Vegetative Roofs: Ensuring Proper Design and Installation

By Eric J. Seaverson, P.E.  
OTHER PARTS OF THIS ARTICLEPt. 1: What are the Benefits of Vegetative Roofs?Pt. 2: Vegetative Roofs: A Look at the DisadvantagesPt. 3: Specification Tips for Extensive and Intensive Vegetative RoofsPt. 4: Vegetative Roofs: Secondary Components Include Root Barriers and Vapor RetardersPt. 5: This PagePt. 6: Vegetative Roofs: Pay Attention to Base Flashing and Penetrations

Managers also have a host of additional issues to consider in making a final decision on a roofing system and its installation.

Managers should not rely on warranties. Instead, they should focus on installation first and the warranty second.

When possible, managers should work with manufacturers that supply all system components, from the waterproofing membrane to the planting system. This strategy provides a single-source warranty, and the warranties typically include burden removal to find leak sources.

Managers need to ensure proper design and installation by engaging a design professional. Each roof is different, so managers should not rely on "boxed" systems.

Before installation of the overburden, managers should schedule a flood test of the system. Water should be at least 2 inches deep at all details. If a detail fails, the installer must retest it after repairs.

Finally, managers should consider electronic field vector monitoring (EFVM), which uses electrical charges to trace leak paths. EFVM technology is suitable for existing membrane systems with leaks, as well as for new systems. But it might not be as effective as flood testing, which backs up water against details, providing pressure that can cause improper detailing to fail. EFVM uses only a mist of water, and improper detailing might not fail until after the overburden is in place.

Vegetative roofs offer significant benefits related to sustainability that building owners and managers seek. But to ensure system longevity, managers must specify proper materials and detailing. Otherwise, the cost to repair or replace a leaking vegetative roof system dramatically reduces these sustainability benefits.

Eric J. Seaverson, P.E., is manager of restoration with StructureTec — a building-envelope consulting firm headquartered in Kalamazoo, Mich.

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  posted on 12/30/2009   Article Use Policy

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