Allowable area for for separated mixed use w/ obstructions in open area

[Kevin]

I have some questions on the allowable area for a 1-story, mixed use, separated building that contains a Hazardous Occupancy. I'd love to hear opinions on how to be code compliant and any strategies I should consider.

I'm designating the Hazardous area as H-2 since it will have flammable gas and H-2 is the most restrictive of the H occupancies that apply. The gas comes from a landfill and it is processed into a higher percentage of methane. The gas composition also contains some inert gas percentages, some oxygen (considered as oxidizer level II per IFC) and some toxic gases that will be destroyed in the process.

There's a few support spaces that flank the H-2 Processing area, like a sprinkler room, electric room and a space for mechanical equipment. The areas of those rooms exceeds 10 percent of the overall plan, so I thought they should be classified as Utility?

There's also a question on what should be considered for the frontage increase. The building has processing equipment that runs along each side of the H-2 processing area which will partially obstruct fire department access. There's no definition of open area, but I've seen comments here the public ways often have trees or other objects that partially obscure a façade. The exact equipment is unknown right now, but we have a rough idea on size. If I factor the equipment in, I still qualify for a 25% increase for the H-2 area. I'd think that the hose stream could get through and over some of the obstructions and that maybe 50% increase could be considered appropriate? Hoses and Egress will be able to fit through spacing in the equipment. I qualify for 50% area increase for the Electric Room on the right since it's open to the exterior on 3 sides.

Working Left to Right w/ equation 5-1 for each occupancy (IBC 2021 - 506.2.2) and considering the building as type IB sprinklered I get:

Electric Room Allowable Area = 142,000 sf + (35,500 x .5) = 159,750 sf.
H-2 Allowable Area - 16,500 sf + (16,500 x .25) = 20,625 sf.
Sprinkler/ Remaining Utility areas - 142,000 sf
Business = Unlimited.

Per 508.4.2 the the building area shall be such that the sum of the ratios of the actual building area of each separated occupancy divided by the allowable building area of each separated occupancy shall not exceed 1. I'm assuming the Business area doesn't even need to be part of the calculation since X/ infinity is 0?. Again, left to right:

3,517 sf actual/ 159,750 sf allowable + 20,040 sf actual/ 20,625 sf actual + 1,517 sf actual/ 142,000 sf allowable =

.022 +.971+.010= 1.003 - I barely exceed 1 . Does this mean I need a firewall between the Electric Room and the rest of the building to meet code, if frontage is increase is only accepted for a 25% increase ?

 

[RLGA]

I haven't had the time to have a detailed look through your issue, but the thing that pops out at me is that the frontage increase is based on the frontage of the entire building--not each occupancy group.

If the building has 30-foot or wider yards all around the building, you can get up to a 75% increase of the 'NS' value added to the allowable area.

Also, Group U is limited to "Buildings and structures." Unlike the descriptions of other occupancy groups, it does not include the phrase "or a portion thereof."

Thus, I would consider the "utility" areas to be classified as either part of the main occupancy or Group F-1, since the building (as a whole) is processing a product and, per the description of Group F, is "not classified as a Group H hazardous or Group S storage occupancy."

 

[Kevin]

There was another scenario I ran by the plan reviewer, that he wasn't quite buying into. At the time, I was not subtracting the equipment from the frontage because I thought it was allowed to be in the open area since open area isn't defined and there is no recourse or exceptions spelled out if public ways have obstructions in them. So I used the 75% frontage increase. However, If I factor the equipment in, I have 55% of the perimeter being open, so I'm allowed 50% frontage increase.

In that scenario, I factored the utility spaces as being part of the H-2 spaces (they'd still get fire barriers as required per incidental use), which brought he actual area of the H-2 space up to 25,371 sf.

So 16,500 x (16,500 + 50%) = 24,750 sf allowable, which is still 621 sf over the allowable.


Also, per my original post, the hall between the two utility spaces on the right side, is an additional 102 sf. So my ratio for the H-2 would be .9765 instead of .971.

 

[Kevin]

I haven't had the time to have a detailed look through your issue, but the thing that pops out at me is that the frontage increase is based on the frontage of the entire building--not each occupancy group.

If the building has 30-foot or wider yards all around the building, you can get up to a 75% increase of the 'NS' value added to the allowable area.

Also, Group U is limited to "Buildings and structures." Unlike the descriptions of other occupancy groups, it does not include the phrase "or a portion thereof."

Thus, I would consider the "utility" areas to be classified as either part of the main occupancy or Group F-1, since the building (as a whole) is processing a product and, per the description of Group F, is "not classified as a Group H hazardous or Group S storage occupancy."

Thank you for your response. Yes, I questioned the difference in langue for Utility and I like your suggestion of Group F.

The entire building perimeter is 832 LF and 207'-2" LF is obstructed (leaving 624.83 LF of frontage), so 624.83 LF/832 LF = .751

Redoing my math w/ F-1 uses and 75% frontage:

Working Left to Right w/ equation 5-1 for each occupancy (IBC 2021 - 506.2.2) and considering the building as type IB sprinklered I get:

Electric Room Allowable Area as F-1 = UL
H-2 Allowable Area - 16,500 sf + (16,500 x .75) = 28,875 sf.
Sprinkler/ Remaining Utility areas as F-1 = UL
Business = UL

Per 508.4.2 the the building area shall be such that the sum of the ratios of the actual building area of each separated occupancy divided by the allowable building area of each separated occupancy shall not exceed 1. since X/ infinity is 0?. Again, left to right:

3,517 sf actual/ UL + 20,142 sf actual/ 28,875 sf allowable + 1,517 sf actual/ UL sf allowable + 3,422sf/UL sf allowable =

0 + .698 + 0 + 0 is under 1, which meets code per my interpretation.

 

[RLGA]

Thank you for your response. Yes, I questioned the difference in langue for Utility and I like your suggestion of Group F.

The entire building perimeter is 832 LF and 207'-2" LF is obstructed (leaving 624.83 LF of frontage), so 624.83 LF/832 LF = .751

Redoing my math w/ F-1 uses and 75% frontage:

Working Left to Right w/ equation 5-1 for each occupancy (IBC 2021 - 506.2.2) and considering the building as type IB sprinklered I get:

Electric Room Allowable Area as F-1 = UL
H-2 Allowable Area - 16,500 sf + (16,500 x .75) = 28,875 sf.
Sprinkler/ Remaining Utility areas as F-1 = UL
Business = UL

Per 508.4.2 the the building area shall be such that the sum of the ratios of the actual building area of each separated occupancy divided by the allowable building area of each separated occupancy shall not exceed 1. since X/ infinity is 0?. Again, left to right:

3,517 sf actual/ UL + 20,142 sf actual/ 28,875 sf allowable + 1,517 sf actual/ UL sf allowable + 3,422sf/UL sf allowable =

0 + .698 + 0 + 0 is under 1, which meets code per my interpretation.

That is how I would do it.

 

[Kevin]

Thank you Ron! Very much appreciated!


In a related question to this, does anyone here think that the constructing 3 hour fire walls out of 12" CMU to a height,30" above the roof line of the business area and electric area could be cheaper than fire rating the entire building for 2 hours per IB construction? I could lower the primary structural frame to 1 hour since I'm only supporting a roof in the space. This is more theoretical than anything, I'll probably get asked this by other team members.

The biggest issue with this rationale I think, is that the H-2 space (even with the sprinkler and mechanical space thrown in, would be considered it's own building, and I'd be limited w/ the 25% frontage factor instead of 75%





This math is for my own reference.... I'm considering that I will present him with the different calculation scenarios.

H- 2 uses and 75% frontage complying w/ the 508.4.3 ratio:

Working Left to Right w/ equation 5-1 for each occupancy (IBC 2021 - 506.2.2) and considering the building as type IB sprinklered I get:

Electric Room Allowable Area (H-2) = 16,500 sf x 1.75 = 28,875
H-2 Allowable Area = 16,500 sf x 1.75 = 28,875
Sprinkler/ Remaining Utility areas = 16,500 sf x 1.75 = 28,875
Business = Unlimited.

3,517 sf actual/ 28,875 sf allowable + 20,142 sf actual/ 28,875 sf allowable + 1,517 sf actual/ 28,875 allowable + 3,422sf/UL sf allowable =

.122 + .698 + .053 + 0 = .873, so I'm still under 1

 

[Yankee Chronicler]

I haven't had the time to have a detailed look through your issue, but the thing that pops out at me is that the frontage increase is based on the frontage of the entire building--not each occupancy group.

If the building has 30-foot or wider yards all around the building, you can get up to a 75% increase of the 'NS' value added to the allowable area.

Also, Group U is limited to "Buildings and structures." Unlike the descriptions of other occupancy groups, it does not include the phrase "or a portion thereof."

Thus, I would consider the "utility" areas to be classified as either part of the main occupancy or Group F-1, since the building (as a whole) is processing a product and, per the description of Group F, is "not classified as a Group H hazardous or Group S storage occupancy."

If there is a firewall between the Business occupancy and the rest of the building, then by definition the right end of the larger building has no open perimeter on that side, and the Business portion has no open perimeter on the left side. Remember, for purposes of tabular and allowable areas, a firewall creates two buildings.

As to the exterior equipment and the hose stream comment -- it's not just hose stream. Access for fire fighting operations also includes the ability of fire fighters to approach the building and to place ladders against it for access to the roof. If the exterior equipment obstructs such operations, I would not allow it as "open" perimeter.