kelvin8or
REGISTERED
Greetings all - I have a question about a possible conflict in the IBC (2018) regarding the ventilation of open parking garages. We are designing a mixed-use multi-family project, with a multi-story parking garage partially surrounded by an R-2 residential wrap (on 3-sides), utilizing IBC Special Provision 510.2 to achieve 5-stories of stick frame (Type IIIA) over a podium of Type IA construction. This was originally supposed to be an enclosed garage with mechanical ventilation, but our client is now wanting to completely surround the garage on all sides with residential, with a 10' separation between the garage and residential on 2-adjacent sides of the garage, and change the garage to "open", with no mech. ventilation (or fire sprinklers), providing the required 40% length/20% area of openings on those 2-sides. The assumed property line would be at the residential wall 10' from the garage. Table 602 Note C allows for open garages with a fire separation distance of 10’ or greater to have non-rated walls. That means they can have unlimited openings (or no wall at all). It also means that a multi-story (above grade) garage can have openings required for ventilation facing another multi-story building as close as 10’ away.
Which leads me to the conflict: since this is a sloping site, one side of the garage will be 2-3 levels below grade. Section 406.5.2.1 requires openings for natural ventilation below grade have an exterior horizontal clear space 1.5 x the depth of the openings. In the code commentary it talks about how as the distance of the openings below the adjoining grade level increases, the min. required exterior horizontal clear space also increases proportionally. It also refers to Section 1202.5.1.2, which basically says the same thing. So, although our openings will likely be no more than 6' tall, some will be roughly 28' below grade, which would require a horizontal clear space of 42'. Why isn't a similar requirement for increasing the clear space outside of above grade open garages, as levels are added, included in the IBC?
We posed this condition to one of our local codes officials, and he concluded that, because of the allowance in Table 602, that even the below grade levels only need 10' of horizontal clear space outside the openings, regardless of how deep they are below grade. Is his interpretation correct?
Which leads me to the conflict: since this is a sloping site, one side of the garage will be 2-3 levels below grade. Section 406.5.2.1 requires openings for natural ventilation below grade have an exterior horizontal clear space 1.5 x the depth of the openings. In the code commentary it talks about how as the distance of the openings below the adjoining grade level increases, the min. required exterior horizontal clear space also increases proportionally. It also refers to Section 1202.5.1.2, which basically says the same thing. So, although our openings will likely be no more than 6' tall, some will be roughly 28' below grade, which would require a horizontal clear space of 42'. Why isn't a similar requirement for increasing the clear space outside of above grade open garages, as levels are added, included in the IBC?
We posed this condition to one of our local codes officials, and he concluded that, because of the allowance in Table 602, that even the below grade levels only need 10' of horizontal clear space outside the openings, regardless of how deep they are below grade. Is his interpretation correct?