Connecting Framed Walls.
Interior wood- or steel-framed walls are easily attached to ICF shells.
The issue of how to fasten wood- or steel-framed walls to the exterior ICF shell is a common concern for new builders. Fortunately, these attachments are easily made. Like many of the questions these contractors have with ICF construction techniques, there are several solutions, all of which are relatively simple and straightforward.
The easiest way to tie framed walls into the concrete shell is to take advantage of the furring strips on the ICF block. If the location of the interior wall aligns with a column of ties, it’s simply a matter of driving a series of 3-inch drywall screws through the stud and into the furring strips.
One major drawback to this method is that most of your walls probably won’t match up with a furring strip. Depending on the brand of ICF, the 1.5- or 2-inch-wide strips occur every 6, 8, or 12 inches on center.
Tom McClain, core products manager at Simpson Strong-Tie, says this method is probably adequate, although he would recommend something a little stronger for long walls. “It’s probably okay for small rooms,” he says, “but personally, I’d put something a little more solid in there. If someone tips over a dresser, or slams a bed against the wall, I’m not sure that that type of connection would hold.”
Some contractors claim that positively attaching framed walls to the ICF shell is unnecessary. “You just connect the wall to the floor, basically,” says Keith Hern, an ICF builder in Golden, British Columbia. Ted Hartner, manager of residential sales and marketing at Dietrich Metal Framing, agrees. “Interior walls are secured using the floor and ceiling diaphragms,” he says, “so the connection to the exterior shell is secondary.”
Floor connections are simple. So are the ceiling connections for walls that run perpendicular to the trusses. Walls that run parallel to the trusses, however, need a little more work. Blocks are set between the joists or trusses at regular intervals, and the walls are attached to the blocks “Blocking requirements are something the structural engineer has to call out,” notes Grant Ricks, a senior project engineer with Rudolph & Sletton. He added that interior walls should not be framed too tightly against the trusses. “If the wall becomes bearing, it alters the forces within the truss,” which could potentially weaken the entire roof.
“On most walls, you can set the roof trusses right on top of the wall,” says Hern, “but [in cold climates] you have to account for a fairly significant snow load.” His current project involves a nearly flat roof with 38-foot clear span. “It will flex up to ¾ of an inch with the snow load, and has to be allowed to float, so we can’t have a rigid connection,” he says. Deprived of a ceiling connection, he secured the interior walls by tying them to each other.
Heavy Duty Attachments.
Occasionally plans may require a solid, structural connection between ICF walls and the interior. Three options exist.
The first is to use anchor bolts. Often used to attach ledgers and sill plates, the process is virtually identical when used to attach walls.
The second method is to use Simpson’s ICF Ledger Connector (ICFLC). Made of 14 gauge steel, the piece is inserted through a vertical slot in the foam prior to the pour. Once the concrete has set, the framed wall is secured to the exposed steel flange with screws.
The product was designed specifically for ICFs, says McClain, and works well in foam up to 2 ¾ inches thick. He recommends using it on all stud-to-ICF wall connections, but admits that price-conscious home buyers may be reluctant to pay $6 to $8 for a non-structural part.
A third option is to use the ICF Connector from ICF Connect, Ltd. Designed to work with all brands of ICFs, the Connector consists of two pieces of stamped steel, inserted through vertical slots cut in the ICF foam. For a regular 2x4 wall, the plates would be inserted 3 ½ inches apart, just wide enough for the stud. Once in place, the wood or steel stud can be secured to the plates with #6 pan screws.
Whatever method you choose, be sure the attachments will meet code and are approved by the engineer. “Everything has to get passed by the engineers,” Hern says, “the roof truss engineer and the building engineer. We took a lot of time to decide that our solution was spot-on before we went ahead with it.”