Commercial ICFs

Wind Resistance

Concrete provides built-in safety.
Debris driven by high winds presents the greatest hazard to buildings during tornadoes and hurricanes. Recent laboratory testing at Texas Tech University's Wind Engineering Research Center compared the impact resistance of residential concrete wall construction to conventionally-framed walls. The frame walls failed to stop the penetration of airborne hazards, while the concrete walls successfully demonstrated the strength and mass necessary to resist the impact of wind-driven debris.

What was tested?
Various wall specimens were subjected to the impact of a 2x4 wood stud traveling at up to 100 miles per hour. This is equivalent to the weight and speed of debris generated during a tornado with 250 mile-per-hour winds. This testing covers the maximum wind speed generated in 99 percent of the tornadoes occurring in the United States. Wind speeds are less than 150 miles per hour in 90 percent of tornadoes.

Ten wall specimens were constructed, each representative of the type of construction now used to build frame homes and concrete homes in the U.S. Tables 1 and 2 describe each wall assembly tested.

The Wind Engineering Research Center used a compressed air cannon to propel the wood stud debris "missile" at the test walls. The stud was propelled along its axis with the leading end hitting the specimen. Electronic timing devices measured the speed of the debris as it traveled from the cannon to the test walls located 16’ to 6" away.

How did the frame walls perform?
The frame walls lacked the weight and mass to resist the impact of the wind-driven debris. In each case, the debris traveled completely through the wall assembly with little or no damage to the "missile."

Table 1: Frame Wall Test Results

Wall Type	Test Wall Description	Speed of Debris	Results
Wood Frame	⅝" gypsum board interior finish, 2 x 4 wood studs at 16" o.c., 3-½" batt insulation, ¾" plywood sheathing, vinyl siding exterior finish.	109.0 mph	The debris missile perforated completely through the wall assembly. Little damage to missile.
Wood Frame	⅝" gypsum board interior finish, 2 x 4 wood studs at 16" o.c., 3-½" batt insulation, ¾" plywood sheathing, 4" brick veneer with 1" air space.	69.4 mph	The debris missile perforated completely through the brick veneer and the interior finish. Minor damage to missile.
Steel Frame	⅝" gypsum board interior finish, steel studs at 16" o.c., 3-½" batt insulation, ¾" plywood sheathing, vinyl siding exterior finish.	103.5 mph	The debris missile perforated completely through the wall assembly. Little damage to missile.
Steel Frame	⅝" gypsum board interior finish, 2 x 4 wood studs at 16" o.c., 3-½" batt insulation, ⅝" gypsum board sheathing, synthetic stucco exterior finish.	50.9 mph	The debris missile perforated completely through the wall assembly. No damage to missile.

How did the concrete walls perform?
The concrete stopped the debris from traveling through the wall. Exterior finishes were damaged by the impact, but the concrete walls themselves remained unscathed. Even the narrowest, 2" thick section of "waffle grid" ICF wall was undamaged by the direct impact of the debris at over 100 mph.

Table 2: Concrete Wall Test Results

Wall Type	Test Wall Description	Speed of Debris	Results
Concrete	6" thick reinforced concrete wall, #4 vert. reinforcing bars, 12" o.c., no finishes.	109.0 mph	No cracking, front face scabbing, or back face spalling of concrete observed.
Concrete	6" thick reinforced concrete wall, #4 vert. reinforcing bars, 24" o.c., no finishes.	102.4 mph	No cracking, front face scabbing, or back face spalling of concrete observed.
ICF	Block ICF foam forms, 6" thick flat concrete wall, #4 vert. reinforcing bars, 12" o.c., vinyl siding. (Tested a second time with similar results)	103.8 mph	Debris penetrated vinyl siding and foam form. No cracking, front face scabbing, or back face spalling of concrete wall observed.
ICF	Block ICF foam forms, 6" thick flat concrete wall, #4 vert. reinforcing bars, 24" o.c., 3" brick veneer with ties spaced 1'-0" each way.	99.0 mph	Debris penetrated and cracked brick veneer. Foam form dented. No cracking, front face scabbing, or back face spalling of concrete wall observed.
ICF	Panel ICF foam forms, 4" thick flat concrete wall, #4 vert. reinforcing bars, 24" o.c., vinyl siding.	96.7 mph	Debris penetrated vinyl siding and foam form. No cracking, front face scabbing, or back face spalling of concrete wall observed.
ICF	Block ICF foam forms, variable thickness "waffle" concrete wall, 6" max. 2" min. thickness, #4 vert. reinforcing bars in each 6" vertical core at 24" o.c., synthetic stucco finish(Tested a second time with similar results).	100.2 mph	Debris penetrated synthetic stucco finish and foam form. Impact on wall at 2" thick section. No cracking, front face scabbing, or back face spalling of concrete wall observed.

Note: All concrete tested: 3000 PSI compressive strength, maximum aggregate size ¾", 6" slump.

What about damage from hurricanes?
Hurricane wind velocities would be less than the equivalent maximum speeds modeled in these tests. Missile testing designed to mitigate property damage losses from hurricanes uses a 9-pound missile traveling about 34 mph as criterion.

What's the bottom line?
The strength and durability of concrete walls formed with ICFs offer unmatched resistance to the devastation of major storms. Concrete buildings are less likely to suffer major damage from debris than conventionally-framed structures. This greater measure of built-in safety makes ICF construction the quality choice for your building.

More Information?
The following publication and video are available from the Portland Cement Association:

• VC511 "Concrete Homes: Built-In Safety" ($4.95)
Videotape documenting the results of the wind-driven debris impact testing. All

ten of the impact tests are featured.

• RP122 "Investigation of Wind Projectile Resistance of ICF Homes" (June 1998)
Written report with photos detailing the results of the wind-driven debris impact

research. Background information on the critter and assumptions used to

generate the test design are included.

To order, call PCA Publications at 1-800-868-6733.