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.
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. Using Frontage to Increase Allowable Building Area
There is no requirement for a building to use the frontage increase provisions of IBC Section 506.3, but when used, the following requirements apply:
Performing the Frontage Calculation
The frontage calculation can be performed by hand, but I recommend the building frontage calculator. If you want to do the calculation on your own, here are the steps:
1. Determine the weighted average of the width of open space (W). This value, W, is determined by the following equation:
W = (L_{1} x W_{1} + L_{2} x W_{2}...)/F
Where: L_{n} and W_{n} are the length of wall segment and width of open space adjacent to that wall segment. Remember that W has to be at least 20 feet. If the width of the public way or open space is greater than 30 feet, you are required to use a maximum value of 30 feet for the calculation. F is total building perimeter fronting a public way or open space with a width of 20 feet or more.
2. Determine the total building perimeter, P.
3. Solve IBC Equation 55 to determine the frontage increase factor.
I_{f} = [F/P  0.25] W/30
The frontage increase factor can then be used with IBC Equations 52 or 53 to determine the allowable area the building. You can input the If value directly into the allowable area calculator as well. Notice that with Equation 55, the maximum possible frontage increase factor is 0.75. In order to achieve this maximum value, the entire building perimeter has to front an open space or public way with width of 30 feet or more. If the width at any point is less than 30 feet, or if a portion of the building perimeter does not have any frontage, the frontage increase factor will be reduced. Conclusion
Using the frontage increase provisions of IBC 506.3 is a common way to increase the allowable area of a building. There is no requirement to use these provisions, but when you do, the requirement described above do apply.
When working with architects, I frequently see code summary sheets with a frontage calculation for Type I buildings that have an unlimited allowable area. Since there is no requirement to take a frontage increase, I typically remind architects they don’t need to perform the frontage calculations if the building already has an unlimited allowable area. This saves time and also prevents possible permit review comments on a code provision that wasn’t needed in the first place.
2 Comments
Stephen M. Mesich
5/11/2022 02:51:25 pm
Thank you very much !
Reply
Leave a Reply. 
Archives
March 2022
Categories
All
