IRC vs. IBC and Structural Requirements

[radioatlas]

In general, would it be safe to say that a building engineered under the IRC would have reduced structural requirements (and is therefore slightly more economical under normal conditions) than the same building engineered to meet the IBC?

 

[Mark K]

The IRC is an attempt to provide a simpler code for residential structures. They do this by removing a lot of options that are not normally common to single family residences. When the structural provisions in the IRC were being developed the authors of the IRC were guided by the structural provisions in the IBC but tradeoffs were made..

The laws of physics apply equally regardless of what code you use. The codes we have are based on tradeoffs.

My sense is that while in in some situations the IRC provisions may comply with the provisions in the IBC there are other situations where the safety factors in the IRC are slightly less than in the IBC. This is especially the case where individuals try to apply the IRC provisions to situations that the authors did not consider. So in order to have what some consider a simpler code you may have a slightly less safe code in some situations. But some consider this tradeoff acceptable because all they want is a simpler code.

If you are considering a design that pushes the limits of what was assumed by the IRC you should use the IBC.

Because the IBC structural provisions give the designer more tools and allow for the consideration of special cases I would expect the use of the IBC to in many cases result in a cheaper design. In my experience when engineers are involved with the design of a residential structure where the IRC could apply, the engineer will inevitably use the IBC structural provisions.

If you have s simple single story residence I would not expect the choice of code to have significant impact on the price of the materials. This is because many of the issues are governed by other considerations. For example it is not uncommon to use 2x6 exterior wall studs to allow more insulation to be used when structurally a 2x4 stud would be acceptable.

 

[mtlogcabin]

Because the IBC structural provisions give the designer more tools and allow for the consideration of special cases I would expect the use of the IBC to in many cases result in a cheaper design.

The state allows us to accept a "master plan" for single family homes. Due to our seismic zone (D1) we encouraged some of our developers to go this direction. They balked at first because of the cost of the engineer but then found they would recoup those cost after 3 or 4 homes. So when you can save for example $3,000.00 per house and you build 100 homes per year the developer saved $30,000.00 over a year and we have 9 year code cycle the last time around that savings just adds up year after year.