Green Roof Plants, C3? C4? CAM? and OMG! Fertilizers!

We are still discussing the difference between C3, C4 and CAM plants for green roofs.  Today's blog article is very simple but carries a very important message.

C3, C4 and CAM plants all have different metabolisms so they grow and add biomass at different rates.

Why is this maxim important?

Because no matter how much fertilizer you add to a C4 or CAM plant they may not grow as fast as a C3 plant grows.

In haste to make the green roof plants grow quickly and provide roof coverage, additional fertilizers are sometimes added (the magic potent) to encourage more biomass growth.

If the green roof is planted with C4 and CAM plants and heavily fertilized, the green roof plant growth rate will probably not be as fast as an unfertilized planting of C3 plants.  Adding more and more fertilizers may even kill the plants.

Some may feel there is comfort in adding fertilizers to a green roof.  The small, round little pellets impart a sense of 'doing more than one has to' to make the green roof grow.  In fact, adding fertilizers is truly 'doing more than one has to'.

Green Roof Fertilizer Runoff, Algae on Concrete

Fertilizers contain nitrogen and phosphorous, nutrients the plants use to grow.

However we need to remember these nutrients may run off the green roof during storm events and feed algae in local waterways.  Here in Jacksonville the St. Johns River becomes green with algae blooms as a result of fertilizer runoff.

Dead fish can litter the banks of the river due to the river's algae blooms.

Green Roof Fertilizer Runoff, Algae on Concrete

Understanding that C3 plants grow faster than C4 and CAM plants allows the green roof designer to specify appropriate fertilization applications appropriate for the species of plants.

The included photos here show a tale-tell sign of excess fertilizer or nutrients running of the green roof, encouraging algae growth across the concrete walls.

Like infra-red signatures for water leaks, the green stains of algae are a 'spot-on' indicator of the presence of fertilizer and other nutrients.

Remembering  C3, C4 and CAM plants all have different metabolisms and grow and add biomass at different rates will help reduce nutrient and fertilizer loading into our waterways.

Work with your local agriculture information staff to pick the right fertilizer for your green roof plants.  Spot fertilizer application is best and can be customized to the types of plants and where they are planted on the green roof.

Broadcast fertilizer applications are not recommended because no matter how much fertilizer you add to a C4 or CAM plant they may not grow as fast as a C3 plant grows.


Unless the green roof is a permaculture or food roof I recommend designing a nature irrigated habitat-type green roof and specifying the vegetation to take advantage of the natural nitrogen and phosphorous content in rainfall, supplemented by biomass from the roof leaf litter, bird feces and other natural sources.   These natural sources still contain nutrients for algae to feed on, but may be more manageable.

The simple message is this, do not broadcast fertilize a green roof.  One size does not fit all.  Finally, be sure to scrub the algae off the concrete if you do fertilize using an eco-friendly cleanser and not bleach.

As always, email your questions and comments here.

Happy Green Roofing!

Kevin

New! Informative Urban Farming Blog by Pesculane.

Check out the Urban Farming Website at http://naturenvilles.blogspot.com/ for great insight into what I call Volumetric Green in the Urban Core.

You can follow Pescalune and Nature Photography on twitter also here - well worth the visit!

Happy Green Roofing!  Kevin

Green Roof Plants - "Assumption of Relative Consistency Models (Plant Behavior) Artistic Intuition and Plants Having a Mind of Their Own

Good morning!  We've been discussing the difference between C3, C4 and CAM plants over the last couple of days.

The discussion of the different types of plants focuses on varying patterns of photosynthesis metabolism processes.  All of this may sound complicated but it is really quite simple and the reason we are distinguishing between plants is so we can predict behavior and select the best plant for each individual and unique green roof!

Having the ability to predict how plants will survive, thrive and grow on a green roof is vitally important to the green roof profession.

Moreover, understanding how plants will behave allows for the project's economic costs and impacts to be analyzed.  Of course, there are many variables to consider when choosing what blend of C3, C4 and CAM plants to use, factors such as;

• Wind direction and speed
• Sunlight exposure
• Temperature ranges
• Average humidity per month
• Rainfall amounts per month
• Existing local seed source
• Nearby allopathic plants
• Smog and air pollution
• and other factors

The important component of modeling or predicting how the roof will behave with plants is the "assumption of relative consistency".

The "assumption of relative consistency" is a phrase that means - we know what to expect.

So for green roofs the assumption of relative consistency means we know there will be times when the roof will be very hot (mid day summer) and times when the roof may be very cold (early winter mornings).  There will be times when the green roof will have plenty of sunshine for photosynthesis (when the sun is high in the sky) and times when the days are short and the sun is low on the horizon (winter solstice).

The times when the days are short is when every bit of sunlight is important.  During the shorter days there is an assumption of relative consistency that deciduous trees will loose there leaves and sunlight can filter through the tree to the roof.

This assumption of relative consistency about winter sunlight where summer leaves had provided shade is a factor green roof design incorporates.

Yet plants, like children - and many adults - have a mind of their own also.

Deciduous sweet gum left, wont loose its leaves

The photo to the left is of a deciduous tree, Sweetgum , Liquidambar styraciflua.   This sweetgum is planted adjacent to a greenhouse and a green roof and provides summer shade but is supposed drop leaves during the winter to allow sunshine exposure.

There have been record cold temperatures and the solstice has come and gone so the environmental triggers for leaf drop have been present.

But the plant has a mind of its own.

And the leaves just will not fall off the tree - no matter how long I stare at this tree!

And the greenhouse and green roof are not getting the sun exposure I expected this year.

So the theory of assumption of relative consistency of plant behavior may not always hold true and definitely will have exceptions.

Certainly the exceptions to the rule do not justify discarding plant behavior through modeling.

But what is important is to realize that plants do have a mind of their own and green roof design, though highly technical is also a function of art.  The green roof artist has an understanding of how plants may behave on the green roof based not only on assumption of relative consistency data, but also on an inner intuition only a plant person can understand.

Happy Green Roofing!

Kevin

CAM Plants for Green Roofs, Effects of Heat and of Humidity

We discussed how some cold tender CAM plants, such as many of the succulents, can be damaged by freezing temperatures.  CAM plants are called CAM plants because they possess a specific form of metabolism called Crassulacean acid metabolism.

The CAM metabolic process helps succulents and other CAM plants survive in dry, arid regions by working to keep stomata closed during the day when high temperatures and hot drying winds.  If temperatures are high, the sun is bright and stomata are open the plants can rapidly dehydrate. 


CAM plants open stomata at night when temperatures are cooler and solar radiation minimal.  When stomata are open CAM plants take in carbon dioxide (CO2) and store the CO2 in their leaf cells.  Once the sun rises and temperatures increase, CAM plants close their stomata and take the CO2 absorbed from the evening air and begin photosynthesis, producing the substances the plant requires and also oxygen, O2.

An analogy I like to use in comparing CAM plants to C3 plants is thinking about the difference between a gas guzzling 1970's sedan as compared to a new hybrid-type car with a highly efficient engine.  The C3 plants' metabolism is like the 1970's V8 gas guzzler - they both take in lots of fuel, fire up quickly, get to where they are going/growing quickly but are inefficient with respect to fuel utilization.  In the 1970's V8 wasted, unburned fuel leaves the engine as exhaust.  In the C3 plants we see volatilization and evaporation out of the leaf of photosynthesis substances through numerous opened stomata.  Yet both get where they are going/growing - quickly!

CAM plants though are like the highly efficient hybrid electric/petroleum engine.  In addition to conserving CO2 and preventing desiccation by keeping their stomata closed during the day, they are also very efficient at uptaking and using nutrients like nitrogen.  Because a CAM plant's CO2 is limited, the plants have developed mechanisms to become ultra-efficient at nutrient utilization.  Little is wasted.

Because of CAM plants adaptations to hot, arid, dry and drought-like conditions, they make great green roof plants and have been used historically across Europe as such.

Interestingly, some plants like the sedums can switch back and forth between the C3 and CAM metabolic processes depending upon the amount of water and nutrients available in the environment.  This process is called acclimation and is very similar to what we may imagine a grizzly bear's hibernation may be like.

Sedums are considerably more cold hardier than many of the other succulents that are members of the Crassulacaea family and so are popular in colder climates as green roof plants.  Some sedums are so popular for use on green roofs that they have become pest plants, exotic invasive species displacing some types of native vegetation.

Several CAM plants (Agave) surrounded by C3 plants

However, though CAM plants are excellent at surviving heat, aridity, and bright solar radiation and frost if protected, another climatic condition often is a limiting factor.  Though CAM plants, if protected can survive freezing temperatures and certainly can survive long periods of drought, many are susceptible to humidity-heat combination related issues.

Sedums and other succulents are highly prone to fungal attacks during the summer months when the temperatures range between 90 F and 100 F (35 - 37C).

The Southern Blight fungus, Sclerotium rolfsii, also known by the common names 'crown rot' and 'white mold' can decimate a well established roof of succulents or sedums.  Fortunately, southern blight does not seem to bother the succulents during cooler or dryer months.  However the everyday rainfall and resulting high air water vapor combined with high temperatures found during the summer months produce an environment just right for Sclerotium rolfsii, to proliferate.

CAM plants (Graptopetalum) with C3 and C4 Green Roof Plants

But what does all this technical information about photosynthesis and botany have to do with green roofs?

For the nature irrigated green roof, an understanding of C3, C4 and CAM plants and their advantages and disadvantages, their benefits and their limitations, is critical for a successful design.

Green Roof Succulent Injured by Southern Blight

As we continue our discussion of C3, C4 and CAM plants over the next several days we will begin to clearly see how 'Right Plant, Right Place' is important even on green roofs.

Water supplies are limited across the world.  We cannot continue to rely on irrigation use of potable water on landscapes or green roofs.

Designing a nature irrigated green roof will require utilization of a combination of C3, C4 and CAM plants, planted on the roof according to a number of biophysical variables we will discuss.

And so, to date we now understand that CAM plants are ideal for arid, hot areas and can survive drought.  We also know CAM plants may be susceptible to frost or also to fungal attacks encouraged by hot, humid weather.  We know C3 plants grow quickly.

Finally, as we discuss other important factors about plants suitable for a nature irrigated green roof we will begin to develop a sense of understanding as to the type of plant that will work long term on the green roof if planted in associations with other plants and in the right roof location.

As always, email us with questions or comments and Happy Green Roofing!  Kevin

Green Roofs and CAM Plants - Frost or Freeze Damage

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.

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 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.

As always, feel free to email us with questions or comments & Happy Green Roofing!

Kevin

Green Roof Plants - Frost Damage and Photosynthesis

Welcome to 2011.  We look forward to kicking off the new year with interesting articles and discussions about green roofs.

Two of the areas we will be focusing on this year are:

A.  Roofs for permaculture and feeding the world, and
B.  Native wildflower and native plant green roofs irrigated by nature alone (dew, fog, rainfall)

The two are somewhat diametrically opposed as one requires higher nutrient and irrigation input using a variety of non-native food species.  The other focuses on native plant species, their soil organism relationships and natural irrigation in the spirit of water conservation.

Every day is a new educational opportunity for learning about green roof plants.  As we study rooftop permaculture and nature based green roofs we will be trying to first understand the difference in a basic plant physiological process, that of photosynthesis.

There are three basic types of photosynthesis processes that occur in plants and they are termed "C3", "C4", and "CAM".  We will be discussing the differences in future articles but in general, the majority of the world's plants are "C3" plants.

C3 plants conduct photosynthesis directly at and beneath the leaf surface in cells called mesophyll cells.

Frost on Green Roof Plants

In C4 and CAM plants photosynthesis occurs in a different manner with different cells - we will discuss those in future blogs.  Understand now though C4 and CAM plants may use a combination of different cells, some deeper in the plant and plant leaf for photosynthesis.

As mentioned, in C3 plants photosynthesis occurs generally on the leaf surface or just beneath the surface.  Remember, stomata are the openings in the leaf allowing for exchange of gases - intake of CO2 and output of O2 and on the C3 plants stomata can be found widespread across the leaf.

The proximity of the photosynthesis process and numerous stomata on the C3 plant leaves create a situation where the plant's vital photosynthesis process is more exposed to the climate and elements.  C3 plants may sometimes quickly loose water and become desiccated due to hot temperatures or strong winds.  Also the leaf's photosynthesis process and cells may be susceptible to frost damage.

The above photo is of frost on green roof plants.  Examine the frost crystals and you can see they are sharp!  As water vapor freezes before fully evaporating, frost crystals form.  The formation of frost crystals may damage photosynthesis responsible mechanisms within the leaf and injure or kill the plant.

There is a place for all types of plants on green roofs, C3, C4 and CAM.  Understanding the processes and nature of each are important to the green roof designer.

Over the next few months we will be examining many of these plant differences.

Happy New Year and Happy Green Roofing!

Kevin

Green Roofs and Customer Relationships

I subscribe to few newsletters mostly because I don't have much excess time.

But I always look forward to the Daily Feed - now rebranded the Weekly Feed, put out by Mark Maunder of Feedjit (the company who provides the blog visitor software here on my blog).

Mark's free newsletter has really helped me with my blog.  As a botanist and lawyer, my IT skills earlier this year were the not so good to say the least.  In fact - over the holiday season I will be redoing our www.metroverde.com website as it is not very user friendly right now.

However with Mark's advice my green roof blog went from 4 visitors per week to over 100 per day in less than 3 months.  But that is not the reason I am posting an article from his newsletter today.

I have read and re-read Marks latest newsletter article about customer service because it is so true.

As with newsletters, I am also choosy about the stores I go into and can relate to what Mark says.  So here is the excerpt - enjoy!  Kevin

Happy Holidays and Happy Green Roofing!

Welcome to Issue #52 of The Weekly Feed. If this email was forwarded to you by a friend, you can subscribe on this page. The Weekly Feed is published once a week when we have news, information and helpful tips to share. Unsubscribe instructions are at the end of this message. You can read previous editions of The Weekly Feed on our blog but note that posts to our blog are delayed 24 hours or more.

We have rebranded The Daily Feed to The Weekly Feed. We'll be publishing the newsletter once a week from now on usually at the beginning of the week.

If you, like me, have left your holiday shopping until the last minute, you've probably paid a visit to the Apple store recently. I'm in Colorado right now and paid a visit to the Park Meadows Apple store to get something I didn't really need but that made a good excuse to give Steve more of my money.

A few minutes later I walked into the Microsoft store. I've managed to get over the fact that they cloned Apple the same way I don't mind that Pepsi cloned Coke. Hey, competition is good for all of us. The experience was basically the same but the details were different and there were so many of them it was startling:

The store employees weren't smiling, there were less of them and it was hard to get their attention. I wanted to buy Windows 7 and the price was $200 and the sales guy told me that "sorry, but that's what it costs" even though I bought a new licensed copy (also the full install) on eBay this morning for $117. When the attendant swiped my card for my PC game he had to reach under a table and use a non-portable swiper. They didn't offer me an email receipt or even take my email address. They assumed I wanted a paper receipt so that's what I got. The guy who helped us had this look on his face like we weren't supposed to be there.

The Apple store on the other hand was friendly, portable card swipes, email receipts, the store was packed and about 1 in 5 people were super helpful Apple employees. I stood in the wrong line (for the genius bar) and a guy came up to me and offered a checkout without making me feel like I'd screwed up. It was awesome and it's the reason we own more Apples at Feedjit than PC's for the first time this year.

Apple is big on the details of the impression they leave you with. Note the Apple Keynote Cutdown video. Not a single cut is repeated in that video. Business insider has a blog entry today about how Apple refers to it's products grammatically as person's and not as objects.

All these little touches add up to a whole that has far more marketing power than the sum of it's parts. When you are thinking about your blog or website, take note of the details. Load times, color scheme, unpleasant distractions, how long you take to reply to your comments or respond to customer requests, the tone and language you use, how you moderate your comments, forums or wiki. All these details add up into a complete user experience and they all matter a whole lot.

Our news roundup for today:

Royal Pingdom published some revealing data today. They did a survey of a handlful of popular blogging platforms over 2 months to see which provide the best uptime. Blogger, Wordpress and Typepad came up on top with Tumblr performing terribly. Tumblr had a total of 47 hours of down-time over a 2 month period. You can read the full report here.

Thomas Weber has a guide in The Daily Beast today that shares how he cracked the New York Times "Most Emailed" story list and got his story to #3 on the list. Thomas and his team figured out that the TImes counts individual senders per story. After 1,270 individual (volunteer) senders had emailed a story they made it to number 3 on the overall list. The times gets roughly 30 million visitors per month, and it takes around 1 in every 25,000 readers to email a story to get that story on to the top 10 most emailed story list.

And finally, if you're in the Northern Hemisphere tonight at 12:41 Mountain Standard Time, enjoy the Lunar Eclipse. The Feedjit founders will be watching it at 7000 ft from Colorado.

Happy Holidays!!

Mark Maunder
Feedjit Founder & CEO

Green Roofs for Birdhouses, Doghouses and Every Conceivable Roof We Can Find...

Green roofs are found on a wide variety of structures and not just commercial, institutional or residential buildings.

Cedar Roof Decking - Birdhouse Green Roof

Included are several DIY photos of how to put a green roof on a birdhouse and more of a LEED Platinum Doghouse (we won 1st place in AIA Barkitecture competition)!

Birdhouse Green Roof - Double Sided Roofing Tape

First photo is of the birdhouse roof decking.

Green Roof Birdhouse - Membrane Installation

Next photos is the double sided tape allied to the cedar decking.

Third is the waterproofing membrance serving also as a root barrier.

Green Roof Birdhouse - Grow Weave Mat

Fourth is the grow weave mat, then the ridge cap (made from recycled copper flashing) and trim work.

Green ROof Birdhouse - Copper Ridge Cap

Agaves and succulents are added, along with a mixture of drought resilient wildflower seed.

Green Roof Birdhouse - Plants and seed added...

The concept here is exactly the same process we use on large, large green roofs.  This type of system is called an extensive green roof and on the sloped birdhouse roof the soil is stabilized with a natural stabilizer such as agar (you can use flour also if you cannot find agar)...

For other unique holiday gift suggestions - how about a LEED Platinum qualifying doghouse with a green roof!

Green Roof Doghouse

Green Roof Doghouse

 

This doghouse won the AIA Barkitecture contest!  We used a variety of succulents and perennial peanut.  Rainwater is cleaned through the special roof soil media and then recycled into the stainless steel watering bowl.

Happy Holidays and Happy Green Roofing!

Kevin

Green Roof DIY Plant Starter Greenhouse - On the Cheap

Green roofs are harsh mini-eco-climates and may not always be the best place to germinate seeds.

So if you have a seed source for a particular plant you want to use on your green roof - or elsewhere in your permaculture gardens - a seed starting greenhouse or hothouse may be helpful.

Greenhouse for Green Roof Plants - Cheapo but Works!

Yet in today's economy many of us do not have the extra dollars or euros to spend on a hothouse or greenhouse.

The photos here and sketch are of a very nice greenhouse we recently built out of scraps.  Our total out-of-pocket cost was about US $20!

The greenhouse is 12' wide by 18' long by 8' tall - 3.7M wide x 4.5M long  x 2.4M tall (approximate dimensions).

Green Roof Plant Seedlings

Surprisingly, this week as the temperatures outside dropped to around 20F  -6.7C  ice formed on the inner portion of the pastic however the jugs of water we had sitting in the greenhouse did not freeze.

All the seedlings were cold but fine - not frozen.

The greenhouse's performance pointed to two important facts - 1. you can build a great little greenhouse out of scrap and, 2. by adding jugs of water to the inside of the greenhouse you can keep the hothouse warm enough to protect plants.

Water Jugs Store Heat - Keeps Greenhouse Warm

Water has a high specific heat value and stores heat absorbed during the day from sunshine, releasing the heat back into the greenhouse at night when the temperatures are cooler.

To build the hothouse, first find 6 lengths of scrap pipe.  We used metal fence posts we had found in a scrap pile where someone was remodeling a house.  Take a big hammer - we used a sledge hammer and drive the pipe into the ground spacing them about eight or nine feet apart (2.5M).  Make 2 parallel rows of these installed pipes - see the sketch.

DIY Hothouse by Kevin

To the pipes we added flexible 1/2" electrical conduit we had left over from a construction job.  This conduit is very inexpensive to buy at the hardware store - about US$1.50 each - you need 7 total.

Attach one side with a ZipTie (WireTie) of the conduit to a pipe in the ground and then easily bend the other side over to the opposing pipe.  Proceed to attach, bend and attach all the conduit to the pipes to make the hoops.

We then covered the hoops with a piece of left over greenhouse plastic and attached the plastic to the hoops and pipes with Big Office Paper Clips - they work great.

Presto - the greenhouse was built!  Green Roof Seedlings are now growing!

Good luck with yours and as always - Happy Green Roofing....Kevin

Green Roof Ethnobotany - Chinese Tallow, Sapium sebiferum (Triadica sebifera)

Chinese Tallow tree, also known as Popcorn Tree (due to seeds that resemble popped Jiffy Popcorn), Sapium sebiferum (Triadica sebifera), is one of the most persistent invasive species affecting green roofs in Florida and across the southeastern US.

Chinese Tallow Green Roof Exotic Plant

Benjamin Franklin introduced Chinese Tallow to the US East Coast.

With beautiful fall color, Chinese Tallow was originally brought from Asia.  The tree has rapidly spread across the Gulf Coast region.  According to Wikipedia, 25% of all trees in Houston are Chinese Tallow.

Chinese Tallow is the third most important vegetable oil crop, ranking only behind algae and palm oil.

Bees love the plant and the tree produces larges amounts of nectar.  Beekeepers seek out groves of Chinese Tallow for their colonies.


Chinese Tallow is listed as a Class 1 Invasive plant in Florida by the Florida Exotic Pest Plant Council (FLEPPC).

Birds love the seeds of this plant and we find Chinese Tallow plants sprouting across green roofs each spring.

Understanding the types of local plants is key to maintaining a successful green roof long term.


As always, email your comments or questions!

Happy Green Roofing!

Kevin

Green Roof Design - New Years Resolution - Back to Green Roof Basics!

The copper and net dew catchers are coming down from green roofs today and we making a Green Roof New Years Resolution and concerted effort to 'Get Back To Basics" on Green Roofs.

Technology can be alluring and distracting.

Sometimes alluring technology can unintentionally shift core focuses.

 Development of metal and plastic dew and fog catching apparatus based on biomimicry is just 'that' - biomimicry.  The biomimicry approach of copying nature's solutions can be successfully substituted with nature's back-to-basics on Green Roofs  - simply use plants with dew and fog catching characteristics rather than mechanical  contraptions.

In fact advantages of alluring technology can be so great we sometimes tend to gloss over the downside, or disadvantages or serious problems.

Example:

(Advantage)  Copper dew catchers shine brightly in the afternoon sunlight and the plastic netting does a great job of harvesting air moisture.  Aesthetically pleasing.

(Disadvantage)  The metal and plastic dew catchers and fog harvesters may become launched projectiles, hurled dangerously through the air in hurricane force winds.  Something not normally considered on a day to day basis.

(Solution) Use plants nature has perfected to capture dew and fog - there are many.  Growing plants is what green roofs are all about anyway.

Solutions like the above are often over-shadowed by the alluring glow of technology.

Another technology with an alluring name is "Pollution Control Media".  Pollution Control Media is now required to be embedded in Florida green roofs under the drafted State of Florida Stormwater Quality Applicant's Handbook to receive stormwater credit.

The handbook begins with a short-sighted approach to green roofs by allowing for only stormwater volume credit for green roofs.   No allowance for water quality improvements is given.   Unfortunately, this may be due to the misconception that nitrogen and phosphorous fertilizers, pesticides and herbicides are necessary for successful green roofs.

Even the American Rainwater Catchment Systems Association (ARCSA) has questioned the approach and intent of the handbook's unusual requirements for green roofs and cisterns design.

Apparently, the Pollution Control Media is supposed to capture the nitrogen and phosphorous from the fertilizers, pesticides and herbicides applied to and sprayed on the green roof - from entering stormwater runoff.  In fact, according to the handbook, all green roof runoff should be captured by the cistern and then recycled back to the roof for irrigation on dryer days.  The green roof plants would then evaporate off the water through normal transpiration, leaving the nitrogen, phosphorous, herbicides and pesticides to accumulate in the closed loop system over time.  We wonder at what point the accumulating slurry of fertilizers, pesticides and herbicides would become a hazardous green roof waste.

A topic for another article - green roofs can and do actually clean stormwater.  Green Roofs do not have to be considered just another stormwater volume retention system. In fact, by allowing stormwater credit only for rooftop systems that have the structural capability of supporting deeper amounts of stormwater, incentive disappears for other types of green roofs.

But what is Pollution Control Media?

Pollution Control Media is primarily a blend of sand, crushed limestone, sawdust and mostly crushed or ground up rubber automotive and construction vehicle tires.

Pollution Control Media has shown promising results in removing nitrogen and phosphorous from spetic tank systems and other waste cleaning applications (Pollution Control Media was originally proposed to be installed under certain types of newly constructed stormwater ponds in an early handbook draft but was removed).

Therein lies the alluring technology scenario referred to earlier.  If fertilizers and herbicides and pesticides are to be used on green roofs (there are other more eco-friendly approaches) then why not add Pollution Control Media to keep the fertilizers and organo-herbicides and pesticides on the roof and out of the stormwater.

Studies even referenced a few bio-assay toxicity tests conducted around 2003 showing acceptable mortality levels.

A short-term acute bio-assay is one measure of safety but long term chronic exposure is an all together different issue, one acknowledged not to be answered about tire crumb in the supporting studies.

In fact EPA has changed their stance from recommendation of recycled tire products to one of - further study is now required - and listed the following substances as existing on ground recycled tires:

• acetone
• aniline
• arsenic
• barium
• benzene
• benzothiazole
• cadmium
• chloroethane
• chromium
• cobalt
• copper
• halogenated flame retardants
• isoprene
• latex
• lead
• manganese
• mercury
• methyl ethyl ketone
• methyl isobutyl ketone
• naphthalene
• nickel
• nylon
• phenol
• pigments
• polycyclic aromatic hydrocarbons
• polyester
• rayon
• styrene‑butadiene
• toluene
• trichloroethylene

Click here for more details.

For an interesting EPA memo about the questions on recycled tire products click here.

So by the State of Florida requiring an alluring technology to be a part of Florida green roofs for stormwater credit, we may be missing the more important issue of the potential wide-spread and long-term leaching of the above substances while nitrogen and phosphorous are kept in check.

While there has already been numerous installations in Florida of the Pollution Control Media, a pause in its use - until EPA completes their studies - may be a good idea.

Certainly the requirement for Pollution Control Media should be removed from the State of Florida Stormwater Quality Applicant's Handbook's requirement for green roofs to receive stormwater credit.

Efforts to recycle used tires are noble.  Applying ground up tires to green roofs is not an appropriate recommendation the State of Florida should be making until all questions about the long-term toxicity of zinc pollution, aromatic hydrocarbon pollution and the above substances are answered.

In fact - some studies are showing that though ground up tires may be safe for children playground exposure, recycled tire products do exhibit levels of bio-assay toxicity to wildlife in stormwater run-off.

So let's all get back to basics on green roof design.  Let's keep a wary eye on all the shiny dew catchers that may become projectiles during a hurricane and let's certainly not require use of Pollution Control Media that may contain substances no one wants on a green roof or in stormwater.

As always, email your comments and questions.

Happy Green Roofing!

Kevin

Green Roof Fertilizer, Irrigation with Potable Water, Invasive Species and Mark Madoff

Mark Madoff's death is a tragedy no doubt, but no more so than any of the other countless lives lost to the end result of another  Ponzi Scheme - the use of Persistent Organic Pollutants (POPs) - and the associated denial of silent environmental and health impacts.

Having read the article posted by @psustentavel on Twitter - click here for the article about Persistent Organic Pollutants - the imagery of 'inorganic chemical 'fertilizers across countless green roofs,  the use of drinking water for irrigation - even backup irrigation - and the reckless abandon with which we use non-native species for landscapes, including those on rooftops, made me think - in our rush to install green roofs atop buildings, are we too creating a Ponzi Scheme someone else will have to pay for?

The value of green roofs is unquestionable.  There is solid scientific data to back up claimed benefits of habitat creation, carbon sequestration, oxygen production. greenhouse gas reduction, heat island effect tempering, cleaning of stormwater, integrated pest management and so much more.

Florida Extensive Green Roof Nature Irrigated

There is no doubt about the value properly designed and maintained green roofs can bring to the Urban Core.

Green roofs can be used to support Urban Permaculture - small scale, individualized rooftop farming operations providing food, fiber and medicine to city residents.

And many urban areas around the world are moving ahead with plans to increase urban agriculture.  Singapore, for example, produces 25% of the entire city's vegetable crop within the city limits. For a fascinating look at the importance of urban permaculture  read foodsecurity.org's white paper entitled Urban Agriculture and Community Food Security in the United States; Farming From the City Center to the Urban Fringe.


Rooftops are the new frontier of real estate in many urban areas.  Cities with limited available ground level real estate have acres of open rooftops.

Vegetated and green roofs are increasing in popularity, showing an impressive growth rate trend over the past decade.  According to Greenroofs.com, public awareness of and interest in green roofs is steadily growing.

Yet we must learn from the Madoff venture's collapse, the immense loss incurred by investors and also those innocent persons affected worldwide by careless and widespread use of persistent organic pollutants commonly associated with some inorganic fertilizers.

In our noble rush to restore volumetric green to the urban core we hopefully will recognize the potential environmental costs associated with mass production of green roofs.  The 'One Size Fits All' approach to green rooftops will not work for the worlds vastly different ecosystems.  Sadly and reminiscent of mega-agriculture's damaging past practices, we as an industry turn to potent chemicals to fertilize, control pests and then use much needed drinking water to either irrigate or serve as backup irrigation.

Independent and craftsman-like green roof design and construction could disappear.


As with the POPs causing health issues in Pakistan and other places, our indiscriminate use of hardy invasive species, potentially toxic chemical fertilizers, pesticides and herbicides on green roofs is a Ponzi Scheme our children too will pay for.


Importantly, we as an industry have already moved far in the direction of ecologically inappropriate and environmentally dangerous green roof design.  Florida's FDEP green roof in Pensacola, Florida possesses a large drip irrigation system, backed up with potable drinking water and planted with slow-release fertilizer compounds and soil amendments.


As in Ponzi Schemes, denial of reality is the basis of success.  Though the 'green' benefits of the FDEP green roof are often touted in the media - the fact that chemical fertilizers are applied and potentially damaging to Escambia Bay's ecosystem are hidden.


Yet FDEP is fully aware of the environmental problems resulting from POPs, fertilization and pesticide use on green roofs.  In the proposed, new State of Florida Stormwater Applicant's Handbook,   FDEP allows green roof credit for volume retention of stormwater only (no water quality credit),  and recognizes fertilizers and pesticides will be used on green roofs (why no water quality credit is given), an approach we must reject.  Moreover, FDEP is requiring the purchase and use of a 'pollution control media' made from ground up automobile tires under the green roof soil media to keep the fertilizer's nutrients on the roof. 

Over time and as water evaporates, added pesticides, herbicides and fertilizers will concentrate back into the surface waters and become an issue for our children.

In the rush to add volumetric green to the Urban Core, the Ponzi Scheme could easily go unnoticed.

Temper the hurry to install a green roof with the knowledge of a local native species botanist and a soils expert.  Rather than ordering large amounts of hothouse pampered plant material, find a local nursery with individual plants acclimated to the climate.

Green roofs can be crafted to add artistic, educational, ecological and ethnobotanical value.

But we must first reject the Ponzi Scheme that green roofs must be fertilized, irrigated with drinking water and doused in pesticides.

As always, email your questions here!

Happy Green Roofing...

Kevin

Green Roof Plants - Thermogenesis and Plants With Heating and Cooling Properties

All plants possess biological systems that directly impact our ecology and the immediate environment surrounding our day to day activities.

After purchasing a truck load of plants on Saturday we unloaded most, however forgot to remove all of the plants from the cab.

Though the night air was cold (4C) when I opened the truck door and climbed in to drive to the market yesterday evening, after dark, I was enveloped with warm, moist air and confused as to why - with the cold dry air outside - the truck windows were fogged over with moisture.  Then I realized the plants were still in the truck, taking in CO2 and pumping moist O2 back into the air.

After spending much of Saturday evening outside taking temperatures with the ExTech IR thermometer, the oxygen and moisture filled truck cab emphasized what I already knew - plant's biological process are complex and have definite effects on their surroundings.

Sometimes we forget just how much plants impact our environment.

However in addition to the wonderful visual greenery (again we sometimes take for granted), plants sequester CO2, produce O2, provide habitat for wildlife in the Urban Core, provide food, fiber and medicine, clean stormwater and provide a myriad of other functions.

All of these factors and processes impact green roofs.  Understanding how these factors interact with the building is important.

This weekend I wanted to gather additional data on heat and green roofs.  My questions were many and included;

* Do green roofs really act as insulation?
* Do green roofs act as a heat sink - storing heat - instead of being an insulator?
* Does green roof plant selection impact the energy efficiency of green roofs?
* Does green roof soil composition impact energy efficiencies of green roofs - and if so, how?
* and a host of other questions.

After spending several hours with the IR, examining plants and green roof systems after dark - and in 4C ambient air, I can say much data needs to be collected, many studies completed and analysis done before we really understand the dynamics of green roofs.

Just as with the fertilizer and irrigation issues (I am always amazed at how some promote green roofs as ecologically friendly and important yet insist for the inclusion of potable water irrigation systems and fertilizer applications), the insulation or heat sink issues just don't seem to be adequately answered.

After collecting temperature data from under green roofs we see a green roof behavioral trend pointing to a heat sink rather than an insulator type system.  In other words, green roofs may tend to absorb heat during the day and then slowly release it back into the atmosphere and building during cooler evening hours.

Yet the complexities of plant species, plant growth characteristics, root systems, stomata to leaf surface area ratios, soil media specific heat qualities and other issues all contribute towards a complex model.

Getting back to the IR thermometer field  foray, some of the more interesting observations we noted were;

* Night time green roof plant leaf temperatures were approximately the same as ambient air temperatures,
* There were variable levels of warmer temperature readings found in the air space under the green roof plant leaves and above the green roof soil media, depending on the time of night and wind exposure - suggesting a level of insulation occurring as a result of leave structure
* The underside of an extensive green roof (3" soil media) stayed 10F warmer than a similar roof with no green roof system - and stayed warmer all night -- up until 5am the next morning,
* Banana plants stayed considerably warmer than ambient air for up to three hours after dark - unlike other plants,
* and other observations.

The banana plant elevated temperatures pointed us in the direction of thermogenesis in plants.  Thermogenic plants are those plants that can generate heat as a result of biological processes. The voodoo lily, Sauromatum guttatum, can generate temperatures of up to 110F - 32C!

There is a great video on thermogenic plants here.

However, the banana plant is not a thermogenic plant and the reason the banana plant stayed warmer than ambient air for several hours after sunset was the plant's high water content.  Water has one of the highest specific heat values of any compound or substance - four times than of limestone for instance.  Because the banana tree was full of water, the solar heat gain experienced during the day only slowly dissipated after nightfall.  Banana trees stayed warmer than most plants after dark because of the heat stored in the large volume if interstitial water within the plant.

It is possible the succulent filled extensive green roofs we are studying that emanate heat throughout the night are behaving like the banana plants.  The combination of green roof soil media and the water therein is absorbing heat during the day - maybe quite a bit of heat - then slowly releasing the heat at night.

The factors involved in modeling this complex heating and cooling dynamic are many and not well documented today.

We think the heating behavior of the extensive green roof is due to water in the extensive green roof plant root systems.  Because the system studied was non-irrigated (nature only irrigation), the soil media was rather dry.  However for heat to continue to be released for long hours, the heat source probably was water - and probably water stored in the underground parts of plants.

We ask ourselves many questions - if water is a significant heat sink and heat source, then do green roofs really act as insulating systems?

If green roofs are heat sinks then how much heat do they dissipate back into a building at night?

Are irrigated green roof systems actually hotter than non-irrigated vegetated roofs or reflective white roofs?  If so by how much?  How much cooling does plant transpiration and evapo-transpiration on irrigated green roofs?

There are many questions to be answered.

As an industry we need to sponsor and encourage more study of green roof thermodynamics.

I'm sure that over time a design model will be developed and accepted by the industry.  in the meantime - data sharing is crucial and important.


As always, feel free to leave comments or send us an email here.

Happy Green Roofing!

Kevin

Urban Green - Roofs and Food in Overton - Miami - Revitalization

Check out the excellent Collins Center Article about Urban Agriculture here.

Happy Green Roofing!  Kevin

Importance of Green Roofs for Endangered Species and Wildlife

Both wildlife and plant species struggle to compete with humankind for survival.  As a top level predator, humans possess a distinct advantage over most plants and species of the animal kingdom.  Scientists say 98% of all documented species ever to have lived on our planet are now extinct.

Fueled with the explosive energies of petroleum, humans have developed machines that can level vast expanses of forests with quick efficiencies.

Once the land is cleared of trees, natural hydrology, plants and wildlife, then the soil is chopped and leveled to make way for imprevious roads of asphalt and concrete.

Buildings rise where trees once stood.  Greenhouse gasses capture solar heat and along with the concrete and asphalt structures, cities and surrounding landscapes become increasingly hot and hostile to plants and wildlife.

Trees and plants, the most important primary producers of life sustaining oxygen, fade to the outskirts.

The lone endangered reptile, bird or butterfly, making their way across the vast expanse of now unrecognizable terrain, faces a number of exotic, invasive species and lack of habitat protection to escape to.

No place to mate, no place to feed, no place to hide.

Except for those Urban Core Green areas such as parks, conservation areas and especially green roofs.

Green roofs offer volumetric green - green with an altitude.  Volumetric green is an important component for survival with many species.

For example, the Florida anole requires greenery above 2 meters to escape the larger, more aggressive Cuban anole.

Green roofs, be they on a shed, garage, house, commercial building, apartment complex or bus stop - can make the difference between death and survival for wildlife.

Green Roofs & Gulf Fritillary, Agraulis vanillae

Importantly, wildlife will seek out and utilize green roofs, very quickly.  We have seen the progression, time after time, of - after installation of a vegetated roof - the arrival of the first wave of smaller creatures - lizards, anoles, frogs and tree frogs, insects and crickets, june bugs and dragonflies, butterflies and moths - each vying for their own space within the vegetation of the green roof.

Night pollinators, especially are drawn to the vertical greenery.

With the arrival of the first group of wildlife species comes an unexpected benefit - an Integrated Pest Management System.

Anoles and tree frogs devour large amounts of  mosquitoes, flies, roaches and termites, adding fertilizer to the green roof plants and keeping plant pests such as aphids under control.

We have witnessed areas that have always been subject to house fly infestations become virtually fly-free with the installation of a nearby green roof.

As the first generation of smaller wildlife species becomes established on the green roof the next populations of larger birds and reptiles begin to appear.

Witnessing black racer snakes and other beneficial snakes and reptiles inhabit the green roof is like watching a Discovery Channel Video.  The snakes forage across the green roof plants for lizards and frogs, maintaining population control.

Following the snakes are the raptors - birds of prey tracking snakes and smaller birds (Mourning Doves), squirrels and other green roof species.

Owls, red-tailed hawks, peregrine falcons, swallow-tail kites, osprey and a pair of eagles regularly visit nearby green roofs, choosing perches in nearby trees - and taking the opportunity to feed on the occasional ground mouse running through the neighborhood.

To borrow a phrase from a popular movie, - You build it and they will come...

Green roofs are important sanctuaries in the concrete jungle for wildlife, especially those species endangered because of habitat loss.

Build a green roof and they will come.  Save a species from extinction.

Happy Green Roofing and Happy Friday Afternoon!

Kevin

Garinesville Regional Utilities (GRU) Proactive Approach to Invasive Species

We posted an article a week ago about the inclusion of a Class 1 FLEPPC (Florida Exotic Pest Plant Council) on the proposed planting schedule for the Gainesville Regional utilities (GRU) Green Roof.  The design called for use of Heavenly Bamboo, Nandina domestica.  Nandina domestica is listed by FLEPPC as an invasive plant.

Responding proactively, GRU has posted a comment informing the removal of Heavenly Bamboo, Nandina domestica from the GRU green roof plant species list - and is reviewing additional landscape requirements to ensure avoidance of use of any FLEPPC invasive plants.

We applaud GRU's approach and concern about the Central Florida ecological systems and the relationship exotic invasive species may have.

Providing educational information and data is essential in assisting efforts of ecological organizations such as FLEPPC.

Thanks are in order to the University of Florida's (IFAS) Center for Aquatic and Invasive Plants and their efforts to promote understanding of the issues associated with landscape plants with aggressive growth patterns and few or no natural predators.

As always, feel free to submit questions and comments here.

Happy Green Roofing!

Kevin

Lightweight Nature-Irrigated Extensive Green Roof Florida

Photos here are of an extensive green roof in Jacksonville, Florida.

33kg per M2 - 8 lbs per SF lightweight green roof

One of the important requirements for the roof was the weight restrictions.  Because the existing roof was flat and the center distance the existing rafters were placed on, the architect specified a green roof system weighing less than 8 lbs/SF - 39.2 kg/M2 live load saturated with water.

Insulation and TPO were added per the design and the green roof system installed.

Non-irrigated - nature based irrigation for green roofs

The green roof system is a woven polyethylene (UV resilient) mat with a soil media especially designed to move water off the roof.

Metroverde Extensive Green Roof Florida

Existing roof contours create a slight swale or low spot where stormwater runoff would accumulate during large rain events.  Certain green roof plants where chosen for the areas where rainwater might be expected to accumulate.  These plants were chosen based on their ability to survive on natural rainfall, dew and fog.  Additional considerations factoring into plant choice were: the ability to grow under both extended wet and extended dry conditions; wildlife value, evergreen color, simplicity in form and root systems that would adapt to growing horizontally rather than vertically.

The Yucca filamentosa is an excellent shallow soil plant because of the roots habit of growing horizontally.  Many times this plant can be seen growing in natural areas with very shallow or rocky soils.  Click here for a Floridata plant sheet describing Yucca filamentosa, also know as Adam's Needle.

Yucca filamentosa will grow upright when provided with adequate soil depth.  The plant is ideally suited for green roofs because it also possesses the ability to acclimate its habit and height to a more "bonsai" form when limited by shallow or rockier soils.

Another excellent green roof trait the Yucca filamentosa possesses is the low stomata to leaf surface ratio - the S/LSR ratio equation we typically use in green roof plant suitability determinations.

Average soil media depth of the green roof is approximately 1".

The roof is subject to moderate shade, especially on the southern end.  Sunlight exposure is greatest between the hours of 10:00 am and 4:00 PM.

After seventeen months in the field the roof is looking good and the plants are well established.

As always, feel free to email us with your questions and comments here.

Happy Green Roofing!

Kevin

Green Roofs and Exotic Invasive Species - Koelreuteria elegans

Koelreuteria elegans is a species we see sprout across Florida green roofs on a regular basis.

The plant was first brought to the USA from Taiwan as a landscape plant.

Koelreuteria elegans is also know as the Golden Rain Tree and offers bright, stunning colors in the fall and winter months.

Each tree produces numerous seeds during the year.  Seeds are then quickly spread by both birds and water - stormwater runoff.

Once the seeds find organic material, dirt or sand they quickly sprout and send out agressive roots.

The plant is now classified as a Class Two Exotic Invasive species by the Florida Exotic Pest Plant Council.

According to the University of Florida's Center for Aquatic and Invasive Plants, the species is difficult to eradicate and has no know biological control mechanism.

The important factor for green roof designers and owners is realizing this species spreads quickly and should not be used as a green roof plant.  Green roof maintenance procedures should identify juvenile sprout appearances so that they may quickly be removed from the green roofs.

Water and Wind Spread Invasive Plant Seeds

It is probably safe to say that it is not 'If" a Florida Green Roof will sprout a volunteer Golden Rain Tree but "When".

The photo here is of a mature Koelreuteria elegans growing on the bank of a creek in Jacksonville, Florida.  Each year thousands of seeds are dropped and picked up by the flowing water and carried about a half mile to Pottsburg Creek and then the St. Johns River.  Over time this one tree has probably contributed tens of thousands of new Golden Rain Trees along the banks of the St. Johns River - each themselves contributing tens of thousands more.

Green Roofs are situated high in the air, and poised much like the tree in the photo here to spread plant genetic matter across a wide geographic range.

Is is therefore important for the green roof designer and the green roof maintenance staff to understand the ecological implications of the "Right Plant Right Place' concept.

As always, email us with your questions or comments here.

Happy Green Roofing!

Kevin

Rooftop Ethnobotany - Serenoa repens - Tropical, Native, Medicinal Green Roof Plant!

Serenoa repens - Cemetery Green Roof Ethnobotany

Green Roofs in a cemetery!  Tomb it may concern - check out the Serenoa repens atop the mausoleums in NOLA.

Serenoa repens, also know as saw palmetto is a tough plant - resilient to drought, flooding, hurricanes and possesses an extremely tough root system.

Wikipedia has an informative webpage about Serenoa - click here and the Wikipedia page will open in a new window. 

Serenoa repens - Cemetery Green Roof Ethnobotany

 

 

Serenoa is one of the most prolific native plant species found across the southeastern US. 

A wonderful medicinal plant, the Serenoa berries have been used for centuries to help reduce prostate inflammation and urinary tract infections due to the content of fatty acids and phytosterols found in the fruit.

Consider using Serenoa repens on your next nature-irrigated vegetated roof...

Happy Green Roofing!

Kevin

Serenoa repens - Cemetery Green Roof Ethnobotany

Green Roofs - Slow Absorption & Release Heat Sinks

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.

Happy Green Roofing!

Kevin