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Insulation Formed Concrete - Best ICF

Star The building science driven enhancements to ICF. 

Having gained experience with ICF (Insulated Concrete Form) construction and having studied building science, this describes what I believe to be the ideal "ICF" system.  As we shall see, it is probably better to call it an "IFC" (Insulation Formed Concrete) system.  I refer to it as Carnation Walling.  In accordance with building science best practices it puts all the EPS insulation on the outside of the concrete wall to couple the concrete thermal mass with the house inside temperature.  On the inside of the wall, Carnation Walling uses regular low cost construction grade plywood that is stripped off after the concrete hardens and is reused.  As well as being better from a building science perspective, Carnation Walling is about half the cost compared with traditional ICF.

Carnation Walling is a *method* of building walls rather than a proprietary product.  It requires a particular set of steps and these steps are described in detail here (but it's best to read the current page first).


Building Science

Everything needs to start with Building Science, ie start by figuring out the perfect wall design (that meets building code requirements).

Insulation requirements

Insulation is measured in R-value.  Type 1 EPS gives you about R-4.17 per inch thickness (in cold climates).  Type 2 EPS gives about R-4.5 per inch (in cold climates).  For walls, 2012 energy code in cold climates in America (climate zones 6, 7, and 8 which includes Wyoming, Montana, North Dakota, South Dakota, Minnesota, Wisconsin, Vermont, New Hampshire, and Maine) requires a minimum R-value of 25.  That equates to a Type 1 EPS thickness of 6 inches.  That is the minimum code requirement, but many people in cold climates will want to make a super energy efficient house and that means they will want to go up to about R-40 for the walls (10" of Type 1 EPS or 9" of Type 2 EPS), but a more common choice will be about R-36 which is about 8.6" of Type 1 EPS or 8" of Type 2 EPS.

What is needed is a walling system that meets 2012 Energy Code in cold climates at least cost and yet is easy to optionally increase to a greater R-value for those who want a super insulated house.

Insulation on outside

The next question is where to put the insulation.  Traditional ICF systems (in addition to only providing about R-23) have half the insulation on the inside of the concrete and half on the outside.  By considering building science and the perfect wall design we see that the insulation should actually all be on the outside of the structure, ie on the outside of the concrete.  You want the structure (the concrete) on the inside of the building envelope so it stays warm and dry.  For maximum occupant comfort you want to get the concrete as close to the inside of the wall as possible in order to thermally couple the huge thermal mass that concrete provides with the warm inside house temperature.  You want the thermal mass to be at the same temperature as the inside living space, ie about 70 degrees F.  The water liquid control layer wants to be on the outside of the wall and EPS (plus stucco) with its low water permeability provides this nicely.