The IBC offers 3 approaches to mixed occupancy buildings: accessory, nonseparated and separated. Any building with two or more occupancy types must choose one or more of these approaches for compliance. In this post, we will cover all three of these approaches and the specific requirements related to each.

If you have designed a building of Type II, III, IV or V construction, you probably considered the allowable building area, which depends on the construction type, occupancy classifications, presence of fire sprinkler systems, and a few other criteria.
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One common way to increase the allowable area for a building is to use a frontage increase. The frontage increase provision in the IBC, found in Section 506.3, recognizes the safety benefits of having open space directly adjacent to a building. When a fire department or other emergency responders arrive to a site, there is an increased level of effectiveness when those personnel can access a large portion of the building exterior.

As more and more states move to adopt the 2018 IBC, it's important to know about a few code updates that impact the design of occupied roof spaces. And if you're jurisdiction is on the ball and already adopted the 2021 IBC, there are a few additional items that apply to you.

In the past few months, I've had several clients ask me questions regarding grade plane calculations - most often related to determining whether a particular story counts as a story above grade plane or as a basement. Here is quick rundown of how to do the calculation and the implications.

October 2020 Update: I am moving all calculators to the Tools menu at the top right of the screen. I have also added in a slider bar to allow for varying frontage amounts (see the new tools page for this function).

​After several weeks of working on this, I'm excited to release a beta version of the 2015 IBC Allowable Height, Area and Number of Stories Calculator. Take a look and let me know what you think!

A few notes:

• Calculator is for single occupancy or non-separated mixed occupancy buildings. Separated mixed-occupancy functionality is coming later.
• There are some error notes that I've programmed in (for example, using an NFPA 13R sprinkler system in a non-residential occupancy), but the calculator is not foolproof. Some background code knowledge is needed.
• Allowable area results are displayed for no frontage increase and full frontage increase. You'll need to do your own exact frontage calculation if needed.