Tag Archives: 1 hour firewall

Establishing Fire Resistance

Establishing Fire Resistance

Table 601 of the International Building Code (IBC) establishes the required fire resistance of building elements (usually the structural frame, walls, floors and roofs) due to the construction type of the building (most post frame buildings being either Type III or V). Required ratings are given in hours.

burning-matchesFire resistance describes the rate at which a building material degrades due to a fire. Resistance is based on how fast a material will burn, how rapidly the strength of the member of assembly is affected by the fire and whether the member or assembly can maintain its design strength. Fire resistance of wood members and assemblies may be established by any one of five means listed in IBC Section 703.3.

Tested Assemblies.

Tested assemblies include wood assemblies which have been tested to ASTM E 119 or UL 263 standards. Using one of these standards, an assembly is typically assigned a 1- or 2-hour fire rating depending on its performance in the fire test(s). Designers choose listed assemblies from various fire resistance publications or directories, such as the UL Fire Resistance Directory or the Gypsum Association Fire Resistance Design Manual.

Prescriptive Assemblies

The fire resistance of certain wood assemblies is prescribed in Section 720 based on testing using ASTM E 119 or UL 263. Section 703.3 permits the use of other sources, as well. Often used is the AWC publication AWC DCA 3, Fire Rated Wood Floor and Wall Assemblies, which is available for free download at www.awc.org/codes/dca/.

Calculated Fire Resistance

The fire resistance of exposed wood members may be calculated using the provisions of Chapter 16 of the National Design Specification (NDS) (see Section 721.1). AWC’s Technical Report No. 10 (TR10), Calculating the Fire Resistance of Exposed Wood Members, contains full details of the NDS method as well as design examples, and is available for free download at www.awc.org/publications/tr10. Although Section 721.6.3 contains an acceptable calculation method as well, it is limited to 1-hour fire resistance.

The fire resistance of wood frame assemblies also may be calculated using the provisions of Section 721.6, which is based on the known fire resistance of many tested assemblies. The information in AWC publication AWC DCA 4, Component Additive Method (CAM) for Calculating and Demonstrating Assembly Fire Endurance, was the basis for these code provisions. It is available for free download at www.awc.org/codes/dca4.

The National Post Frame Building Association (NFBA) has sponsored two approved post frame firewall assemblies. The first of these was for a one-hour firewall and was done in 1990. The Report number is WHI-651-0319. The most recent tests were on a three-hour assembly. For details of this testing read more at: https://www.hansenpolebuildings.com/blog/2012/03/firewall/.

The 3 Hour Firewall for Pole Buildings

Guest blog by J.A.Hansen, owner of Hansen Buildings…

There were several concurrent conferences with great speakers at the NFBA expo Mike the Pole Barn Guru, Eric (my business partner and President of Hansen Buildings) and myself recently attended in St. Louis, MO. The National Frame Builders’ Association website: www.nfba.org

gives this description:  “NFBA is the only national trade association that represents post-frame industry professionals. The association is the country’s primary source of post-frame building resources, research, networking, news and education.”

And educational it was!  Every morning there were break-out sessions with key-note speakers and top rated leaders in the post frame industry to speak on issues relating specifically to pole buildings.  I was fortunate to attend one of the best presentations this year which outlined the design and testing of a 3 hour fire wall for post frame buildings.  There have been tests for 1 hour fire walls, but not 3 hours. This test design required the fire wall framing had to be built completely out of wood, and tested in a UL laboratory under strict testing conditions.

Firewalls are sometimes required in order to enclose egress paths, often hallways.  This is so that people (or animals) trying to escape (or be rescued) from a burning building have a good chance of getting out without the building collapsing on them.  Besides testing to see if the walls didn’t let the fire through, they also were tested for structural integrity to keep the weight of the roof from collapsing and crushing whoever is inside.

Why would you perform such a test?  Number one on the list is of course for safety.  Fire marshalls and county officials have a huge responsibility in writing and enforcing requirements for buildings which will best protect the lives of those using them. Number two on the list is ease of building and cost. What has typically been done to create a firewall is using concrete blocks (8” or 10”) to build a structurally independent wall to separate a building into two completely separate areas.  This requires having to possibly hire a concrete block contractor to build the wall, which involves more time and expense overall.  Material costs are estimated at $11/square foot for a concrete wall versus $2/square foot for a wood/gypsum board fire wall.  Even adding in the labor for attaching 4 separate layers of gypsum board, the guesstimate is the wood/drywall would conservatively come in at half the price of a concrete fire wall.

Tim Royer, PE of Timber Tech Engineering, Inc., gave an enlightening presentation on the UL test he was involved in planning, and was present to observe as the fire wall was tested.

Keep in mind the wall must be “structurally independent”.  This means the wall must not depend upon the balance of the building to hold it up.

The test involved these components (my simplified explanation):

Wood columns – minimum 5-1/2 x 6 inch.

  1. Wood girts – 2×4 girts applied horizontally to the face of the columns at 16 inches on center.
  2. Wood Blocking – 2×6 inch blocking vertically applied to the column face between each girt. This intermediate blocking is applied with four 16d nails, equally spaced.
  3. Gypsum Board – (4) layers 5/8 inch thick applied horizontally.  Joints in adjacent layers are staggered a minimum 16 inches o.c.

There is more about the nailing requirements for the layers of the drywall, but suffice it to say, 4 layers with lots of nails makes for a heavy duty firewall!

Controlled fire in a UL laboratory then took the temperature up to 1600 degrees in 10 minutes and then gradually up to 1800 degrees.  There were some great videos of the testing, showing the both the effects of fire and also pressure placed on the structurally independent fire wall.  Pressure was added by using hydraulic jacks to exert pressures of up to 21,000 pounds per column.  Normal pressures calculated on a wall are 4,000 pounds per post.

The test used lots of gauges with wires inserted into the wall assembly.  So, they stoked up the fire within 3 feet of the wall assembly, and began to watch and document the results.  The results were absolutely amazing to watch on video…so come back for tomorrow’s blog on “did the wall work?”