Green Roofs and Hurricanes, Design for Wind and Rain

Hurricane season is upon us.  Importantly, Florida Green Roofs should have adequate design consideration provided for keeping plants on the roof during storm events.

One of my favorite design tools is use of three dimensional geo synthetic fabrics to allow a plant's root architecture to form a strong bond between plant and roofing system.

The above video shows a green roof panel containing a three dimensional weave and soil media along with some organic compost.  The panel is being pressure washed to remove the soil media.

As the video shows, the green roof soil media is not easily removed.  Three dimensional weaving provides excellent wind and water resistance and can be very helpful for sloped green roof stabilization or any green roof subject to extreme weather conditions.

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.

Green Roofs & Cyclones - A Continuous Vegetated Assemble Design for Hurricane Impacted Areas

The 2012 Hurricane season will be upon us in a couple months, if not sooner.  Cyclones, hurricanes and tornadoes are all important factors to consider when designing a green roof.

Of course no amount of design and construction can preclude extremely high wind damage as we have recently witnessed across the midwestern United States.

Continuous Vegetated Assembly Drawing for Green Roofs in High Wind Velocity Areas

However, common sense tells us that any object on a roof should be permanently fastened in some manner if the building is subject to high velocity winds.  Even then, these extra-velocity winds can rip up heavy items and toss them to the roadway below.

However, though it may be impossible to prevent all wind damage, use of three dimensional geogrid and tri-dimensional non-woven and woven fabrics can provide a platform for green roof plants to anchor themselves in a permanent fashion to the roof.

Choosing the correct bi or tri-axial geogrid for your green roof design can be confusing.  Attaching the geogrid to your roofing system can be even more perplexing.

After years of field trials with a number of popular fabrics, I have seen some work well while others disintegrated under the stress of sunlight or wind or both.

Most are a PPE or other petro-synthetic compound.  Some, more sustainable than the plastics, such as jute and hemp work well under certain conditions yet fail quickly under other environmental factors.

Importantly though, a properly chosen geogrid can not only form the basis for a cyclone resilient roof, but can allow the green roof designer to build continuous vegetated assemblies on slopes.  In fact, I have seen some innovative living walls based on these geogrid fabrics.

The sketch provided here is a depiction of a flat roof continuous vegetated assembly system for hurricane influenced geographic areas.  The three dimensional geogrid can be permanently attached to the roof through a variety of either mechanical of chemical bonding mechanisms.

Keeping plants on a roof is important.  Parapets help.  Good prudence also calls for permanent fastening systems too.

Hurricane Season, Green Roof Design and Negligence

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.

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.

With hurricane season here, now is the time to educate ourselves about proper design and installations for green roofs in cyclone prone areas.

Green Roofs and Hurricanes

The Eastern Pacific Hurricane season begins in about two weeks, on May 15th and the Atlantic Hurricane season follows shortly thereafter.

Hurricane design is an important consideration for green roofs.  If a green roof is to be built in areas subject to hurricane or cyclone impacts then a few simple guidelines will help make the design more resilient against wind and storm damage.

At a minimum, we recommend;

1. No large trees on a roof.
1. Small shrubs and small trees may be used successfully depending upon the final design.  This may seem like a common-sense guideline but people try to put all types of tall, large trees on patio or garden roofs.  During a 130 mph cyclone, the tree will probably be blown over and may cause damage from the fall against the structure or to the street below.  It may also become airborne if the winds are strong enough.
2. Anything and everything on a roof should be permanently attached.  
1. Walkways should be constructed from a permanently attached TPO, EDPM or other mat and permanently affixed to the roof.
2. No loose chairs, tables or other items should be present.  If you wish to have a chair and table stay on a roof during a cyclone, they must be permanently attached.
3. All green roof components must be permanently attached to the structure.
4. Any trays, plastics, pots, containers or other green roof components must be permanently attached to the building structure.  Florida Building Code does not allow for loose items to be installed on a roof - they must be attached.
5. Green Roof Irrigation components must be permanently attached to the roof.
3. Make sure all tools and gardening utensils are picked up and put away.
1. It is very easy to forget the pair of shears, scissors or pliers on a roof.  Remember what you were using and where you liad them.
4. Plant selection should be focused on those species that have historically survived cyclone and hurricane incidents.  There are several good books available at most bookstores here in Florida on proper cyclone resistent landscaping and many resources on the web, such as the Brevard County Landscaping Guide for Hurricane Areas.
5. Check on the NOAA National Hurricane Center website daily.  The NHC webpage is a wonderful resource, full of links to climatic data.

Always use a green roof design or green roof system already proven in actual field trials with hurricane simulation testing.  Watching a green roof blow off during a storm is an avoidable event.  Due diligence upfront and preparedness is important for green roofs in hurricane prone and cyclone impacted areas.

Green Roofs, Florida and Hurricane Wind Force Testing

Green roofs in Florida must be designed to withstand tropical storms and hurricane force winds.

Hurricane winds speeds can easily reach 130 mph.

Loose edges or other exposed corners, trays on a Florida green roof can be grabbed by the winds and flung across and off the building.

The photo below depicts the hurricane simulator at the University of Florida.  The system will be conducting a hurricane simulation test on a MetroVerde green roof panel.

Hurricane Simulator at UF - Testing MetroVerde Green Roof Panel

The tested panel is a mat based system.

We will be posting results soon.

As always, feel free to email us with your Green Roof or Green Roof Design questions.

Happy Green Roofing!

Kevin.