Discussion: View Thread

  • 1.  Roof

    Posted 11-16-2017 11:27 AM
    How does putting plants (or using plants) on a roof effect the long term structural integrity of the roof. Would the roots cause damage to the roofing material?

    Joshua Sims S.M.ASCE
    Falls Church VA

  • 2.  RE: Roof
    Best Answer

    Posted 11-16-2017 05:21 PM
    Edited by Chad Morrison 11-20-2017 12:01 PM
    The number one concern to the integrity of the roof is water damage.  If the planters do not have proper drainage you will have way more trouble  before you need to start worrying about roots.  It is possible that the roots would be problematic near any rubber membrane (especially the seam).  Most likely the planters will have a concrete or steel base, that would be impenetrable.

    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI

  • 3.  RE: Roof

    Posted 11-17-2017 12:31 PM
    ​FM Approvals Standard 4470 "vegetative Roof Systems includes an evaluation or Root barriers used with these systems in addition to other requirements.  The standard can be reviewed at RoofNav-Login Page under reference materials TAB.  Systems meeting this standard can be found under Products - Surfacing - Material - vegetation.

    Phillip Smith P.E., M.ASCE
    FM Approvals


  • 4.  RE: Roof

    Posted 11-17-2017 12:30 PM
    It depends on the type of your flat roof... if you have a concrete roof, make sure it is grouted properly and since concrete is water friendly, you don't have be worry about plants direction unless it is a cucumber. If your roof is steel deck  and it's in contact with water that  can cause long term damage to the roof structure.

  • 5.  RE: Roof

    Posted 11-17-2017 12:31 PM
    Exposed ​roof membranes need walkway pads for access to equipment areas to avoid damage from foot traffic and tool boxes etc.
    Pavers over the roof membrane can support small planters.  Pavers on pedestals have point loads that should be taken into account from a load compression capacity.  Placing planters directly on membrane roofs most likely will void roof warrantees and lessen the roof life significantly.

    Martin Fradua P.E., F.ASCE
    Vice President
    Huntington NY

  • 6.  RE: Roof

    Posted 11-17-2017 12:31 PM
    An issue that is often left out of the green roof discussion is that plants attract insects ... like mosquitos.   Remember to budget for pest control.

    Ethan Grossman P.E., M.ASCE
    EDG Corp
    Washington DC

  • 7.  RE: Roof

    Posted 11-20-2017 10:35 AM
    Water damage is key to prevent, so make sure you design a waterproof built up roof, I would recommend Checking out EPIC Deck to reduce the need for rebar and thickness of concrete. Having a long spanning roof system can help with a sustainable design. Good luck with your Green Roof!

    EPIC Metals
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    EPIC Metals
    For more than 48 years, EPIC Metals has been practicing the Art and Science of structural deck engineering. EPIC systems enable a designer to create unique, visually open public spaces with responsible materials and unmatched acoustics.
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    Alexander Burg EIT, A.M.ASCE
    Sales Engineer/Manager
    EPIC Metals Corp
    Coral Gables FL

  • 8.  RE: Roof

    Posted 11-20-2017 10:34 AM
    Also of concern is the increasing caliper and canopy of trees and bushes over time with corresponding gravity and wind loads.  Stability considerations may require guying and attachments. to structural components.

    Robert Antonucci P.E., M.ASCE
    Antonucci & Associates
    Pelham NY

  • 9.  RE: Roof

    Posted 11-20-2017 10:35 AM
    This is a great question. Modern green roof technology has evolved significantly in the past 30 to 40 years. It took root (no pun intended) originally in Germany. In the US it has seen significant growth alongside the adoption of LEED certification for buildings as green roof can earn credits towards certification. One of the main benefits is storm water retention.

    There are extensive resources and industry guidelines on the proper and acceptable system designs. A successful installation involves input from many professionals on the design and construction team; Architecture, Structural and Civil Engineering, Landscape Architecture, Roofing Consultant, to name a few. For the Structural Engineer, accommodating the structural loading is of primary importance. The potential damage to the structure is taken care off and has been addressed  by the advancement in material design (planters, media, etc) and the roofing system design (waterproofing as opposed to the structure itself). For the Civil Engineer, the water retention capacity is of primary concern and is an integral part in the overall site planning.

    Check out some of the resources online for a good overview of modern system designs, characteristics, and benefits.

    Green Roofs for Healthier Cities (GRHC) The governing body for green roof industry standards in North America
    Greenroofs.com Network An industry's resource and online information portal
    National Roofing Contractors Association A trade association and a leading authority in the roofing industry for information, education, technology and advocacy.

    Gaby Sader P.E., C.Eng, M.ASCE
    N Bethesda MD