Straw Bale Fire Ratings

Fire Tests of Straw Bale Building Construction Materials

Straw in a field or in a loose pile could be flammable.  Once it is compressed into a dense block it starts to slow down and smolder & smoke more due to the lack of airflow in the centre.  And as soon as it get’s sealed in a plastered wall system, it reduces the risk of fire significantly.  When the straw is compressed into a dense block bale it dramatically decreases the ability of oxygen to feed the fire into the straw. Straw Bale walls are generally given from a 1 to 2 hour fire rating.

Straw Bale Fire Test Videos

Right-click or ctrl-click this link to see Video 1 

Right-click or ctrl-click this link to see Video 2

ASTM Straw Bale Fire Tests

In July 2006, the Ecological Building Network funded and oversaw the following ASTM E119-05a – Straw Bale Fire Tests. Both walls withstood the fire and hose stream tests, as described in the below two documents.

1 Hour Fire Resistance of a Non-Loadbearing Wall w/ Earth-Plaster

A 12 ft x 14 ft non-loadbearing wall constructed with 7.5 pcf rectangular wheat straw bales stacked in a running bond pattern, clad on each surface with 1″ of earthen-plaster, produced, assembled and tested herein, successfully met the conditions of acceptance as outlined in ASTM Method E119?05a Fire Tests of Building Construction and Materials for a fire endurance rating of 1 hour.

www.ecobuildnetwork.org/images/stories/ebnet_pdfs/Non?Bearing_Clay_Wall.pdf

2 Hour Fire Resistance of a Non-Loadbearing Wall w/ Cement-Stucco

A 10 ft x 10 ft non-loadbearing wall constructed with 7.5 pcf rectangular wheat straw bales stacked in a running bond pattern, clad on each surface with 17 GA stucco netting and 1″ of cement/stucco, produced, assembled and tested as described herein, successfully met the conditions of acceptance in ASTM Method E119-05a Fire Tests of Building Construction and Materials for a fire endurance rating of 2 hours.

www.ecobuildnetwork.org/images/stories/ebnet_pdfs/Cement_Stucco_Wall.pdf

STRAW BALE FIRE SAFETY

A review of testing and experience to date
July 30, 2003
Bob Theis
Excerpts:

“…fire requires high temperature, fuel, and oxygen; compressing the straw into a dense block dramatically decreases the ability of oxygen to feed a fire at the straw. After the surface of a bale or bale wall has been charred (providing that the wall of exposed bales remains intact), the worst it will generally do is smolder…

…once a bale wall has been plastered on both faces, the combination of an incombustible surface and an insulating interior that neither burns well nor melts makes a straw bale wall a very fire resistive assembly.

1. 1993 Two small scale ASTM E?119 fire tests at the SHB Agra lab in Sandia, New Mexico—one test wall with plastered faces, the other unplastered—showed bales to be very fire?resistant. The unplastered bale wall withstood the heat and flames of the furnace for 30 minutes before flames penetrated a joint between bales. The plastered bale wall was naturally much better, resisting the transmission of flame and heat for two hours.

2. 1996 A full scale ASTM E?119 fire test at the University of California Richmond Field Station easily passed the criteria to qualify as a one hour wall. In the opinion of the experts present at the test [personal communication with R. Brady Williamson], the wall would probably have passed as a two hour assembly.

3. 2001 The Appropriate Technology Group at Vienna Technical Institute conducted an F90 test (similar to the ASTM E?119 test), which gave a plastered straw bale wall a 90 minute (1 ?1/2 hour) rating. 

4. 2001 The Danish Fire Technical Institute tested a plastered straw bale wall with exposed studs on the fire side as a worst?case scenario, and got these results: in a 30 minute test with a 1832 °F. (1000 °C) fire on the exposed side, the unexposed side rose just 1.8 °F (1 °C). The maximum average increase permitted to in order to pass that test is 144 °F (80 °C).

5. 2002 Bohdan Dorniak and members of AUSBALE tested individually plastered bales to the Australian standard simulating the heat of a bushfire. Subjected to a maximum heat intensity of 29 kilowatts per square meter, none of the nine plastered bales ignited, or even developed v+isible cracks. According to Mr. Dorniak, this qualifies them as noncombustible under the current Australian Bushfire Code AS 3959

….an ASTM E84?98 test on unplastered straw bales in 2000 at the Omega Point Laboratories. They passed the test easily; where the Uniform Building Code allows a flame spread of no more than 25 , the test produced a flame spread of 10; where the codes allows a smoke density of no more than 450, the bales
produced a smoke density of 350…..”

www.osbbc.ca/Resources/Documents/Technical/strawbale_fire_safety.pdf