, etc. In a "typical" wall in the old days anyway, framing might account for up to 20% of your wall area. Thus the R-value for boundary air, (inside and out), interior wall finish, framing, sheathing and exterior wall finish, times the percentage of wall area occupied by framed areas, plus the R-value for boundary air, (inside and out), interior wall finish, insulation, sheathing and exterior wall finish times the percentage of wall area occupied by the insulated areas, equals the effective R-value of the wall system. Obviously, this is somewhat simplified, especially as it relates to other types of wall construction. but the principles remain the same. Air infiltration and other considerations are separate issues. While they may affect the R-value of the components in the wall to some degree, they do not in and of themselves add or detract from R-value. Before you go off on a new tirade, I know that air infiltration does affect the useful R-value of whatever insulation used, particularly fiberglass, and to a lesser degree, cellulose. This is where sip's AND icf's will excell, as they are not affected by air passing through the insulation itself.

Another tongue in cheek: Have you ever heard of spell check?

Please define 'boundry air'.

I am looking at designing a passive solar home in MN on a lot w/ southern exposure. How does that affect the choice of building systems? SIP, ICF, Concrete sandwich wall, etc....

It really doesn't. You'll probably need to plan for some thermal mass inside your thermal envelope, but the envelope itself can constructed with anything. Anything, as long as it's well insulated and has very low air infiltration. SIPS & ICF's both fit the bill.

I also recommend super insulating, as it will reduce energy needs no matter what system you are using for heating and cooling.

Good Luck!

PC, the problem here is that the ICF guys are at a disadvantage. They are correct that their mass provides benefit in some situations. And their benefit does not show up if you do straight R-value comparisons. Basically both SIP and ICF seal the house tight and kill thermal bridging. One adds mass and one does not. Assuming you have equal foam in both, you have essentially equal resistance to heat transfer... the mass envelope just takes longer to charge up. And it does soak up energy during the day to offset load at night. Good stuff.

But, nothing that is relevant to a typical heat load calculation. You can't calculate peak heat loss with the mass effect in place, because that would require some serious assumptions about what the conditions are on that design day you are sizing for. For that reason, when you are sizing your heating system, I believe that mass should be ignored.

HOWEVER, if you are doing yearly energy calculations, the mass effect has some effect I'm sure. I am not positive how to quantify it, but I think the ICF guys are trying to relate that to buyers using the only thing buyers understand as far as energy ratings go for heating/cooling.. and that's R-value.

So generally I do SIP and ICF load calcs exactly the same way, and I just note that the yearly energy use will probably be lower in the ICF home. and until we're all running accurate modelling software on custom home designs, that's going to have to do I think.

I do wish the ICF guys would stop with the "equivalence" stuff myself though. It does confuse the issue and it is in fact, illegal to advertise anything intended as insulation with anything other than a tested R-value.

To be fair, I have seen SIP manufacturers use the equivalence thing as well though to try and address infiltration. They seemed to have stopped a couple of years ago, or maybe I just stopped asking people what the R-value of their panels were and just started asking how thick the foam was....

Hello. I am a current student in a community college in ohio. I have a question-  what is the purpose of performing “heat loss” calculations for a building? Please reply as soon as possible.

To determine the size(BTU's) of your heating equipment.