When we first worked with ICFs, we — like most contractors — used the foam forms only for foundations and simple structures. Eventually, though, we began to build entire houses with them.
The Alamo, Calif., custom home featured here was such a project. The plans called for curved walls with large arch-top openings. Given that combination — curved walls and arched windows — most builders would have chosen to stick-frame. But the house was also designed to be extremely energy-efficient, with triple-glazed windows, radiant-barrier roof sheathing, a NiteBreeze ventilation system for cooling, and vacuum-tube solar collectors backed up by on-demand water heaters for hot water and hydronic heating. For all these elements to work, the walls would have to be airtight and well insulated — which made ICFs a good fit.
The house sits on a hill — two stories in front, and one in back — with a crawlspace, garages, and mechanical rooms below and a single level of living space above. The upper floor is framed with I-joists attached to the ICF walls. The exterior finish is synthetic stucco applied directly to the ICFs.
The home's foundation — a poured-concrete grade beam on poured concrete piers — is typical for hillside residences in this area. Because the piers are designed to carry the weight of the house, the grade beams don't need to be as wide as conventional footings; on this house, most are 12 inches wide. We took great care to lay out and form an accurate foundation so we could install the ICFs flush to the outside face of the grade beams. In the few places where the grade beams were wider, we used the more standard method of installing the blocks to snapped lines.
Stacking the Blocks
Our company uses Logix blocks (888/415-6449, www.logixicf.com). Like most brands of ICF, they're based on a 48-inch-long by 16-inch-high module and come in a variety of wall thicknesses. On this job we used 11 1/2-inch blocks, which have a 6-inch cavity flanked by 2 3/4-inch EPS foam.
When setting blocks, we start from corners and work toward the center. Ideally, the length of every wall would be a multiple of 48 inches so we wouldn't have to cut blocks. That almost never happens, but we can usually limit cuts to one per course. The problem with cuts is that you lose the tongue or groove that keys one block to the next, which leaves a weak joint that might blow out during the pour. These joints have to be reinforced, so we either glue them with canned spray foam or screw a plywood gusset to the plastic webs in the foam.
Two at once. We lay the first two courses at once, fastening the first course together with zip ties, snapping in the horizontal rebar, then stacking the second course on top and zip-tying it to the course below. This gives us a long run of blocks that can be positioned and leveled as a unit. We use a laser to check the wall for level, then shim or trim the bottom edge as necessary. Once the wall sits straight and level on the foundation, we glue it down with low-expansion polyurethane foam.
Each successive course keys onto the one below and is secured to it with zip ties. We install the horizontal rebar as we go, according to the plans, and every few courses we put in "form lock" — zigzag wire bracing that snaps into the plastic webs and helps straighten and stiffen the forms. When the ICFs reach the top of the vertical rebar — which starts at the footing — we splice on new pieces with tie wires so that the reinforcing is continuous to the top of the wall.
