# Exterior one hour assembly



## Kim M. (Nov 19, 2021)

Any suggestion for a one hour assembly, exterior rated wall needs to be rated for exposure on both sides, 2x6 wood studs, with sheathing used for shear, min r20 insulation and multiple sidings including thin cut stone, hardcoat stucco and James Hardie firber cement siding?


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## redeyedfly (Nov 19, 2021)

U305, add gyp over the ply sheathing.


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## Kim M. (Nov 19, 2021)

redeyedfly said:


> U305, add gyp over the ply sheathing.


Thanks. Any idea where to find a detail that shows u305 with full 5.5 insulation? All I've seen have 3 1/2" or 5 1/2" compressed to r13 which is not flying with the  plan checker.


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## mtlogcabin (Nov 19, 2021)

Your plan checker needs to learn more. Click on the link and you will find an assembly that will work. JFYI all wall assemblies are tested as a 4 inch wall. Read the general explanatory notes starting on page 18. There you will learn that you can increase stud size, add insulation to fill the stud spacing without negatively impacting the fire rating. You can reduce the stud spacing however you will reduce the STC rating. I prefer the GA-600 manual since it does have some non-proprietary system which in todays world of shortages it would be nice to be able to be able to use what is available in your area. 





						View Only: Prior Editions of Code-Referenced Documents – Gypsum Association
					

A not-for-profit trade association founded in 1930, promoting the use of gypsum while advancing the development, growth, and general welfare of the gypsum industry in the United States and Canada on behalf of its member companies




					gypsum.org


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## redeyedfly (Nov 22, 2021)

Kim M. said:


> Thanks. Any idea where to find a detail that shows u305 with full 5.5 insulation? All I've seen have 3 1/2" or 5 1/2" compressed to r13 which is not flying with the  plan checker.


See mtlogcabin's post.  Insulation is optional in the U305 assy.  You can add whatever batt insul you want per the general notes and 2x4 is the minimum stud size.

I like U305 because it has practically every gyp board you would ever use listed.  

Always refer to the actual UL assy, not a manufacturer's version of the assy.  The manufacturers only show you their products in the assembly. The actual UL assy will show you all the possible options.

https://iq.ulprospector.com/en/profile?e=14888


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## Kim M. (Dec 2, 2021)

redeyedfly said:


> See mtlogcabin's post.  Insulation is optional in the U305 assy.  You can add whatever batt insul you want per the general notes and 2x4 is the minimum stud size.
> 
> I like U305 because it has practically every gyp board you would ever use listed.
> 
> ...


This link was very helpful, and I see the info as far as the 2x4 being a minimum and the insulation being able to be added. I run into a roadblock with the exterior finishes.  When I look at  BXUV.GuideInfo - Fire-resistance Ratings - ANSI/UL 263, I'm not finding any options to add to add exterior materials,  (see below).  I need the wall to have a moisture barrier, then thin cut stone, hardcoat stucco and some fiber cement lap siding. How do I address this using u 305? Or is there another design I should consider?  

*10. Exterior Walls*
The fire-resistive designs and UL-certified materials for walls and partitions are investigated to UL 263, which addresses fire-resistive requirements only with the understanding that their use is intended for interior applications. Where an exterior application of a UL-certified wall or partition design is desired, the local building code and Authority Having Jurisdiction should be consulted to ensure compliance with other code requirements applicable to exterior walls.


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## redeyedfly (Dec 2, 2021)

I've never had a BO question it.  I only consider it an issue if the cladding is part of the rated assembly.  If you meet the IBC cladding requirements it should not be a problem.


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