Thursday, February 14, 2013

Florida Green Roofs and Insulation Value

Do Florida Green Roofs provide insulation or not?  Good question.  There are several different perspectives on the topic.

One current belief is that green roofs may moderate roof temperature fluctuations, leveling out daily swings with respect to heat and cold.

Some of the data we have accumulated points to green roof soil media acting as a heat sink unless the soil is completely covered with shade from plants.


We've compiled data over the last year on how an Extensive Vegetated Roof absorbed and released solar energy (heat) over a twenty four hour cycle.

The roof under study is not insulated.  It has a tongue and groove pine deck with asphalt roll paper and asphalt shingles.  The interior was non-temperature (no heat or HVAC) controlled during the study periods.

The temperature measuring points were the exposed roof tongue and groove decking surfaces and consisted of multiple point averages.  Readings were taken with an EXTECH IR AN200 Unit.

The following illustrations depict a trend we've seen over and over.

The extensive vegetated roof systems absorb solar heat slower than asphalt roofing.  The extensive vegetated roof systems also retain the heat longer and then release the absorbed solar heat slower than asphalt roofing.

The linear trendlines for the temperature curves tell an important story also.  The ambient air temperature and the decking under the non-insulated asphalt shingle roof temperature possess more significant vertical trendline movements.

The temperature swings of the decking under the green roof are much more linear - showing a narrower range in temperature swings.

The data shown here is representative of spring, summer, autumn and winter with summer and winter having the more pronounced curves.

Importantly, we believe extensive green roofs, such as the one we are studying in this case, moderate temperature swings.

The data also points to the fact that green roofs serve as a heat sink, slowly absorbing solar heat during the daylight hours then slowly releasing the heat during the evening dark periods.

During the winter, green roofs may help by moderating cold temperatures at night by releasing heat back into the structure.  However if insulation separated the green roof from the structure then little or no heat would be recaptured unless a heat capture coil or other mechanism existed.

The inverse holds true for the summer.  During the day the green roof would moderate the solar heat gain to the structure by intercepting the solar radiation and absorbing it.  However at night, the green roof would radiate heat back into the structure, slowing the cooling process.

Again, if the roofs are insulated from the green roofs then there is no real benefit from a linear trendline perspective of sink and release.

We believe maybe this data points to the need for a method of harvesting the solar heat captured in the green roof during the day.  Potential capture processes could include water or silicon filled coils or tubes interwoven into the vegetated roof or other similar mechanical systems.

Harvesting the absorbed heat would allow for a more managed use of the solar heat resource.

We do believe that the notion of green roofs working to cool buildings should be more appropriately described as a moderating effect of absorption and slow release of solar heat.

Check out the range bars on the temperature curve chart to the left.

The green roof decking temperature has a much narrower temperature range.

Data points to the fact that green roofs absorb heat and quite a bit of it.

We always welcome your comments - feel free to email us anytime here.

Green roofs offer the potential to collect and harvest solar energy.  They may not be the cooling system we sometimes represent them to be.


Wednesday, February 13, 2013

Green Roofs Fight Cancer

Green roofs and living walls can help clean the air and allow us to breath easier.

Many geographic locations acros the globe have air contaminated with Volatile Organice Compounds also known as VOCs.
Green Roof plants remove cancer causing VOCs from the air
Volatile Organic Compounds (VOCs) are chemicals created by industrial pollution and automobile engines among other processes.  VOCs are the primary cause of Urban Smog.  

They are also responsible for the formation of cancers, respiratory problems and other serious health issues.

According to the US EPA, the Health Effects of VOCs include:

Eye, nose, and throat irritation; headaches, loss of coordination, nausea; damage to liver, kidney, and central nervous system. Some organics can cause cancer in animals; some are suspected or known to cause cancer in humans. Key signs or symptoms associated with exposure to VOCs include conjunctival irritation, nose and throat discomfort, headache, allergic skin reaction, dyspnea, declines in serum cholinesterase levels, nausea, emesis, epistaxis, fatigue, dizziness.

The ability of organic chemicals to cause health effects varies greatly from those that are highly toxic, to those with no known health effect. As with other pollutants, the extent and nature of the health effect will depend on many factors including level of exposure and length of time exposed. Eye and respiratory tract irritation, headaches, dizziness, visual disorders, and memory impairment are among the immediate symptoms that some people have experienced soon after exposure to some organics. At present, not much is known about what health effects occur from the levels of organics usually found in homes. Many organic compounds are known to cause cancer in animals; some are suspected of causing, or are known to cause, cancer in humans.

For more health information on VOCs from the EPA click here. 

According to a new study - one confirming what we already know - plants -  - clean these harmful VOCs out of the air.   Read about the study in a National Science Foundation Article here.

This study makes it clear that it is especially important to have as many plants inside your building or home as the levels of VOCs inside a structure can be up to ten times the ambient levels outside.

Plants act as filters for air and rainfall, actually removing and utilizing harmful nitrogen.  They also remove carbon from the atmosphere by using CO2 to produce much needed energy compounds and then plants pump oxygen back into the atmosphere.

As we are bombarded with pollutants each day, in our water and in the air - installing interior living walls, exterior vertical green - green roofs and living walls, Urban Permaculture - City Gardens, wildflowers and trees - can pay off with significant benefits.

Ultimately, we may live longer.  Ultimately, we may beat the odds with cancer or respiratory diseases.

Restoring Volumetric Green to the Urban Core is critical.  Today, go out and plant a seed or a grown plant.  Bring another inside.  Hang plants from your patio walls and your kitchen window.  Keep plants in your home.  Install a green roof.

Green roofs and living walls - cleaning stormwater, creating habitat, providing a sense of place and beauty and - importantly - fighting disease by removing pollutants!

Surround yourself with plants today.  You may breath better and live longer. 

Remember, the benefits of adding volumetric green to the Urban Core include;

  • Cleaning Rainfall runoff and stormwater
  • Providing wildlife habitat
  • Supporting biodiversity
  • Creating habitat for endangered plants
  • Integrated pest management - supporting pest consuming invertebrates and amphibians
  • Noise insulation
  • Reducing Heat Island effect
  • Creating a Sense of Place and Landscape Beauty
  • and more

Tuesday, February 12, 2013

Easy Florida Living Wall

Yesterday we posted a note about a struggling living wall.  Yet living walls, if planned properly, can be easy too.

Ficus punila, living wall Tallahassee

Florida Living Wall, Low maintenance 
Living walls such as those pictured here provide many benefits, including; stormwater attenuation, urban heat island effect mitigation, carbon sequestration, air purification, beauty and wildlife habitat.

This particular wall provides a home to a large population of our native Florida Anoles.  Florida Anoles need vertical green above one meter or so to escape the larger, more predatory Cuban Anole and themselves are an important pest control species as their diet includes flies, roaches and other bugs.

Creeping fig, ficus pumila is a drought tolerant vine and although it is not a Floria native it does not exhibit significant invasive characteristics.  More information on the creeping fig vine is available on the UF IFAS website here.

The vine is planted in urban soils amended with organic matter at the base of a concrete wall surrounding the gasoline station.

Soil preparation is crucial when considering a living wall.

Monday, February 11, 2013

Living Wall Update, Whole Foods, Jacksonville

One year ago, during February 2012 we examined in a post dying 'living walls' across the Whole Foods store in Jacksonville, proposing the theory of inadequate soil makeup as the primary reason for the living wall plant's poor performance.
Whole Foods 'living wall', Jacksonville

Briefly examining the site history led us to realize that another concrete block building, including a foundation and concrete floor existed prior to the present building. The site soils were what we would characterize as Urban Soils with abnormally high pH levels.
Whole Foods 'living wall', Jacksonville

Our post recommended removing some of the existing soil and amending the planters with rich organic laden soil.
Urban Soil fill existing planters

The Whole Foods living wall structures are quite expensive, a high-end stainless steel wall system appearing to be a CarlStahl Decorcable design.
Expensive, high-end living wall system

It is a shame these beautiful living wall frames are not covered with brilliant blooming Passiflora, Trumpet Vine, Coral Honeysuckle, Carolina jessamine and other beautiful landscape or native vines.
Instead, today wisteria (a relatively invasive species) is struggling to maintain even a small bit of coverage on the facade of the building. Fertilizers do appear to have been added, providing for a short lived spurt of growth in some areas.

I suspect that a stunning array of flowering vines doing very well on the trellis system would actually increase sales at the store. Paradoxically, the 'puny' vines send a message of 'unhealthyness' across the entire facade of the health foods store.

Our suggestion still stands. Remove as much of the high pH Urban Soils as possible and replace with a higher organic matter content soil. Add soil pH stabilizers. Remove the wisteria and other plants not suited for the site and add those species destined to thrive in the existing planters.

Next year the Whole Foods store could be well on it's way to a vibrant series of living walls, or....... the topic of yet again another post like this one.

Friday, February 8, 2013

Awesome Stormwater Drainage Filtration (Plants of Course!)

Though native species would have been better than grasses, I am still awarding the designer of the below stormwater collection system an A+ for common sense.
Grass filters stormwater before entering collection system
Grasses planted around the stormwater drain grate will effectively filter out most pollutants, sequestering many in their biomass, before the runoff enters the collection system and heads to our lakes and rivers.

If this application were used worldwide for stormwater then we'd be taking a dramatic step towards clean water.

Kudos to the unknown designer!

Florida Green Roof Plants in Action

Lovely photo of an older green roof in Jacksonville ( 8+ years old ).  Note this roof is nature irrigated only and has survived several Tropical Storms, one with 23 inches ( 58 cm ) rainfall.  The roof has a 5/12 slope.
Lightweight Green Roof over sloped decking and asphalt shingles
Notice that I cut out a square of the Green Roof mat to examine the underlying waterproof barrier.   In doing so I removed the outside perimeter edges.  It is important to note that raw edges should never be left exposed to wind damage potential.

The entire system live loaded weighs less than ten pounds per square foot.

Green Roofs constructed on large commercial or institutional buildings are important, however just as important are those residential applications where existing asphalt shingles and sloped roofs can be incorporated.

Saturday, February 2, 2013

Green Roof Plants, Frost Damage to Certain CAM Plants

In earlier posts, we examined the damage frost can do to the mesophyll cells of C3 plants. Mesophyll cells are those cells across the surface of the leaf. C3 plants usually possess lots of stomata and C3 photosynthesis is a quick and rapid process, allowing C3 plants to grow rapidly, filling in a green roof.

In C4 and CAM plants photosynthesis occurs in a different manner with different cells. Today we will briefly examine one aspect of CAM plants and look at damage incurred by freezing temperatures.

Many CAM Plants, such as some sedum may die back to their roots upon experiencing a frost, others die completely.  There are some CAM plants however, in the genus Yucca and similar genus who can survive mild freezes.

CAM stands for Crassulacean acid metabolism. CAM plants generally have stomata adapted to open at night and not during the day, preserving water during hot periods or drought. Many plants living in arid ecosystems are CAM plants and can be recognized by smaller leaves with a higher leaf volume ratio (fat, fleshy leaves where water is stored in vacuoles), waxy leaf surfaces, sunken stomata areas. 

Examples of CAM plants popular in Florida include;
  • Pineapple
  • Jade Plant
  • Euphorbias
  • Sansevierias
  • Aloes and others
Green Roof CAM Plant, Graptopetalum spp.

 The photo to the left is of a Mexican Ghost plant, many of us call a sedum, however it is really a not really a sedum but a Graptopetalum.

For an informative article with many reference links about CAM and Graptopetalum, see the blog post linked here.

Many succulents such as the Mexican Ghost plant and others can endure a little frost, though some of the more tropical varieties are tender to any type of frost damage.

However unlike C3 and C4 plants, many CAM plants store water in cells called vacuoles.  I call vacuoles 'smart blobs'.  Vacuoles are storage cells used for a number of plant physiological purposes.  In CAM plants vacuoles are used to store water and other photosynthesis related substances like the carbon dioxide.

Green Roof Plant, CAM Type After Hard Dreeze, Graptopetalum spp.
As mentioned, most CAM plants have thicker leaves - because of the presence of the stored water.  We have collected data over the years showing how the Mexican Ghost plant and other similar succulents survive minor frosts yet because of the expansion of water as it freezes, their cells rupture and the plant usually dies during a hard freeze.

Water stored in the vacuoles and other parts of the succulent's leaves expands as the temperature drops into the lower 20'S F (-6 to -8C).  As the stored fluid freezes and expands in size the vacuole wall and other cells rupture, injuring or killing the plants.

Though this phenomena can be observed across the green roof, it is especially prevalent in plants along the edges of the green roof.

CAM type succulents planted along green roof edges are exposed to unbroken cold, dry winds.  However within the interior of the green roof plantings we observe less freezing damage, probably due to stored heat in the planting media and the break from constant winds.

What lessons can we learn from the Mexican Ghost plant and freezing temperatures?  Many, including plant placement on a green roof and inter-relations between C3, C4 and CAM type plants.   We will discuss some of the hardier CAM plants in a future blog.

Friday, February 1, 2013

Green Roof & Living Wall Plants and Wind Exposure

Wind can seriously impact the long term survival of Green Roof and Living Wall plants.

Included here are two photos of the same black-eye pea plants growing on Green Roofs (Rooftop Garden).  

One is on a wind protected green roof, the other is on a wind exposed green roof.  Note the wind burn on the wind exposed roof plants.

Both looked the same prior to the 48 hour wind storm just leaving.

We recorded between 10 and 20 Km/Hr winds on a continual basis for the 48 hours with almost non-existent water vapor or air humidity.  Winds of these speeds will draw most, if not all of the water out of a Green Roof plant. 

Florida Green Roof, Wind Protected Green Roof Plants

Florida Green Roof, Wind Exposed Green Roof Plants


Wind can burn or kill green roof plants quickly, taking an otherwise beautiful planting and turning into a brown mess within a matter of days.  Even with more than adequate irrigation water applied - simply because the vascular system of the plants cannot keep up with the demand for water in the leaves. 

Proper Green Roof and Living Wall plant selection involves knowledge of how a plant physiologically interacts with wind stresses.

In windy areas, CAM plants and those plants with stomata remaining closed or closing under lack of water conditions must be used as perimeter wind break plants on green roofs with out parapets or other wind protection if the green roof is not otherwise sheltered.

Understand the different types of photosynthesis green roof plants have.  For a primer, check out the many articles we have posted before on CAM, C4 and C3 plants.

Other helpful sites are included here;

Great Irish Gardening blog article on wind damage in Ireland to garden plants.

North Carolina State University has another brief yet informative note on wind desiccation of plants.

Very interesting and informative Permaculture Wind Break Site.

Remember, your green roof site may receive plenty or precipitation or irrigation water, but if it is constantly exposed to desiccating winds the plants will experience the effects of wind damage.