Fire wall and Frontage increase

[YongMNLad]

Greetings,

2012 IBC
Type IIB construction
H-3 classification

Client desires a 120 x 400 = 48,000 SF. Open yard is more than 60 feet. Per 506.3 a sprinkler system increase is not allowed due to the H-3. I assume that a front yard increase is still allowed as I am not reading anything different.

If one 3-hour fire wall splits the building into two 120 x 200 buildings, my allowable area depends on whether or not I can include the fire wall perimeter as frontage. My assumption is that I cannot.

Here's some fun math:

Frontage Increase (IBC 506.2)
Building 1 - Group H-3:
If = [F/P-0.25]W/30
If = [440/640-0.25]30/30
If = [0.438]1
If = 0.438

Building 2 - Group H-3:
If = [F/P-0.25]W/30
If = [440/640-0.25]30/30
If = [0.438]1
If = 0.438

Total Area Modification - Aa = {At + [At x If] + [At x Is]}
Building 1 - Group H-3:
Aa = {14,000 + [6,132] + [0]}
Aa = 20,132 SF
Building 2 - Group H-3:
Aa = {14,000 + [6,132] + [0]}
Aa = 20,132 SF
Proposed Floor Area
Building 1 - Group H-3: 24,000 SF > 20,132 SF
Building 2 - Group H-3: 24,000 SF > 20,132 SF

Therefore, there would need to be two fire walls separating the building into 3 separate buildings, correct?

 

[RLGA]

Frontage perimeter should be 520 feet: 200' + 200' + 120' = 520'

Thus, the frontage increase would be: [520'/640' - 0.25]30/30 = 0.563

Allowable area: 14,000 s.f. + (14,000 s.f. x 0.563) + 0 = 21,882 s.f., which is still too little

Why not go to Type IIA construction? 1-hour construction is easy to achieve, and probably costs less than adding another 3-hour fire wall.

Allowable Area (Type IIA): 26,500 s.f. + (26,500 s.f. x 0.563) + 0 = 41,420 s.f.

 

[YongMNLad]

RLGA, thanks for the correction on the math.

The building is currently designed as a pre-engineered metal building. It seems that it would be just as costly, if not more, to go to Type IIA construction.

If I'm reading Table 601 correctly, the frames and roof structure would have to be rated 1 hour for IIA.

Could someone clarify subnote b on Table 601 - it's saying that F-1, M, H, and S-1 would have to be rated, correct? Meaning it would still be required in this scenario since it's H-3?

 

[cda]

H-3

As what is being stored in it???

Or and processes also???

Has someone done the hazard assessment

 

[YongMNLad]

Yes, I've reviewed the hazardous materials. Bulk storage of Class IB, II, IIA, IIIA, and IIIB liquids. Some toxic, some highly toxic. Quantities well exceed those allowed.

 

[RLGA]

Footnote b of Table 601 would apply in your case; the "H" means all of Group H occupancies.

In my area (Phoenix), it seems that most large storage facilities are constructed of tilt-up concrete panels, so I assumed your building would be similar. If using steel, then a second fire wall may be less expensive than fireproofing the steel.

 

[YongMNLad]

Footnote b of Table 601 would apply in your case; the "H" means all of Group H occupancies.

Am I understanding correctly that since this is an H occupancy, the 1 hour rating of roof construction would be required? Sorry, the language of footnote b is a bit confusing to me. Hypothetically, a Type IIA Group B building would not require the 1 hour roof construction (if above 20 feet which this building is)?

 

[RLGA]

Am I understanding correctly that since this is an H occupancy, the 1 hour rating of roof construction would be required? Sorry, the language of footnote b is a bit confusing to me. Hypothetically, a Type IIA Group B building would not require the 1 hour roof construction (if above 20 feet which this building is)?

The 1-hour rating of structural members, even if located above 20 feet, would be required of any Group H occupancy.