If the term “insulated concrete form” (ICF) is foreign to you, it might be time to expand your vocabulary of above-wall building systems. With a 20-year track record in the U.S., these interlocking, open-cell foam blocks that are field-filled with concrete address a variety of current housing issues, from a shrinking pool of skilled construction labor to demand for more energy-efficient and environmentally responsible homes.

In many aspects, ICFs offer a simpler and arguably better mousetrap to conventional sticks and blocks to meet those issues, and those who have tried and succeeded with the technology swear by it. “Once you learn how to work with ICFs, it’s the only system you want to build,” says Ben Lazowski, co-founder of P&P Construction in Camano Island, Wash., north of Seattle.

But even Lazowski and other converts concede a learning curve and culture shift with ICFs, as well as some tricks of the trade not found in most instruction manuals that are the keys to optimizing the system and avoiding costly problems. And, as with any building system, ICFs are still just one piece of a larger green-building puzzle.

How They Work

ICFs are molded from expanded or extruded polystyrene into lightweight, open-cell blocks or panels that serve, like CMUs, as the forms for poured concrete above- and below-grade walls.

The molded blocks are preassembled with metal or high-density plastic inserts (“ties”) within the open cell that add strength and stability to the blocks for the concrete pour. Ties also provide vertical nailing strips, usually just below the outside surfaces and marked for reference on the blocks, for the application of interior and exterior finishes.

Panel systems, also called “knock-down” ICFs, are similar to blocks except they are field-assembled into the permanent wall forms. Simply, the panels (and their ties) ship more efficiently compared to molded blocks that take up a lot of room on a flatbed; it’s a builder’s choice to balance the trade-off between shipping costs and field assembly. Most ICF manufacturers make the pre­assembled/molded blocks, but some make both blocks and panels to enable “hybrid” systems that integrate the best of both, and even more so with components and accessories, like corners, that are designed to be reversible—as left or right corners, for instance, or either-side-up to help speed installation and reduce on-site waste.