Report (34)The equation in the 2015 National Design Specification for Wood Construction (NDS), Chapter
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16 — Fire Design of Wood Members to determine the fire rating of the exposed wood decking
City of Tigard Community Development
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Attn: Jeff Grove
2" member.
13125 SW Hall Blvd
Reff= 1.2Rn/to.187= 1.2(1.5)/ 1= 1.8]
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Tigard, Oregon 97223
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Table 16.2.1.A, of 1.8.
(T): 503.718.2436
Section 16.2.5 — Provisions for Timber Decks places a 1/3 reduction on the effective char rate
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JeffG@Tigard-OR.gov
WWW.11-ED.corr
16 -May -2017
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Mr. Grove,
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Below is the response to your field inquiry on May 16, 2017, as relayed to me by the general
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contractor Dave Whitney of Radian Construction, regarding the fire resistance rating of the
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exposed wood decking of the second floor.
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In accordance with the 2014 Oregon Structural Specialty Code, Chapter 7 — Fire and Smoke
Protection, Section 722 — Calculated Fire Resistance, Sub -Section 722.1— General: "...The
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calculated fire resistance of exposed wood members and wood decking shall be permitted in
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accordance with Chapter 16 of ANSI / AF&PA National Design Specification for Wood
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Construction (NDS)."; as published by the American Wood Council.
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The exposed wood floor decking is calculated as shown on Sheet G102 under Fire
Calculations the floor assembly is calculated to have a fire rating of sixty (60) minutes, as
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required by Table 601— Fire Resistance Rating Requirements for Building Elements in Chapter
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6 — Types of Construction in the 2014 Oregon Structural Specialty Code for Type V-A
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construction.
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The equation in the 2015 National Design Specification for Wood Construction (NDS), Chapter
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16 — Fire Design of Wood Members to determine the fire rating of the exposed wood decking
is as follows:
3" Tongue & Groove Decking (2-5/8" actual dimension) has an effective char rate of 1.8 for a
2" member.
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Reff= 1.2Rn/to.187= 1.2(1.5)/ 1= 1.8]
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Meeting the requirements of an effective char rate for an 1 -hour rating, in accordance with
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Table 16.2.1.A, of 1.8.
Section 16.2.5 — Provisions for Timber Decks places a 1/3 reduction on the effective char rate
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for exposed wood decking. For a 2-5/8" member this reduces the fire rating to 52 minutes.
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2.625" / 2" = 1.31 1 1.31 x 60 min. = 78.6 min. 1 75 min. (67%) = 52.66 min.
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However in the technical report published by the American Wood Council regarding the UL
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testing for the 2015 NDS, the 3x6 tongue & groove decking is placed between 45 — 54 minute
fire ratings. For the purpose of our calculations the 45 minute fire rating was used; and when
coupled with the diaphragm sheathing (5 minute rating) and the flooring subfloor (10 minute
rating) the exposed wood floor assembly achieves the required 60 minute fire rating as
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shown on sheet G102 under the Fire Calculations.
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If you have any questions, please contact me at the information below.
Thank you,
Nate Carter, Architect
Eleven Engineering & Design
971.344.1919
Nate.Carter@ll-ED.com
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