DEAR TIM: I saw the strangest thing today. A new house was being built using hollow foam blocks. I found out that the blocks are going to be filled with concrete. Is this method of construction substantial? Can you finish the interior and exterior as you would a wood framed house? Are these houses well insulated? Do you think this method of building will just be a fad? Cathy B. Oregon, OH

DEAR CATHY: You saw an Insulated Concrete Form (ICF) house under construction. It is a fledgling industry that, in my opinion, will soar to incredible heights. Fad you ask? The ICF method of construction is so revolutionary that I venture to say it will go down in history right next to asphalt shingles, drywall, plywood, and plastic laminate. When these building materials were introduced years ago, they dramatically changed residential construction methods. These innovative products increased productivity, eventually lowered building costs, and made major strides forward in building technology. I feel that ICFs will also be a shoe-in for the building products "Hall of Fame".

The ICF system uses insulating foam panels as a form to accept steel reinforced poured concrete. Once the concrete hardens, you have a wall system that outperforms standard wood frame construction in the following categories: heating & cooling costs, strength, fire resistence, structural pest resistence, sound deadening, and natural disaster resistence just to name a few. You can apply any interior and exterior wall treatment to ICF houses. You install exterior wall treatment systems in the same manner as you would on a wood framed wall.

There are three basic types of ICF systems each with variations. The categories describe the way the hardened concrete looks with the foam stripped away. One system - the flat wall - resembles traditional poured concrete walls. Another system is called the waffle pattern. The concrete configuration looks nearly identical to the waffles I commonly eat for breakfast. The final system is classified as the screen grid. These systems resemble an oversized window screen. With the foam out of the way, you could actually pass an object through a screen grid wall.

The foam panels and block systems contain either plastic or steel components. These hold together the forms during construction. Screws or nails driven into the plastic or steel members allow you to apply your wood or fiber cement siding, brick, traditional or synthetic stucco, artificial stone, drywall/plaster, or wood paneling. The manufacturers have designed the systems so that you can easily cut horizontal and vertical channels in the interior foam layer to accommodate electrical wiring and plumbing pipes.

ICF houses will undoubtedly be attractive to people who live in areas plagued by natural disasters such as wild fires, hurricanes, and tornadoes. The foam used in just about every system has been treated with a fire retardant and will not support fire on its own. Concrete is a fireproof material. Steel reinforced concrete walls are known to withstand strong winds much better than traditional wood framed wall systems, especially if the roof is blown off the walls. Steel strapping members can be poured into the top of ICF walls that allow you to attach the roof framing more securely than in wood houses.

Energy savings are substantial in ICF houses. The walls in most systems approach an R-factor of approximately 25. Some systems are as high as R-35. A traditional 2x4 wood frame wall in comparison might have an R-factor of 13 to 17. The thermal mass of the ICF system employs technology that was developed thousands of years ago by native Americans. Adobe houses stay cooler in the day and radiate stored heat back into the house during the night.

Air infiltration in a typical ICF house is far less than a traditional wood framed house. This is actually a slight negative. So little air leaks past the outer shell that it is almost always necessary to install a fresh air exchanger or a simple makeup air duct to lower indoor pollution levels that can build up over a heating or cooling season.

Currently an ICF house costs just 1 to 4 percent more to build than a traditional wood framed home. This cost will drop as more houses are built and the manufacturing economy of scale filters through to consumers. I intend to use the ICF system when I construct my new office. It will definitely transport me back to my toy house block building days!

Author's Notes:

October, 2002:

How popular are ICF homes? Very popular. The growth from 2000 to 2001 was 29%. ICF homes accounted for 2.7% of all above-grade homes built in the USA in 2001. That is up from 2.1 % in 2000. Look for strong continued growth in this sector.