Design professionals (architects and professional engineers) work with the International Building Code (IBC) almost every day.  Builders, owners and even a few code enforcement officials often question why we bother with all the complicated verbiage and rules outlined in the various building codes.  It is a common complaint that code requirements tend to over – build and confuse the design process, the building permit process and the construction of Post – Frame buildings.  Why must we use a building code to design and construct Post – Frame buildings?  Is the building code just another government intrusion that wastes everyone’s time and gets in the way?  Do we produce a better, less expensive, safer building if we follow code?  In this article, I would like to discuss some of the history background of our modern building codes and try to answer the questions I’ve posed above.

The main reason to exactly follow a building code is that in most states, counties and towns it is the law.  When a building code is legislated into state or local law, it is not just a set of rules that is nice to follow.  It is the law, no different than the laws that govern speeding, trespass and taxes.  The state legislature of most states have adopted some recognized building code as a set of laws to be followed by all citizens and corporations.  Building code enforcement officials are law enforcement officers that are charged to uphold state or local law.  I have been told that building inspectors in the State of California are required to know how to make an arrest.

Building codes in various forms have been around as law since The Code of Hammurabi. This code was written about 1775 BC in what is now the city of Baghdad.  Of the 282 laws that King Hammurabi decreed, six of them dealt with residential construction.  The full text with commentary is at: http://avalon.law.yale.edu/subject_menus/hammenu.asp

Law 228 set the fee a contractor could charge for construction based on square footage (two shekels per sar or about 1 oz of silver per 3.3 sf).  The remaining five laws (229 through 233) delineate penalties the contractor would suffer in the event of collapse or faulty construction.  The Hammurabi Code prescribed penalties that ranged from fines to death.  My own personal favorite is 229:

If a builder build a house for some one, and does not construct it properly, and the house which he built fall in and kill its owner, then that builder shall be put to death.

Did the Hammurabi Code drive construction costs up with the builder’s own life on the line?  It probably did increase construction costs and thereby decrease the contractor’s profits.  Even without available data we can speculate that the Code drove the building collapse rate to a very low number.  Since this area of Iraq is in what we would now call a seismic Zone 3, 80 mph wind and all exposure C, the local contractors were forced to construct houses that responded favorably to wind and seismic loads.

The most interesting question about The Code of Hammurabi is why it was written at all.  It is likely that King Hammurabi got tired of dealing with house collapses and dead occupants.  He wanted a uniform and equitable standard to which house construction could be measured with a clear set of penalties for those houses that failed to meet the standard.  In short, he wrote a building code to protect the health, safety and welfare of his subjects.

The main difference between today’s building codes and the Code of Hammurabi (besides the penalties) is the point at which the code is applied.  The Code of Hammurabi dealt exclusively with impending or total collapse.  As long as the house remained standing, the contractor was not liable.  This philosophy actually allowed for the construction of unsafe structures; the owner did not know if his house was not code compliant until it fell down upon his head.  He had a Certificate of Occupancy but he had to wait for a seismic event or a wind storm to get his “Plan Review”.

With the IBC in place, we no longer have to wait for collapse to determine the structural adequacy of a structure.  It is now believed that structural collapse is an unacceptable risk to the public health, safety and welfare.  Modern building codes mitigate against failure not collapse.  The difference between failure and collapse is what separates modern building codes from the Code of Hammurabi.  What is the difference between failure and collapse?

The difference between failure and collapse is why Hammurabi needed just six rules and our modern codes run to seven or eight hundred pages.  The mitigation against failure rather than collapse also explains why we enjoy such a low rate of structural collapse under extreme load conditions such as wind, earthquakes and heavy snow fall.

A structural component fails when actual or calculated stresses exceed allowable stresses.  Allowable stress levels are developed in laboratories and at universities by various material agencies such as The American Concrete Association (ACI), The American Society of Steel Construction (AISC) and The American Forest and Paper Association.  Allowable stresses are published in various formats for use by design professionals.  To give just one example, consider an unbraced, 12’ length of #2 DOUG – FIR 2 x 6 lumber.  The 1997 edition of the National Design Specification for Wood Construction (NDS) published by the American Forest and Paper Association can be used to determine the allowable stress due to bending (Fb) for this member as 916.4 psi.  The important thing to understand here is that this 2 x 6 has an extremely low probability of actually snapping in two at this stress level.  The design professional, however, is required by state law to keep the calculated bending stress at or below 916.4 psi.  At an Fb of 916.5 psi, the 2 x 6 is said to have failed in bending.  To get some kind of feel for the load condition that would fail this DOUG – FIR 2 x 6, imagine a pair of saw horses 12’ apart with the 2 x 6 spanning between them (with the 1 ½” edge up).  A 192.6 lb weight in the exact middle of the span will fail this structural member (Fb = 916.8 psi), whereas a 192.5 lb is within the allowable bending stress limit (Fb = 916.4 psi).

The real genius of the “failure” code philosophy over the “collapse” code mentality is that it allows for maximum stress levels while minimizing actual instances of collapse.  It further minimizes structural costs while minimizing collapse.  The IBC mitigates against failure and thus recognize the fact that over time and over the full range of application, the weakest graded member will experience the maximum load condition.  The IBC is thus able to insure public health, safety and welfare at minimum cost.

The Code of Hammurabi did not place a time limit on collapse and it may well be asked how the IBC deals with the endurance of structures over extended periods of time.  Are IBC compliant structures guaranteed forever?  They are not guaranteed forever but they are designed to resist environmental loads predicted to occur only once in every 50 years.  I’ve often heard comments such as: “You want me to install 6 x 12 posts?!!  I built one just like it 20 years ago with 6 x 6’s and it’s still standing.”  These structures have probably not seen or experienced a code mandated 50 year wind, snow or seismic event.

I looked up weather history for western Oregon and found that 47” of snow fell in Eugene, Oregon in January of 1969.  This is seven times the average snowfall for Eugene in January  and nearly three times the design snow load.  Hundreds of farm buildings collapsed as a result of this snow storm.  In October of 1962, wind gusts reached 116 mph in downtown Portland.  During this Columbus Day Storm, scores of livestock were killed when barns collapsed in rural communities.  Both these events took place less than 50 years ago.

The IBC goes a long way toward balancing risk and construction costs.  It is not possible to erect a structure that will withstand all environmental loads but it is reasonable and prudent to design a building for load conditions that are very likely to occur within its economic life.  Modern building codes must strike a balance between public safety and reasonable construction costs.  The IBC serves these needs very well.

With the background above we can finally look at why the IBC must be used to design and construct a post – frame building.  It is important to understand that post – frame construction employs very highly stressed structural components and as such must be carefully sized to ensure public safety.  Let’s compare stick – frame construction to post – frame construction and see how they differ.

The stick – framer has the CABO Code (Council of American Building Officials) and the IRC (International Residential Code) to tell him exactly how to frame and sheet his building.  It’s a cook book.  Every nail, every member size, every anchor bolt, every sheet of wood sheathing is specified for the stick – framer in the CABO and IRC Codes.  The Post – Frame builder, on the other hand, must analyze, size and locate every structural component in every structure based on the configuration of the building and the environmental conditions at the building site.  Since there is no such thing as a “Post – Frame Building Cook Book”, we have to rely on the IBC to tell us what the wind, snow and seismic loads are, how the building will respond and where the stresses are.  We have to do this every time for every building.  Each nail in every girt and purlin and truss block must be sized and installed accurately.  We have to pay attention to not only lumber grade but species as well.  All of us, builders, engineers, architects and building officials, must remember that we are dealing with highly stressed structural elements and that it is our responsibility to see that the state laws are upheld.   The IBC is our guide.  It allows us to safely load the structural elements and maintain our competitive advantage.

As Post – Frame builders, we must pay special attention to the requirements of the IBC because the structural components of our buildings are highly stressed.  We know we can always beat the sick – framers on cost and erection time.  We know our buildings are safe and durable.  We gain every one of these advantages by highly stressing all the structural elements in our buildings.  To give an example: a typical 2 x 6 girt installed in the Pacific Northwest is stressed by IBC design wind loads to 95% of allowable values.  A typical 2 x 6 wall stud is loaded to less than 20%.  That is to say that for each dollar spent on girts, the owner gets $0.95 worth of use.  The same dollar buys $0.20 worth of use in a stick frame structure.  Who needs to be more careful?  Who has more margin for error?  The IBC is our guide.  It provides us with safe limits.  It tells us exactly how to provide our clients with a robust and economical structure.

The writers of the IBC know that our structural components are highly stressed and they intend for us to be closely monitored by the Building Official.  Let me site the Oregon Interpretive Manual (Oregon Alternate Method Ruling No. 92-27, “Design of Post-frame Buildings Not Required To Be Designed Under the Architects Law”) as it concerns the design and construction of Post – Frame buildings.  This ruling was written in response to the question: “To what standard are Post – Frame buildings which fall below the requirements of the Architects Law required to be designed?”

“The perception by both the builder and some building officials is that these are simple buildings (referring to post-frame buildings)…These buildings are actually more complex because they are often structurally indeterminate; i.e., they mix embedded poles, knee braces and shear walls, so they cannot be analyzed by normal engineering methods.  Buildings or structures not required to be designed by the Architect’s Law, and which do not use conventional wood frame construction as provided in Section 2517; i.e.,…pole buildings…are required to be engineered or tested.” (emphasis added)

It is because we take our structural components right up to the very limit that we need and depend on the wise counsel of the Uniform Building Code and the International Building Code.  It takes an experienced and multi disciplined team to deliver a safe and economical structure to our customers.  Every building must be analyzed and designed by a Design Professional who knows how post frame structures respond to environmental loads and who knows the actual building techniques used in post frame construction.  Every set of design drawings and structural calculations must be checked for code compliance by a Plans Examiner who knows the Building Code and knows post frame construction.  Every Building Department must be overseen by a Building Official whose primary concern is the insurance of public safety and welfare.  Every building must be built by a Builder who knows post frame construction and whose primary concern should be the delivery of a safe, economical and robust structure erected exactly as specified by the approved design documents.  And finally every post frame structure must be observed and inspected by a Building Inspector who knows what to look for and who is prepared to make certain that the approved plans are followed and that the Owner will be presented with a safe, code compliant building.