All About ICFs

If you’ve been reading this blog (thank you!), you’ve probably had the following thought: “Wait a minute! What’s all this about a barn? I thought you were building a house!”

Well, wonder no more. Everything we’ve built so far… that’s just the garage. We call it the Barn because it’s shaped like one and there’ll be a tractor inside. But the owner doesn’t plan to insulate the structure or even finish the interior, for the simple reason that it’s not the house. THIS is the house:

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Some assembly required.

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Proposed façade; note the breezeway to garage on the left. I think we’re calling it the Farmhouse.

The floor plan is around 3000 square feet with two stories plus a finished basement. Todd the excavator came today to begin digging out the basement and grading the land for a raised first-floor verandah and a walk-out below. We’ll need to survey some points tomorrow to guide the excavation relative to the Barn location. Once the hole is dug, we’ll begin installing the basement walls… and now we arrive at the main topic for today, insulated concrete forms or ICFs.

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A typical ICF. (creative commons)

Developed as a faster, energy-efficient alternative to traditional concrete wallbuilding (custom-built, heavily braced plywood forms that get removed once the concrete sets), ICFs are interlocking modular units that stack together like Lego bricks (no glue or fasteners required!) and become an integral part of the finished wall. Ours are basically made of expanded polystyrene aka Styrofoam, super light and easy to transport, with a built-in cavity to enclose concrete. Only two shapes are required for simple geometries like ours: the straight wall (4 feet long) and the 90-degree corner. Each ICF is 21 inches tall and the top course can be cut to obtain a wall of any height. Nylon webs spaced 6 inches apart provide strength to support the wet concrete, and include built-in clips to hold vertical reinforcing steel.

ICFs don’t eliminate the bracing issue, but companies like Vermont ICF (our distributor) provide temporary bracing towers designed to work well with the forms. Wet concrete is very heavy, about 150 pounds per cubic foot (similar to sand or gravel… because after all, concrete is mostly sand and gravel), and braces need to hold all that weight back so the formwork doesn’t collapse. Vermont ICF gave us steel bracing towers that weigh about 60 pounds apiece, unfold to provide a truss backspan, and adjust to match the height of any one-story wall. We’ll place a tower every 4 feet along the inside of the wall; no need to connect them with lateral wales. And to prevent blow-out on the outside of the wall, we’ll cinch the modules together using… zip ties.

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Shed full of ICFs, with bracing towers folded up on the right. Stay tuned for assembly pictures.

Terry has tremendous experience with ICFs and loves how easy they are to assemble compared to traditional formwork. I’m excited to work with them and to see just how quickly our basement walls go up.

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