Some people who are not very familiar with post-frame construction may harbor a misconception that it is just for temporary structures. They think it is an inexpensive way to erect a shed or farm building, but not useful for much else.

Nothing could be further from the truth.

Illustration at right: Sunnypoint Gardens retail establishment, Egg Harbor, Wis.

Public buildings, strip malls, warehouses, convenience stores, airplane hangers, shops and other commercial, institutional and residential buildings have long been erected using post-frame design. These are all permanent structures that have withstood the test of time.

Post-frame engineering is codified by pertinent standards set by respected organizations.  These standards are referred to by the International Building Code to ensure that post-frame is entirely code-compliant.

Post-frame structures incorporate diaphragm design, metal plate-connected wood roof trusses, shear walls and other engineered elements that make them very resilient. Diaphragm design makes buildings capable of flexing and returning to their designed shape, making them more resistant to extreme environmental and seismic loads than other structures. Numerous studies have demonstrated that post-frame performs well in high winds and seismic loading conditions.

Here is a summary of facts regarding post-frame construction that make it stronger for its weight and therefor more resilient than conventional types of construction:

1. Posts in the ground add to the building’s stability and wind resistance. 
2. Horizontally-strapped posts form a tremendously strong box, which adds to wind and seismic resistance. 
3. In post-frame construction, the direct attachment of trusses to the post frame makes it virtually impossible for the roof to detach from the building.
4. The diaphragm effect created by post-frame structures allows them to flex under stress instead of cracking, crumbling, or collapsing like many other structures.

Some people think that because post-frame construction uses wood posts embedded in the ground, it is temporary construction. They wonder, “If you put a wood post in the ground, won’t it eventually rot?”

The public at large and even some construction industry professionals mistakenly think that all treated wood is the same and will always perform in the same way in different applications. However, the fact is there are many different categories of treated wood for various purposes. Treated wood for post-frame contains significantly more chemical preservative than is found in most treated wood, and the chemical is embedded more deeply within the wood’s structure.

Wooden posts are pressure-treated with preservatives approved by the Environmental Protection Agency (EPA) or other approved wood protection systems in accordance with standards set by the American Wood Protection Association (AWPA). In-ground testing of post-frame quality preservative-treated wood in ground contact in harsh environments has been conducted by the USFS Forest Products Laboratory since the 1940's. 

Does this mean that each and every post that was placed in the ground will last indefinitely? I asked former NFBA Technical and Research Committee Chairman Pat McGuire, P.E. this question, and he answered, “As with all building materials, it depends on quality.”

“As with any industrial process, the key is that the preservative treatment be performed properly,” McGuire says. “As a consumer, your best assurance of proper treatment is to insist that all treated lumber bear the quality mark of a code-approved third-party inspection agency.”

There are various grades of treatment, and post-frame builders should always use the highest grade of treated lumber available. In the rare case of rot, it is possible to replace or reinforce a faulty section on most buildings with much less expense than a similar repair to a concrete foundation. Some concrete foundations fail after several decades, occasionally requiring repair - the same may be said of all types of foundations, including treated wood foundations. 

Quality of materials and workmanship are key to any building's longevity. Builders and customers should check the inspection quality mark to ensure they are using a quality of post that will last.

If an inexperienced builder were to use whatever treated wood he found at a local lumberyard, most likely the building would not last - lumber treated for ground embedment of critical structural elements is of a completely different quality than that used for decks and other exterior uses.  Wood treated in accordance with AWPA Use Category 4B (or CCA .60 pcf) should be used for building posts embedded in the ground. Under normal conditions with proper drainage, high-quality posts may last indefinitely.

Post-frame buildings may also be installed atop concrete piers, a concrete slab or masonry wall. There are a growing number of enhanced wood protection products, pre-cast concrete posts and pier systems developed specifically for post-frame.  For more information about various foundation options, click here.

“We reflected over the past year and realized the significant improvement in the quality and efficiency of our operation directly results from our new school building. We believe that the building’s quality of design and construction is equal in significance to the fact that we needed additional space.”
- Anthony Argiros, The Family Foundation School, Hancock, N.Y.

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.