Separated VS non-separated area calculations

[georgia plans exam]

Here is an interesting question that was sent to me in an e-mail. It is the plan review code question of the month by I Code Consultants. I had to think about it a while. "A set of plans have been submitted for a building that contains adjoining F-1 and S-1 occupancies. The documents do not show any fire separation between the two occupancies, which is allowed by Table 508.4 of the 2012 IBC. Are these occupancies considered "separated" for the purpose of calculating allowable height and area?" GPE

 

[steveray]

Hunh....looks like you could do it whichever way works better for you......because the tabulars are a bit different...

 

[hlfireinspector]

Step 2: Determine the minimum type of construction

based on the height and area of the building for each

occupancy in accordance with this chapter and Table

503 as if each occupancy occurred throughout the

building. Compare the requirements for each occupancy

and then apply the requirement for the highest

type of construction to the entire building (see Section

508.3.2).

508.3.2 Allowable building area and height. The allowable

building area and height of the building or portion thereof

shall be based on the most restrictive allowances for the occupancy

groups under consideration for the type of construction

of the building in accordance with Section 503.1.

The fundamental concept underlying the nonseparated

occupancies option is that the allowable building

heights and allowable building areas are based

on the most restrictive requirements of Table 503

applicable to each of the occupancy groups in the

mixed occupancy building.

For example, the tabular area for Group S-1 in

Table 503 is less than the corresponding tabular area

for Group B; therefore, Group S-1 results in a requirement

for a higher type of construction for buildings of

equal size and will, therefore, determine the minimum

construction type of the building. If the building were,

say, Type IIB construction, then the allowable area

for the building would be 17,500 square feet (1626

m2), based on the allowable area of Group S-1 occupancies

for Type IIB construction in Table 503. Area

increases for sprinklers and frontage could be

applied. The same methodology of applying the most

restrictive criteria of Table 503 (with any permitted

sprinkler increase) is used to evaluate the maximum

permitted height in stories above grade plane.

 

[mtlogcabin]

NO

Table 503

Building area limitations shown in square feet, as determined by the definition of “Area, building,” per story

AREA, BUILDING. The area included within surrounding exterior walls (or exterior walls and fire walls) exclusive of vent shafts and courts. Areas of the building not provided with surrounding walls shall be included in the building area if such areas are included within the horizontal projection of the roof or floor above.

So unless the building areas are separated by "Fire Walls" as required by Table 706.44 then the most restrictive applies as pointed out in the post above

 

[RLGA]

When considering nonseparated versus separated occupancies in a mixed occupancy building, separated occupancies must be separated per the Table. However, if the building contains occupancy groups that do not require separation, then they can be considered either separated or nonseparated.

I would consider the nonseparated method first, because the calculations are simpler. If the building area still exceeds the allowable based on the most restrictive occupancy per the nonseparated method, then next try the separated method. It may allow a slightly larger building by working with the ratios for each occupancy.

If the building area still exceeds the allowable area, then one or more options must be implemented:

- Use a fire wall.

- Use increases if not already used.

- Change construction type.

 

[steveray]

Mixed uses is what we are talking about here...Correct?...Not separate "buildings"?......Call it separated, Table 508.4 required separation is none.....Run the calcs, see how it comes out......Then use Table 503 for F1 (because that seems to be more restrictive) and see how that comes out...Pick the better number for you....

 

[georgia plans exam]

Here is an example - One story, mixed use building type V-B. 4,500 sq. ft. S-1 and 4,250 sq. ft. F-1. Using Separated (2012 IBC 508.4) 4,500 (actual) / 9,000 (allowable) = .50 + 4250 / 8,500 = .50 = 1. So, allowable area = 8,750 sq. ft. Using non-separated (508.3) the allowable area would be the most restrictive, or 8,500 sq. ft. You have gained 250 sq. ft. Sprinkler the building and you gain 1,000 sq. ft. The Code Commentary, I Code Consultants and I agree that this is allowable. GPE

 

[RLGA]

Good example, GPE.

 

[steveray]

Wouldn't you gain 300% from sprinklers?

 

[RLGA]

Steveray:

For a single building, the sprinkler increase, which is 3 times the tabular area, is added to the tabular area; thus, it is essentially 4 times the tabular area.

Using GPE's example:

One story, mixed use building type V-B. 18,000 sq. ft. for S-1 (4 times previous actual) and 17,000 sq. ft. for F-1 (also 4 times previous actual).

Using Separated (2012 IBC 508.4):

18,000 (actual) / 9,000 + (9,000 x 3) (allowable) = 18,000 / 36,000 = 0.50

17,000 (actual) / 8,500 + (8,500 x 3) (allowable) = 17,000 / 34,000 = 0.50

0.50 + 0.50 = 1, therefore, okay

Using non-separated (2012 IBC 508.3):

F-1 is most restrictive

Allowable area = 8,500 + (8,500 x 3) = 34,000 sq. ft.

Actual area = 18,000 + 17,000 = 35,000 sq. ft. (thus, the difference is 1,000 sq. ft.)

 

[steveray]

Got it...just got stuck on the "sprinkler the builing and gain 1000 ft" thing....Good that nonsep works out better, there is also less math....

 

[georgia plans exam]

steveray, Actually,the separated method gives you the extra 1,000 sq. ft. (18,000 + 17,000) = 35,000 sq. ft. as opposed to non-separated (34,000 sq. ft.) GPE

 

[steveray]

I am going to shut up now...Apparently I am reading way too fast and typing faster....

steveray, Actually,the separated method gives you the extra 1,000 sq. ft. (18,000 + 17,000) = 35,000 sq. ft. as opposed to non-separated (34,000 sq. ft.) GPE

 

[georgia plans exam]

Hey, it's Friday - what the heck... GPE