Green Roofs and Hurricanes - Miami Dade Uplift Testing Issues - Sustainable Green Roofs

Welcome Back!  I've been busy putting my thoughts down on Tom Cooper's comments.  We addressed the first couple - about Sustainability and Irrigation in the last post and I thought I could whip out an answer to his Miami-Dade Uplift Requirement comment.  However as I started writing I quickly realized I am a Green Roof Systems Expert and not a Roofing Expert or not even a licensed roofer.

I always work with a licensed roofer on the install.  I've said it before and I'll quickly say it again - as a lawyer by graduate education I am always 'Tort Aware'!  Florida law is very specific about roofing requirements and contractors and who can do what.  Research the law and code requirements and your life will always be easier.


So I called Robert Solomon.  I've known Robert for quite some time now - he is the go to guy if you have a question about sustainable roofs in Florida (the non-vegetated type - white TPO et al).  Robert is all for breaking our dependence on foreign oil - and doing so quickly by eliminating asphalt roof use and design.

Robert writes a blog called Wiki Roof and can I ever say it is enlightening.  He has served multiple times on the Florida Governor's Green and Sustainable School Competition Judging Board and well I could go on but won't.

So feeling a little uncomfortable about commenting on roofing issues that impact green roofing but are actually more of a roofing issue, I emailed Mr. Solomon and asked him to think about Tom Cooper's comments and offer his advice.

Mr. Solomon graciously agreed, even though he is a busy person.  Thanks Robert!

My thoughts in this post article are in black, Tom Cooper's questions and comments are in red, and Mr. Solomon's comments are in dark blue.

Again, Mr. Cooper is CEO of Green Roof Solutions, Inc. in Chicago

Robert's Blog Wiki Roof is a must Read - click here for the blog in a new window - but finish this post first.

OK - Tom's question -

I do have a question for you. How do you propose the State of Florida address codes for the:

1.) Components of green roofing under wind uplift requires such as those for Dade County?

My comment first - then Robert's thoughts.  Two things enter my mind when I think of tropical winds and vegetated roofs.

First a quick background.  I grew up in Hialeah (great black beans, yellow rice and yucca) and we had several direct hits from hurricanes in the 1960's.  I've seen cars turned over, huge trees ripped out of the ground, our above ground kids pool lifted up out of our backyard and dumped in the neighbors and more.  Dad boarded up all the windows with plywood but as a child I still remember the wind sounding like a train roaring across the top of our roof.  

So I am biased.  But if a hurricane can pick up a car and flip it, then a hurricane can pick up anything loose on a roof and send it missile like through the air.  That is why I would never plant a tree on a roof in Florida or put a birdbath on a roof in Florida.

But for those who have never directly experienced the terror of unleashed 120 mph winds, I suggest the State of Florida and Miami Dade uplift codes are there for a purpose.  That purpose is to make sure anything manufactured for a roof - that could become a projectile someday - stay on the roof.

As a tort aware lawyer I also suggest that any product placed on a roof without Miami Dade approval or State of Florida approval would be good reason for a lawsuit if that product ends up damaging the fenestration of something else on or in an adjacent structure.

My thoughts are - I get really aggravated with the process but it is there for a purpose, and should include all green roof materials.

Now for Robert's thoughts... 

The actual "ROOF" , or waterproofing element, is accepted by Miami-Dade in many applications.  The most reasonable, cost effective, and environmentally acceptable material for vegetative roof systems is without question, Thermoplastic Polyolefin (TPO), as it contains no oil, no plasticizers, and would not contribute additional nitrogen or phosphorous into water supplies.

I suggest a major manufacturer (Firestone, GAF, Carlisle, Manville, etc.) that is distributed by local supply houses, and stay away from "boutique" manufacturers.  In this way, material is readily available, and you will not find yourself in a "proprietary" scenario that eliminates competition, and drastically increases cost.

For the sake of illustration, I will choose Firestone as our representative manufacturer, and a few Miami-Dade approvals over various roof deck types.  Structural issues regarding design load will greatly impact your options.  Of course, structural concrete, or post tensioned concrete will be your safest route.

target=new* Miami Dade Building Code General Roof

Miami Dade Concrete Deck NOA Requirements Click Here

Miami Dade Wooden Deck NOA Requirements Click Here

Miami Dade Steel Deck NOA Requirements Click Here

FM-I90 wind uplift, and in some cases FM-120 can be achieved.


2.) DO we design part of the roof to blow off as typical landscaping would?  

My thoughts - No.  Under maximum wind load the plants and soils will probably be blown off.  However all other system components must be designed to stay on the roof per code.  Again - I speak from a tort perspective.  I can't imagine having to defend a negligence lawsuit where loose trays or pavers were laid just on the roof.  Not that it is not being done - I just can't imagine defending a client who has designed or installed a part of the roof to blow off in a negligence case - and I can't imagine an insurance company providing product liability insurance for such a system (although I am sure they are out there).

However, plants and soil will probably come off and there is no cost-effective way to completely prevent this.

Whereas Robert says...

NO.  Assuming we are discussing the actual "roof" or waterproofing element.  In this case, TPO, or even liquid applied coating/mesh systems (this can be very humbling if you are not infinitely knowledgeable regarding coatings and reinforcement).  I would far prefer the actual roofing membrane system (TPO).  There are cases when "fully adhered" will be best, and of course, we would use low VOC approved adhesives supplied by the membrane manufacturer.

3.) Yet fix all retention articles to the structure such as edging. 

Robert suggests -

Sheet metal components are no different with vegetative systems, than they are with standard systems, but they must meet the ANSI/SPRI ES-1 Wind Design Standard.  This would include perimeter edge (drip edge), parapet wall coping, gutters, etc.

 My thoughts are - 

In Florida I don't like vertical penetrations through a roof because sooner or later, in under the harsh conditions here, a leak may develop.

But there is the code issue and I agree with Robert - the roof's retention articles should be secure enough to meet code - it would be grossly negligent to, here in Florida or anywhere a tropical storm could impact a green roof, not secure any component of a green roof per uplift requirements.

Soil and Plants are the exception.  I'd note that all soils must be given design consideration to ensure the particles are not gravel like or large enough to harm or do damage.  Plants the same way.  Though highly unlikely, a thorny blackberry brier grown on a roof as a green roof plant would expose the installer to liability for negligence if ripped off the roof in a storm and injured someone below.

4.) Ballast pavers for patios and perhaps root barriers?

 Robert's insight -  (And I'll take the liberty here to suggest Tom's reference to ballast is different than Robert's idea of ballast (( a roofer considers ballast to be gravel or stones placed over asphalt to hold down the asphalt)).  Ballast can be lifted off a roof like shotgun pellets during a hurricane.

Robert - 

I'm somewhat confused why you would require ballast.  The ballast itself can become airborne with devastating results.  It would seem to me that root barriers, or mats, would always be incorporated, regardless of deck type.

I agree with Robert - all components of a vegetated roofing system in Florida must be secured, including the root barrier, mats, trays, etc...

Lots of issues here - for instance you could glue the components down - but what about VOC's?

Cost shoots up with more attachment requirements - but what about good old American Ingenuity?

Would enjoy this discussion.

More of Robert's insight (I paid him to flatter me...)

Height, width, and length of the structure are (of course) determining factors when designing roof systems.  I can easily illustrate, or design a  proper "roof" system, and keep the structure watertight.  But since Mr. Songer is pioneering the attachment of vegetative systems, cannot say with absolute certainty, how the root barrier or mat (hopefully, retaining the root system) would be fastened.

Keeping in mind, our primary roof deck type to be structural concrete, and the wind uplift characteristics of the mat and root barrier would be our most critical component.  Please keep in mind the roof meets wind uplift requirement, thus creating a foundation for additional components (and water) , which affect live load.  A moment ago, I spoke to Firestone, and they will be more than happy to assist in computations and design, which I feel to be a fine gesture on their part.  Always keeping in mind, Firestone is the "Guarantor", and vegetative assembly must be acceptable to them.

I can make these claims, as I am a state certified roofing contractor, licensed roofing consultant, environmentalist, and spent 37 years in the roofing discipline at the highest level.

I hope my comments have at least been marginally informative, and would be very pleased if I've somehow advanced the topic.  

My final, wrap up comments.

I am genuinely suspicious of regulators.  I think the market should ultimately and can regulate itself. 

However having witnessed the brute strength of hurricane force winds time again, I would probably have to say that Miami Dade's requirements have a good measure of validity.  But that having been said, a regulation should never be accepted carte blanche!

Again, with American Ingenuity we can develop systems that satisfy the intent of regulations.  Take for example parapet walls.  There is considerable recent research showing how certain height parapet walls can reduce wind uplift by magnitudes.

So maybe one answer to avoiding permanent attachment of green roof system components is a parapet wall sufficient to protect.  I'm sure with time this possibility will be researched, tested and utilized.

Another facet to consider is the turbulence green roof plants can cause the over blowing wind, decreasing uplift shear.  I've witnessed this phenomena personally during Tropical Storm Fay.  Wind gusts would grab at shingles but the irregular surface of the plants seemed to break the lift vacuum.  I'm sure more research will tell us if textures can break uplift.

We are an evolving industry nation-wide but especially here in Florida!  I always refer to the 5 H's - High Heat (140 F leaf surface temperature on a regular basis), High Humidity (that afternoon sprinkle turns to steam like a pressure cooker), Hard Freezes and Frosts, Hurricanes, Hard Desiccating Winds and more....  Solutions are being developed daily.

It is interest and comments like those Tom Cooper has set forth that will help us make the green roof industry in Florida profitable and effective.

Tom - we'd love to hear your thoughts and comments.

Happy Green Roofing!  

As always - email us with your questions. kevin@metroverde.com