GAF Dens-Deck Roof Board Roof Insulation

GAF Dens-Deck Roof Board Roof Insulation


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).
  • A perforated base sheet is required as the first ply when hot mopping over Dens-Deck .
  • 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™.
  • Ensure proper torching technique. Limit the heat to the Dens-Deck substrate. Maintain a majority of the torch flame directly on the roll.
  • Use flat insulation plates.
  • 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.
  • 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.
  • 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.
  • In accordance with approved shop drawings, FM-approved fasteners shall be installed with plates through the Dens-Deck . flush with the surface.
  • 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.
  • Edge joints should be located on, and parallel to, deck ribs. End joints of adjacent lengths of Dens-Deck should be staggered.
  • The securement of the roof system must be enhanced at the building corners and perimeter per FM.
  • 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.
  • Dens-Deck shall be installed with ends and edges butted tightly.
  • Dens-Deck is manufactured to conform to ASTM C1177.
  • Product Specifications (Nominal)

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