Insulated Concrete Form (ICF) Construction

The outer walls of our home are all constructed of Insulated Concrete Forms (ICF).  What is ICF?  The Portland Cement Association website says, "ICFs are basically forms for poured concrete walls, that stay in place as a permanent part of the wall assembly. The forms, made of foam insulation or other insulating material, are either pre-formed interlocking blocks or separate panels connected with plastic ties. The left-in-place forms not only provide a continuous insulation and sound barrier, but also a backing for drywall on the inside, and stucco, lap siding, or brick on the outside."

With a steel and concrete core and two layers or insulation, these walls are tougher and more energy efficient than just about anything else on the market.  They also have a high thermal mass, which makes them a good choice for use with passive heating and cooling.  Their bulk keeps the interior of the house quieter, too.  We've got some aggressive winds around here at times and I usually don't hear them inside the house.  It's actually a little bit funny, as there have been any number of times I didn't realize how windy it was until I walked outside and got pelted with a blast of cold air.  The structure is very secure and resistant to damage from fire, high winds and other impacts.  (I read a story about a Florida couple who had someone drive into their bedroom wall and didn't hear anything beyond a dull "thud".  There house cost a few hundred dollars to repair, the car was totaled.)  The Insulating Concrete Form Association gives a detailed inventory of the benefits of building with ICF on their website.
 

The thermal performance of ICF is much higher than the listed R-factor would indicate.  Stick built homes have the problem of the 6” stud carrying exterior temperature through the wall.  Wood is on average 1R per inch so its only R5.5 where the wood is.  This creates a 2^nd problem in that it attracts moisture and therefore creates a point for mold to form.  Many stick built homes protect from this through spray foam and vapor barriers, but the materials and different R-factors inherently make it more likely.  If you do a stick built use spray in foam with an exterior layer of styro-insulation (foam board) under the house wrap to further decrease infiltration and increase the true R-value.  The photo below compares a SIP (structural insulated panel) house on the left with a stick built house on the right.  SIP construction, like ICF, prevents heat loss along the studs.  See this site from zeropowerhouse.com for an even more graphic photo comparison of stick built and ICF.

Some ICF industry folks claim that ICF is at least 44% more efficient than stick built.  This seems high, but it's possible if you consider total thermal performance .  A DOE study places this number closer to 20%.  Our energy consumption per square foot is in the bottom 12% of all homes in the U.S., according to one reference I found online (we averaged around 2.2 btus/sq ft/HDD from propane).  The temperature in the house doesn't swing as abruptly as it did in our old house, either, although obviously some of this due to the change in heating systems.  We now use a masonry stove, passive solar and radiant in floor heating, we used to use a forced air system.  The current arrangement is much more comfortable.

I have heard claims that ICF construction is not "green" because it uses too much embodied energy.  On the contrary, it represents a very green choice.  The article "ICFs in the LEED" explains:

The sustainability of concrete used in ICF construction also promotes green building. On average, cement comprises about 10 to 15 percent of concrete's overall volume. Its remaining ingredients — water, air, coarse and fine aggregates — are locally derived, so cross-country shipping is not required. And, the bulk of concrete is generally limestone, the most abundant mineral on earth.

A study was sponsored by the Canadian government in 1994 to determine the environmental toll of raw material extraction for wood, steel and concrete. Of the three materials, wood harvesting was found to have the most deleterious environmental impact and concrete the least, due to the relatively small scale of quarries and the potential for site restoration.

While carbon dioxide is a byproduct of concrete production, “cradle to grave” analysis reveals that 90 percent of the compound produced by a home is generated during operation, i.e., heating and cooling. An Inventory Life Cycle analysis performed by Construction Technology Laboratories, Skokie, Ill., indicates that the initial CO2 burden of a concrete home is surpassed in about five to seven years by the additional heating and cooling energy required for a typical wood-frame house.

Additionally, even conservative values touted by the National Association of Home Builders demonstrate that concrete has a much longer life span than either wood or steel. Once it reaches the end of its useful life in a structure, furthermore, concrete is 100 percent recyclable.
 

We have no complaints about using ICF, other than it's a little trickier to hang thing on exterior walls (you need to hit one of the plastic strips, which run every eight inches).  We like the "feel" of the house - it's very solid.  The extra deep window wells (which are around ten inches) are a nice architectural feature.  The initial price is slightly higher in our area, but lifetime costs more than make up the difference.  Best of all, it's a sound green building option.