Consider the Source


By Chris Wark, Energy Editor
August 29, 2011
Graphics Courtesy Chris Wark Unless Otherwise Noted





I used my free will to become an engineer.  It has something to do with my innate desire to know how things work – not just machines, but nature itself.  This choice meant that I also had to accept, albeit grudgingly, the stereotype of social ineptitude that too often goes along with the life title of "Engineer."  On the other hand, an engineer is also expected to provide accurate answers to technical questions, regardless of how painfully boring it may be to the audience.  So when another engineer or prominent engineering publication fails miserably at communicating technical information in an appropriate manner, I am at once sympathetic and horrified.

Let’s take, for instance, the Building Sciences column of the June 2011 issue of ASHRAE Journal.  Before starting in, let me explain that this article needs to be taken seriously for two reasons:

1. ASHRAE Journal is the trade publication for the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).  This is the organization whose standards for commercial and residential building energy use and indoor environmental quality (IEQ) are officially recognized throughout North America and referenced around the world.  They are partnered with the USGBC to establish energy savings and IEQ criteria for LEED.

2. The author of the article, Joseph Lstiburek, Ph.D., P.Eng., ASHRAE Fellow, is a recognized authority on building physics, specializing in moisture control in building envelopes.  He is from Toronto but is an advisor to the U.S. Dept. of Energy and the U.S. EPA.

The article, entitled "Seeing Red Over Green Roofs," can be read in its entirety with footnotes and pictures by downloading it here.

To let us know straight off that he is not your stereotypical engineer, Mr. Lstiburek gives us an immediate dose of what some consider a gruff-but-lovable style by declaring "This green roof stuff is getting out of hand.  It is dumb to do a green roof to save energy.  If dirt were energy efficient, we would call it insulation and put it in walls.  It is just dirt.”

He follows this up with much praise for polystyrene over natural materials by explaining that “It works better and costs less than adding dirt and grass.  Tastes great, less filling.  Now you don't need a goat to keep the grass in check.  It gets complicated figuring out what to do with the goat."

Ha, ha, ha!  How refreshing to see such folksy banter coming from an engineering nerd – breaking down stuffy technical jargon into simple language that anyone can understand.  After all, Mr. Lstiburek makes it clear later in the article that he loves green roofs...but only because they are nice to look at, nothing else.  Besides the lack of energy benefits, he declares throughout the article that there is no water control benefit that couldn’t be handled better another way (although he never says what that way is, just that Toronto is doing it wrong), no urban heat island mitigation that couldn’t be solved with a cheap, shiny cool roof, and certainly no benefit of wildlife support or CO2 reduction.

"Typical" green roof? Coombs, B.C., Canada.
Photo Source: Harmony Inn

Those who have read my series Cooler than Cool Roofs: How Heat Doesn’t Move Through a Green Roof should have a pretty good idea of the complexity of heat transfer through a green roof.  My guess is that Mr. Lstiburek missed it, along with all those light-weight soil data sheets which tell us that something like 85-90% of a green roof substrate is not regular old dirt but low-density mineral products like expanded clay, perlite, etc.  In the world of building sciences, these materials are known as “insulation.”  I think he has also overlooked insulation requirements for places like Miami and San Francisco which ASHRAE makes clear should be different from those in Toronto's building codes.

Not to say that Mr. Lstiburek has any reason to take me seriously since he is an influential expert in building envelope physics while I still depend on my heat transfer textbooks and the research of plant biologists.  He simply takes a less sophisticated view of energy analysis than I do and insists that all a building needs is R-20 insulation and a shiny surface and that thermal mass has virtually no effect.

As I explained in Part 4 of the series, the primary role of the growing media in controlling heat transfer is its thermal mass – its ability to store heat and maintain a fairly level temperature.  The ultimate example of this is the ground, which, as most people understand, stays at a fairly constant temperature several feet below the surface, keeping cellars and basements cool during the summer and unfrozen during the winter.  To the contrary, Mr. Lstiburek bluntly corrects "the crazies who like underground houses" by letting everyone know that dirt is a bad insulator and implying that the benefit of thermal mass is just an illusion. 

No need for air conditioning here at Nine Houses.

Of the 10 factoids Mr. Lstiburek presents to support his argument that green roofs are useless for anything other than esthetics, he got exactly 1 completely correct: that a green roof will protect the waterproofing membrane, but then he adds that they are way too expensive for protection alone without giving a cost comparison between a typical protected-membrane roof and a reasonably priced extensive green roof.

Well, maybe 9 factoids, since one is not, strictly, a statement of fact.  Regarding storm water retention, he merely asks "Storing rainwater on top of your building?  Are you on crack?"  No.

Storing water on rooftops in New York City.

Besides Mr. Lstiburek's credentials and support from ASHRAE, his assumptions of how heat moves through a green roof are widely held in engineering circles.  I do not mind that green roof energy benefits are misunderstood, only that such misconceptions are perpetuated by some engineers with such great confidence and so little analysis to back them up.  After all, the engineer that is willing and able to invest more than a few minutes in a subject as arcane as green roof heat management is pretty rare.

Correcting a presumptive engineer on technical details is one thing, but going up against a regularly published ASHRAE Fellow whose scientific opinions are shaped by a strong political bias is quite another.  It is when Mr. Lstiburek reveals his contempt for any pro-environmental government policies that we see him take a pathetic stab at being the Rush Limbaugh of architectural engineering.  The political ranting begins with "When Chicago went green roof crazy, I didn't care.  I mean, it is Chicago.  Why get worked up over a city that doesn't have a real baseball team?  But when Toronto got the green roof bug my world was rocked.  What happened to Toronto the Good? ...Was it because of all those politically correct ecocrazy neighborhood activists from the Annex on City Council?"  His world was rocked? Really?

Mr. Lstiburek continues on the anti-eco warpath, including an incorrect claim that it is impossible to get any building permits in some cities without including a green roof and then takes an unnecessary swipe at members of the USGBC.  He tells architects that "If you are so unsure of your ability...that you need to use someone else's arbitrary and pretty capricious checklist to be a part of some silly club, knock yourself out" and then invokes the cliché of LEED points for installing bike racks.

Many of us in the green roof world have had to listen to this kind of nonsense for a long time and learn to tune most of it out, but we also learn to consider the source.  I know the process of Mr. Lstiburek's formal training because it was the same as mine.  We were taught that shoddy research would make us look like fools, promoting deceptive conclusions is intolerable, and getting 9 of your 10 facts wrong will get you flunked or fired.  We were taught to regard with the utmost respect those to whom we were charged with providing accurate information.

"Green roof crazy" Chicago and its famous
Chicago City Hall Green Roof.  Photo via Wikipedia.

One of the most important sources of technical information on building envelope performance just failed on all these counts and ASHRAE Journal supported it in their attempt to be entertaining.  Instead of sticking with the tedious yet informative technical communication at which engineers excel, they misinformed everyone considering a green roof while inadvertently picking a fight with those of us who know better.

When it comes to making an investment in something as significant as a green roof, I'll take annoying and accurate over funny and wrong any day.

Disclosure note: I wrote a letter to the editor of the ASHRAE Journal in response to the June 2011 Building Sciences column but was told that it was too long to be published.  Editing it down to the required 300 words was painful, having to leave out a few critical corrections. The letter was rejected again because it was "just going to pick a fight." Fighting for accuracy so that we can be as sure as possible of how things work and make them work better is why I became an engineer in the first place.

Copyright 2011 Christopher Wark

Publisher's Note:  Read about Chris Wark in the Speakers page of the Greenroofs & Walls of the World™ Virtual Summit  2011, and come join us on September 27 and 28, 2011 to watch him present "E = MC2 of Green Roofs: Ranking Energy Benefits by Mission, Climate and Construction."

Chris Wark
Senior Energy Analyst
Viridian Energy & Environmental

Christopher Wark has over 20 years of multidisciplinary engineering experience providing mechanical, thermodynamic, and electronics support and services to manufacturers, universities and national labs. For the past 8 years, he has focused his efforts on the development and promotion of technical solutions in architecture and construction. Chris is currently a Senior Energy Analyst for Viridian Energy & Environmental, which was previously a division of Steven Winter Associates. At Viridian, he conducts whole-building energy analysis, air flow modeling, and provides green roof design consulting.

Before joining Viridian, Chris provided energy analysis and LEED consulting services for several companies, including subsidiaries of the Integral Group and previous to that served as Technical Sales Manager for Mentor Graphics Mechanical Analysis Division (formerly Flomerics Inc.), offering energy and air flow analysis solutions for architectural engineers. In 2002, Chris established SHADE Consulting/Green Roof Innovations with his wife Wendy.
With SHADE/GRI, Chris developed and marketed several innovative modular eco-roof systems, a roof system heat transfer and cost computer program, and conducted green roof system heat transfer analyses for 5 major cities and organizations. He continues to develop modular planting systems in partnership with Guiyang Chuangjia High-Tech Accelerator Co. LTD in Guiyang, China where their first project will be installed this spring.

Chris has also been involved in other thermodynamic related work, including advanced engine research and fuel cell system development at Caterpillar Inc. and laser development at Lawrence Livermore National Lab and 2 private research laser development companies. He has presented at numerous conferences, has several articles published on a wide variety of engineering topics, and has had the privilege of working directly with several universities, including Stanford’s Center for Integrated Facility Engineering (CIFE) program.

Chris holds Bachelor’s and Master’s of Science degrees in Mechanical Engineering (with a minor in Materials Science) from Washington State University. His graduate work focused on thermodynamics, fluid dynamics and combustion.

Contact Chris at:

Past Green Roof Energy Series Articles

Download Chris Wark's complete 32-page Green Roof Energy Series (PDF).

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