For windows and doors, among other components, it only makes sense to spec a 32-inch-high window for a system of 16-inch-high blocks rather than having to shave them down prior to the pour to accommodate something slightly larger. “It’s not an aesthetic impact, but it will save you time and materials,” says Lennox.
Penetrations for mechanical services are also critical to consider (and make) before the concrete fills the forms. “It’s a lot cheaper and easier than drilling through a [concrete] wall later,” says Lazowski, who plots and spots plastic conduit for various mechanical runs before the pour.
It’s also important to clean out the cells of foam dust, dirt, and debris, ideally washing them out instead of using compressed air (which can cause a static-cling effect) to ensure clear cavities.
The concrete mix is critical. The slurry should meet the ICF supplier’s specs for slump and aggregate—and be confirmed when it arrives on the jobsite. “A typical mix for 4- to 6-inch-wide cells [interior width] is a 6- or 7-inch slump with 3/8- to 1/2-inch aggregate,” says Troy Gibson of Reward Wall Systems. The wrong mix, he says, might reduce the wall’s strength, damage the forms, or won’t set up.
Once the pour commences, the priority becomes providing adequate bracing, checking for plumb, and vibrating the mix as you go. “I always overbrace them,” says Lazowski, beyond manufacturer recommendations. “You have to respect the weight of the concrete, and any slight movement can be a big problem,” such as bowed walls or, worse, a blowout.
Lazowski also uses 32-inch-long zip ties to connect the web inserts of the first two and last two blocks along the course of a wall, supplementing their interlocking design to add stability. For two-story walls, he fills the top course of blocks at the point of the first-floor platform halfway so that the joint between wall sections, and the lag bolts for the joist ledgers, are contained within the ICFs, not between blocks.
Inexperienced builders may race through or neglect these nuances and end up with a bad taste for ICFs. “It’s not the block, it’s the install,” says Bob Cenk, vice president of operations for Homecrete Homes in Stuart, Fla., which has built exclusively with ICFs since 2004. “If you rush it and the wall gets out of whack, don’t blame the block.”
Until there’s a critical mass of experienced ICF installers, builders should expect to see higher bids to install them, at least until their subs breach the learning curve. The PCA says that installation costs—about 1% to 4% higher than traditional framing—drop sharply after four or five houses; after that, says Gibson, “you start to cut hours and days from the schedule.”
Cenk also has been able to lower the bids of his drywaller and electrician because ICFs are easier for them to work with compared to the CMU walls he used to build, although he still has to strong-arm his HVAC contractor to properly size heating and cooling equipment to the improved energy efficiencies of an ICF wall compared to a standard framed wall.
Myths vs. Reality
Like any alternative building system trying to emerge from the shadows of a wood-centric building culture, not to mention those of other innovative alternatives such as SIPS and light-gauge steel, the case for ICFs is occasionally overstated.
For instance, they are not as easy to install as the “adult Legos” that some manufacturers tout them to be, nor are they inherently or entirely fireproof, waterproof, mold-proof, termite-resistant, or able to withstand any storm or seismic event.
While the concrete within the forms may, in fact, resist some or all of those forces, the blocks’ expanded polystyrene (the same stuff used for coffee cups and cheap beer coolers) can boil away and fuel a house fire and emit toxins if not protected by a fire-rated sheathing; similarly, the foam requires a separate drainage plane to shed water and hydrostatic pressure away from a below-grade wall to be considered waterproof. While the foam may not be food for termites, the insects can bore through it.
And, like any structural system, ICFs need to be engineered as part of a whole-house approach against high winds and earthquake activity for them to weather those instances.
ICFs may not be the answer to all of housing’s ills, but they arguably address more of them than any other option. Both labor and distribution are expanding and leveraging conventional channels, and the technology is building a track record of success from a decade of product refinements that have resulted in stronger and more reliable components and finished walls. “There’s a lot less risk than there was 10 years ago,” says Gibson.
Recent economic realities, meanwhile, from the housing recession to energy price volatility, are pushing ICFs further into the limelight. “It should be an easier sell now as home buyers have changed their attitudes about home energy use and durability,” says Gibson. “People are coming to us because they know it’s a viable option. The introductory phase is over.”
Rich Binsacca is a contributing editor for EcoHome.