The post-frame construction industry has grown steadily in North America, gaining more and more widespread application in the past 100 years. Yet, many people still wonder, “what is post-frame construction?”
Post-frame buildings are structurally efficient buildings composed primarily of, trusses, purlins, girts, bracing and sheathing. The primary element of the design incorporates square posts or wood columns, which are typically embedded in the ground or surface-mounted to a concrete or masonry foundation.
The post-frame building concept is not new. Many pre-historic peoples throughout the world used posts embedded in the ground to fashion sturdy structures for residences and other uses. For centuries, buildings along shorelines and in low-lying areas have been built on poles to elevate the structures above the guideline and/or water hazards. In rural areas, poles were used to erect sheds or temporary structures in 19th-century America. In all these cases, the limited life-span of poles in contact with the ground made them unsuitable for use longer than a few years, except in very dry areas or when rot-resistant strains of wood were used.
However, two significant technological developments in the twentieth century allowed the post-frame building to develop into a viable, long-lived structural system. First, pressure-treated materials that provided excellent durability, particularly poles that were initially developed for the electrical industry, became available for the construction of buildings. Secondly, large, lightweight metal sheeting was produced that could span supports spaced several feet apart. What remained was for builders to optimally use the advantageous features of these two materials in what is now known as the post-frame or laminated column building.
The availability of pressure-treated wood permitted the replacement of a continuous concrete foundation in conventional buildings with a vertical structural member that carried the live roof and dead building loads directly to the ground below the frost line.
The availability of lightweight, formed, metal roofing material permitted the use of spaced roof decking. The strength of the roofing materials resulted in a significant portion of the lateral building loads being transmitted to the end walls, to reduce the load on the supporting posts. The availability of trusses for a wide variety of spans further enhanced and aided in the development of the post-frame building. Whereas trusses in conventional light-frame buildings are generally spaced 2-ft. or less on-center on stud walls, trusses became readily available that permitted truss spacing of anywhere from 4 to 12 ft. in post-frame construction. Each of these features contributed to the evolution of the modern post-frame building and its increasing popularity.
H. Howard Doane is credited with being the innovator who, in 1930, first combined the availability of poles and metal roof sheeting into a “modern” building concept. The founder of Doane’s Agricultural Service, Doane was looking for a way to reduce the cost of agricultural structures. He did not believe the traditional barns being built on farms could be economically justified. Doane believed that the “pole” building could provide the needed economy in construction and still have the necessary durability.
The Depression of the early 1930’s called for practical structures to be built on farms across the country. For Doane, it made good business sense to use a pole construction method, rather than build an extravagant structure that would outlast its usefulness on a farm.
He began to build barns that utilized round poles as the primary supporting member for the sidewalls and roof systems of the agricultural structures. These barns used read cedar poles as the primary structural support. Rafters were constructed every 2 ft., on which 1 in. of sheathing material was placed 12- to 18-in. apart. The sidewalls were covered with galvanized steel. This building method eliminated much of the structural material used in other methods, and best of all, it reduced costs.
Doane’s Agricultural Service’s farm manager, Bernon G. Perkins, has been credited with refining the evolution of the modern pole building from a temporary to long-lasting structure. Red cedar poles were used at the time, lending up to a decade or more of longevity to structures at that time. When red cedar poles became scarce in the mid-1930’s, Perkins used creosote-treated poles to provide the primary structural support. This extended a typical pole building’s life by some decades. By the early 1940’s, creosote-treated poles became the mainstay of the building concept.
Another mainstay of this ‘pole-barn’ building method was to use 2×4 lumber placed on edge as purlins. With this design change, pioneered by Perkins, it was possible to place the rafters and trusses from 4- to 12-ft. apart, making it possible for the roof to support the loads to which it would be subjected.
Ever the pioneer, Perkins had other ideas on improving the building method. He began to overlap the roof purlins, without cutting, by using 2×4 lumber direct from the yard with whatever length was available. This eliminated the extra handwork required to cut the purlins to size, saving time and money. The pole-building method proved to be an economical way to construct rural buildings.
During World War II, the U.S. government imposed a $1,500 limitation on the amount it could spend on constructing new barns. The pole-barn building method, which eliminated up to two-thirds of the lumber needed by other systems, made the government’s guidelines attainable.
Doane’s Agricultural Service actually received a patent for the “pole building design concept” on June 6, 1953. However, rather than protect the patent, they widely publicized the concept and encouraged its use throughout the United States. Doane’s Agricultural Service made its pole barn building plans available worldwide to anyone interested in the concept. Perkins spoke to farmers all over the country on the benefits of pole-building construction. They listened.
Initially, the nation’s college and university personnel were hesitant to accept pole buildings. But doubts about the ability of the structures to withstand wind and snow loads were put to rest, as time proved the buildings’ capabilities. After scientific tests proved its superior performance, the academic community became an invaluable ally to the growing industry.
As the concept developed, the performance of post-frame buildings proved excellent. Structures with smaller columns and post-soil embedment depths less than those indicated by accepted design techniques at that time withstood high wind forces and snow loads. It was clear that post-frame buildings were transmitting loads in a manner unaccountable in previously used design processes. Academically-based researchers began to study the phenomenon to unlock the secret of its superior performance. They attributed the manner in which the frame interacted with trusses to absorb loads and resiliently return to its intended shape as “diaphragm interaction” or “diaphragm design.”
In the 1960s, post-frame structures began popping up on farms all over the country. The concept quickly spread beyond the farm into commercial and other applications. The method’s name also changed from pole construction to post-frame construction around this time, as round poles became less commonly used. Post-frame was distinctly improved from the “pole buildings” of the past by use of rectangular solid-sawn posts and laminated columns.
The movement of the post-frame building into the commercial marketplace necessitated compliance with building codes. For many years, agricultural buildings in many rural areas were exempt from building code requirements. Since the design was not understood by building officials, and since no approved and recognized design procedure had previously existed, the suitability of the post-frame structure was often questioned before the end of the twentieth century.
The post-frame building had its origin in agricultural applications, primarily for cold livestock housing, machinery storage, and hay or other crop storage. Post-frame is still used for these applications, but non-farm commercial buildings now represent the major market for most post-frame builders. In terms of durability, performance, and cost, the post-frame building is a viable structural concept for any form of single-story building. With the use of solid-sawn posts or laminated columns, the buildings offer a large wall cavity that can be highly insulated to achieve the higher thermal resistance or “R-Values” greater than those possible using other building methods.
Countless structures are now erected using post-frame methods, including strip malls, convenience stores, restaurants, office complexes, and many other types of retail, public, commercial and residential applications. Schools, churches, fire stations, airplane hangars, and many other kinds of structures may be erected using post-frame design.
Although for reasons of economy many post-frame buildings were and are externally finished using metal cladding, almost any exterior or interior wall, roof or ceiling finish material may be applied. A wide variety of materials never envisioned by industry forefathers are now routinely incorporated into post-frame design. So many types of materials may be used on the façade, one may easily mistake a post-frame structure for another kind of building. Today it makes little difference whether the building purchaser favors the esthetics of wood siding, brick or stucco; virtually any look is available in post-frame. New concrete siding materials have even made it possible to build a post-frame building that looks like it was made of cement block, at a fraction of the cost. They are aesthetically pleasing and durable structures that are typically easier on the eye than most commercial buildings.
Since the framing in post-frame buildings can be spaced at modular distances to make finishing the interior a straight-forward process, the post frame building has found increased applications in office, retail, religious, public and recreational buildings. Greater awareness of the potential for post-frame buildings in residential housing has also developed. There are excellent examples of post-frame buildings with upper floors or lofts. Concrete floors are found in most commercial post-frame buildings. In some of these buildings, the posts are supported on a foundation wall or on the concrete slab, eliminating the need for the post embedment.
New products are also now available that will extend the life of embedded posts. For instance, plastic sleeves or post protectors may extend the life of embedded posts. Pre-cast concrete columns with unusually high compressive strength are also now available upon which wooden columns are affixed above ground, eliminating any chance of rot caused by ground contact and making it possible for post-frame structures to be designed that may well last for centuries.
The history of the modern post-frame building is only the beginning. New developments in building materials and design will lead to further improvements. The economic and strategic advantages of the post-frame design ensure the industry’s continued success well into the future.