Posted By mnelson61 on 15 Jan 2012 08:41 PM
The design of our new home requires L footings with rebar locking the footing and wall on two sides to handle the load of the backfill. For this reason we have decided that concrete is a better choice than PWF SIPS or Stick built PWF. The decision comes down to ICF or CIP concrete with insulation. I am located in Ottawa Canada where we have 4,600 HDD. My understanding of where ICF really excels is when the daily outside temperature rises above and falls below the inside house temperature daily or frequently during the year. This condition lends itself well to the concrete's mass transfer being very slow and, therefore, moderating the daily temperature swings. My concern with ICF in my location is that with many days of continuous cold with only a thin layer of insulation on the outside that the concrete will cool down and stay cold. Then we are really relying on the thin layer inside to insulate as the concrete is basically the same temperature as outside. Would it not make sense in colder climates to use CIP and insulate the entire foundation on the outside with say 4" of rigid foam? This way the thermal mass concept can be taken advantage of as the concrete will always be 20 C or inside room temperature. If anyone has done this or can advise me why it is or is not a good idea, please comment.
When you say "requires L footings" I'm reading that to mean your engineer wants to use the basement wall as an independent of floors and opposing wall retaining wall. In other words if just that wall was being built it would still resist overturn based on the weight of soils on the "L". That mean you need to carry significant rebar through the footing and into the wall to the height of the backfill. While this is a possibility in many different products it is very simple in ICF. Your engineer will layout the amount of bar required. Pay attention. Do it right. If you think the engineer is over building than get a different engineer! Don't simple ignore his advice.
There is much debate about the R value of ICF and when it performs best. Some would even suggest that you shouldn't use it in cold climate. I live in the Calgary Alberta area which is a little cooler than your area. I can tell you that almost all engineers and heat loss professionals out here assign a "R" value of between 40 and 50 to ICFs. My house is just over 6000 sq. ft. of heated space. It has lots of windows and doors. The 6000 includes the basement (about half the walls at walk out level) and the garage which has two large garage doors. My heat loss calc's were based on R50 for the icf walls (footings to trusses in a two storey) and the house stays comfortably warm. I am heating a hydronic system right now with electric water heaters so I can calculate the exact heat required and the R50 is right based on my power consumption. Todays temps are around -27ºC.
When you read articles about ICF's make sure the writer is in the same climate as you or has actually surveyed existing icf houses in your area. There are several ICF contractors in your area that should be able to put you in touch with home owners that have lived in their homes for a number of years and should be able to give you an unbiased opinion. Most ICF home owners a quite willing to show you their heat bills even if it leads to a little bragging ;-).
You should find that for the basement the cost of ICF should be within a percent or two of other methods. For the upper walls it will be a bit more but if the rest of you insulation and air barrier is right you WILL recoup that investment in a reasonable time. If you go ICF all the way, you need to make sure you insulate under the basement slab floor (and under the footings is my preference) and R50 in the attic paying close attention to the air seal between the conditioned space and the attic.
If you want to add additional insulation to the outside of the basement, it won't harm anything but it is a limiting roi. There is no way that the concrete will "stay cold" Please take the time to see some of you local ICF houses. A couple of real life situations in your area will by far out weigh all the literate you can read!
Bob