Waterproof Decks FAQ

 Slope, Ponding, & Puddling

Since Duradek membranes are predominantly applied directly to structural substrates like plywood sheathing or concrete, then the structural roof deck must be designed and built to ensure positive drainage.
Duradek’s recommendation for a nominal deck slope is ¼” in 12” or 2%, which is required by some Building Codes and Roofing Associations. The roof designer, to ensure positive drainage, should consider the following: building settlement, frame shrinkage, drain locations, roof layout, overlayment weight (for Plazadek projects), structural deflection (L/720 for Tiledek projects).
Lower slopes can be considered, on existing structural roof assemblies, if adequate slope is provided to allow for positive drainage of the roof/deck area. For lower sloped decks, the membrane should be installed in the direction of the slope so as the membrane seams do not impede water flow.
On all decks, Duradek recommends the membrane be cleaned four times per year, more often if acid rain or airborne pollution is a problem in the project’s area.

What is considered “ponded water” or “inadequate slope”?
Duradek defers to Industry and Government standards when it comes to slope and ponded water clarification. The National Roofing Contractor Association (NRCA) Roofing and Waterproofing manual defines ponding water as “the excessive accumulation of water at low-lying areas on the roof.” To avoid ponding water, NRCA recommends that all roofing systems be designed and built to ensure positive drainage.


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