# 3/8" plaster board rating



## Inspector 102 (Oct 18, 2010)

Where would someone find the equivilent rating for 3/8" plaster board installed in the 1970's to compare to the drywall we install today. I seem to recall that 3/8" plaster was equivilent to 5/8" gypsum wall board but do not remember where I read this. Can it be found in the Gypsum Manual or is this a UL Fire resistive Directory issue. Guidance appreciated.


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## Coug Dad (Oct 18, 2010)

Look at the different assemblies in Table 720.1 and see if there is one similar to yours.


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## rshuey (Oct 18, 2010)

According to Resource A in the back of the 2009 IEBC, Table 1.5.1 shows 3/8 gypsum wallboard to have a rating of 10 minutes


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## Inspector 102 (Oct 18, 2010)

The material I am referencing is not the gypsum wallboard found today, but the plaster type used 40 years ago. There is a layer of 3/8" plaster (cementious) material between the paper facings. I thought the plaster material carried a longer rating than the gypsum. Much like a plaster/Lath assembly has a rating, but this is wallboard style, not lath. Thanks


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## rshuey (Oct 18, 2010)

I'm pretty sure that's what that table refers to as the Resource A is entitled "Archaic Materials"


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## rshuey (Oct 18, 2010)

Believe me, it's most likely the design professionals telling people the rating is higher than it actually is. they hate having to design 2 hr separations in historic structures...lol


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## Inspector 102 (Oct 18, 2010)

rshuey - I am sorry, I do not have access to the IEBC, so it is hard for me to reference. My state does very little to adopt a comprehensive set of code documents. The main issue is the ceiling located in a single family dwelling built in the early 1970's. The lender is indicating they need 5/8" gyp board applied over the ceiling for code compliance. I argued that the home complies because there has been no change since it was built but who do you think is going to win the arguement. I was looking for a refence to match equivilent protection. Since you say it indicates a 10 min. rating, I lose the arguement. Thanks again.


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## rshuey (Oct 18, 2010)

Wow, that's crazy. I can see lenders having a problem with knob & tube wiring, but finish products on a ceiling of a single-family home? Strange....unless the same lender has a lead paint abatement division....


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## Code Neophyte (Oct 18, 2010)

From the '06 IEBC - Table 1.5.1 (Resource A) - "Inorganic Materials" - (There is no specific detail for 3/8" plaster), but:

3/4" thick 1:2, 1:3 gypsum plaster over paper backed metal lath - 20 minutes

3/4" thick portland cement plaster on metal lath - 10 minutes

3/4" thick 1:5, 1:7.5 lime plaster on metal lath - 10 minutes

1/2" thick 1:5, 1:7.5 lime plaster on wood lath - 15 minutes

1/2" thick 1:2, 1:3 gypsum plaster on wood lath - 15 minutes

Maybe you can reasonably interpolate from this data?


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## rshuey (Oct 18, 2010)

Code Neophyte said:
			
		

> From the '06 IEBC - Table 1.5.1 (Resource A) - "Inorganic Materials" - (There is no specific detail for 3/8" plaster), but:3/4" thick 1:2, 1:3 gypsum plaster over paper backed metal lath - 20 minutes
> 
> 3/4" thick portland cement plaster on metal lath - 10 minutes
> 
> ...


yep, just shows 3/8 gypsum wallboard


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## JBI (Oct 18, 2010)

Inspector 102 - http://publicecodes.citation.com/icod/iebc/2009/index.htm  Now you have access to the IEBC... ;-)


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## JBI (Oct 18, 2010)

_*3.2*_ _*THE THEORETICAL APPROACH*_ 

_There will be instances when materials and assemblies in a building undergoing rehabilitation cannot be found in the Appendix Tables. Even where test results are available for more or less similar construction, the proper classification may not be immediately apparent. Variations in dimensions, loading conditions, materials, or workmanship may markedly affect the performance of the individual building elements, and the extent of such a possible effect cannot be evaluated from the tables. _

_Theoretical methods being developed offer an alternative to the full-scale fire tests discussed above. For example, Section 4302(b) of the 1979 edition of the Uniform Building Code specifically allows an engineering design for fire resistance in lieu of conducting full-scale tests. These techniques draw upon computer simulation and mathematical modeling, thermodynamics, heat-flow analysis, and materials science to predict the fire performance of building materials and assemblies._

_One theoretical method, known as the "Ten Rules of Fire Endurance Ratings," was published by T. Z. Harmathy in the May, 1965 edition of Fire Technology. (35) Harmathy's Rules provide a foundation for extending the data within the Appendix Tables to analyze or upgrade current as well as archaic building materials or assemblies._

Was the plaster board listed by UL (or other lab)? Find an old UL Directory and you may get your answer as well. If the product has a lower organic content than 'modern' GWB, it may well have a slightly better performance rating...


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