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Advertising supplement provided by Duradek

Many decks have posts and columns that require proper construction and sequencing of moisture barriers to prevent water from seeping under the PVC membrane. Water may find an entry point in the post itself and get in behind the waterproof membrane. As wood posts or columns will crack and allow water to get into the subsurface, they should be covered with a moisture barrier and then finished with siding. Where the dramatic effect of a rough-hewn wood post is required, special consideration must be made for post attachment. When fastening metal rails or posts to the deck surface, all pilot holes should be filled with a sealant before screws are inserted. Curbs, knee walls, posts, and wall openings must be constructed and detailed properly to ensure the performance of the membrane. In constructing or modifying door openings, door sills should be sloped toward the deck surface for optimum drainage. In addition, the waterproof membrane should continue into and waterproof the rough door opening saddle in order to deflect any moisture intrusion.

Building authorities may require overflow drains or scupper boxes on trapped decks to provide a path for water to drain from the deck. Drains and scuppers should be sloped toward the outside, and scuppers should be inserted into the deck surface so as to prevent ponding. In general, scuppers are very difficult to detail in such a way as to make them truly impervious to wind, rain, snow, and structural deflection. ABS-shower drains are only approved for showers and are not suitable for any roof deck or multi-family building applications. Drains should be approved roof drains. PVC-coated drains or drains with a positive clamping system are suitable to allow water to drain into the building's storm water system. With PVC-coated overflow devices, the PVC decking membrane can be welded directly to the PVC-coated surface, with no caulking required.

Drying refers to any features of the building assembly that speed the drying of materials that have been exposed to moisture. Drying can be aided by the use of a rain screen wall assembly or by the venting of trapped air spaces. Proper ventilation is critical and insufficient ventilation of the deck space can lead to mold, mildew, and rot. Venting of the air space underneath decks, balconies, and walkways with a closed soffit or ceiling is especially important for adequate drying. If the underside of a roof deck, balcony or walkway has a closed soffit or ceiling, venting is required in order to reduce moisture buildup. To be effective, the vent area should be a minimum of 1/150th of the insulated ceiling area. If equal venting can’t be provided at both ends of the joist runs, then purlins should be installed above the joists in order to allow for cross ventilation.

To facilitate ventilation, some manufacturers offer deck ventilation systems that allow for venting of the roof space joists in new and retrofit construction. “These deck ventilation systems work by allowing air from the roof space to circulate up and through a type of snorkel vent which includes a perforated mesh bug screen,” says Ogilvie. “And they can be installed without altering the elevation of the deck, door openings, railings or through-wall flashing details.”

Durability refers to assemblies and materials that stand up to foot traffic, moisture, mildew, chemicals, and environmental conditions. The durability of the assembly will be affected by the quality of the waterproofing membrane, and by its overall maintenance. While two waterproofing membranes may have a similar appearance, the quality of their ingredients can give the product a price differential of up to 25 percent, and a difference in life expectancy of as much as 75 percent. Model building codes that dictate the requirements for roof and walking deck membranes should be consulted. Roof membranes, for example, are tested in accordance with nationally recognized standards, such as the American Society of Testing and Materials (ASTM) E-108 (International Codes), ULC-S107 (NBC), for Class “A”, “B” or “C” Fire Endurance Rating. PVC roof and walking deck membranes must conform to the same material standards as PVC Roofing and Waterproofing Membranes.

Any alternative material, type or method of construction can be accepted as long as it demonstrates compliance with the performance features of the applicable code. In the United States, the International Code Council Evaluation Service (ICC-ES) evaluates Roof and Walking Deck Membranes in accordance with the ICC-ES interim Criteria for Walking decks (AC39), dated March 2000.

In addition, waterproofing membrane products must be manufactured under an approved quality-control program with inspections by an inspection agency accredited by the International Accreditation Service (IAS).

Also key to the durability of a PVC membrane is to ensure that all components of the waterproofing system are compatible and will not adversely affect performance. This includes the membrane, along with any tapes, sealants, adhesives, drains, scupper boxes, flashings, or perimeter fastening devices.