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Log Jam - UL Fire Resistance Rating Explained

Log Jam - UL Fire Resistance Rating Explained

What is UL?

UL stands for Underwriters Laboratory.

UL develops standards and test procedures for products, materials, components, assemblies, tools and equipment, chiefly dealing with product safety.

UL has developed more than 1,000 Standards for Safety, many of which are American National (ANSI) Standards, and evaluates nearly 20,000 types of products. A typical standard for electronic products includes not only requirements for electrical safety, but also spread of fire and mechanical hazards. UL evaluates products for compliance with specific safety requirements. UL certification does not guarantee the product will perform acceptably or that it is safe under all conditions (such as product misuse).

Fire Resistance Ratings - ANSI/UL 263

The Log Jam design test was conducted in accordance with Fire Resistance Ratings - ANSI/UL 263.

One of the 1,000 standards for safety is ANSI/UL 263. This category covers fire-rating classifications. These requirements are intended to evaluate the length of time that the types of assemblies will contain a fire or retain their structural integrity, or both, dependent upon the type of assembly involved, during a predetermined test exposure.

The test evaluates the assembly's resistance to heat, and in some instances to a hose stream, while carrying an applied load, if the assembly is load bearing.

Why apply for a fire resistance rating?

The rebirth of the log industry in North America could be described in a number of terms. "Easy" would not be one of them.

Log home companies and their product suppliers have constantly faced resistance from architect, building code inspectors, loan officers and governmental agencies steeped in the doctrines of conventional "stick" construction. The fledgling industry has often found itself in the frustrating position of being condemned not by facts but by biases.

One such bias has been that water-based chinking materials used to seal the courses of log walls could never pass a one-hour fire test. The experts felt that since many of the compounds used to make water-based chinking decompose at temperature far below the 1700 degrees required by the test, a chinked log wall could not survive it. This belief persisted in spite of the fact that a one-hour fire test had never been attempted on any log wall system, chinked or otherwise.

The end result of this widely shared view was that many log projects were held up or stopped completely since most major building codes required a one-hour fire rating in critical areas such as between the garage and house or in commercial structures. Often, log home customers were told that their log partitions would have to be covered by drywall in the critical areas. Certainly, this tended to dampen enthusiasms for solid timber walls.

Now, a test conducted by Underwriters Laboratories has laid this belief to rest. Recently, it tested a complete chinked wall system which passed the one-hour fire test. The chinking compound under scrutiny was Sashco Sealants Log Jam Chinking compound.

It cost Sashco, a Colorado-based company, about $10,000 and months of research and testing to perfect the formula for Log Jam Chinking. But the company believed an answer had to be found to the problem.

The First Experiment

According to company officials Sashco began with a pragmatic “back yard” approach. A miniature log wall section was constructed out of 4 fence posts. In a crude simulation of the one-hour test, they exposed the section directly to flame from a propane torch for one hour.

Researchers quickly discovered that they could not prevent decomposition of the chinking material. So, instead, they found a way to make the decomposition work in their favor. They reasoned that if they could not get the chinking to stay put and not melt away, the burned exterior might act as an insulator in much the same way as the charred surface of wood provides a thin barrier between the flames and the material behind it.

They arrived at a formula which actually formed small “heat shields” as it charred. It gave an unexpected bonus in that it also expanded as temperatures increased. This further protected the integrity of the log joint. Funds were then made available for the Underwriters Laboratory test which essentially was to certify the results found by the Sashco researchers.

Certification by UL meant that building inspection could be passed by log walls using Log Jam Chinking. Correspondingly, this would expand the availability of log structures for many commercial and residential applications where one-hour fire ratings were required.

The UL Testing Procedure for Log Jam

The UL test involved the use of a giant furnace.

  • At Underwriters Northbrook, Illinois laboratories a 10 foot high by 10 foot wide wall of 9 inch round lodge pole pine logs was constructed leaving one inch gaps between the logs.
  • Round backer rods were then fixed in the joints and Log Jam Chinking was tooled over the top to a minimum depth of ½ inch.
  • The wall was framed in brick and insulation to insure that no flames passed through the assembly which was not a result of wall failure.
  • Because it was felt that any residual water left might artificially aid the fire resistance of the chinking material, the assembly was left to stand for 30 days t allow all of the water to leave the Log Jam Chinking for a thorough cure.
  • The test wall was then rolled into the furnace where it was exposed to 68 gas jets throwing flames which raised the surface temperature to 1000 degrees F in 5 minutes, 1300 degrees F. in ten minutes and, ultimately 1700 degrees F. in one hour.
  • The unexposed side was left at room temperature.

    Of course, to pass the test, the chinked joint obviously could not fail allowing fire to pass through the wall. But this was only a single aspect of the experiment.

    In order to pass the one-hour fire test, the unexposed side of the wall could only climb 250 degrees F. above its starting temperature.

    In other words, the Log Jam Chinking had to be a good insulator as well as being fire resistant.

  • Finally, the test wall was rolled out of the blast furnace and exposed immediately to a blast of water form a 2-1/2 inch diameter fire hose, exposing it to "impact, erosion and cooling" from a fire house stream of 30 pounds per square inch of force.
  • Of course, as UL officials explained, water could not be allowed to spray through the wall.


    The investment Sashco made in time and money paid off. In July 1986 Sashco received the full UL test report. Not only did its Log Jam Chinking pass all aspects of the one-hour fire test, the unexposed side showed a rise in temperature of only 160 degrees F. qualifying it as an excellent insulator.

    “Log Jam Chinking is now the only answer to a one-hour fire wall needed” said one Sashco official, “unless, of course, you’d like drywall over your logs”

    Information Courtesy of Sashco Inc.

    Reprinted from the Online Certifications Directory with permission from Underwriters Laboratories Inc. Copyright © 2008 Underwriters Laboratories Inc.®