ICF Formwork for a Parallelogram Foundation

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Out of square on purpose: Here's how carpenters create the custom formwork to realize an architect's vision.

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Last winter, standing next to a newly placed ICF concrete foundation on Peaks Island near Portland, Maine, lead carpenter Mark Pollard told JLC: "I hate concrete."

Fair enough: Pollard is a carpenter, not a mason. But these days, as the local real estate market heats up and foundation contractors get busier, Pollard and the skilled crew he leads are having to get used to pouring concrete, whether they like it or not. This fall and winter, JLC is following Pollard and his crew from Thompson Johnson Woodworking as the company builds a custom home designed by Portland architects Kaplan Thompson Architects (KTA) (Facebook) — an out-of-the-ordinary design with a parallelogram footprint and a low-slope, monopitch roof. To make things even more interesting, the design aims to achieve net-zero-energy performance. With its distinctive massing and its unusual interior spaces, the home presents an assortment of technical challenges for the builder—starting with the parallelogram foundation. When their go-to foundation contractor got the contract for a 60-unit multifamily project on the mainland, he told them he couldn't travel out to the island for a small basement job. So Thompson Johnson decided to go the ICF route.

Custom Corners

The wooded site, with ledge just a few feet down, was an excavation puzzle. The final choice was to dig just deep enough into the rock for a low basement (about 6 feet deep). The crew built footing forms with wood, tailoring the footing to the stepped excavation, then poured the 2-foot-wide strip footings and the column bases. Next they set the ICF formwork, using a handsaw to custom-cut the 80-degree and 100-degree angles for the foundation ends. Then they custom-built the pier forms for the columns for the raised-floor half of the house.

Parallelogram Foundation: Pumping Concrete

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On a Maine island, a crew of carpenters hustles to pour an unusual out-of-square concrete foundation.

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An Island Pour

On the day of the pour, the concrete truck and pump truck had to catch an early morning ferry for the 20-minute ride from the mainland. After setting up the pump truck, operator Allen Moore encountered an immediate hitch: Hardened concrete and debris from a previous job had clogged one of the angle bends on his pump boom, requiring Moore to locate the clog and disassemble the elbow to remove the blockage. But after a brief delay, the rig was back in operation and the crew started to place concrete in the ICF walls.

The job went smoothly until the crew started pumping concrete into the custom site-built pier forms. On the first pier, pressure of the wet concrete broke a seam on the form. So the pump had to stop again for 20 minutes, as the crew rushed to patch the broken form and reinforce the remaining pier forms with extra screws. Again, however, the delay was brief, and the rest of the pour went according to plan.