I'm looking into buying a modular home here in Maine and have been offered an ICF foundation by a contractor. He claims that he had an energy audit performed on one of his homes with an ICF basement and claims I should expect about a 30% reduction in my heating costs as compared to a regular uninsulated basement. These numbers seem high to me. Can anyone give me a professional opinion? The cost of going with ICF in this particular instance is $3,500 over the cost of a regular foundation. I know this isn't a ton of money but I'm on a tight budget and don't want to spend any extra money on something that might not make much of a difference on my heating costs. Any help or suggestions would be appreciated. Thanks.

I would be willing to bet that the 30% savings value is valid for "the basement". I want to emphasize the basement because i don't know anything about the energy efficiency of the rest of the home. Therefore, your basement may not require much in the way of heating and cooling in the first place so it may take you a bit of time to recoup your investment. A regular uninsulated basement will provide virtually no R-value at all while the ICF system you choose should provide somewhere well above R-20. If it's a fully basement (not a walk out with windows and etc. you should very easily hit 30% savings.

Rigatoni, does that estimate include at least 2" of insulation under the basement slab which would help greatly in saving energy costs?

Thanks for the replies.

I'll check with the contractor to see if there's insulation under the slab.

How much heat can actually be lost through a home's foundation?

According to the attached paper from the Building Science website, about a third of the energy loss in a typical US home is through the basement.  There is also info about how to insulate the basement walls on the exterior and interior.  Important to consider moisture control. 

http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems/view?searchterm=basementinsulation  

Eric, here in Texas, ICF is often actually less than your typical poured in place basement (not including sheetrock). I believe this is because basements are somewhat scarce and there's very little competition amoung the few basement installers. Regards.

Thanks for the link farmboy. That paper was very helpful.

The contractor said he usually only installs insulation under the foundation's slab if they install radiant floor heating, which I won't have. I'll see how much extra he wants for this extra insulation.

Thanks for all the help.

The reason for that is because of the temperatures involved. With radiant heating the concrete will be on the order of 80 - 85°F. Used as living space with warm air heating the room air temp will be on the order of 65 - 70°F. The ground under the slab will likely be around 55°F, which means there is not a very high thermal gradient through the slab. Heat will move to the ground from the slab, but when the slab is only 65 vs 85°, it's not going to be a great amount. If you are planning on using carpet, or some other floor material that is in itself somewhat of an insulator, you will have a lot less heat loss.

In the radiant heat forum I participated in a discussion about the value of crawl space and basement floor insulation. I came to the conclusion that with a crawl space temp as high as 100F the payback wasn't there for blue board thicker than about 3/4". I use the crawl space as the supply plenum for my heating/cooling system.

I suggest you do a search in the radiant heat forum for slab insulation. You may come to the the conclusion for your design it's not worth the cost. Dow blue board, or Owens-Corning pink board ain't cheap.

Having an uninsulated foundations is like walking around in the winter without your boots on.