Hurricanes. Tornadoes. Oppressive heat. Bone chilling cold. Sooner or later, every home in the United States will be affected by at least one of these weather conditions. But there's a home construction method that can take almost anything Mother Nature can throw at it — insulating concrete forms or ICFs.
What are ICFs?
ICFs are typically made of expanded polystyrene. An ICF system provides an exoskeleton for creating the reinforced concrete wall. "The way the forms are designed, reinforcement bars can be spaced in a specified arrangement or grid, so the architect can specify the steel to withstand wind loads, projectiles, excessive backfill pressures and multistory," Jim Buttrey of ICF manufacturer IntegraSpec explains. Depending on the ICF form manufacturer, webs or spacers made of plastic are inserted between the forms in the factory or on-site to hold the forms in place. After being set up and reinforced, concrete in a standard wall mix of 3,000 psi with a 5- to 6-in. slump is poured between the forms. The concrete core thickness can be varied as needed based on project requirements.
The forms come with built-in furring strips so the outside of the house can be finished with any desired material, while the inside gets the normal drywall. "They're used for sheetrock, siding, masonry with brick ties, and the furring strips are buried for stucco friendliness," says Buttrey. Another benefit of building with ICFs is that fewer trades are needed to complete the job, as the wall structure, furring, vapor barrier, insulation and air barrier are all done in one step by one crew.
Concrete contractors who already know how to build masonry or poured concrete homes can learn how to build with ICFs in one week. Manufacturers support users in several ways. For example, IntegraSpec provides technical manuals online, as well as offering help from its regional representatives and in-house training department.
The basic North American configuration of a residential ICF wall is a conventional 6-in. wall containing a 1/2-in. steel grid. Buttrey says this wall can withstand wind speeds of up to 150 mph. With thicker walls and more steel, higher wind resistance is achieved. The walls are also highly resistant to flying projectiles. When a 2x4 was shot at an ICF wall at 100 mph, the wall was not penetrated.
This suggests an ICF house will remain standing during almost any hurricane or tornado. The Grand Caribbean Condominium in Orange Beach, Ala., was built using ICFs, and it sustained almost no damage during a nearly direct hit from Hurricane Ivan. Single-family homes and other ICF buildings designed by the same ICF contractor, IntegraSpec Gulfsouth, also had no structural damage from Hurricanes Ivan and Katrina.
These results cannot be compared directly with masonry or poured concrete homes because "typically in this area they don't build concrete homes," explains architect David Lindsey. "All of our competition is wood frame. There is nothing else standing there on the water. They've completely lost their homes."
Although he didn't build it, Lindsey has seen an ICF condo on the beach in Biloxi, Miss. Built in 1999, it was surrounded by wood frame buildings, but it's all that remains after Katrina. The building was affected by the storm surge and needed some repairs, but the owners were able to live there while those repairs were made. "People who have looked at it said there could not be anything else to build with than ICF after seeing this building," he notes.
"In certain areas, if a home is destroyed by a hurricane, the insurance company requires the replacement to be an ICF home," Buttrey points out.
ICF homes might even serve as hurricane shelters under certain circumstances. "What we tell people is if you're in a flood plain, we're building a home to protect your property," Lindsey cautions. "You need to leave. In an upland area, depending on the design, it might be a safe place to stay. "