Plans (106) 6'667015= Uiifl
• Dan Nelson /117947,7? A/., A9zrc..
From: Josh Cabot <joshc@serapdx.com>
Sent: Monday, November 30, 2015 4:44 PM
To: Dan Nelson
Cc: Mark VanDomelen
Subject: Burnham &Ash: Fire Rating of Exterior Shear Walls from Inside Only
Attachments: 2015-11.30 Burnham &Ash - Shear Walls to be Fire-Rated from Inside_opt.pdf
Dan,
Hope you had a nice Thanksgiving. I'm finally getting a chance to e-mail you about the wall question I had asked you
during our PreCon meeting a couple of weeks back.
We have a number of exterior shear walls where we have plywood to handle the shear, but we also have Dens Glass
(gypsum sheathing)to provide the fire rating. These two layers together create some constructability problems for us
when this kind of shear wall is run next to another exterior wall with the same kind of cladding but no shear. Basically,
the extra layer of plywood on the shear wall makes that piece of wall%z" thicker than the wall beside it,which means we
have a bump in the wall or we have to conceal it with another layer of sheet rock on the inside.
We have realized that per OSSC 705.5, when we have more than 10'-0" of fire separation distance, we only need to rate
the wall from the inside. With this in mind, I want to let you know that we'd like remove the Dens Glass from any
exterior shear wall that fits this criteria so that we can take care of this issue. Do you see an issue with this?
I have attached a set of plans showing the walls I'm talking about, and I have explained our methodology below:
For a 4-story building of Type V-A Construction:
• Exterior walls are required to be 1-hour rated.
• 705.5 Fire-resistance ratings. Exterior walls shall be fire-resistance rated in accordance with Tables 601 and 602
and this section.The required fire-resistance rating of exterior walls with a fire separation distance of greater
than 10 feet (3048 mm) shall be rated for exposure to fire from the inside.The required fire-resistance rating of
exterior walls with a fire separation distance of less than or equal to 10 feet(3048 mm) shall be rated for
exposure to fire from both sides.
• The wall still needs to be 1-hr rated, but we can use the component method for materials on fire exposed side
of wall in order to calculate a 60—min rating.
• Table 721.6.2(1) lists 5/8"Type X drywall as 40-min, and Table 721.6.2(2) lists wood studs @ 16"oc is equal to
20-min. 40+20=60=1hr from interior side.
Here is how it would affect the wall assemblies:
1
of
L5 I
tu 2"
4-4-
Y ' ;
1:. > >-‹
; .0r99/ 1° 04 20 01-MASONRY VENEER
04 20 01-VENEER TIE,SEE
STRUCTURAL
...
. I 07 25 00-WEATHER BARRIER,ALL
•.- s
v4/ SEAMS SEALED
06 16 53-5/T TYPE X EXTERIOR
. • • 4‘,, SHEATHING BOARD
• / 06 10 00-WOOD SHEATHING,SEE
; i..
/ STRUCTURAL
t f- 0 / 07 21 00-THERMAL INSULATION,MIN
, 4:71// / R21
i 09 21 16-5/&TYPE X GYPSUM
. -
..----\v. 'ry i BOARD
--->-<- ., /\r-l/ i
_ ..
On- i 09 21 16-VAPOR RETARDING PRIMER
, REMOVE THIS EXTRA LAYER OF GYPSUM
NOTES:
i SHEATHING OUT IN FRONT Of THE
1)1 HR FIRE RATED(BASED ON GA FILE NO.WP 8105)is_
--PLYWOOD WHEN EXTERIOR WALL HAS
GREATER THAN 10-0- EIRE SEPARATION
DISTANCE PER OSSC 705 5
EXT - BRICK - SHEAR / 72
REFER TO CODE COMPLIANCE SUMMARY AND PLANS FOR RATED WALL LOCATIONS ' "-
2
REMOVE THIS EXTRA LAYER OF GYPSUM
SHEATHING OUT IN FRONT OF THE
PLYWOOD WHEN EXTERIOR WALL HAS
GREATER THAN 1O'-O"FIRE SEPARATION
DISTANCE PER OSSC 705 5
cn
' -t
07 4646-FIBER CEMENT SIDING
.1>-->_< ';
0610 00-112"WOOD FURRING,
FIRE/PRESSURE TREATED
',. 07 2500-WEATHER BARRIER,AU.
• �` N SEAMS SEALED
1- ,0 "'0616 53-518'TYPE X EXTERIOR
I sh_ SHEATHING BOARD
P• _f06 10 00-WOOD SHEATHING,SEE
STRUCTURAL
1 a1. ` 07 2100•THERMAL INSULATION,MIN
IN:t R21
09 21 16-518`TYPE X GYPSUM
7 r BOARD
09 21 16-VAPOR RETARDING PRIMER
1�
., 09 21 16-RESILIANT CHANNEL AT
`i■r► t ALTERNATE TYPE ONLY
NOTES:
1)1 HR FIRE RATED(BASED ON GA FILE NO.WP 8103)
EXT - FIBER CEMENT PANEL - SHEAR cm]
ALTERNATE TYPE - RESILIENT CHANNEL
REFER TO CODE COMPLIANCE SUMMARY AND PLANS FOR RATED WALL LOCATIONS
If this all sounds good to you, we can reissue you the pertinent sheets that will show updated wall types for these shear
walls with plywood only and no Dens Glass.
Thanks,
Josh Cabot. LEED AP r,+u-c
d: 5031105 7898
o: 503 4,15 78.72
SERA
sustainable design for the built environment
sera pdx.com
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