High Performance Building Envelope: Tough Enough?
April 26, 2007
At the November 2004 Greenbuild Conference held in Portland, Ore., it was announced that the U.S. Green Building Council and the Canadian Green Building Council had agreed to a formal licensing agreement. This agreement allows the CaGBC to adapt the USGBC’s Leadership in Energy & Environmental Design - New Construction green building rating/certification program to its own needs, culture and regional influences. As part of the agreement, both the USGBC and CaGBC agreed to recognize each other’s certified projects. Also, as part of the CaGBC’s adaptation of LEED (LEED-Canada-NC-1.0), a building’s durability is explicitly addressed under Credit 8 for Materials & Resources. LEED-NC under the USGBC had no such credit/point criteria concerning a building’s durability. As such, the USGBC has been watching Canada’s initiative in this area carefully for possible inclusion in their programs.
Pursuant to the Canadian Standards Association’s Guideline on Durability (CSA S478-95), one point can be earned for developing and implementing a building durability plan. Paradoxically, this sole point for durability has met with a firestorm of resistance from insurance companies who consider it an implied warranty. As such, they are advising developers not to seek the durability credit, lest they invite potential litigation if/when the building does not meet expectations. Another part of the resistance equation is cost. Entailing a mountain of paperwork, the cost to comply with the CSA durability standard is estimated to be about $6,000 Canadian.
Into the LightIronically, two relatively recent phenomena have made the industry and public-at-large aware of the importance of durability to the built environment. First, the green building movement itself has been a major factor in this epiphany. European countries, particularly Scandanavian nations such as Norway and Sweden, have been applying elements of durable design into wood-framed structures for centuries. Japanese temples and French cathedrals, some well over 1,000 years old, testify to mankind’s ability to build durable, lasting structures. Yet, the life expectancy of a suburban mall or tract house in the United States is only about 50 years.
In August 2005, a pilot version for a new LEED “product” was released: LEED for Homes (LEED-H). This program requires a detailed durability plan for implementation entailing third-party inspection. Moisture intrusion (in the form of precipitation) being one of the major “elements” of durable design, LEED-H recognizes that moisture control/damage is greatly influenced by climatic conditions. This being the case, LEED-H utilizes a graduated point system based on expected annual precipitation. Under this graduated scale, up to five points can be earned depending on the region.
Additional points can be earned for having automated controls on exhaust fans whereby local exhaust moisture sources (i.e. kitchens and bathrooms) are greatest (third-party testing of airflow rates required). Also, an additional point can be earned for humidity control.
When you come to a fork in the road...Take it! These are words of wisdom from Yankee great and resident philosopher Yogi Berra. In the case of durability, rather than just two choices, there are typically three forks in the road (approaches) to choose from. For a wide range of users and for adaptation to change, a process-based approach such as LEED-H and LEED-CA-NC works best. The simplest, most manageable approach is the prescriptive method doing what its name implies: prescribing specific measures. However, to be effective, these measures must recognize and take into consideration regional influences and building type/size. Though difficult to document and verify, most flexible and adaptable for initiative is a performance-based approach.
A good example of both the performance and prescriptive approaches to durable building design and construction is a program sponsored by Nisco Services Group. Launched in 2000, more than 70,000 homes have been constructed under the Environments for Living program. Six of the nation’s largest homebuilders are participating in the program, which addresses moisture management, ventilation and air pressure. With the support of both leading building science experts and organizations, the program establishes criteria for “tight” construction of the building envelope, thermal systems improvements, combustion safety and performance testing.
Known as a “comfort guarantee,” it is the highest level of certification offered as an option by the builder. In 2005, a new “Diamond Class” level of certification was added to the program. This certification level recognizes green building elements such as water efficiency improvements.
Taking the LeadPrograms like Environments for Living address durability in home warranty programs. Organizations such as the Athena Sustainable Materials Institute have been intimately involved with establishing durability levels. At the governmental level, you might think that the U.S. Department of Housing and Urban Development would be in the lead in terms of promoting durability but, to date, it has not taken such a position. Another federal agency, the Department of Energy, has stepped up to the plate and taken the lead where durability is concerned with their Building America program. The innovative program makes use of DOE’s national laboratories for applied research in the field of building sciences and durable design.
A building built of durable materials requires less maintenance and repair over the long haul and amortizes its economic and environmental impacts over an extended period of time. Simply put, a building that doubles the average life cycle of a similar structure halves the environmental impacts of building it. The GreenSpec Directory considers both durability and low maintenance as criteria for inclusion in the directory. Very often, durable materials are inherently low maintenance. A building should be consider for both its life cycle and service life expectations in its design and construction. Ironically, it is not for a lack of structural integrity that buildings are most often modified and/or replaced.
A Little TLCThere are many tangibles and intangibles that contribute to a structure’s durability. For example, a house in which George Washington spent the night will probably have a better chance of being maintained, restored and/or cared for in perpetuity than the house down the road. Essentially, the elements by which a structure’s durability can be defined/determined include moisture intrusion, material selection and failure, heat stress, pollutants, insect infestation, building functionality, architectural design/style and natural and man-made disasters.
We can begin this conversation about these elements with a look at moisture intrusion – one of the main reasons there has been a preponderance of mold litigation in recent years.
Old Man TroubleOf the three conditions needed to have a mold problem – ambient air temperature range, food source and liquid water – far and away, liquid water is first among equals for laying blame when mold appears. All that is needed for moisture intrusion into a wall cavity are three things: a hole, the presence of liquid water and a force to drive it.
This is a simple formula for disaster. In large part, durability is an issue of water management, so much so that HUD devotes 75 percent of the content to it in its publication “Durability by Design” – published by Partnership for Advanced Technology in Housing. Of critical importance is a structure’s design and construction. Providing deep roof eaves to deflect rainwater away from the façade, damp-proofing foundation walls, proper flashing at roof/wall interfaces, chimneys etc., grading away rather than towards the building perimeter, rainscreen detailing for exterior walls and breaks (drip stops) to deter water migration by surface tension all are essential in keeping the building envelope dry.
Beyond design and construction, sources of moisture range from precipitation (rain) to occupant behavior. “Wicking,” the ability of water to migrate through foundation walls and floors by way of capillary movement, is a source of moisture within the building envelope. Wicking can easily be demonstrated by dipping the corner of a paper napkin in a glass of water. “Damp-rise” refers to the observed phenomenon of the water rising by capillary action up and across the surface of the napkin. A leaky plumbing fixture is just as likely to introduce moisture as is wicking. Other internal sources of moisture include drying of building materials (i.e. concrete, plaster), high relative humidity, cooking, showers and clothes drying.
Once temperature conditions are right (typically 50-100 degrees Fahrenheit), a food source is available and – most importantly – the stage is set for damage from mold, mildew, dry-rot etc. thus undermining the integrity and, ultimately, the durability of a structure.
MaterialsSimply understood, many building materials wear out prior to the completion of a structure’s life cycle. As such, the material choice should be as or more enduring than the expected service life of the structure itself. Choosing more durable materials that require less maintenance and/or replacement makes a lot of sense. Even if it costs more up front, that cost is amortized over time. For materials that will need replacement, ease-of-replacement is critical and must be considered.
There exist myriad building materials that both resist and repel water and moisture (those that repel water are known as “hydrophobic”). Foil-back gypsum board, foil/paper-face insulation etc. serve as vapor, a retarder/barrier slowing down the movement of water vapor (water in its gaseous state). Other materials block capillary and/or airflow.
The corrosive nature of water must also be considered when selecting materials, in particular where metal will be exposed to ocean breezes and/or salt-spray.
Tug of WarInherent in many building materials,
especially steel and other metals, is their ability to expand and/or contract due to thermal stresses placed upon them. When the two cantilever arms of the East Bay span of the San Francisco-Oakland Bay Bridge met to be joined, they were off by 10 inches due to the sun heating one side of the bridge (thus expanding it) and a cool wind contracting the other side. Only by using hydraulic jacks and battering rams were the two halves of the cantilever joined in the morning hours when the sun was still low in the sky. Such is the power of solar radiation. Likewise, an aluminum window will expand at a higher rate of expansion than the glass within its frame, causing leaks to occur over time. So too, metal roofing will expand and contract with the possibility of loosening fasteners. In recent years, the premature degradation of fire-treated plywood used as roof sheathing was directly related to high roof temperatures.
Here Comes the SunAlong with heat, ultraviolet light is a major cause of roofing material failures. One of the benefits of green roofs, besides mitigating the “urban heat island effect” and relieving storm sewers from storm water run-off via the “percolation effect,”, is their ability to keep the roof surface cool. This inherent “insulating effect” helps prolong the life of the roof surface due to heat degradation. Plastics, fabric, paint and wood are all degraded by UV light both inside and outside the building envelope. Widespread use of “Low-E” (Emissivity) coatings on modern window glazing allows light in but blocks and keeps harmful UV light out of interior spaces.
Atmospheric PollutantsIn this category, there are two major contributors to building material degradation: Ozone and Acid Rain.
Especially vulnerable to ozone damage are synthetic materials such as rubber, polyester, nylon, dyes and paints. Ozone is both a blessing and a curse. In the stratosphere, it blocks harmful UV light from penetrating the atmosphere. The “hole” in the ozone layer in the southern hemisphere is a grim fact of life, a result of greenhouse gas emissions into the atmosphere. However, quite the opposite is true of ozone (an unstable form of oxygen) at ground level. Nitrous oxide in the presence of sunlight reacts chemically with volatile organic compounds to form ozone. Thus, it is considered a pollutant at ground level causing serious health problems – particularly for people with respiratory illnesses such as asthma, bronchitis, emphysema, etc.
Acid rain became a major problem with the advent of the industrial age. Limestone facades of ancient structures such as the great cathedrals of Europe began and continue to erode as a result of the combustion of hydrocarbon (high sulfur-content coal) emissions into the atmosphere (sulfur oxides) generating acid rain. Acid rain is corrosive and affects a wide range of building materials. The production of synthetic gypsum via the flu gas desulfurization process has gone a long way in helping mitigate the acid rain problem here in the United States. Combining the sulfur present in the chimney effluent of coal burning power plants and mixing it with calcium and water, calcium sulfate – gypsum, is produced. This process satisfied the federal mandate of the Clean Air & Water Act passed by Congress in 1990, gave the gypsum industry a practically limitless supply of the purest and most economically produced gypsum in the world while, at the same time, reducing sulfur emissions into the atmosphere by about 96 percent.
One very effective way of mitigating the harmful effects of acid rain is the use of a rainscreen to manage water coming in contact with the building envelope. A masonry cavity wall with a brick veneer, air space, flashing, weep-holes and concrete masonry unit backer is a good example of a rainscreen. By allowing for gravity drainage to occur behind the facing material, any incidental water that penetrates the outside plane of the exterior surface (membrane) of the wall assembly is removed by the weep holes denying liquid water the opportunity to remain trapped in the wall cavity.
Insect InfestationIt might surprise you to learn that termites cause more damage to American houses annually than fires – about $2 billion worth. In particular, the FST (Formosan Subterranean Termite) is the scourge of Hawaii, the gulf and southeastern states. It was first introduced to the U.S. after WWII by ships carrying cargo from Asia. A queen FST lays a prolific 2,000 eggs per day and can live up to 30 years in a colony over an acre in size. Because it is inorganic and therefore inedible to termites, carpenter ants, beetles, silverfish etc., light-gauge metal framing is gaining ground as a piece-for-piece replacement for traditional wood frame structures.
Building Functionality & Architectural Design/StyleHuman nature plays an interesting role in determining the endurance and durability of a given structure. The more value the owners/occupants place on the structure, the more likely it will endure – it’s that simple. As building components wear out, the owners are much more likely to repair/replace what needs to be repaired and/or replaced. A similar analogy is the owner of a luxury car vs. a basic car owner. All things being equal, the luxury car has a greater chance of lasting longer since it is of more value (pride of ownership, status symbol, cost to purchase etc.) to its owner than the basic car is to its owner.
It’s estimated that about 30 percent of commercial buildings will be reconfigured during their service life. It stands to reason then that the more adaptable a commercial space is to change, the more durable it will be.
Gone Before Their TimeA St. Paul, Minn., study found that of 227 commercial and residential buildings torn down between the years 2000 and 2003, only 31 percent were demolished due to their physical condition. Area redevelopment and/or unsuitability for intended/anticipated use accounted for 57 percent of these 227 buildings. This demonstrates the fact that it is the building’s functionality rather than its durability that promotes longevity in a structure.
Structures that represent “timeless architecture” – those that are both functional and aesthetically pleasing, like Notre Dame cathedral in Paris or Frank Lloyd Wright’s masterpiece “Fallingwater” – stand a much better chance of surviving the test of time. As the saying goes, “A thing of beauty is a joy forever.”
Natural DisastersThe Boxing Day Tsunami of 2004 made it clear that nature’s wrath can be devastating both to the natural and built environment. Few structures could survive a wall of water hitting them dead-on as happened that day. However, in 1923, the Imperial Hotel survived the Tokyo earthquake thanks to Frank Lloyd Wright’s incorporating a “floating foundation” into its design thus proving the forces of a powerful earthquake could be resisted successfully.
Hurricanes, tornadoes, floods, fires, earthquakes, tidal waves, avalanches, volcanoes etc. are beyond our control. The spate of destructive hurricanes, droughts and wildfires in recent years is demonstrative of this warming effect. Aside from environmental activism on the global front, development along flood plains and heavily wooded areas where both floods and wildfires, respectively, are likely to occur should be discouraged. A structure in such a location essentially has one foot in the grave whereby its durability is concerned.
Man-Made DisastersHow much of the architectural heritage of Europe was lost in the two world wars - particularly from aerial bombardment in WWII, can only be imagined. The events of Sept. 11, 2001 are demonstrative of how man-made disasters can/do impact a building’s durability. Seven World Trade Center, a 40-story office building, collapsed in the late afternoon of that day. Out of the ashes of that day of infamy it has risen anew, this time “hardened” with the specter of terrorism in mind. So too, certain types of structures like embassies must take extraordinary measures to resist blasts making their very existence, much less their durability, feasible.
Beyond natural and man-made disasters in all their varieties, eminent domain – the power of the state to seize property for public projects such as roads and bridges will end a structure’s existence no matter what it is made of. In the final analysis, having withstood the “test of time” is the ultimate goal and compliment a structure can receive.