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What exactly is an ICF system?

QuestionMy wife and I are exploring alternative materials for a new house we plan to build.  What exactly is an ICF system?  Would it be appropriate for residential construction?  Thanks! 

AnswerAn ICF (insulating concrete form) system is an insulated wall system that stays in place once the concrete has been poured.  Its insulating value and overall faster construction make it very useful for residential applications.

With the development of insulated wall systems, concrete offers new opportunities for residential and commercial wall construction. The insulating concrete form (ICF) is basically lightweight stackable interlocking polystyrene insulating blocks that are easy to install. After installation, their cavities are filled with concrete and the forms are left in place, creating a wall with an R-20 to R-25 insulating value (depending on the product) ready to accept interior wallboard and exterior finish.

The beauty of this system is that you are not limited to the foundation. You can build the entire house this way.

The framework of an ICF is made up of three basic systems: panel, plank, and block. If you strip away the polystyrene to get to the concrete cavity, three basic shapes emerge:  flat (similar to conventional concrete wall), grid (similar to that of a breakfast waffle), and post-and-beam. In this system, the posts and beams are spaced as close together or as far apart as you want. While the post is continuous (vertically), the beam (horizontally) is achieved when a special "lintel block" is installed.

The blocks are held together with plastic or metal ties. Some ties are designed carefully enough so the concrete flows horizontally and fills the vertical cavities with no problems—others don't allow proper movement of the concrete. This is something you will want to research when choosing a system.

Almost every system requires concrete with smaller aggregate and a medium to high slump (how thick or runny the concrete is) to ensure that the mix will thoroughly flow through the cavities within the system. Be sure to check with the manufacturer on the recommended concrete mix for their system.

Some manufacturers also incorporate nailing strips. Some are exposed; some, like the ends of the ties, are embedded. Whatever the case, it's recommended that you use screws or hot-dipped galvanized nails to attach to these nailing strips, as common nails don't hold.

For more details about available systems and other avenues to consider if you plan to use such a system, I recommend that you read Build Smarter with Alternative Materials. To order your autographed copy, click here or click the purchase button below!

Click to Purchase

Copyright © 2004 & 2007 LAF/C.R.S., Inc. All rights reserved.
Question answered by Leon A. Frechette.

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