Unlimited Unprotected Openings in IIIB Building

[davidw42]

Hello Everyone,

First time posting and looking for some input. I am doing a preliminary code analysis of an existing building to asses the possibility of a change of occupancy. I am pretty new to Type III construction (background in Type V) so please bear with me if this is a simple one. Specifics are as follows:

• 2021 IBC
• Type IIIB building (tilt up conc walls, wood framing inside) with an attached Greenhouse (metal framing, polycarb walls and roof) and an attached Covered Parking Area (metal framing, open sided), think mid-sized hardware store.
• 26' fire separation distance on the greenhouse side
• NFPA 13 sprinklers inside and out, including in the greenhouse
• The building meets the requirements for unlimited unprotected openings per IBC Table 705.8

I believe the Covered Parking Area would count as 100% unprotected openings, as it is open on 3 sides. No problem there.

What I am unsure about is if I can classify the greenhouse sides as unprotected openings, rather walls which would require them to have 1hr rating (per 705.5)?

I have attached a picture of the exterior for reference. Any assistance would be much appreciated.

Thanks in advance,

Dave

 

[RLGA]

Before I answer, I am just curious, what is the building area?

 

[davidw42]

Thanks for the quick reply.

Total building area is 46,000 sf, including the greenhouse and covered parking. Under the max allowable per table 506.2 (E occ, S1, Type IIIB = 58,000 sf).

 

[RLGA]

Well, I'll address it this way. It is an existing building already approved for Type IIIB construction (I assume). Therefore, the existing construction and opening protection is a non-issue, in my opinion.

You are not moving the building any closer to any lot lines; thus, the conditions have not changed since the original construction other than the occupancy group, which affects the allowable area, means of egress, and other specific requirements that do not affect the building envelope or its structure.

I cannot see the AHJ telling you to protect openings for a building they already approved with that construction type and location on site--especially if you are permitted unlimited opening area. Going through the exercise of calculating allowable opening area (if that is what you are attempting to do) is, also in my opinion, a wasted effort.

I would just state that the building was permitted as Type IIIB construction with unlimited openings, and focus on the occupancy group changes, which includes showing the allowable area based on the established construction type.