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For a roof deck installation with PVC and metal elements, the inside back corner and outside front corner of the PVC membrane are folded and welded, not cut. Galvanized flashing with a PVC clip holds the PVC membrane in place. A roof-quality drain with clamping ring holds the PVC membrane in place and provides drainage. Colored metal flashing installed over the PVC membrane completes the waterproofing of the deck curb. This trim metal actually holds the PVC membrane in place and prevents it from curling or shrinking.

For a roof deck membrane installation featuring PVC and coated metal elements, the PVC membrane is heat-welded to a PVC-coated flashing that provides a drip edge at the outside perimeter of the deck surface. The PVC membrane is heat-welded to a PVC-coated scupper box, which provides drainage, and to a PVC-coated overflow drain that also provides drainage for trapped or curbed decks.

In roof deck membrane installations using “L” trim, a metal “L” trim is used to secure the PVC membrane to both the outside and inside edges of the deck, balcony or walkway surface, and extended up the wall by a minimum of six inches to meet some building codes. In order to ensure a waterproof installation, the PVC membrane is overlapped by the building paper and exterior finish.

In “fully wrapped” roof deck membrane installations, the PVC membrane is fully wrapped over the fascia at the exterior edge of the deck surface, and secured to the inside edge with an inverted "L" trim and gumstop sealant. To provide an extra measure of strength and a secondary sealant, butyl tape is applied at the inside edge. Alternatively, a metal "L" trim can also be used to secure the PVC membrane to the bottom of the fascia.

Specifying Roof Deck Systems

Planning goes a long way to achieve superior results and roof deck systems that are attractive and watertight. The manufacturer of the PVC membrane should have 25 years experience with the product to be used; installers should be trained and approved by manufacturer. For best results, installation and seaming plans showing joints, termination details, and material interfaces should be prepared, along with two labeled samples (8-1/2 by 11 inches) of the specified PVC membrane showing finish, pattern, color, and backing. At least one week prior to the start of installation, a pre-installation meeting should be held involving the client's representative, manufacturer's representative, contractor, and installer to discuss pedestrian deck waterproofing practices, as well as any precautions applicable to the specific project.

When it comes to the actual PVC product used for the roof deck system, there are several factors to keep in mind. It is important to specify a polyester-reinforced PVC membrane with ultra-violet resistance for fully-adhered installation with heat-welded seams and perimeter attachment. Always specify overall sheet thickness, as well as width and color.

With the exception of cap flashings, which are typically manufactured and installed by other parties, all perimeter fasteners and PVC-coated metal scuppers, overflow drains, roof drains, and trim should be provided by the membrane manufacturer. Whenever possible, the color of the perimeter fasteners should be coordinated with the membrane. Prior to installation, PVC membranes should be stored in a sheltered place without direct contact to the ground.

Model building codes are designed to ensure that buildings are structurally sound, safe from fire, free from health hazards, and accessible. In the U.S. and Canada, walkable roof deck membrane building requirements include:

• Provide class A, B or C fire protection classification. Conform to ASTM E-108 (United States); Conform to ULC-S107 (Canada)
• Conform to CAN/CGSB – 37.54 polyvinyl chloride roofing and waterproofing membrane
• Suitability of product as a walkable roof membrane. ICC evaluation services (United States); CCMC (Canada)
• Product listed by accredited quality-control provider