Ask the Expert: Pros and cons of Insulated Concrete Form?
ProudGreenHome: What are the benefits of ICF?
The first advantage is the structural strength inherent in a reinforced concrete wall. In one simple operation, you have the structural qualities of concrete, with the air-sealing and insulation qualities of a SIPS wall...sometimes.
The ICF wall has half of its insulation on each side of the thermal mass. This means that when the heat energy gets just half way through the insulation, it gets to the concrete, which transfers a large amount of that energy to the ground through the footings. This can be a very good thing in a hot climate, where you do not want the heat to get into the dwelling. This can be a very bad thing in a cold climate, where you do not want the heat to leave the interior of the dwelling.
If I were building along the Gulf Coast, or in the Southwestern desert, I would use ICFs almost exclusively. In the rest of the country, not so much, except for closed crawlspace designs, and daylight basement homes.
Waffle style ICFs will use up to 10 percent less concrete than straight form ICFs, and even the straight form blocks can often develop more strength in 6 inches of concrete than a traditionally formed wall can develop in an 8-inch wall, saving up to 25 percent of your concrete cost and placement cost. (Pumper trucks are expensive!) The reason the ICF wall will develop more strength is because the concrete is left in the form forever, holding the moisture in the wall, assisting the curing process. Walls that are exposed after just 24 hours are significantly compromised. Unfortunately, this is the norm in the concrete industry today, and the engineers know it, so they will often require a thicker wall than might otherwise be necessary.
I often use ICFs in conjunction with SIPS walls, where I need an especially strong sheer wall, for example. We are in seismic zone D-1, so we often need the structural strength of a concrete wall where lots of glass is desired to take advantage of a spectacular view. The ICFs can provide the same air-sealing ability, with nearly the same effective U-value as SIPS, which I then use for the rest of the walls and roof.
Wiring and plumbing are not a problem, the foam is thick enough that it can be grooved out, the wires or pipes inserted, and then spray-foam used to cover the tracks.
The speed with which ICFs can be set, and the elimination of time spent stripping and cleaning forms will usually offset the extra cost of the ICFs, once the alternative insulation method is factored in.
To summarize, there is no one building method that is right for all situations. An astute builder will evaluate all methods for each project to determine which is right for that time and place.
Ted Clifton / Ted L. Clifton is a designer-builder from Coupeville, Wa., with over 45 years of hands-on experience in the construction industry. His two companies, Zero-Energy Plans LLC, and CVH Inc. have won five Energy Value Housing Awards, and two National Green Building Awards for Concept and Research. Ted has been closely involved with the development of both his local Built Green program and Built Green Washington.