Specification No. 920-4 (4-ply) - Premium Tar-Glas
  Specification No. 420-4 (4-ply) - Standard Tar-Glas
Non-nailable decks or approved roof insulation:

Premium Coal Tar Impregnated Glass Fiber Felt for Spec 920-4

Standard Coal Tar Impregnated Glass Fiber Felt for Spec 420-4

Aggregate Surface

Non-nailable decks: Precast Concrete, Poured Concrete, Metal and Structural Wood Fiber (see NOTE 1)

Roof Insulations: See Insulation Sections: Built Up Roofing: Insulation

Slope requirements: 1/4" per foot (2%) maximum. See Slopes for possible slope restrictions or variations.
Materials per 100 sq. ft. (9.3mē) of roof area *Approximate Weights
Tarred Glas (Mopped in Pitch) 4 plies 40 lbs. (27.2kg)
Premium Tar-Glas (Mopped in Pitch) 4 plies 46 lbs. (20.9kg)
Roofing Pitch (4 moppings @ not less than 20 lbs. (9.1kg) each) 80 lbs. (36.3 kg) (min)
Top Pour (not less than 70 lbs.) (31.8kg) 70 lbs. (31.8kg)
Surfacing: Gravel   400 lbs. (181kg)
*Actual weights used will vary depending on many job site factors; therefore, Koppers does not assume responsibility for actual weights applied.

Application of Membrane
  1. Mop deck (or insulation . as applicable) completely with coal tar.
  2. Apply over the entire surface, (4) plies of Koppers Tar-Glas (Premium Tar-Glas for Spec. 920-4 or Standard Tar-Glas for Spec. 420-4), lapping plies twenty-seven and one-half (27-1/2) inches (699mm), so that in no place shall felt touch felt.
  3. On short run slopes in excess of one-quarter (1/4) inch per foot (2%), such as on crickets and saddles, and when the deck permits nailing, nail along back of upper edge of each sheet six (6) inches (152mm) from the back edge on twenty-four (24) inch (610mm) centers. Where deck does not permit nailing, nailing strips are required and each sheet must be nailed along back of upper edge at spacings to assure penetration of nailers.
  4. For enveloping procedures, see section regarding . Bitumen Control. .
  5. Pour over the entire surface of the roofing membrane, a continuous coating of coal tar, and, while hot, apply not less than four hundred (400) pounds (181kg) of gravel or three hundred (300) pounds (136kg) of slag for each one hundred (100) square feet (9.3m2)
    NOTE 1:
    On structural wood fiber decks, board insulation is required, and the first ply of the roofing membrane must be a Koppers non-perforated coated base sheet set in a solid mopping of steep asphalt. If two layers of insulation are used see NOTE III in the Deck Requirements and Roofing Specification Guide.
    NOTE 2:
    3 ply application specifications (No. 420-3 and 495-3) are available from your Koppers Representative.


 Return to Application Considerations and Specifications