Insulated Concrete Forms (ICFs) are becoming more common in both residential and commercial applications. However, as the construction market continues to recover, finding subcontractors familiar with ICF construction can be challenging, especially for electrical and plumbing work. In Texas, one builder reports that finding and retaining quality subs is one of the most pressing issues he deals with.
Some subcontractors can be convinced to bid ICF work, but at a premium to their regular rates. Nearly always, if the ICF contractor has done their job well and left a smooth, void-free wall, the subcontractors will realize that working on ICF projects is no more difficult than other jobs.
This article provides a basic overview of ICF construction for the trades, including electrical, plumbing, drywall, and interior and exterior finishes.
ICF walls consist of a core of steel-reinforced concrete—usually six or eight inches thick— sandwiched between two EPS foam panels, typically 2 ½ inches per side. Embedded just below the foam surface on each face are polypropylene furring strips for attaching finishes. (A few brands use light-gauge steel.) These furring strips are aligned vertically and spaced at six- or eight-inch intervals, depending on the brand. A few brands feature “full-height” furring strips, but most are slightly shorter than the block height to allow for horizontal chases to be cut into the foam.
Nearly always, ICFs are used for exterior walls only, so for most trades, the majority of the job will follow regular methods. Occasionally, ICFs are used for demising walls between units in multifamily construction, or for acoustic separation in multiplex theaters, or between an attached garage and the rest of the home.
This is no cause for concern. From hanging drywall to installing utilities, many of the trades’ tasks are simpler with ICF walls compared to regular frame construction.
Let’s look at just one example, installing drywall. Typically, drywallers must ensure that panel seams align with the wall studs to provide adequate support. With ICFs, that’s not necessary because the joints are continuously supported by the EPS. Additionally, the furring strips are closer together (6-8″ instead of 16″) and are typically wider than the 1 ½ wood or light-gauge steel stud. The furring strips accept regular drywall screws, and screw pull-out ratings performed in accordance with ASTM test reveal they have more than enough holding power.
Even heavy items like kitchen cabinets can be hung from the furring strips.
For lightweight items, a small piece of expanded steel lath behind the drywall can provide enough holding power. Wind-Lock sells a 4”x 8” mesh “Grappler” that pushes onto the foam wall before the drywall is installed. It can hold 175 pounds per screw, more than enough for crown molding, baseboards, curtain rods, picture frames and mirrors.
When specifying an interior finish, you should first request from the manufacturer a fire code test certificate from an authorized testing agency. An ICF assembly test using the ICF wall along with the prescribed finish for compliance with the applicable requirements of the following criteria: NFPA 286 Standard Methods of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth and International Building Code (IBC) 2009 sentence 803.1.2. This test should be obtained from the material manufacturer in order to be code compliant prior to submitting permits. This test is very rigorous and is difficult to pass. Gypsum drywall is nearly universal as an interior finish due to national fire codes along GigaCrete’s PlasterMax.
For exterior finishes, ICFs work well with virtually any material. A comprehensive overview is beyond the scope of this article, but it’s usually easier and cheaper to apply finishes over foam substrates than conventional wood-framed walls.
Textured acrylic finish systems (TAFS) are one of the most common, and also most cost-effective to apply. The ICF foam provides an ideal substrate, and the basecoat and mesh is typically troweled directly onto the wall. Any effect that can be achieved with EIFS can also be achieved with ICF.
Brick, stone, and manufactured stone are a great complement to TAFS.
Manufactured stone, sometimes known by its trade name of cultured stone, is light enough to be cemented directly to the wall using mortar (usually type S or N), eliminating masonry ties and brickledge. Some stone manufacturers do require metal lath to validate the warranty.
Vertical stamped concrete finishes are applied in a similar method.
True stone and masonry finishes are more complex, but only slightly. Nearly all major ICF manufacturers make a brickledge block specifically for use at the base of these walls. Masonry ties can be pushed through the sides of the ICF prior to the pour to tie into the concrete core of the wall, or screwed to the furring strips after the concrete has set. ICF manufacturers have detail and drawings available.
Siding is another popular exterior finish, especially for residential work. While ICF walls look dramatically different from plywood-sheathed frame construction, any siding that can be applied to a wood-frame building can be applied to ICFs, and installation methods are surprisingly similar.
Cement-board, cedar lap, and even vinyl siding can be fastened directly to the furring strips. Because the concrete core of the ICF wall qualifies as an air barrier, no housewrap is needed.
Often, ICF walls are straighter than stick frame, which leads to a smoother job.
The biggest challenge areas are at the corners and the horizontal joints between blocks, when an occasional row of siding will match up with the horizontal gap between furring strips. If this is an issue, light-gauge metal flashing can be installed over the problem area to hold fasteners.
The biggest question for installing siding on ICFs is whether screws or nails are the better option. Siding and ICF manufacturers recommend screws. Contractors in the field report good results with air-powered nail guns.
Installing electrical wire, telephone jacks, or audio-video cable in ICF walls is a lot less complicated that most people think, as there’s not much of the work tied up in the outside walls of a house; usually just a porch light and a few outlet boxes.
The two most popular approaches are either to place conduit in the concrete core of the wall, or cut chases into the foam after the wall is poured.
For commercial contractors, code requires conduit. It’s more expensive than cutting chases in after the fact, but it allows for more flexibility.
The easiest method is to pour the wall, then come back later and cut in the chases. The fastest and cleanest way is to buy or rent an electric hot knife for the job. One attachment is sized for the boxes, another is used to cut in the chases. Vertical chases can run virtually anywhere. Horizontal chases typically run along the block seams between furring strips.
There are other options. Some have used routers or electric chainsaws with a depth stop. Both are incredibly fast and can also cut through plastic (but not metal) ties, However, they generate a blizzard of EPS dust, and are considered less safe than the hot
After the wire is in place, it can be secured with expanding foam glue. Some prefer to fill the entire chase to restore the insulative value of the wall.
Plumbing an ICF structure, like electrical, seems more complex than it actually is. The smartest solution is careful design work, so that all the water lines and vent stacks are placed in the interior framed walls. If they must be placed along exterior walls, there are several options.
Water lines can typically be cut into the foam like electrical wires. Vent pipes are more challenging, but only slightly. One option is to furr out a short section of the wall—typically the back wall of a bathroom—to accommodate the vent. Other contractors will place a column of scrap foam in the cavity of the wall where the vent pipe will be placed. After the wall is poured, the extra foam allows the vent to be cut into the wall. A related method is to cut a larger pipe in half lengthwise, and secure half of the pipe vertically inside the core of the wall against the interior foam sidewall. After the concrete is placed, the foam is cut away to reveal the pipe, which created a chase for the vent.
ICF construction looks so different from other construction methods that the trades are sometimes apprehensive with their first job. Yet, once they’ve done it, they almost always discover that it’s really no different that their usual methods of work. And, with the increasing popularity of ICF construction, an increasing number of trades are becoming familiar with the material.
General contractors who have done ICF work report that they’ve had the best success working with tradesmen that have a passion for construction, a commitment to quality work, and are willing to learn and grow in their profession.