Thursday, July 19, 2012

Green Roofs and Hurricanes, Wind Events and Tropical Storms

Hurricane and cyclone season is here.  The month of May marks the time each year when the National Hurricane Center says potential for tropical storms begin.  We are in the middle of July and have already had numerous tropical storms hit here in Florida.  Though wind damage was not as bad as it could have been, flooding was severe in certain areas.

But we are moving into the heart of summer and with warmer waters, one should expect an increase in tropical storms and cyclones soon.

Residents of areas prone to cyclones are familiar with the damage high velocity winds can do to buildings and especially roofs.  It is important that any green roof design installed on structures in Florida or other tropical climates subject to storms be fully tested with hurricane simulators for resistance to blow off and destruction.

Hurricane testing of green roofs is important for several reasons.

University of Florida Hurricane Simulator

First is the health, safety and welfare of people.  Placing any object on a roof not permanently attached is a violation of many building codes and can cause serious damage when blown off in high winds.

Parapets and other wind breaks around flat roofs may help up to certain speeds but trays, mats, pots or containers must be permanently attached.  This means each pot and each tray.  Otherwise liability in negligence may exist (consult your construction tort attorney) if the system blows off and causes damage.

Hurricane simulation testing is not the same as wind tunnel testing.  Be sure your green roof system has been tested out-doors on an engineer designed roof testing system with a wind turbine process.  Wind tunnel testing may not offer sufficient design support to protect against negligence (again consult your attorney).

Secondly, a good designer wants to know if the plants they are specifying will hold up in hurricane conditions.

Many plants may loose upper leaves but their root systems stay in place and they regrow quickly.  There are many good reference articles available on the when concerning right plant selection for hurricane prone areas.

I like built in place systems for hurricane prone areas.  Unless modular systems are permanently attached - I suggest permanently attaching each tray with adhesive - and a blow off occurs with resulting damage - then the issue of tort liability potentially arises (consult your attorney).  In our litigation prone society it is prudent to always hurricane test green roof systems before specifying and installing in those areas possibly subject to tropical storms.

Cyclone winds flowing across a flat roof create uplift like a vacuum and can pull shingles or other roofing material up into the air.  Roof accessories such as pipes, vents, skylights, green roofs, planters and HVAC units are also subject to the wind stresses and may become problematic.

Green roof hurricane preparedness involves several fairly simple and straightforward steps, including;
  • Make sure there are no loose objects on the green roof, such as pruning shears, hand trowels or other hand tools
  • Check to see if there are any dead plants or large pieces of fallen plant material and remove
  • Inspect the green roof system for integrity
    • If the green roof system is a tray system, make sure the trays and not damaged by UV degradation and ensure no loose edges are exposed
    • If the tray system is a mat system, check for loose mat edges
  • Review the underside decking in the attic for any water stains or other indicators or leaks
  • Check to make sure the underlying structure is holding its form and nto sagging fromt he weight of the green roof
  • Replace organic material and soil amendments as needed
  • Look for adjacent dead tree branches or limbs that could fall on the green roof and have removed
  • Make sure there are no mechanical system repair parts left on the roof from maintenance - you'd be surprised at what gets left on a roof - look for loose screws especially!
Well established green roof plants create turbulence across a roof surface, and may act to reduce uplift in some instances.

We'll be posting several articles over the next few weeks dealing with the  topic of winds and green roof plants, with a focus on cyclones, hurricanes and tropical storms.

1 comment:

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