By Dave Gowers, P.E. – DG Engineering
This excerpt is from an article written for ICF Builder Magazine
As I sat in Oregon writing this article, wildfires were raging through Southern California. The devastating blazes tore through Pacific Palisades and nearby areas, destroying thousands of buildings, claiming 30 lives, and displacing around 150,000 people. It’s a stark reminder that the entire western seaboard remains highly vulnerable to wildfires for the foreseeable future.
This raises an urgent question: why do we continue to rely so heavily on wood-framed construction? For those who recognize the risks, Insulated Concrete Form (ICF) construction presents a clear and compelling alternative. With a 6-inch concrete core offering a fire rating of up to three hours, ICF isn’t completely “fireproof,” but it is significantly more fire-resistant than traditional wood framing.
Using ICF for wall construction is a major step toward creating a highly fire-resistant structure. However, even greater protection can be achieved by extending the concrete envelope to include the roof. While this may sound ambitious, it’s very achievable.
Concrete with a 4-inch slump has a natural repose angle of approximately 17 degrees—remarkably close to a 4:12 roof pitch, which is common in many Southern California homes. This similarity presents a real opportunity: entire homes, not just walls, could be rebuilt with concrete systems, offering significantly enhanced fire resistance.
In ICF construction, two primary types of lateral forming systems are used to achieve this. Each is described in detail below.
Foam-Based Lateral Systems
Foam-based lateral systems are a key component in ICF construction and include products such as Insul-Deck, Quad-Deck, Amdeck, LiteDeck, BuildDeck, and Fortruss. This list is not exhaustive—many other systems are available (see the Decking Chart at icfmag.com for more information). These systems all function similarly, forming a concrete T-beam joist matrix with permanent EPS forms left in place.
Typically, the “T” joists are spaced at 24 inches on center and topped with a 3- to 4-inch structural concrete slab. Rebar dowels provide shear transfer between the joists and slab, resulting in a strong and rigid lateral concrete diaphragm.
These systems are suitable for horizontal applications like floors and flat roofs, but they can also be adapted for sloped roofs. For pitches up to 4:12, the system is simply installed at the desired slope, and concrete is carefully placed. Controlling the concrete slump is critical—it should remain between 3 and 4 inches. Fortunately, modern boom pumps are capable of handling lower slump concrete, though close monitoring is still essential.
For steeper roof pitches beyond 4:12, a top form is typically required. This can be accomplished by securely attaching a modular ICF wall system over the foam deck, effectively creating a sloped ICF wall above the foam-based lateral form. I’ve personally used this method to design roofs with pitches as steep as 12:12, with excellent results.
Temporary shoring is required for these systems during construction. This typically involves a post-supported stringer system installed perpendicular to the T-beam direction. Shoring spacing is determined by the combined dead and live loads, with a maximum spacing of about 6 feet in most cases. For multi-story structures, reshoring may be required on lower floors. The design of all shoring and reshoring systems should be provided by the ICF structural engineer.
Metal Joist-Based Lateral Systems
Several metal joist-based systems are available for lateral forming in concrete construction. Common examples include Ecospan, TotalJoist, Super Joist, and Super Floor. This list is not exhaustive, and many other similar systems may be available.
These systems use metal joists spaced as far apart as 5 feet, depending on the span and overall floor depth. A pan deck is placed over the joists to support a structural concrete topping slab, typically 3 to 4 inches thick. Once the concrete cures, it forms a composite diaphragm by bonding to the joists through shear connectors, resulting in a strong, unified structural system.
One of the key advantages of metal joist systems compared to foam-based systems is the elimination of temporary shoring. Metal joists are designed to span between permanent supports—walls or beams—without requiring shoring or reshoring. This can significantly reduce both construction time and labor costs.
However, unlike foam-based systems, which retain the insulation in place, metal joist systems require insulation to be added separately. This can be achieved using rigid foam or batt insulation after the concrete is poured.
Metal joists may feature solid webs with utility ports, or open lattice web designs. Both configurations allow mechanical, electrical, and plumbing (MEPS) systems to pass through the joists without modifying the structure—an advantage over foam-based systems, which require more upfront coordination and planning.
These systems are highly effective for floor construction and equally suitable for roof applications—provided the roof pitch does not exceed 4:12. Beyond that slope, top-forming becomes problematic, limiting the practical use of metal joist systems for steeper roofs.
Speed of Construction
In general, both foam-based and metal joist systems can be installed in roughly the same timeframe, even when accounting for the added steps involved in temporary shoring. However, it’s important to note that temporary shoring—and especially reshoring—can obstruct follow-on trades. This is particularly relevant in commercial projects where multiple trades are working on tight schedules, and frequently on the same floor level simultaneously.
Conclusion
Adopting one of the ICF-compatible lateral forming systems outlined above offers substantial benefits. By extending the ICF approach to include floors and roofs—creating a full concrete envelope—the gains in fire resistance, structural rigidity, and seismic performance are significant.
My hope is that the devastation caused by recent California wildfires serves as a wake-up call, leading to stronger building codes that prioritize fire-resistant construction methods. With proven alternatives already available, there’s a real opportunity to build safer, more resilient structures for the future.
