Friday, March 7, 2014

Coastal Green Roof Plants and Cross Section Design for Florida and the Tropics

Designing any green roof involves integration of many site physical, meteorological and biological variables, the actual creation of an ecosystem so to speak.  Coastal green roofs, those with salt impacts, are especially complicated.
Green roofs for coastal structures can present complicated issues to overcome +MetroVerde
Among the biggest variables to be considered during design are wind, salt and fire.  Salt spray will kill most landscape plants.  Around the clock steady to cyclone-strength winds can strip soil media right off and out of a green roof, rendering the system uninhabitable and possibly sandblasting an adjacent structure.  Accumulated biomass can fuel a lighting started wildfire across adjacent lots, wind carried sparks igniting a dry living roof and burning through a roof deck.

So we look for those plants that will grow despite salt, continual desiccation, fire potential and the geological components that successfully support them when designing a coastal green roof.
Coastal Green Roof succulent, seashore elder, Iva imbricata +MetroVerde 
Not only do I enjoy walking along the dunes because of the sense of beauty, the salty smell, the warm sun and sense of relaxation, but the seashore is rich in examples of vertical green, nature created green roofs and native living walls.
Coastal Green Roof plant, seashore elder, Iva imbricata +MetroVerde #greenroofs
Surprisingly, here in Florida there are some really good plants for a coastal green roof.  A walk along the dunes relaxes and teaches.  I recommend a good handbook, one such as The Smithsonian Guide to Seaside Plants of the Gulf and Atlantic Coasts or Florida's Living Beaches.
Native salt tolerant living walls by mother nature +MetroVerde , Florida living walls, Dune Daisy
Mother nature also does an awesome job creating spectacular salt and drought tolerant living walls along the shoreline.  Better than any design guide, beach strolls with camera, pencil and paper will show the designer what works and what does not.
Native salt tolerant living walls by mother nature +MetroVerde , Florida living walls, purslane
The following is a partial list I usually see growing well along the frontal portion of the dunes, in the harshest and most exposed areas.  I would use most any of these on a coastal green roof in the tropics or along the Gulf and Atlantic shoreline.
But there are many more waiting for the designer to discover themselves!

Of course wind is a big challenge.  Wind can kill those plants not possessing protected photosynthesis pathways.  It is always good to review the differences in C3, C4 and CAM pathways when designing any green roof, but absolutely crucial for a coastal green roof.

Coastal Green Roof Cross Section - Typical Design +MetroVerde copyright MetroVerde 2014

Above is a general sketch of a design approach we may take in creating a coastal free roof subject to cyclone winds.  Of course the roofing assembly will need to be fire rated Class One.  Your roofing contractor working with the roofing supplier can specify the appropriate fire rated materials.

If you use all succulents on the coastal green roof you may not need to design in buffers, yet even the juiciest succulents can burn under the right conditions.

Be sure to follow ANSI, IBC and local standards and codes when designing a coastal green roof.

Seaside green roofs can be very complicated to design, but the very best teacher is always available.  Just hop in your car and drive down to the beach.  Mother nature's creations are phenomenal!

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