It’s impossible to have a green building without paying close attention to building science. 

It’s impossible to have a green building without paying close attention to building science. A building constructed without building science will be green in name only and begin showing its un-greenness eventually-by using more energy than predicted, exhibiting moisture problems and suffering premature failures of systems, components and materials. This point is driven home in every building science paper I have read and in every building science seminar I have attended.

I was fortunate to have attended a recent building science fundamentals seminar put on by the gods of building science, Drs. Joe Lstiburek (pronounced STEE-brook) and John Straube. The seminar was done in a tag team format; Lstiburek and Straube took turns, going back and forth 45 minutes each for eight hours a day over two days. It was intense and informative. The list of subjects on the agenda included rain control, air control, heat, air and moisture movement, insulation and thermal bridges. Last on the list was green building/sustainability. Near the end of the second day a participant asked: “When were we going to talk about green buildings?” to which Dr. Straube replied: “Isn’t that what we’ve been doing?”



A long time ago, buildings were made of simple materials like timber and stone. They were durable and relatively maintenance free but not all that comfortable. As time went on, new building materials like steel, concrete and float glazing became available, which allowed designers to create lighter, less massive buildings with lots of windows. Discovery of cheap, abundant fuel sources allowed buildings to be built in less hospitable climates. As the price of energy went up, awareness of the importance of air control and insulation followed. The real problems began when these new buildings got tighter and better insulated without a thorough understanding among designers and builders of the relationship between light building enclosure assemblies and heat, air and moisture movement.

Building science as we know it today began as a fix for one problem which caused others to erupt. Higher energy costs led to an increase in insulation which led to rotting, corroding moldy walls (cold condensing surfaces in cavities were created) which led to the requirement for a vapor retarder which led to more rotting, corroding, moldy walls (moisture in the wall cavity no longer able to dry out) which led to the discovery that an air barrier is necessary (holes in the assembly allow a much greater transfer of moisture than a vapor retarder) which led to the discovery that ventilation is necessary (tight buildings with poor ventilation have high relative humidity, more moisture problems and poor indoor air quality) which led to more HVAC equipment to move more air which led to pressures created within the building sucking and blowing within and across the enclosure which led, you guessed it, to yet more moisture problems.

Most of us are still trying to figure this stuff out, which means that many buildings are still being designed without enough attention to building science fundamentals resulting in buildings that do not perform as well as they could.


Building codes are an excellent example of a reactive response to problems that arise in buildings. Historically, building codes change after problems in buildings occur through requirements meant to prevent known problems from recurring-and for good reason! It would be impossible to anticipate all things that could go wrong with a building before they actually happen. Reactive responses such as building codes usually result in prescriptive requirements. An example of this is the prescriptive requirement that a vapor retarder with a perm rating of less than 1.0 installed on the warm side of the exterior enclosure, no exceptions. Those that are up to snuff in their building science knowledge will recognize that this requirement could, in fact, create more moisture problems in certain situations such as reverse vapor drive in an air conditioned building with a reservoir cladding like brick veneer. A vapor retarder on the interior can cause condensation to occur with the wall cavity when the sun heats up the wet brick and drives moisture inward. A proactive approach moves away from a prescriptive requirement to a performance-based requirement. A recent performance-based change to the International Building Code includes three classifications of vapor retarders, and provides options for using each type depending on the climate zone, the cladding and the insulation used-it only took 40 years!

In addition to causing moisture problems, buildings with poor air tightness can require significantly more energy to heat and cool. A recent NIST study designed to evaluate the energy impact of improved air barriers found that buildings in hot climates use up to 16 percent less energy with a good air barrier and buildings in cold climates up to 37 percent less. The reactive energy code approach to solve this problem merely requires that the building have tight-fitting dampers at flues and vents, that they use materials that pass an air barrier test and that they be adequately sealed. These measures do not guarantee an adequate reduction of air leakage. The current City of Seattle Energy Code offers an example of a proactive, performance-based requirement with regard to air tightness. The new code requires that construction documents show a continuous air barrier at the exterior enclosure and that the building be tested for air leakage upon completion.



 Building science is confusing. It is a subject that is not addressed very well by university architecture programs in North America and not well understood among practitioners. To design a building enclosure properly, for any given building, in any given climate, a building designer must be able to answer the following questions:

 Is a vapor retarder required? If so, at what perm rating?

 What is the proper location of the vapor retarder if required?

 What is an air barrier? What is the proper location of the air barrier?

 What is required to make the air barrier continuous?

 What is the required R value of the enclosure?

 How is the R value of the enclosure calculated?

 What measures are employed to prevent thermal bridging?

 What is the condensation potential with the enclosure assembly? In the summer? In the winter?

 Is reverse vapor drive a potential problem?

 Is the drying potential of the enclosure compromised in any way?


Answering these questions for every enclosure assembly for every building in every climate would probably give most building designers a headache. Lstiburek and Straube have made life simpler for them, however, by developing what they call the Perfect Wall (turned up to make the perfect roof and down to make the perfect floor to complete the enclosure). The Perfect Wall keeps water from getting into the building from the outside (rain and reverse vapor drive), from the inside (vapor diffusion and air transport) and lets the water that starts out in the assembly (water saturated wood for example) escape. It locates the vapor diffusion retarder correctly for every climate while simultaneously acting as an air barrier. It addresses thermal bridging which results in a high R value. It addresses each question above in an elegant, cost effective and efficient way and the buildings constructed under the program will last for decades.



A green building must begin with an enclosure that satisfies building science fundamentals. A well-designed enclosure ensures that heat, moisture and air are properly and effectively managed resulting in a building that is comfortable and safe for occupants, thermally efficient, dry and very durable. Building codes are getting there, but as a reactionary approach to problems, they can’t get you all the way there. To find the best source of information on the subject, I invite readers to go to where they will find dozens of articles, case studies and technical documents on building science fundamentals and examples of the Perfect Wall-all offered to the public by Building Science Corporation free of charge!