Bullet Resistant Wall Construction
Awhile ago I came across some general information which summarized a bullet resistant wall construction technique that had been recommended to the city of Boulder, Colorado.
For those who are concerned about their security in this regard (bullet resistance of their walls), you may be interested to know the details of their method:
Poured Concrete Wall For Bullet Resistance
“Based on these tests, it is my professional recommendation, when practical, that we utilize the combination of Oriented Strand Board (OSB) and concrete. For new construction this combination appears to offer the best results at a cost far less than the commercially available ballistic fiberglass.”
While there are many ways to go about building a bullet resistant wall or beefing up the resistance of a wall to slow or stop a bullet, this particular recommendation was made to the city of Boulder following a series of bullet penetration tests conducted by the city facility manager there.
He concluded that the best bullet resistant wall construction (versus cost) is poured concrete filling the cavity between 2″X4″ studs, using 1-1/8″ OSB (oriented strand board) fastened to both sides, followed by 5/8″ Gypsum.
The OSB is screwed to to the 2×4’s and used as a material strong enough to hold the poured concrete, and then apparently left in place afterwards as an integral part of the wall. The Gypsum (drywall) is fastened for the interior wall aesthetic appearance.
Bullet Caliber Penetration Tests
The bullet penetration tests were performed to determine the ability to withstand penetrations by a number of commonly used bullets.
9mm, .45 auto, .357, .44, 12 ga. slug, .223, .270 Win
The calibers were selected based on press coverage of incidents around the nation, as weapons-calibers commonly used in attacks on citizens.
All test shots were from 7 yards downrange.
The materials cost for the recommended solution above (at the time) was determined to be a little more than $3 per square foot (approximately $100 for a 4×8 section).
Of course your own cost of materials may vary and labor costs also need to be considered, be it DIY or otherwise. At the time of the recommendation to Boulder, the labor costs were estimated to be similar to the materials cost itself.
Note: If seriously considering constructing a bullet-resistant wall such as this, some cost (and weight) savings would be gained by filling the wall with concrete only to 4-feet high, while still maintaining a safe zone from that height to the floor.
Concrete Weight Density
Typically, concrete has a density of 150 pounds per cubic foot, which means that a block of concrete that is one foot wide, one foot long, and one foot high would weigh 150 pounds.
The gap in a 2×4 stud constructed wall (studs are actually 1.5 x 3.5) is approximately 8.6 – 9 cubic feet within a 4×8 section (depending on stud spacing). Therefore, each 4×8 section when filled with concrete will have a downward force weight of approximately 1,300 pounds.
If you’re filling to a height of 4′ then you’re looking at about 160-lbs per linear foot.
If you’re filling the entire wall, then you’re looking at about 320-lbs per linear foot.
Be sure that your floor and foundation can support it, and be sure to use techniques such that the wall(s) are properly supported from toppling, etc.
Note: Plywood is stronger than OSB and resists moisture better. It is more expensive – although you won’t need 1-1/8″ – while 3/4″ should suffice. Having said that, the OSB used in this recommendation to the city of Boulder was apparently acceptable given it’s lesser cost.
There are other ways to accomplish this.
This is for educational-informational purposes only.
When in doubt, get architectural-engineering advice.
Check your own local codes and do your own due-diligence.