Equation 5-2 (Area Increase) Per Tier?

[Rchapman]

Is the calculated value from equation 5-2 showing TOTAL area of building (which would be divided by number of tiers to get the SF/tier), or is that the area per tier?

 

[cda]

Welcome,

I do not do above kindergarten math, but give it a day or two for great answers::

Mean while, not sure if this helps you::


http://www.specsandcodes.com/articl...r No. 16 - Allowable Building Area Part 1.pdf


http://www.specsandcodes.com/articl...r No. 17 - Allowable Building Area Part 2.pdf

Other great reading:::


http://www.specsandcodes.com/articles/default.html

 

[RLGA]

"Tier" is used for open parking garages per Section 406.5. Equation 5-2 is used for "stories."

To answer your question, Equation 5-2 determines the allowable building (all stories). As stated at the end of Section 506.2.3, the area of a single story is calculated using Sa = 1.

 

[Rchapman]

"Tier" is used for open parking garages per Section 406.5. Equation 5-2 is used for "stories."

To answer your question, Equation 5-2 determines the allowable building (all stories). As stated at the end of Section 506.2.3, the area of a single story is calculated using Sa = 1.

I mispoke by using the term tier*, yes, in this case we are talking about stories. Okay, so that equation is to determine the total SF of the building. It seems like the values listed in table 506.2 are for total SF of the building, correct?

*Me using the term "tier" outed me, my background is in designing parking garages which points me to always using table 406.5.4, where they list limited square footage per tier; so I was wondering if 506.2 is speaking in the same language (per story), or not (total SF of building).

 

[RLGA]

I mispoke by using the term tier*, yes, in this case we are talking about stories. Okay, so that equation is to determine the total SF of the building. It seems like the values listed in table 506.2 are for total SF of the building, correct?

*Me using the term "tier" outed me, my background is in designing parking garages which points me to always using table 406.5.4, where they list limited square footage per tier; so I was wondering if 506.2 is speaking in the same language (per story), or not (total SF of building).

No, Table 506.2 provides allowable area per story without an increase for frontage. Equation 5-2 takes the tabular area per Table 506.2, adds the increase for frontage, and then multiplies it times the number of stories (limited to 3 for NFPA 13 sprinklered buildings and 4 for NFPA 13R sprinklered buildings).

 

[Rchapman]

No, Table 506.2 provides allowable area per story without an increase for frontage. Equation 5-2 takes the tabular area per Table 506.2, adds the increase for frontage, and then multiplies it times the number of stories (limited to 3 for NFPA 13 sprinklered buildings and 4 for NFPA 13R sprinklered buildings).

For example, Occupancy B, Type IIA construction, with sprinklers per NFPA 13, 6 story building. Let's say my frontage increase percent is 25% per equation 5-5.
Tables in chapter 5 arrives at the conclusion of a 6 story building, each floor being 112,500 SF. Equation 5-2 would give me [112,000+(37,500 x 0.25)]x3 = 364,125.

Does this mean each story can be 364,125 SF?
Or is that the total SF of my building, meaning each story would be 364,125/6 stories = 60,687 SF per story. If that's the case, why even go for the frontage increase? Because I'm limited to 60,687 SF per story, less than what I was originally given of 112,000 SF. That's where I'm confused. What is that 364,125 SF describing?

 

[RLGA]

For example, Occupancy B, Type IIA construction, with sprinklers per NFPA 13, 6 story building. Let's say my frontage increase percent is 25% per equation 5-5.
Tables in chapter 5 arrives at the conclusion of a 6 story building, each floor being 112,500 SF. Equation 5-2 would give me [112,000+(37,500 x 0.25)]x3 = 364,125.

Does this mean each story can be 364,125 SF?
Or is that the total SF of my building, meaning each story would be 364,125/6 stories = 60,687 SF per story. If that's the case, why even go for the frontage increase? Because I'm limited to 60,687 SF per story, less than what I was originally given of 112,000 SF. That's where I'm confused. What is that 364,125 SF describing?

Neither.

Here's how it should work:

Total allowable building area (excluding allowed basement) = 112,500 + (37,500 x 0.25) x 3 = 365,625 sq. ft.
Any single story allowable area = 112,500 + (37,500 x 0.25) x 1 = 121,875 sq. ft.
​

You can take the total allowable area of 365,625 sq. ft. and divide it by 6 to get an area per story, but a story can be as large as 121,875 sq. ft.; however, to make one story larger, another story will have to get smaller so that the total area does not exceed 365,625 sq. ft.

 

[Rchapman]

Neither.

Here's how it should work:

Total allowable building area (excluding allowed basement) = 112,500 + (37,500 x 0.25) x 3 = 365,625 sq. ft.
Any single story allowable area = 112,500 + (37,500 x 0.25) x 1 = 121,875 sq. ft.
​

You can take the total allowable area of 365,625 sq. ft. and divide it by 6 to get an area per story, but a story can be as large as 121,875 sq. ft.; however, to make one story larger, another story will have to get smaller so that the total area does not exceed 365,625 sq. ft.

Thanks for responding and walking me through this.

I don't see why this equation is necessary (other than increasing the footprint of one floor to 121,875 sq ft.) If I am trying to maximize my building footprint, if I take the 112,500 SF/story, for 6 stories, I get 675,000 total sq ft, way bigger than 365,625. So how does this equation serve a purpose? It seems to be limiting me in the amount of square footage I feel I should be allowed to use from Table 506.2.

Or, does this equation have to be used INSTEAD of the table 506.2?

 

[Paul Sweet]

It limits the area for that construction type. You have to go to a construction with a greater fire resistance to exceed that area .

You also have to consider local zoning - lot coverage and building height.

 

[RLGA]

There are two area limitations in the IBC: allowable story area and allowable building area--and allowable building area does not always equal allowable story area times the number of actual stories. Just because Table 504.4 says you can have six stories does not mean you can have six stories using the allowable area per story.

Imagine if you had six 1-gallon empty buckets (representing the six stories that are allowed 121,875 sq. ft. each) and you are given only three gallons of water to work with (representing the 365,625 sq. ft. allowed for the entire building). Your job is to pour the three gallons into the 6 buckets without overflowing a bucket.

That is essentially what you're doing with Table 506.2 and Equation 5-2. Table 506.2 tells you the size of each bucket. You can increase the size of the buckets based on a frontage increase (using Equation 5-2 with an S(a) of 1, which represents a single story). Then, Equation 5-2 also tells you how much water you get (you're allowed up to three times the amount per bucket for buildings three stories and taller). For a 3-story building, you can pour water into each of the buckets filling them up to the brim without overflowing. However, for a building of 4 stories or more, you can fill some buckets up to the brim, but then that will leave less for the other buckets; or, you can fill each bucket up equally, but none will be filled to the brim.

 

[classicT]

There are two area limitations in the IBC: allowable story area and allowable building area--and allowable building area does not always equal allowable story area times the number of actual stories. Just because Table 504.4 says you can have six stories does not mean you can have six stories using the allowable area per story.

Imagine if you had six 1-gallon empty buckets (representing the six stories that are allowed 121,875 sq. ft. each) and you are given only three gallons of water to work with (representing the 365,625 sq. ft. allowed for the entire building). Your job is to pour the three gallons into the 6 buckets without overflowing a bucket.

That is essentially what you're doing with Table 506.2 and Equation 5-2. Table 506.2 tells you the size of each bucket. You can increase the size of the buckets based on a frontage increase (using Equation 5-2 with an S(a) of 1, which represents a single story). Then, Equation 5-2 also tells you how much water you get (you're allowed up to three times the amount per bucket for buildings three stories and taller). For a 3-story building, you can pour water into each of the buckets filling them up to the brim without overflowing. However, for a building of 4 stories or more, you can fill some buckets up to the brim, but then that will leave less for the other buckets; or, you can fill each bucket up equally, but none will be filled to the brim.

This may just be one of the best analogies I've heard in a long time. I'll have to save this somehow.

Thanks Ron!