Eaglerock Log Homes general information.

How resistant to fire are log homes and cabins?

There is a recognizeable growth in the number of log homes, resorts and other buildings being built from log. One frequently asked question is "how do log walls perform in a fire" with the key question being "how long will log construction be able to withstand a fire until the manpower, equipment, and water can be deployed to extinguish it?"

Acceptance by code officials of solid wood walls has been elusive in the past years, in regards to their capacity to be fire-resistive construction. "The Log Homes Council (LHC) and its Members have used various resources that relate the performance of solid wood walls to fire endurance. Some performed in-house tests while others tested their products in certified labs followed by specific standard procedures. And as the years pass, the number of fire survival stories continues to increase."

The LHC maintains the position that a 4" log wall can achieve a 1-hr fire-resistive rating, with even longer ratings provided by the solid wood wall. A nominal 6" log wall achieved a 1-1/2 hr fire-rating in full scale testing.
"As the log wall thickness increases, so does the fire rating"
It is important to mention that handcrafted log homes use a much larger diameter log than those involved in the testing, further increasing log mass and wall thickness.
"As an organic material, wood is combustible. Yet its insulation and charring characteristics produce an astounding response to fire. The charring effects of wood results in a protective coating over the surface of the material.

This protective char coat is very similar to the effect created by some fire-retardant chemicals used to protect materials and assemblies." According to Barbara Martin, Log Homes Council's Executive Director, "it does take a long time for a log to burn to the point where they lose their load-carrying capacity."

The information provided above is quoted from:
The Fire Performance of Log Structures prepared by the Technical Committee of the
Log Homes Council Building Systems Councils National Association of Home Builders
March 2001 Rough Draft -A Test on the Fire Resistance of Log Walls.

CLINICAL TEST.

The following test is quoted from:

Log Building News International Log Builders Association - Fire Restance of Log Walls, by Dalibor Houdek, Ph.D.
Number 35, September 2001
"The Technical University of Zvolen, Slovakia, has commenced research to answer questions of fire resistance of a chinkless log wall used primarily in North America, and to develop a model for estimating the fire resistance of log walls. The large scale experiment according to ISO 834 was undertaken in PAVUS-Fire Research Institute, Czech Republic.

EXPERIMENT: The test sample consisted of twelve spruce logs of 257 mm (10") average diameter. They were joined in the traditional chinkless, full-scribe fit style. The cupped lateral grooves were approx. 15mm (3/4") deeper than necessary, to accommodate the mineral wool insulation. The test wall was 3250 mm (10'-8") long, and 2800 mm (9'-2") tall.
Eleven logs were kiln-dried to an average moisture content (MC) of about 19% and one log was conditioned to 36%. The long grooves were filled with mineral wool (rock-wool type). due to the natural irregularities of each log, the width of the grooves varied between 89mm and 130mm with an average of 105mm (4").
The ends of the panel were splined (like a door opening) and 3 spruce pegs per log, 30 mm in diameter, were driven approximately 800 mm (30") apart to support the wall logs. They were driven only through two vertically-adjacent logs.
The log wall was exposed to fire, and temperatures inside the log, inside the grooves, and on the unexposed side were continually monitered and recorded.
The log wall was continuously vertically loaded on the centerline with 15kN m(-1) using a hydraulic loading system built in the furnace loading frame. The load figure derived from the calculation of a one-and-a half storey log house.

RESULTS:

According to ISO 834, structural walls can fail in three ways during a fire resistance test:
1. fail in integrity, causing ignition of a cotton pad, permitting the penetration of flames resulting in sustained flaming, or
2. fail in insulation, causing an increase of the average temperature above the initial average temperature by more than 140 degree Celcius, or increase above the initial temperature at any location by more than 180 degress Celcius, or
3. fail in load bearing capacity -basically if the wall loses 1% of its height, it has failed.
Inside the furnace, the log wall surface turned black in the 3rd minute of the test. In the 5th minute the surface ignited and continued to burn for the duration of the test. Large deep cracks developed around the 11th minute. From about the 30th minute the walls surface was red and charred with large deep cracks for the rest of the test. It was observed that when the fire-exposed edge of the lateral groove burned off, the mineral insulation inside the long groove protruded, and expanded to about its initial thickness of 50mm.
No flame penetration through the wall was observed during the test. The side unexposed to fire showed no visible changes, smoke penetration was not observed through the wall joints.

Comparing the results of chinkless log wall joint with the chinked wall joint tested by Sashco Sealants Inc., the scribe-fit log wall has a much higher insulation value. At 60 minutes of the test duration, the chinkless log wall showed absolutely no increase in surface temperature, compared to an average 71 degrees Celsius temperature increase of the chinked log wall tested by Sashco Sealants Inc.
The temperature on the hot side of the scribe-fit log wall exceeded 1100 degrees Celsius, but the cool side never got above 48 degrees Celsius, even after almost 3 hours of burning.
Conclusions;
Knowing how log walls react to fire exposure is important for evaluating newly constructed buildings and existing log structures. A large-scale laboratory test showed that a massive wooden wall with considerable numbers of lateral wood-to-wood joints can maintain the fire safety requirements prescribed by the ISO 834 for as long as 172 minutes.
The log wall withstood 180 minutes from its integrity and insulation viewpoint and 172 minutes from the point of its load bearing capacity.
The handcrafted chinkless log wall constructed in the manned described above shows better integrity, insulatiion, and load bearing capacity than the chinked or milled log walls tested by other laboratories and detailed in this article - its properties provide significant resistance