Putting the ‘green’ in post frame

As the green building movement continues to grow and become a major force in construction, post-frame building, as an inherently green building system, stands well positioned in this marketplace.

To compete effectively and increase market share in green building, however, more post-frame professionals — including architects, design professionals and builders — need to learn about the many green attributes of post-frame construction, including that it is strong, lightweight and an efficient form of construction. They also need to be aware that, compared to steel-frame construction, post-frame construction causes less site disturbance, uses materials more efficiently, and creates larger insulation cavities to promote energy efficiency. 

Although terms such as green and green building continue to be murky in both meaning and impact, the growing effect of green building on the building landscape is clearly evident. According to Green Outlook 2009: Trends Driving Change (McGraw Hill, 2009), the value of green building is expected to increase to between $96 and $140 billion by 2013. Moreover, a recent study by Good Energies, Inc., finds half of all nonresidential building stock will consist of green buildings by 2015.

Given this anticipated surge, it’s best to focus on the purpose, rather than the precise definition, of green building, which is to create a safer and more efficient structure for both humans and the environment. Without a doubt, post-frame construction is an efficient building system. Unfortunately, green building certification systems often do not take into account efficient building systems and instead focus on conventional wood construction, steel moment frames, or monolithic concrete building systems.

To be considered a green building among any of the green building certification systems, the building needs credit for other green building features. The post-frame building system impacts green building in the following areas:

Site specification
• Minimize soil disturbance and erosion. Post-frame construction requires minimal soil disturbance in most cases, since only post holes need to be dug. Further credit for this reduction in soil could also be obtained in some ‘Innovative Solution’ sections.

• Reduce local heat island effects. Due to the limited soil disturbance for posts, there is less possibility that current trees and shrubs on the site need to be disturbed in order to construct the building. By providing shade and vegetation around the structure, the ‘heat island’ effect, attributed to heat radiated from buildings and surrounding man-made materials, is mitigated.

• Pest control. The use of termite barriers and preservative pressure treated lumber prevents long term decay of a building. Additional points may be gained for use of certain PPT that do not contain arsenic or pentachlorophenol.

Material Efficiency
Typical post-frame construction uses a system of posts and trusses. The structure also is engineered with a specific documentation of framing elements and cut lists. Because little site cutting is needed for these materials, post-frame construction contributes to

• lower framing material waste

• detailed framing documentation

• cut list for lumber

• offsite fabrication. (Some systems re-quire all components to be panelized or constructed offsite for this credit.)

In addition to these credits, post-frame far exceeds so-called framing efficiencies, which are usually realized by spacing 2×4 or 2×6 studs in a wall up to 24 inches on center. The purpose of this credit is to allow larger spaces for insulation and reduce thermal breaks. Additionally, post-frame wall systems offer a great reduction in the amount of concrete needed for securing the post or a pier system compared to a continuous frost wall with footings.

Energy Efficiency
• Exceed IECC insulation. The large cavity created in post-frame walls allows for a higher level of insulation than recommended by the International Energy Conservation Code. Based upon current IECC calculations, filling the cavity with most types of standard wall insulation should provide this level of compliance. This finding should be confirmed with actual energy calculations of the structure.

• Reduced envelope leakage. With fewer wood elements in the exterior walls and more insulation coverage comes the potential for reduced envelope leakage. This finding should be confirmed with actual leakage measurement of the structure. FBN

Dan Hindman is an associate professor in the Department of Wood Science and Forest Products at Virginia Polytechnic Institute and State University in Blacksburg, Va. For more information, please contact him at 540-231-9442 or e-mail dhindman@vt.edu.

Special thanks to the by the NFBA Technical and Research Committee for its assistance in this article.

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