Post-Frame: It's as "Green" as it Gets
University of Wisconsin - Madison Professor David R. Bohnhoff, P.E., Ph.D., has been researching post-frame buildings for more than 30 years. Dr. Bohnhoff is considered one of the leading experts on post-frame building design. In his research of post-frame and other building systems in the context of the modern inclination of building customers to desire "green" or environmentally-friendly buildings, he reached a significant conclusion: "Post-frame buildings are as 'green' as it gets."
<---Post-frame buildings like this award-winning Morton Building feature low embodied energy and exceptionally high insulation R-values.
In his research, Dr. Bohnhoff found that in comparison to other building systems, post-frame buildings are arguably the most ‘green’ buildings one can erect for several important reasons. First, he notes that manufacturers of almost all building materials claim in one way or another that they are 'green' for various reasons, making the notion somewhat murky and leading many people to question the legitimacy of various claims of 'greenness.' He notes that a truly fair and comprehensive life cycle analysis from "cradle to grave" of a building's entire life cycle is crucial to assessing the negative environmental impact of a building, and that the focus of negative effects of erecting a building are largely measured in terms of the quantity of non-renewable and non-recyclable resources expended throughout that life cycle. The majority of non-renewable resources used throughout a building's life cycle consist of fossil fuels burnt to create energy to manufacture the building components, install them, and to power the building throughout its length of service.
Post-frame buildings are wood-framed buildings. Wood is a naturally-occurring and renewable resource, and one of only a few building materials that actually removes carbon dioxide (CO2) from the atmosphere instead of dispersing it as a greenhouse gas that contributes to global climate change. Post-frame buildings may use any type of interior finish or exterior siding or roofing product, so in this sense post-frame buildings are generally not different from any other type of building; however, many post-frame buildings use steel siding and roofing that is of a thinner gauge than other types of buildings with steel finishes (hence requiring less resources) and steel building products are almost entirely composed of recycled content. Compared to masonry products, steel does not use as much energy nor does it produce as many other types of environmental pollutants.
However, it is not only because the materials used may be renewable and/or recyclable and in other ways "environmentally friendly," but because post-frame buildings are the most economical and quickest to erect that makes them the "greenest" of buildings out of the starting gate. Post-frame buildings are design-efficient. Wide spacing between posts and other structural members means that they need fewer materials to achieve equivalent load capacities. There are less structural members for a builder to install. Therefore, they use fewer building material resources, as well as less labor and fuel to erect than other types of buildings.
Post-frame buildings are almost always the most economical buildings to erect, because of these material and labor efficiencies. Dr. Bohnhoff also notes that a basic, rectangular design is more efficient to install and thermal bridging is less likely compared to buildings with staggered roof lines and additional corners or other architectural flare that might result in additional materials, installation time and disruptions in insulation. Although amenable to these architectural flares, post-frame structures may be designed to maximize the inherent efficiency of a basic rectangular design. These efficiencies also mean that post-frame buildings have the lowest embodied energy compared to almost any other type of modern building system.
Over the life span of a building, the amount of energy required to produce and erect building materials is insignificant to the amount of energy consumed by the building's use over the span of many decades. This is where post-frame takes its moderate lead in the "green" building race and turns it into a landslide victory.
Like steel-frame buildings, framing members may interrupt insulation systems installed within the wall cavity. However, wood has natural insulating properties and does not conduct heat around the insulation system like a steel structural member may. ComCheck Analysis confirms that post-frame buildings achieve the highest R-values compared to steel-framed and brick or masonry buildings. Here is an example of Com-Check analysis of post-frame compared to the same building using steel-frame:
On a stud-frame building, studs less than four inches wide are typically installed every 16 inches on center. Most post-frame buildings have a six to eight inch post every eight feet or more on center. Insulation is installed in between these members - so there is a break in the thermal insulation barrier every eight feet or more in a post-frame building, compared to a break every sixteen inches for stud-frame. Larger, contiguous spans of insulation are much more efficient than shorter, more frequently interrupted insulation barriers. Also, because posts for post-frame are usually six inches or wider compared to the four-inch studs used in most stud-frame construction, there is a much wider wall cavity in which one may place thick fiberglass batt or other insulation - insulation may be as thick as eight inches in post-frame walls.
Post-frame buildings also easily accomodate almost any type of insulation system, and a popular choice is reflective air and moisture-resistant barrier systems, such as Thermax, that install between the frame and the exterior cladding, making a completely contiguous external envelope. With wall infill insulation wrapped in an uninterrupted reflective vapor barrier, one may achieve extraordinary insulation R-values. This means that post-frame buildings can achieve the highest insulation R-values of any type of building for long-term energy savings over the life cycle of the building.
Post-frame buildings may be designed to accommodate new technologies, such as passive solar heating, geo-thermal heating and cooling systems, radiant systems and more. There are new photovoltaic systems now available that are ideally-suited for sloped steel post-frame roofs. With proper design, the structure will easily accommodate passive solar water heating systems. Post-frame buildings are also largely maintenance-free, so less fuel, labor and materials are used to maintain the building over its lifetime.
Post-frame buildings not only have the lowest embodied energy and make the least site disturbance during construction, they also may be easily disassembled, recycled or reused leaving the site in clean condition if they are removed. This combined with long-term energy efficiency and low maintenance make post-frame "as 'green' as it gets."
Furthermore, post-frame buildings are almost always the most economical building choice, making the investment in saving the environment "one building at a time" affordable - so post-frame buildings are "Green buildings" that save "Greenbacks."
This story was written by John Fullerton and originally appeared Frame Building News magazine, the official publication of the National Frame Building Association. To subscribe to Frame Building News, please visit www.FrameBuildingNews.com.