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Directions: Enter values for occupancy classification, construction type, sprinklers, and proposed number of stories, as well as building perimeter lengths and distances from building to property lines. Choose 2006, 2009, or 2012 International Building Code (IBC). Press "update" button.
Based on the selected IBC, values are calculated for allowable areas, heights, and numbers of stories. The site plan (Fig. 1) corresponds to the default values indicated below for a proposed 4-story, unsprinklered office building (occupancy class = B) of type III-A construction. Distances may be measured from the building to the far side of a "right-of-way" [R.O.W.], as is shown for the building perimeter facing east. In this case, the distance is 35 feet. Some occupancies require sprinklers under certain circumstances: see notes immediately below calculated values for details.
Notes and clarifications:
Building volume, floor area, and distances to property lines may also be constrained by zoning ordinances, which are not considered here.
"Total allowable area" is computed based on the "Proposed number of stories" selected. To find the maximum possible allowable area for a given building condition (i.e., for a given geometry, frontage, sprinkler status, and so on), set the "Proposed number of stories" to the "Maximum allowable stories."
The "Allowable area per floor" may not be consistent with the site and building geometry used to compute the frontage coefficient. In other words, computing the allowable area per floor doesn't guarantee that the proposed floor/site plan — used in part to calculate that allowable area — is acceptable. This is due, in part, to the way in which the building code is written: it is intended to be used, not primarily as a design tool, but as an analysis tool.
For more information, see my online building code handout.