# allowable building area (frontage and sprinklered),



## Keith (Mar 29, 2011)

The single story sprinklered building in question is open 21' on the sides, 41' in back, and fronts the public way open with 60'

The formula below only considers frontage and sprinklers.

Question:*where in the code does the building get any increase for the sides and back yards in addition to this formula, or does it?*

(my understanding is it has to be 60 all sides to be unlimited)

Aa = At + [(At)(If)/100] + [(At)(Is)/100] = ______________________

Thanks,

Keith


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## Coug Dad (Mar 29, 2011)

from the 2006

506.2 Frontage increase.

Every building shall adjoin or have access to a public way to receive an area increase for frontage. Where a building has more than 25 percent of its perimeter on a public way or open space having a minimum width of 20 feet (6096 mm), the frontage increase shall be determined in accordance with the following:

If = [F / P – 0.25] W / 30   (Equation 5-2)

where:

If    =   Area increase due to frontage.

F   =   Building perimeter that fronts on a public way or open space having 20 feet (6096 mm) open minimum width (feet).

P   =   Perimeter of entire building (feet).

W   =   Width of public way or open space (feet) in accordance with Section 506.2.1.


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## Frank (Mar 29, 2011)

The open space on rear and sides counts as frontage-- would be better titiled open space increase.

Where the width of the open space on the same lot or to the far side of the public way varies, you can break up the portions and integrate over the perimiter to get a weighted average W.

W/30 at any point shall not exceed 1, except if all other unlimited area building requirements are met then it can have a maximum value of 2.

From 2009 IBC

506.2 Frontage increase. Every building shall adjoin or have access to a public way to receive a building area increase for frontage. Where a building has more than 25 percent of its perimeter on a public way or open space having a minimum width of 20 feet (6096 mm), the frontage increase shall be determined in accordance with the following:

If=[F/P-0.25]W/30

 (Equation 5-2)

where:

If= Area increase due to frontage.

F = Building perimeter that fronts on a public way or open space having 20 feet (6096 mm) open minimum width (feet).

P = Perimeter of entire building (feet).

W = Width of public way or open space (feet) in accordance with Section 506.2.1.

506.2.1 Width limits. The value of W shall be at least 20 feet (6096 mm). Where the value of W varies along the perimeter of the building, the calculation performed in accordance with Equation 5-2 shall be based on the weighted average of each portion of exterior wall and open space where the value of W is greater than or equal to 20 feet (6096 mm). Where the value of W exceeds 30 feet (9144 mm), a value of 30 feet (9144 mm) shall be used in calculating the weighted average, regardless of the actual width of the open space. Where two or more buildings are on the same lot, W shall be measured from the exterior face of a building to the exterior face of an opposing building, as applicable.

Exception: The value of W divided by 30 shall be permitted to be a maximum of 2 when the building meets all requirements of Section 507 except for compliance with the 60-foot (18 288 mm) public way or yard requirement, as applicable.

506.2.2 Open space limits. Such open space shall be either on the same lot or dedicated for public use and shall be accessed from a street or approved fire lane.


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## RLGA (Mar 29, 2011)

To add to Coug Dad's and Frank's post, since you have two yards that are less than 30 feet, you have to calculate a "weighted" W instead of using W=30.

W/30 cannot exceed 1, therefore W cannot be more than 30.  If your building could qualify for unlimited area but the only thing preventing that from happening is the 60-foot yards all around, then W/30 cannot exceed 2, thus W cannot be more than 60.

Assuming the former, to calculate a weighted W, you have to know what your building perimeter is.  For the sake of an example, let's assume your building is 100 feet by 200 feet, with the 100-foot portions having the 21-foot yards.

Since the front has a yard that exceeds 30 feet, W=30 for that portion, as well as the back with its 41-foot yard.  For the sides, W=21.  To calculate the weighted average, take each W and multiply it by the portion of the perimeter that W is applicable, sum the totals up and divide by the total perimeter of the building.  Using the example building, the calculation would be as follows:

Weighted W = [(30' x 200') + (30' x 200') + (21' x 100') + (21' x 100')]/600'

Weighted W = 27'

Therefore, your calculation for If would be as follows:

If = [600'/600' - 0.25]27/30

If = {edit - slight calculation error} 0.675 or 67.5%


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## steveray (Mar 29, 2011)

Great simple explanation Ron!


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## TJacobs (Mar 29, 2011)

deleted by poster


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## RLGA (Mar 29, 2011)

I made a calculation error in my earlier post, but I have corrected it.  See above.

Also, you're welcome, steveray.


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## ara4help (Mar 30, 2011)

Keith,

Sec. 506.2.2 Open space limits. Such open space shall be either on the same lot or dedicated for the public use and shall be accessed from a street or approved fire lane.

 Common mistake made when calculating frontage increase - is that rear yard is taken into account and there is no APPROVED FIRE LANE for rear yard access. In your case at least one of your 21 ft wide side yards shall serve as an approved fire lane. Landscaped yards are not considered approved fire lane. In most cases 20 ft wide paving with hummer-head turn around for fire engine will satisfy this requirement (check with your fire department for the definition of approved fire lane).

An example for frontage increase calculation (using weighted average for variable depths of yards) and actual frontage increase calculator is included within “Building Code Height and Area Calculator” at

www.ara4help.com


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## MarkRandall (Mar 30, 2011)

Does anyone have the commentary for section 506.2.2?

I may have made that mistake, I don't recall a specific project, but it's a matter of interpretation. I have always interpreted that the access could be through the side yard to the street. If no side yards, then no using the back yard. Anyone else?


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## RLGA (Mar 30, 2011)

The open space must have access to a public way or fire lane.  You cannot access one open space (i.e. back yard) through another open space (i.e. side yard), unless the through open space is a fire lane.  This is based on the IBC Commentary.

If the back open space of Keith's building did not have an alley, diveway to a public way, or fire lane through one of the side yards, then the back open space cannot be included in the frontage increase.

However, as MarkRandall states, it's a matter of interpretation.  Since the Commentary is not code, I've seen BO's allow yards for the frontage increase if all portions of the building exterior are within the distance prescribed in IFC Section 503.1.1.


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## brudgers (Mar 30, 2011)

The commentary is not the code and is not adopted as such.

Where the commentary states that there are additional requirements beyond those listed in the code, it is no longer a legitimate interpretation of the code as written.


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## mtlogcabin (Mar 31, 2011)

> shall be accessed from a street or approved fire lane.


[F] FIRE LANE. A road or other passageway developed to allow the passage of fire apparatus. A fire lane is not necessarily intended for vehicular traffic other than fire apparatus.



> Common mistake made when calculating frontage increase - is that rear yard is taken into account and there is no APPROVED FIRE LANE for rear yard access


Disagree Not all building access is provided by public streets so the option of an approved fire lane is allowed but not required. The open space areas have to have access to a public street or fire lane. Nothing prohibits accessing one open space from another


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## ara4help (Mar 31, 2011)

mtlogcabin said:
			
		

> [F] FIRE LANE. A road or other passageway developed to allow the passage of fire apparatus. A fire lane is not necessarily intended for vehicular traffic other than fire apparatus. Disagree Not all building access is provided by public streets so the option of an approved fire lane is allowed but not required. The open space areas have to have access to a public street or fire lane. Nothing prohibits accessing one open space from another


I think intend of the code is to provide sufficient space for fire apparatus access to fight the fire, and not just any width of access thru other open spaces.

Let’s say the only access from the public way to the 40 ft wide rear yard is thru a 3 ft side yard. Would you use the rear yard for frontage increase? If yes, then what is the minimum width for the side yard to be considered an access?


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## RLGA (Mar 31, 2011)

mtlogcabin:

I concur, but look in the 2009 Commentary (Before everyone starts posting that the Commentary is not code, I know that and said it previously; however, BOs will look at the Commentary to support their positions) at Figure 506.2.2(1) on page 5-19, which shows a building with a yard to the south accessible by a road, a 15' yard on the west, a 20' yard on the east, and a 100' yard on the north.  The figure has no fire lane to the north yard and there is no alley, drive, etc. to the north yard.  The Commentary text regarding the figure states:

"Example 1: In Figure 506.2.2(1), the south and east side of the building facing the street can be considered open perimeter (frontage). The north side of the building cannot be considered open perimeter for purposes of the increase, since it is not accessible from the street or a fire lane. Even though the 20-foot-wide yard can be included in open frontage because it does not provide a fire lane to the rear of the building, the 100-foot yard cannot be included."

The Commentary clearly provides an interpretation that is not directly supported by actual code text (however, it may have been the intent), but many BOs use the Commentary as the basis for their own interpretations.


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## MarkRandall (Mar 31, 2011)

ara4help,

My interpretation has been a yard that's large enough to be counted towards area increases (20'). As long as the yards are contiguous, not sure why it would matter. Fire personnel need room to move around the building to fight the fire. There's distances in the fire code of 150' to fire access and this number can be increased per IFC503.1.1 exception 1. As long as you meet the distances, I think you should be fine.

I also agree the commentary is not code, thanks RLGA for posting that. I've been known to change my opinion based on what it says, but so far, I'm not convinced to change my interpretation.


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## mtlogcabin (Mar 31, 2011)

The commentary also points out the purpose of the open space

"Provides access to the structure by fire service personel, a temporary refuge area for occupants as they leave the building in a fire emergency and reduced exposure to and from adjacent structures"

I am not a firefighter but I do not believe an operations chief would send his equipment up the side of the building depicted in the commentary to fight a fire. His men with hoses yes, the truck no


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## MarkRandall (Mar 31, 2011)

Mtlogcabin, I was thinking along the same lines, but I'm not a fire fighter (and I don't play one on TV) so I avoided commenting. If a fire lane was provided close to a building, I agree, I can't imagine it being used for the fire truck to fight a fire. The truck would be toast in no time.


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