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Vegetative Roof, FM Global, and Electric Field Vector Mapping

Picture of jlane jlane 8/9/11 7:07 AM

Division 07 Product Applications Specifications testing

So your project has a vegetative roof. Will it be insured
under Factory Mutual? If so did you know you will need to comply with FM 1-35.   Do not get confused and think this has to do
with wind uplift.   FM 1-35 provides
general guidelines for green roof systems.

Here is the link to download the free data sheets produced
by FM Global.  You must register first: http://www.fmglobal.com/fmglobalregistration/

Here are some things we see on vegetative green roof
projects that are not known, missed, or misunderstood for vegetative roofs.

  • Including
    the Electric Field Vector Mapping (EFVM) with the vegetative roof should be
    enough to comply with FM right?
    • Sure including EFVM is a great on detecting a leak
      early before there is a major issue but the EFVM is not even mentioned in
      FM 1-35.   FM 1-35 states you need
      to perform a flood test prior to installing anything above the
      membrane.  The test includes a
      standing water leak test of the entire vegetative roof with no less than
      2 inches of water, blocking all scuppers and downspouts for 24 hours.  The membrane seams are walked before
      and after the water is drained. If there are signs of leaks test cuts are
      made according to the membrane manufacturer and then patched per the membrane
      manufacturer. The flood test will be repeated until no leaks are
      detected.
  • Including and installing the EFVM is the same for
    all membrane roofing.
    • No - We have found that some manufacturers require
      that the grounding screen for the EFVM is installed under a cover board
      because their membrane will not adhere to the grounding screen.   This location is a concern because if
      you get a leak in the membrane the water can travel over the surface of
      the board and show the leak in a different location.   There are some manufacturers that include
      the grounding screen under the membrane which we believe is the correct
      location.

With the above mentioned items be
sure to:

  • Specify a flood test if your project is under FM 1-35 and understand all other requirements within FM 1-35 for the vegetative
    roof assembly. 
  • If you will include the EFVM show the correct
    location of the EFVM materials on your drawings and/or list the correct
    install location in the specification for the selected membrane. Lastly
    don't forget to ask the question "So where did you say the grounding
    screen goes".