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Energy Cost Savings through Green Roofs – a Myth

 

By Jörg Breuning, The Green Roof Patroller
June 28, 2013

It is unavoidable and just common sense that wearing wet clothes in winter will end up in hypothermia.  Wearing the same wet clothes on a hot summer day, however, might help to feel cooler – but do not get confused with feeling more comfortable.  If we have only one set of clothes, all season clothes, these are typically made of two layers.  The first layer protects against direct environmental impacts like direct sun light, rain or wind, and the second layer usually consists of a breathable layer for comfortable wearing and controlled air circulation.

Source: Columbia

I have learned on my travels all across different desserts on Earth that these layers reduce temperature increase on hot sunny days but at the same time they reduce the body heat loss during extreme cold nights.  Indigenous people of extreme environments have learned this lesson over centuries and were able to survive under these extreme conditions with this simple layer strategy.  My dad used to say: “What is good for the cold is also good for the warm.”

Any man-made building is nothing else than a body that requires consistent “body temperature” to make it usable for the purposed design.  A building without reliable all-season clothes is worthless or requires a tremendous effort (energy or operating costs) to make it useful.

To make a building useful for people, the “coat” consists typically of an insulation layer covered with a protective layer against the elements (waterproofing, roofing membrane).  Since we all know that the protective sheet against the elements will deteriorate over time, this sheet (waterproofing) has to be renewed over time - what experts call re-roofing and this is done usually every 18-25 years.

To insulate or not? It seems like common sense. Graphic Source: baulinks

In my experience, (almost 35 years of designing and installing green roofs), it is proven that a green roof can extend the lifespan of the roofing by at least twice.  The green roof acts like an additional all season two layer system on top of the roofing where healthy plants are the first layer and protects against direct environmental impact.  The green roof growing media (green roof soil) is the second breathable layer.

There is only one difference; the breathable layer (growing media) on a green roof is also the basis for the wellbeing of the plants and must be able to store water and air at the same time for a healthy growth.  If this layer doesn’t fully support the plants (and only the plants), the entire coat does not function and the plants will indicate this by suffering or change of plant varieties.

Above we learned that a wet coat in winter causes problems because water is not a good insulator, and so we have to consider heat loss in winter when it comes to a green roof.  We also understand that dry green roof soil in summer will store heat (in the aggregates) which in turn increases the cooling needs.

A green roof (and green walls that grow on growing substrates on the wall with consistent irrigation) are only thermal masses with hardly any insulating value.  Considering and fully understanding this matter of fact should make building owners cautious when somebody tells them that green roofs are good insulators.  This is just not the case, or only if the building envelope is insulated correctly from the beginning.  Fixing heating and cooling loss only through green roofs and/or green walls is simply impossible or the short-term profit thinking of individuals with no long-term experience in advanced building physics.

I believe that current research done in this field saying green roofs are good insulators is eyewash.  Adding a little real insulation below the original coat (waterproofing or walls) would be much more effective (cost-wise and physically) than any vegetated layer combined with growing media or growing substrate alone.

However, the thermal mass “green roof” certainly has lifespan-extending properties for the waterproofing (and – again- I can confirm with projects that are much older than 35 years).  This is the key to start thinking in long terms (50 years+) in the building industry and is most sustainable approach.  Longevity is hardly considered in LEED™ and with emphasis on longevity, many LEED™ awarded buildings might fail for a certification because they can’t be upgraded easily when the costs of energy increase.  I am not talking about how wasteful the footprints of many of these “innovative” building design are.

Photo DM Products: Penn State’s futuristic Millennium Science Complex earns LEED™ Gold for this space wasting empty overhang.  The “water head” of the campus (or of their bureaucracy?). Not even plants can grow below – how can people survive?

In the last 35 years energy costs have gone up by 8-10 times (!) and we all know that they will increase accordingly over the next 3-5 decades (the life span of green roof).  With this fact in mind, selling a green roof for insulation purposes will unavoidably end up in a costly disaster for the building owner when removing a fully functioning green roof in less than 25 years from now just to add more insulation, meet future requirements, or to keep your heating and cooling costs low.

Green roofs do extend the life span of selected and important building components dramatically; this is simply the highest environmental friendly approach in the building industry and the most cost efficient way to promote green roofs to reduce costs for the owner over decades.  However, if scientists and green roof professionals do not understand this unique property of green roofs and don’t design underplaying components accordingly, the building owner won’t be a happy building owner in 20-25 years from now and for sure he or she won’t reinstall the green roof because it just added new costs without benefits as originally promoted.  He might not understand why he should throw away a green roof just when the vegetation has been well established - only because individuals led him in the wrong direction two decades earlier?

Conclusion:

• As a building owner, be careful when people try to sell you a green roof as a good insulator without mentioning that you have to add insulation to the building in first place for future energy needs.

• Building owners have to understand that any available research about the insulation value of green roofs reflect only a current snapshot and potential savings in a very short time (less than half life time of a green roof) and in my opinion are worthless when the intention is to build for half a century.

• There is no energy study done over 50+ years comparing a green roof (plus additional insulation) and a conventional roof that will be re-roofed in 20 years from now and insulation added at the same time (typical re-roofing practice).

Trust only experts that recommend installing additional insulation under the green roof because then they expect that your investment will last a human lifetime, and will be profitable as well as  also affordable during this time.  Designing the roof (or wall) for five decades or more requires a lot responsibility and expertise of the designers – if they value their customers.

By the way, utilizing “Passive House” design principles (ongoing research and development in Germany since 1990) goes beyond LEED™ and is less costly - or if you find no space on the wall to hang-up a little plaque of the certification.  Energy consumption of a Passive House is between 5-10 lower than an average LEED™ building, and the actual footprint to the environment is 2-5 times smaller.  In 2010 there were over 25,000 Passive Houses in Germany and around 13 in the USA.  Passive Houses have green roofs.  (Source: Wikipedia.  Learn more about Passive Houses.)

 One of the original 1990 Passive Houses, located in Darmstadt, Germany.  Source: Wikipedia

In conclusion, regarding insulation, green roofs and energy savings, research is not conforming or shows in this little area it might work and in another it might not.

Why bother with the misleading and unclear general energy savings statements for green roofs when we know they are so site specific?  Energy savings do not even represent a drop in the bucket and claims might bring a false and misleading image to an entire industry!  Instead of just focusing on one benefit, in this case energy savings, let’s look at the bigger picture: Re-roofing and stormwater runoff are such massive issues all produced by any development that is commonly underestimated by people or so called experts.

A proper green roof could save 1 re-roofing, which for a 40,000 sf roof could represent about $300,000 in savings.  Life could be so simple and so green if 80% of the research money would be actually spent in doing things right at the beginning.

We want our next generation to do well with green roofs, too.  It is simply our responsibility that we create nature when we took nature away by a development.  Replacing nature can be done so easily and efficiently with modern green roof technology and without super over engineering and excessive self-promoting research.

Did somebody ever research whether it is better having a back yard with plants instead of concrete?  No, because it’s common sense.  Let's promote common sense and show the true costs of not doing a functional green roof.  Let’s learn from the indigenous people and do the right thing for the specific area where the immobile structure is located.
 

Jörg Breuning

 

Publisher's Note:  For an in-depth look at greenroofs and energy, please revisit the 32-page Green Roof Energy Series (PDF) by Greenroofs.com Contributing Editor Chris Wark.  Contact Jörg below with your commentary.
 

Jörg Breuning, principal of Green Roof Service LLC (Green Roof Technology)

Jörg was born in the green roof capital of world. He began working with green roofs in Stuttgart, Germany in 1980. Since then, he has installed and maintained tens of millions of square feet of green roofs throughout the world.  Remember, everyone, that English is not his mother tongue!

During his career Jörg has earned multiple degrees and certifications in landscaping, horticultural, and green roofing. In January 1983, Jörg Breuning was one of the first people in the world to earn a green roof professional accreditation from Optima, now Optigrün AG, who were the first green roof manufacturer to offer an in depth educational system for the installation and maintenance of their products. In order to be eligible for the accreditation, a candidate had to have completed 3 years of apprenticeship with a certified landscaping company. In 1985 he earned his national certification and horticultural technician degree – a program of work and study that required 5 years of practice in an approved landscaping company and 4 semesters of University study.

In 2003 Jörg transferred his German Company (founded in 1985) to the United States after being the key consultant for Chicago’s City Hall green roof. As an experienced horticultural expert, he has been able to educate many of North America’s green roof pioneers, providing them with fundamental green roof knowledge to start and grow their own businesses.

His company Green Roof Service LLC (Green Roof Technology) has introduced numerous innovations to the North American green roof industry. Many of these innovations have been adopted by companies such as Roofmeadow, Emory Knoll Farm, GAF, CETCO, Rooflite, Green Roof Solutions, Celebrity Cruises Miami and Optigreen.

Jörg’s articles will strongly focus on topics that ensure common sense is always practiced, ensuring that the horse stays in front of the cart, and provide valuable insights into making green roofs as popular and efficient as they are in Europe.

Contact Jörg at GreenRoofPatroller@greenroofs.com.


Past Green Roof Patroller Articles

The opinions expressed by our Guest Feature writers and editors may not necessarily reflect the beliefs of Greenroofs.com, and are offered to our readers to simply present individual views and experiences and open a dialogue of further discussion, debate and research.  Enjoy, and if you have a particular comment, please contact the author or send us an email to:  comments@greenroofs.com.

 

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