GAF -Dens-Deck® Roof Board

Manufacturer G-P Gypsum Corporation 133 Peachtree Street, N.E. Atlanta, GA 30303 Technical Hotline: 1 -800-225-6119 (8-7 ET) Description Dens-Deck ® roof board is an exceptional fire barrier, thermal barrier and recovery board used in various commercial roofing systems. The patented Dens-Deck ®...

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Dens-Deck® Roof Board


G-P Gypsum Corporation
133 Peachtree Street, N.E.
Atlanta, GA 30303
Technical Hotline: 1 -800-225-6119 (8-7 ET)


Dens-Deck® roof board is an exceptional fire barrier, thermal barrier and recovery board used in various commercial roofing systems. The patented Dens-Deck® design employs glass mat facings front and back that are embedded into a water-resistant gypsum core, providing excellent fire resistance, moisture resistance and wind uplift properties. The unique construction of Dens-Deck® provides superior flute spanning that stiffens and provides increased foot traffic resistance to the roof deck. Additionally, Dens-Deck® has been shown to withstand delamination, deterioration, warping and job-site damage more effectively than other roofing membrane substrates such as paper-faced gypsum board, fiberboard and perlite insulation.

Primary Uses

Roof system manufacturers and designers have found Dens-Deck® roof board to be compatible with many types of roofing systems, including: built-up, modified bitumen, single ply, metal systems, wood shingle and shake, tile, slate, recover board, as well as an overlayment protection board for polyisocyanurate and polystyrene insulation. Dens-Deck® can also be used as a form board for poured gypsum concrete deck in roof applications as well as a substrate for spray foam roofing systems. 1/2" and 5/8" Dens-Deck® may also be used in vertical applications as a backer board or liner for the roof side of parapet walls.

Some membrane manufacturers have hot mop asphalt or torch applications directly to Dens-Deck® without using a primer or base sheet. Refer to specific membrane system application instructions. System manufacturers and designers have found Dens-Deck® to be compatible with bonding adhesives for fully-adhered single-ply membrane applications.

Dens-Deck’s exceptional moisture resistance and low R-value make it the preferred substrate for vapor retarders.

An excellent fire barrier, Dens-Deck® features a noncombustible core and inorganic surface that offers greater fire protection than other conventional commercial roofing ­products when applied over combustible roof decks and steel decks. Dens-Deck® is FM tested and approved as the only 1/2" gypsum product to meet the calorimeter requirements for conventionally insulated decks. Tested in accordance with ASTM E 84, its surface burning characteristics are Flame Spread-0 and Smoke Developed-0. 5/8" Dens-Deck® can replace any generic type X gypsum board in any roof assembly in the UL Fire Resistance Directory under the prefix “P”.


Dens-Deck® is designed to act with a properly designed roof system. The actual use of Dens-Deck® roof board as a roofing component is the responsibility of the roofing system’s designing authority.

Conditions beyond the control of G-P Gypsum such as weather conditions, dew, application temperatures and techniques may cause adverse effects with adhered roofing systems. Always consult the roofing system manufacturer’s specific instructions for applying the various roofing types to Dens-Deck® roof board.

Panels must be kept dry before, during and after installation. Apply only as much Dens-Deck® as can be covered by a roof membrane system in the same day.

Accumulation of water due to leaks or condensation in or on Dens-Deck® roof board must be avoided during construction and after construction. Avoid over-use of non-vented direct-fired heaters during winter months. Avoid application of Dens-Deck® during rains, heavy fogs and other conditions that may deposit moisture on the surface.

When applying solvent-based adhesives or primers, allow sufficient time for the solvent to flash off to avoid damage to roofing components.

Maximum flute span is 2-5/8" for 1/4" Dens-Deck®; 5" for 1/2" Dens-Deck®; and 8" for 5/8" Dens-Deck® Fireguard® Type X. 1/4" Dens-Deck® is not recommended for vertical parapet applications.

Hot Mopping over Dens-Deck®:

  1. For mopping applications, use asphalt heated to a maximum application temperature of 425°F (Type III or IV asphalt).
  2. A perforated base sheet is required as the first ply when hot mopping over Dens-Deck®.
  3. Full mopping of fully asphalt coated felts or impermeable base sheets such as modified bitumen is not recommended.

Torch applied directly to Dens-Deck®:

  1. Prime the surface of the Dens-Deck® and allow to dry thoroughly, or use Dens-Deck® Prime.
  2. Ensure proper torching technique. Limit the heat to the Dens-Deck® substrate. Maintain a majority of the torch flame directly on the roll.
  3. Use flat insulation plates.
  4. Ensure proper pressure is applied to the membrane roll to make contact. Brooming may be required at the end of rolls.

Refer to the installation instruction for the specific roof system to be installed for additional requirements.

Technical Data

Flame spread 0, smoke developed 0, when tested in accordance with ASTM E84 or CAN/ULC-S102. Noncombustible when ­tested in accordance with ASTM E136.

Dens-Deck® Fireguard®: UL Classified when tested in accordance with ASTM E119.

1/4" Dens-Deck® has been tested by Factory Mutual for 60 psf and 90 psf wind uplift for BUR, EPDM, thermoplastics and modified bitumen roof systems. Higher wind uplift ratings have been achieved by numerous membrane manufacturers using Dens-Deck® in their FMRC-approved construction designs.


  1. Dens-Deck® should be used with fasteners specified in accordance with FM requirements and roof membrane manufacturer’s written recommendations.
  2. For wind uplift/FMRC compliance where Dens-Deck® is mechanically attached to metal decks, Dens-Deck® shall be installed to the specifics of the FMRC design assembly.
  3. For installations involving BUR, EPDM, thermoplastics and modified bitumen roof systems, call Technical Hotline at 1-800-ROOF-411 for fastener patterns of G-P’s FMRC uplift assemblies.
  4. In accordance with approved shop drawings, FM-approved fasteners shall be installed with plates through the Dens-Deck®, flush with the surface.
  5. Where Dens-Deck® is installed over combustible wood decks or insulation, all joints should be staggered. The optional separator sheet should be installed prior to Dens-Deck® installation.
  6. Edge joints should be located on, and parallel to, deck ribs. End joints of adjacent lengths of Dens-Deck® should be staggered.
  7. The securement of the roof system must be enhanced at the building corners and perimeter per FM.
  8. Adhered Systems: Insta-Foam Products, Inc.’s Insta-Stik Adhesive used with 1/4" Dens-Deck® achieved a FMRC Class I-180 according to test report 1Y7A5.AM in selected Class 1 insulated steel and concrete deck roof construction. Contact Insta-Foam Products, Inc. for details at 1-800-800-FOAM.
  9. Dens-Deck® shall be installed with ends and edges butted tightly.
  10. Dens-Deck® is manufactured to conform to ASTM C1177.

Product Specifications (Nominal)
5/8"—15.9mm Fireguard® type X
Widths4'—1220mm standard,
1/8"—3mm tolerance
Lengths8' — 2440mm standard, tolerance 1/4" — 6.4mm;
Optional: 4' — 1220mm available;
Other lengths special order
Spanning1/4" Dens-Deck® spans flute widths up to 2 5/8";
1/2" Dens-Deck® spans flute widths up to 5";
5/8" Dens-Deck® spans flutes up to 8" wide

Physical properties

Properties 1/4"
Dens-Deck® Fireguard®
Thickness, nominal inches5/16"1/2”5/8"
Width, standard4'4'4'
Length, standard8' ± 1/4"8' ± 1/4"8' ±1/4"
Weight, lbs./M sq. ft., nominal110019502500
SurfacingGlass matGlass matGlass mat
Flexural Strength, Parallel, lbs. min.44058051005
Flexural Strength, Perpendicular, lbs. min.450510051405
Flute Spanability12-5/8"5"8"
Permeance Perms2503532
R Value3.28.56.67
Coefficient of Thermal Expansion, Inches/inch/°F8.5 x 1068.5 x 1068.5 x 106
Linear Variation with Change in Moisture in/in/%RH6.25 x 1066.25 x 1066.25 x 106
Absorption, % max410.010.010.0
Compression, psi500500500
Surface Water Absorption, grams42.52.52.5 Flame Spread
Smoke Developed (ASTM E 84)000
Fire ClassificationUL Class A, ULC S-102, UL 1256, ULC S-126, UL 790, ULC S-107FMRC Class 1, UL 1256, ULC S-126, UL Class A, ULC 102, UL 790, ULC S-107FMRC Class 1, UL Classified ‘‘P’’ assemblies, UL 790, ULC S-107
FM Uplift Approvals60 and 90 psf upliftFMRC 1-60, 1-90FMRC 1-60, 1-90

1 Tested in accordance with ASTM E661 (400 lb. conc. load)
2 Tested in accordance with ASTM C355 (dry cup method)
3 Tested in accordance with ASTM C518 (heat flow meter)
4 Tested in accordance with ASTM C473
5 ASTM C 1177 minimums

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