Hello Everyone, This seems to be a very good forum with a lot of experienced people chiming in. I'm hoping you can help to educate me on the concept of thermal mass as it relates to ICF's. Here is what I'm thinking: If foundation walls are insulated on the inside, than does that effectively eliminate thermal mass from the equation? At least for the foundation walls? If that is true, is it safe to say then that eliminating any thermal bridging is one of the most effective ways to achieve a good R value? What then, is the real benefit of the exterior insulation on an ICF? I confess up front that I am just learning, so please set me straight if anything I've said is not accurate. Just trying to evaluate the actual benefit of ICF vs poured wall with multiple layers of insulation to eliminate thermal bridging. Thanks! Mike Omaha NE

Good posts here - all relevant.

I have built a number of Durisol projects (Ontario Canada).  The consultants/architects have always mentioned the lop sided block is an advantage when designing for passive solar/thermal mass effects.  Durisol has an interesting generalized thermal mass document downloadable from their web site which states facts regarding thermal mass.  Its applicable to any lop sided block available so worth the read.

Nerd
Eliminating as much thermal bridging as possible (thermal break) is one of the most effective ways to achieve good R value. One of the purposes of the concrete core is to act as a thermal break in between the foam. Your thermal flow starts on one side of the exterior part of the foam, traveling through until it hits the thermal bridge of concrete, and then having to go through the foam again. I know that is one way of looking at it.
I am more on the ICF side but it sounds like a good question. I would like to see more tests as referred to by Jake.
Jake.
Is there a link to the test you are talking about?

I was speaking with a builder/owner in Santa Fe yesterday who has been living in a Durisol home for over a year now. December is the coldest month and his heating costs were $238.00 for the month. His home is far from green by virtue of it's size. It is approx 6500 sq.ft of conditioned living space. But the energy efficiencies that he has acheived are impressive. His nearest neighbor has a 2700 sq ft 2x6 home and the heating costs for that home in the same month was $550.00. There was no air conditioning required throughout the summer, so the benefits for both coolling and heating conditions are pretty evident.

I am sure air infiltration is a big part of the difference, but I also believe the thermal mass positioned towards the interior makes a big difference as well. The climate there with the large temperature swings between day and night really contribute to the dynamic / thermal mass effects and the contributing energy efficiency.

I agree with Bruce - ICFs are not magic and you can certainly acheive the same performance with more "traditional" wall assemblies a poured concrete wall (or CMU), with insulation on the exterior. You will also need to strap the interior (or otherwise prepare for finishes). I don't think this will be less expensive than ICF however and will certainly require more steps...

I pretty much agree with Bruce and interject my opinion from always living/building in a seasonal climate such as here in Minnesota.

Thermal mass "provide[s] the most benefit when the daily exterior hi/low temperatures swing above/below the interior temperature." Here in the spring and fall we are used to heating and cooling are houses in the same 24 hr period! And this situation the mass sandwiched between the insulation still functions well.

For us the "free energy" of earth would be nice in the summer, but in the winter when the frost goes down 4' or more. So I push for insulation under the basement floors, yeh almost every house gets a basement here.

"Thermal mass is most effective on the inside. This favors a concrete wall with exterior insulation, lopsided block (more insulation on exterior than interior) and conventional forms (equal interior/exterior insulation) in that order. This is especially true if passive solar will be used." I agree, thermal mass to the living space is the most energy efficient. There are more considerations; Ease of construction, the common ICF is easier to construct with and to attach interior finishes, which translates to cost. the lopsided blocks are more expensive and often have to be assembled on site, again cost.

ICFs are hands down the best overall construction system, with the common evenly insulated ICF being overall better than lopsided. Due in part because cost is ALWAYS a factor.

Thermal Mass
Thermal Mass is a property that enables building materials to absorb, store, and later release significant amounts of heat. Buildings constructed of concrete have a unique energy saving advantage because of their inherent thermal mass. These materials absorb energy slowly and hold it for much longer periods of time than do less massive materials. This delays and reduces heat transfer through a thermal mass building component, leading to three important results. First, there are fewer spikes in the heating and cooling requirements, since mass slows the response time and moderates indoor temperature fluctuations. Second a massive building uses less energy than a similar low mass building due to the reduced heat transfer through the massive elements. Third, thermal mass can shift energy demand to off peak time periods when utility rates are lower.
Thermal Bridging
Thermal bridging is the transfer of heat across building elements, which have less thermal resistance than the added insulation. This decreases the overall R-value. Wall frames and ceiling joists are examples of thermal bridges, having a lower R-value than the insulating material placed between them. Because of this the overall R-value of a typical construction element can be reduced. For example, adding R2.5 bulk insulation between ceiling joists will actually only achieve an overall R-value for the ceiling of R2.2.
"Mass-Enhanced R-Value"
When people refer to the "mass effect" or "effective R-value," they are generally referring to the ability of high-mass materials, when used in certain ways, to achieve better energy performance than would be expected if only the commonly accepted (steady-state) R-value or U-factor of that material were considered. Let's take a look at a typical use of one of these high-mass materials in a wall system. When one side of the wall is warmer than the other side, heat will conduct from the warm side into the material and gradually move through it to the colder side. If both sides are at constant temperatures--say the inside surface at 75°F (42°C) and the outside surface at 32°F (18°C)--conductivity will carry heat out of the building at an easily predicted rate. As described above, this steady-state heat flow is what most test procedures for determining R-value measure.
In real-life situations, however, the inside and outside temperatures are not constant. In fact, in many parts of the country, the driving force for conductive heat flow (remember, heat always moves from warmer to colder) can change dramatically or even reverse during the course of a day. On a summer afternoon in Albuquerque, New Mexico, for example, it might be 90°F (32°C) outside, and the outside wall surface--because it has a dark stucco--might be even hotter. It's cooler inside, so heat conducts from the outside surface of the wall inward. As night falls, however, it cools down outside. The air temperature may drop to 50°F (10°C). The driving force for heat flow changes. As the temperature difference across the wall is reversed, the heat flow is also reversed--drawing heat back towards the outside of the building. As a result of this modulating heat flow through a high-heat-capacity material, less heat from outside the building makes its way inside. Under these conditions, the wall has an effective thermal performance that is higher than the steady-state R-value listed in books (such as ASHRAE's Handbook of Fundamentals). This dynamic process is what some people call the "mass effect."
Another common scenario is when the outside temperature fluctuates but never crosses the indoor set point temperature. In this case, the direction of heat flow never changes, but the thermal lag or time delay in heat flow can still be beneficial by delaying the peak heating or cooling load. For example, if the outdoor temperature in Miami peaks at 95°F (35°C) at 5:00 on a summer afternoon, but it takes eight hours for the heat to travel through the wall, the effect of that peak temperature won't be felt inside the building until the middle of the night. Because most cooling equipment operates at higher efficiency if the outdoor air temperature is lower and because night time thermostat settings may be higher (at least in commercial buildings), potentially significant savings can result. Not only can total cooling energy be reduced, but peak loads can also be reduced. This can lead to smaller (and less costly) mechanical systems and lower demand charges for electricity. This time lag effect can save energy and money, but note that it does not affect the total amount of heat flowing through the wall.
As noted above, the amount of heat flow through a wall is reduced by the use of thermal mass when the temperatures fluctuate above and below the desired indoor temperature, so under these conditions a material might have a "mass-enhanced" R-value that is greater than its steady-state R-value. To estimate this mass-enhanced R-value for a given high-mass material in a particular climate, researchers at Oak Ridge National Laboratory measure the thermal performance of a high-mass wall under dynamic conditions, in which the temperature on one side of the wall is kept constant and the temperature on the other side is made to fluctuate up or down. With this measured heat flow under dynamic conditions as a basis, they then use computer modeling to arrive at steady-state wall R-values that would be required to achieve comparable overall energy performance under various climate conditions. Those results are what we are calling the "mass-enhanced R-values" for the high-mass material under the modeled conditions.
When is Mass-Enhanced R-Value Significant?
The mass effect is real. High-mass walls really can significantly outperform low-mass walls of comparable steady-state R-value--i.e., they can achieve a higher "mass-enhanced R-value." BUT (and this is an important "but"), this mass-enhanced R-value is only significant when the outdoor temperatures cycle above and below indoor temperatures within a 24-hour period. Thus, high-mass walls are most beneficial in moderate climates that have high diurnal (daily) temperature swings around the desired indoor setpoint.
Nearly all areas with significant cooling loads can benefit from thermal mass in exterior walls. The sunny Southwest, particularly high-elevation areas of Arizona, New Mexico and Colorado, benefit the most from the mass effect for heating. In northern climates, when the temperature during a 24-hour period in winter is always well below the indoor temperature, the mass effect offers almost no benefit, and the mass-enhanced R-value is nearly identical to the steady-state R-value. The ASHRAE Handbook of Fundamentals lists "mean daily temperature range" data for hundreds of U.S. climates in the chapter on climate data. These values can be helpful in figuring out how significant mass-enhanced R-value might be for a particular climate, but they do not tell the whole story; also significant is the percentage of days during the heating and cooling seasons when the outdoor temperature cycles above and below the indoor temperature.

Hoowood.......are you an engineer? I see you just joined today.

Very well put by Hoowood. Only one issue with the final remarks....In cold climates where the temp remains well below the indoor temp, there is almost no benefit..... This could be misleading..... The amount of heat energy and time to move across the high mass wall is not the same as a low mass wall...example: When the power goes out during an ice storm in central Minnesota and an ICF home is situated near a low mass home, the low mass wall home will "equalize" with the outdoor temp much faster than the high mass ICF home.(we are talking a matter of a few hours vs. many days with a high mass wall)....this shows that the time it takes to equalize with the constant cold outdoor temp is much slower...even if the outdoor temp remains below the indoor temp, so there is a definite benefit of the high mass wall even when the temps are much lower outside. Same is true of the opposite condition in the south summer. In the south, the predominant exterior cladding is brick or stone (high mass, exposed), these claddings store heat 24/7 and release toward the cooled interior. in low mass construction, the brick acts as a radiant heater 24/7. With high mass walls, the time and heat energy required to move the temps up through the mass is greater.

Hi Aaron,

Try:

www.durisolbuild.com/Downloads.shtml

Then click on the Thermal Performance download.  That write up references CMHC reports, the California Energy Commission and ASHRAE.  I found it an interesting read.

 

Hi @all
I am not an engineer but since 2004 in the zero emmission homes business. We let our homeowners build so called passiv houses or at least low energy homes and we support them with the best available products in the market. Over 30,000 hrs of research was done and it´s time no to deliver my products to the US market. We are headquarted in Atlanta and are open to DIY´s that want to build themselves a home with professional help. Our ICF´s are usable like lego blocks and only with the right triple pane windows and an airingsystem that exchanges 250-300 m³ air per/hr you can reach R-values above 75 ( see my projectalbum with an sample)

From studying this website I learn, that there are many people interessted in the "Green" technologies but it is important to understand what "green " is. Isn´t it much easier like in the auto industry ( gallons/miles) to have a house designed and build that needs only 45$/ month for electricity and no heating or colling is extra, because the airing machine is doing this or even better, to hav an income producing home with solar, where the solar could be sold to the grid.

Our philosophy is to build better with using less technologies and keep the trees in the woods.

More soon or by request.

PS: If I put informations in here, the are not from me but from well researched sources in the building industry out of europe as we are using this technologies since over 35 years already.

Let´s give this crisis an end and start something better NOW

Hoowood

Thanks Jake.

I don't know how many times we have to do this. The dynamic benefit of mass systems can only be measured in 24 hour periods, and in places and seasons when the average ambient temperature is something a homeowner would consider comfortable. Over longer periods, average is average no matter how you build.

When the power comes back on in Minnesota, Atitagain, your adjacent houses will require the same amount of energy to rewarm, all else being equal, even if the low-mass house is 50 degrees and the high-mass house is 65 degrees. As for the outage, a wood stove delivers both charm and emergency heat for pennies on the ICF dollar.