For the thermal mass component of ICFs, read the extensive testing done by the Canadian NRC.

I can't find any testing by the NRC relating to the thermal mass components of ICFs.

As to the long term curing of concrete, last year I constructed a two car garage with living area over. It's bermed into a hill with a 10' high bermed back wall and 10' high slighty bermed side walls. Lots of concrete. I struck a spring when digging in, so I was worried about moisture. The first year was scary. I had strange condensation issues. One time, there was a puddle on the floor. I thought that all of my waterproofing efforts had failed (Certainteed Form-a--Drain footing, additional footer drain, Delta dimple fabric, 15 mill vapor barrier). Garage always felt cold and damp.

I'm now at the one year mark and what a difference. Winter temps in the unheated garage are 10 degrees higher based on my recording thermometer (now approaching ambient ground temperature at about 52 degrees). I saw my last condensation (only on a garage door window) three months ago.

The temperature fluctuation indicated on the recording thermometer shows the effects of thermal mass. Last summer, the highest temperatures were always just after midnight, when the "heat" of the day has worked its way into the structure. The bare concrete walls take several hours of direct sun. During some hot weather last summer, daytime temps were 68, rising to 72 between midnight and 2 am. This was during +90 day temps and 70 night temps.

Here's another picture of an ICF structure and fire damage. The ICF blocks are Rastra, a mixture of concrete and EPS that does not burn or melt. The building had not yet been sided. If it had been bare EPS blocks, they probably would have melted. If sided with wood, it probably would have burned. The tarp is covering Rastra blocks. The Rastra blocks should have been covering the tarp.

http://mmcmillen.com/rastra/pages/11fireDCP_1622_jpg.htm
http://mmcmillen.com/rastra/pages/13DCP_1624_jpg.htm

I researched ICF manufacturers and decied to use Quad-Lock. I bought an older home (built in 1974) out of slump block. All the interior walls were exposed block. I added on 1700 sq.ft to the existing 2140 SqFt and did the addition using ICF manufactured by Quad-Lock. I read mostly positive reviews of the material and their technical help. I live in Tucson Arizona where it gets very hot (up to 115F) in the summer months (June, July, August). In my research, I determined it would be very benificial to use an open cell polyurethane spray foam for attic insulation. I found a product called Sealaction 500 to one of the better products. I put in between 8 to 10 inches sprayed up against the roof to reduce the heat penetration into the area where my A/C ducts are. To improve the performance of the old house, I insulated the walls with extruded polystyrene (2 inches) and replace all the doors and windows with double payne argon filled windows by Sierra Pacific. Their windows were not as pricey as Pella and the quality I felt was very similiar. I also foamed the roof on the old house with since it has a parapit and the roof surface is not visible from the street. That material is approx. R6 per inch. The thickness varies since I had to create the slope for water drainage. My winter heating bills which is made up of 1 gas furnace/10 year old carrier A/C unit and 1 electric A/C /heat pump (SEER 13 for addition) did not exceed $190. This will be my first summer and I am curious to see what my electric bill will be. The house seems thermostats in the winter did not vary much between 72 to 75F even on the very cold (35F) winter mornings. I have the thermostats set to 76F for the summer and will be tracking the monthly usage and cost. So far, I am impressed with how tight the addition is and I am hoping the improvments I made to the existing home keep my energy bills very low in the hot summer months.

I know this is a late post but just want to add my experience with our new ICF home which will be finished in March 2009. Our ICF house is 4 levels and is 3000 sq ft. Our current house is 2x4 construction built in early 80s. Current house uses electric baseboard heat. New ICF is electric plenum heater (air source heat pump will be hooked up closer to finish). We pay about the same to heat the 3000 sq ft ICF house as we do the 1000 sq ft 2x4 house. Last week our contractor turned the thermostat down from 66F to 55F and it took well over 24 hours for it to reach the 55F temp. This was over a time period when the average outdoor temp was a negative 17 degrees F. I know this because I can check a graph of my electric usage that also graphs the temperature via my utiliy providers web site. The ICF house is all ICF 6" concrete core exterior walls. vapor barior and 2" XPS foam under the slabs. 5.5" of closed cell polyurethane foam under the roof deck on the vaulted ceiling. 3.5" of closed cell polyurethane foam on gabel end in vaulted area. 2" closed cell polyurethane foam on top of the sheetrock in the standard attic and 12" of blown in cellulose over the foam in the upper level. Efficiency is great. I have figured heat loss is less than 19,000 BTU/h when the temps are negative 20 degrees F. That exceeds my expectations.

Thanks for posting! THAT'S the kind of info I want to hear!

That is great congratulations!

Our ICF home is in central Minnesota and we have had a lot of very cold weather dips this year. Several have been in the negative teens and down to negative twenties F (-29 C). Only one can light that is into the attic for the walk in show. It's IC rated and is sealed from the spray foam in the attic. Still have a few rough openings for heat pump pipes, wood stove intake, bath exhaust fans that are not foam sealed yet, just a little fiberglass stuffed in them to reduce heat loss. My project manager has been very good about foaming any type of potential air leakage no matter how small. Air exchanger is not running yet but the entire 3000 sq ft is set to the same temp.

One thought I had on the orginal poster was if they have forced air heating where is the duct work? I made sure all our HVAC duct work is in the conditioned space of the home. ICF walls is just one piece of the puzzle. Attention to detail is very important. Also the poster mentioned that the windows were Low-e and argon filled. That is great for the glass panes but the window frames could still be leaky and causing issues.

Well we have been in our icf house for over two years.We live in central North Carolina, no where near as cold as up north.The house is 2800 sq/ft first floor, and 2000 sq/ft second floor, and 900 sq/ft garage,its 6" icf all the way to the roof, with icynene foam insulation sprayed on the roof line.We have a 4' sealed crawlspace with 2" concrete slab, its also condition.Heat/ and cooing first floor with a 2 1/2 ton heat pump /with a natural gas backup furance,upstairs a 2 ton heat pump.Our total power bills for last year was $1305.00, gas $400.00(hot water,cooktop, gaslogs, and backup furnance.

I have multiple clients that we have built icf houses for in the past 10 years that have great testimonials about how great their houses preform.I hope you can figure out whats wrong.
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STACKING THE CAROLINAS ONE BLOCK AT A TIME
TODD BIGGERSTAFF/ TB MACS ICF CONTRACTORS

So basically on average your saying that you are able to heat/cool a ~5000sq ft house and run all your other electrical appliances for $1305/12 = $108.75 per month? Plus a 400/12 = $34 month for gas? That is fantastic!

Yeah it's great, our old houses was 1200sq/ft with average powerbill of $220.00.The most important thing we recommend to our clients that go icf all the way, is to have ther heat and cooling system designed for their house.They are so mant factors that play in to the final equasion, the average HVAC contractor is lost when it comes to houses built this tight.So its been a really helpful being able to backup,what we have been selling all these years.

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STACKING THE CAROLINAS ONE BLOCK AT A TIME
TODD BIGGERSTAFF / TB MACS ICF CONTRACTOR

One of the desired for our building project was to build a VERY efficient home.  (I'm not a typical O-B, I'm in this one for the long haul.)  With our concentration on the energy efficiency aspect we kept trying to find some software or supplier that could quantify how their product would help our efficiency.  We didn't find anybody who could model the types of homes that we were building.

In order to attempt to alleviate some of the confusion, my buddy PJ and I have been tracking the performance of our new houses and we're sharing it with the attached PDF.

The metric we're using is 100% made up by us.  In order to try to compensate for climate, we're using the metric of heating days (more here) per BTU and then dividing by square footage to try to handle the different square footage of the homes involved.  This is NOT a perfect metric.  But it does show remarkable consistency, which gives us hope.

A little bit about the houses:

AG -- my house is ICF walls up to the top of the second floor joists.  From there SIPs are used, and SIPs make up 80% of the roof, with 20% trusses.  The trussed sections are insulated with Icynene sprayed up against the roof deck.  Heat: garage and basement slabs have radiant embedded in them with NO insulation under the basement slab.  All other floors utilize thinset gypcrete over a normal subfloor with radiant in the gypcrete.

PJ -- Identical to above, with the exception of extremely limited SIPs (mostly scissor trusses with Icynene sprayed against the bottom of the roof deck).  Also has insulation under the basement slab.

ME -- A conventional house, 2x6 walls insulated with spray polyurethane foam.  Roof insulation is done using polyurethane foam against the roof deck with fiberglass batts covering the polyurethane to prevent noxious gasses.  Radiant is staple up.  Garage is not heated, basement slab has radiant embedded in it.

Avg 1998-2006 -- a cookie cutter house constructed with 1997 technology. fiberglass batts, blown in fiberglass on the upper floor ceiling, and forced air heat.

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As an Aside, I will answer all questions that I can on how we came up with this methodology.  I acknowledge that there are people smarter than I am on measuring efficiency, and I think we have a valid methodology.  All I'm trying to do is inform people what we've found living in the home.

Having worked at a Big Ten University and teaching Residential construction, I had an opportunity to see all types of construction and construction materials. In 2004 I decided to build a new home. I initially wanted Airiated Concrete Block for my new home after seeing it being used on my son's home in Europe. Unfortunately it was not readily available in this country, so I began to research the items available. At first i looked at SIP's and they did not give me the R-value that I needed. So I turned to ICF's. I now have a 4,000 sq ft home in a 5.900 HDD zone and according to "rule of thumb" for the heating, I should have 8 ton of heating and cooling. ( By the way, I am an HVAC contractor) so the heat loss calculations are correct. I had my 30+ students check the calculations. In the ICF home, I installed a 1 1/2 ton geo thermal unit. This unit works wornderfully because the ICF home is so tight. I also sprayed the underside of my roof decking giving me a conditioned attic. Otherwise I would have had to install 8 ton for a stick built home. There is no way a properly constructed ICF home will under-perform a stick built home. The term "properly" is purely subjective of course and a home is only as good as it's weakest link, so now the question is? What is that link? Would I do it again and build an ICF home? You bet!

You ONLY needed 1 1/2 tons for 4000 sf??? 

Ken, ICF and geothermal is a powerful combo, but how did you do it? Can you fill us in on where you are located, htg/cooling loads, thickness and type of spray under roof deck, sf and type of windows, basement?, wood/pellet heater augment geo? etc. This topic might be of great interest in the Geothermal Forum. Would you consider posting this as a new thread there, so more folks could learn from your experience? This thread is already 5 pages long!! Dave

I know this is a 3 year old thread but it is one I read carefully when deciding on our home we finished a year ago and I wanted to put up my feedback. After more research than I care to remember, we built our home from ICF (Buildblock) on 6in forms. We coupled that with a sealed attic insulated with spray foam and ran a Climatemaster Geothermal unit. We used Pella Low E Fiberglass windows (all large windows with numerous unshaded west facing windows) In terms of conventional construction, we covered all the basics by using the greenest construction I knew of. I would say it has paid off well for us. Last summer during the a major drought and heat wave, our electric bills were roughly half what friends similar sized conventional 2x6 stick houses were running. Our house is all electric and is 2400sq/ft. Our average usage is between 1000/1100kw a month over the last year. In the summer, the geo unit provided 100% of our hot water for about 3 months. House takes this zone 7 sun diriectly from the southern and western exposures all day long. Will be working on shading that with trees and a gazebo this year which I hope will cut down usage even more. Anyway, hope this helps anyone stumbling across this thread.

This thread is more than 3 years old, because I have a post here that's 4 years old. I had just finished stacking the ICF walls. I remembered my password here on Green Building, so here's an update on the completed project. My house is a slab on grade, hydronic heated ICF (Rastra). It's only about 1,600 sf total, just right for my wife and myself and a guest couple (although we have a mother-in-law apartment above a detached garage and have hosted some fairly large groups). There are pictures at http://dewattohouse.blogspot.com/ Our window package (Euroline arched top tilt/turn) was one of the most expensive material costs in construction (more than the ICF), but ultimately worth the money. They not only add to the look and feel I wanted, but are really efficient. The windows are mortored into place in the ICF, so there is no air leakage around them. The walls are all ICF, so no air leakage. The roof was framed and then completely foamed right down to the ICF, so no air leakage. Most of the windows open, but I'm really glad that I bought an entrance door that has a "speak easy" in it. The house is so tight that I have to open the little speak easy to light the wood stove. I had to put a label on the dryer to open the nearest window when using it (otherwise the stove can back draft if the stove door is opened). In fact, without opening a window, the dryer takes considerably longer. An ERV takes care of fresh air, so the tightness of the house hasn't been a problem, in fact, it's wonderful. It runs intermittently about 6 hours a day, so lot's of fresh air and the humidity stays at about 45%. My ICF package was about $13,000 for the ICF block to construct all the exterior walls and one internal fireplace wall. I don't remember exactly, but I probably put at least another $7K in rebar and cement into it. I think that the construction was more work than stick framing and I estimated that 2x6 framing materials would have been about $15K, so I paid at least 30% more for the ICF exterior walls over 2x6 construction. Remember, that only adds less than 5% to the overall construction cost. Would I do it again? Absolutely. The benefits are too many to go into in a single post. The house is incredibly quiet and cozy. The heating costs are minimal in the winter, as we use the hydronic heat to supplement wood. I did forget and left the heat on while I was gone for a month this winter, and the bill for all-electric heat for the house came came to $180. I won't do that again. It's usually under $100, and during the summer we often pay only the utility company's minimum of $30 for connection service. The house is in a remote location, but I just figured out how to use a cell phone to turn the heat up and down. Now I can turn the heat completely off when we're not there and allow the house to cool off to the slab temperature (low 50s, so I have no fear of freezing water pipes after monitoring the temps for a year). Several hours before we arrive, I can now turn on the heat in the slab and then build a fire when we arrive. The hydronic heat is powered by my potable water hot water heater and it has worked perfectly. When circulating water in the slab, only one of the three heating elements comes on (a single 40 amp circuit). If I take a shower or run other hot water, a second element comes on. I have never been able to use enough hot water to get the third element to light up. I cut two cords of wood last year, but I haven't used a full cord yet. The stove is in an ICF wall, mainly because I wanted both thermal mass and a fireproof wall. Rastra is both and accepts direct plaster and tile. http://dewattohouse.blogspot.com/2010_07_01_archive.html The hydronic slab takes about 5 hours to heat the house from completely cold, but I can heat the house in two hours with wood. The combination is a delight and, if the house is warm when I go to bed, I know that even with the heat off and the fire out, it will be warm in the morning. In fact, we turn off the heat on Sunday afternoon if we are leaving on Monday. We have a southern exposure and I designed with that in mind. Because of the wall thickness, it was easy to have the winter sun shine in (which does happen in the Pacific Northwest) and the summer sun angle be too steep to really shine in. On a sunny winter day, the house is always about two degrees warmer than the thermostat setting. The sun doesn't last long enough to really heat the thermal mass, but it's nice. Likewise in the summer, on a 90 degree day, the house will heat up several degrees downstairs. It's gotten into the low 80s upstairs, but as soon as the sun goes down and the windows are opened, it's back into the 70s. Because there's no thermal mass in the roof, once that heat is gone, it's gone. A real joy. I realize that I'm in a temperate rain forest environment and I don't get huge temperature swings from 10 degrees to 100 degrees. Personally, if I had to deal with those temperatures my first solution would be to move someplace with a better climate! Just saying. But I do think that there would still be benefits to ICF construction in that environment. It would just require a different design to maximize the benefits. I suppose it's possible to design so that you don't get any benefit from ICF, and maybe that's what happened to the original poster. Mark

Two words for the OP and anyone else who is building with ICF....SPRAY FOAM

Pretty funny. Why would someone building with ICF want to take a step backward?

That said, I strongly discourage ICF walls without a foamed (sealed) attic.

Regarding the original poster here - I hope he worked it out - I did not go back and read this thread. I will tell you however, that out of the hundred or so houses I've done in the past 5 years I did have ONE that I would say was clearly unhappy. After I went out to his house I discovered that his a/c guy had wired his ERV in to run full whenever the a/c turned on. After we took him back to one hour per day his bill for his 3k sqft house went down approx $500 to 125. If that sounds like an exaggeration try opening all your doors and windows and see if your a/c can keep up. Regards.

If I was the OP, I would try to get Mike Holmes to come out and find the problem. Either on the show or by going with the inspectors he has set up.

If your results are differing from everyone else you can either conclude that A) everyone else is just feeding hype or B) something is screwed up in your case.

Texas....what type of roof are on those houses with a sealed attic? I had my shingles replaced about 12 yrs ago and the roofer(several I talked to) said I did not have enough venting is why I needed to replace the shingles(they were in bad shape). They told me if I had a sealed attic(I asked about this) the shingles would probably only last half of the years expected from them.