1、Printed in U.S.A. Copyright Gypsum Association 2005. All rights reserved. GYPSUM ASSOCIATION 810 FIRST STREET NE, #510 WASHINGTON, DC 20002 GYPSUM BOARD ROOF UNDERLAYMENT SYSTEMS (GA-276-05) Effectively preventing fire from penetrating through the roof eliminates updrafts, both limiting the potentia
2、l for fire spreading on the roof surface and reducing the generation of flying brands. Adding gypsum board to roof systems also inhibits the spread of fire within an attic while protecting against burning brands from fires originating in another unit or from burning vegetation. The use of 5/8in. (15
3、.9 mm) thick type X gypsum board as an underlayment for combustible roofs is the preferred alternate to roof parapets separating dwelling units in multi-family construction. This method of fire protection is de-signed to resist the spread of fire from unit to unit over the top of party walls. To ach
4、ieve this fire protection alternative, the Gypsum Association has developed the following three recom-mended methods of installation. Although the model codes (IBC, BOCA, SBCCI, fit edge joints snugly together without forcing. End and edge joints need not be taped. Protect gypsum board against ex-po
5、sure to inclement weather during installation and until the roof membrane installation is complete. Attach combustible roof sheathing through the gypsum board to the roof framing with sheathing joints offset from the gypsum board joints. Increase fastener length by 5/8in. (16 mm) to account for the
6、thickness of the gypsum board. Apply the roof membrane as specified by the manufacturer. This full roof underlayment method offers a number of advantages over the partial roof underlayment and ledger strip methods. First, it provides the greatest degree of fire protection. Second, it is the least co
7、mplicated of the three methods to install, and finally, it is generally the most cost effective when the additional labor costs incurred by the other methods are considered. GA-276-05 Page 2 PARTIAL ROOF UNDERLAYMENT Install 5/8in. (15.9 mm) type X gypsum board under the combustible roof sheathing o
8、n both sides of the party wall for not less than the minimum distance required by the code. Apply the gypsum board on top of roof framing, with the paper-bound edge perpendicular to the framing, prior to the installation of combustible roof sheathing. All gypsum board ends should occur over and be s
9、upported by the roof framing. Nail the gypsum board to each framing member with at least two minimum 4d common nails, or 13/8in. (35 mm) gypsum wallboard nails. Butt end joints loosely; fit edge joints snugly together without forcing. End and edge joints need not be taped. Protect gypsum board again
10、st exposure to inclement weather during installation and until the roof membrane installation is complete. Shim all remaining trusses and rafters as necessary to provide a straight and uniform base for the attachment of the combustible roof sheathing. Attach roof sheathing through the gypsum board t
11、o the roof framing with sheathing joints offset from the gyp-sum board joints. Increase fastener length by 5/8in. (16 mm) to account for the thickness of the gypsum board and shims. Apply the roof membrane as specified by the manufacturer. This second method offers easy attachment of the gyp-sum boa
12、rd to the roof framing, compared to the ledger strip method. It does however require shimming the roof framing that is not protected with the gypsum board. As an alternate to shimming, two different sizes of rafters or trusses may be used. In typical multi-family housing where individual units are r
13、elatively narrow, it is generally more economical to cover the entire roof. Area Separation WallCombustible RoofSheathingRoof CoveringRoof Framing5/8“ (15.9 mm) Wood Shim5/8“ (15.9 mm) Type XGypsum BoardCOMPARISON OF BURN-THROUGH TIMES WHEN GYPSUM BOARD IS ADDED Tests have been conducted to compare
14、the burn-through times of roofs using gypsum board underlayment to those without gypsum board underlayment. These tests demonstrate the dramatic increase in the amount of time required to burn through a roof into the attic space when gypsum board underlayment is used in conjunction with common roof
15、deck materials. The burning brand test por-tion of Methods of Fire Tests of Roof Coverings (ASTM E 108 & NFPA 256), one of the standard tests used to evalu-ate roof covering materials, was used in the Gypsum Association test program. The Class A brand was used in the test to provide the most severe
16、test conditions. The re-sults of this comparative testing are summarized in Table 1. Dramatic results were also shown on burn-through of the roof from a fire originating in the attic space when gypsum board underlayment was used. Table 1 Roof Covering Felt Roof Sheathing Sub-Sheathing Burn-Through T
17、ime Test Stopped Cedar Shakes Asphalt 1 x 8 None 7:20 7:45 Cedar Shakes Asphalt 1 x 8 Type X Gypsum Board None 71:09 Cedar Shakes Asphalt “ Plywood None 16:45 17:09 Cedar Shakes Asphalt “ Plywood Type X Gypsum Board None 70:00 Fire Retard Cedar Shakes Asphalt 1 x 6, 10“ o.c. None 11:25 11:40 Fire Re
18、tard Cedar Shakes Asphalt 1 x 6, 10“ o.c. Type X Gypsum Board None 70:00 Asphalt Shingles None 1 x 8 None 6:20 6:40 Asphalt Shingles None 1 x 8 “ Reg Gypsum Board None 60:50 Asphalt Shingles None “ Plywood None 40:30 40:30 Asphalt Shingles None “ Plywood Type X Gypsum Board None *30:00 Built-Up Roof
19、 None “ Plywood None 17:30 17:35 Built-Up Roof None Type X Gypsum “ Plywood None 27:40 Built-Up Roof None “ Plywood Type X Gypsum Board None 67:00 Cedar Shingles None 1 x 4, 8“ o.c. None 2:55 5:10 Cedar Shingles None Type X Gypsum 1 x 4, 8“ o.c. None 72:00 Cedar Shingles None 1 x 4, 8“ o.c. Type X G
20、ypsum Board None 76:35 * Test was terminated at 30:00 because the specimen stopped burning Printed in U.S.A. Copyright Gypsum Association 2005. All rights reserved. MEMBERSHIP LIST 2005 AMERICAN GYPSUM BPB AMERICA INC. BPB CANADA INC. CGC INC. G-P GYPSUM CORPORATION LAFARGE NORTH AMERICA INC. NATIONAL GYPSUM COMPANY PABCO GYPSUM A Division of PABCO Building Products, LLC. TEMPLE-INLAND FOREST PRODUCTS CORP. UNITED STATES GYPSUM COMPANY GYPSUM ASSOCIATION 810 First Street NE, #510 Washington, DC 20002 202-289-5440 Fax: 202-289-3707 www.gypsum.org
