In December of 2010, Susan Dowty, then with SKGA, wrote an article for CE News regarding the minimum distance for building separation. The article clarified the code requirements concerning building separation that had been added back in to the 2009 IBC (see figure below) after having been inadvertently removed from the 2006 IBC.

While the required building separation has remained basically the same over the years, its applicability to projects has varied. This was highlighted in a recent question we received.

Q. Does the building separation requirement in the code apply to buildings in all seismic design categories or only some?

A. It depends on the code you are under. See the table below for the building separation requirements and their applicability to certain buildings.

As you can see from the table, back under the 1997 UBC the separation applied to all seismic zones. However, in the 2000 IBC the separation requirement was applicable to only structures in SDC D, E, and F. This held true through the 2009 IBC, but is no longer the case in the 2012 and 2015 IBC codes. In these newer codes the separation requirement is applicable to all structures not just those in high seismic areas. This is a difficult change for the low seismic areas that had gotten used to providing a nominal 1-in. or 2-in. expansion joint. But while this may be difficult for architects and owners to accept, it was a deliberate revision made by the Seismic Subcommittee of ASCE 7.

Another recent question that we received regarding building separations is not quite as easy to answer.

Q. Do buildings constructed at the same time, designed by the same engineer, and of the same construction but that have a property line between them have to follow the code requirement for δ_m from the property line on each side or can the square-root-of-the sum-of-the-squares (SRSS) be used to determine the required separation.

A. The square-root-of-the-sum-of-the-squares separation is intended to prevent damaging contact, as opposed to no contact, between neighboring buildings. ASCE 7 Seismic Subcommittee felt that this should be sufficient for buildings without a property line between them, in which case, they presumably belong to the same owner. When there is a property line between two neighboring buildings, the presumption is that they belong to different owners. Then the separation between them is dictated by the consideration that one owner’s building must not lean onto another owner’s property. Knowing the rationale given here, the engineer should be able to make the right decision concerning building separation, subject to concurrence by the owner and approval by the authority having jurisdiction.