2021 IBC - Unprotected Opening Percentage

[coolethan]

Greetings. We are working on a design of a small office park (B Occupancy) and hung up on the following exemption.

705.8.1

1. In other than Group H occupancies, unlimited unprotected openings are permitted in the first story above grade plane where the wall faces one of the following:
   1. A street and has a fire separation distance of more than 15 feet (4572 mm).
   2. An unoccupied space. The unoccupied space shall be on the same lot or dedicated for public use, shall be not less than 30 feet (9144 mm) in width and shall have access from a street by a posted fire lane in accordance with the International Fire Code.
2. Buildings whose exterior bearing walls, exterior nonbearing walls and exterior primary structural frame are not required to be fire-resistance rated shall be permitted to have unlimited unprotected openings.

The current site plan places each rectangular shaped building (about 1,900 sqft each building) ,12' apart in a single row (no side soffits..). The project is comprised of an exterior insulated CMU block system (non-load bearing.. 2.7 hr rated), interior steel columns / wideflanges / steel joists / metal corrugated deck with standing seam roof system that is not dependent on the exterior walls. (Type II Construction - non-sprinkled).

Would these building meet this exemption and allow unlimited unprotected openings?

The client would like to place several windows on the side wall of the buildings (windows basically facing each other between each building) and we are wondering if we can exceed the 15% allowance (705.8).

Thank you for your feedback in advanced.

 

[NCRooster]

What building code? 2015 Texas? Refer to Table 602 for fire-resistance rating requirements per fire separation distance.

If the buildings are 12' apart, then the fire separation distance is less than 12' because you need to locate an imaginary line between the buildings for the purposes of determining FSD. As an example, if you located this line exactly halfway between the two buildings, then both buildings would have a 6' FSD from that line. Per Table 602, this would require them to be fire rated. However, you could locate the imaginary line so that it is 10' from one building at 2' from the other; that would allow the building with the 10' FSD to have unlimited openings on that side.

 

[coolethan]

International Building Code – 2021 Edition
International Fire Code – 2021 Edition

 

[coolethan]

What building code? 2015 Texas? Refer to Table 602 for fire-resistance rating requirements per fire separation distance.

If the buildings are 12' apart, then the fire separation distance is less than 12' because you need to locate an imaginary line between the buildings for the purposes of determining FSD. As an example, if you located this line exactly halfway between the two buildings, then both buildings would have a 6' FSD from that line. Per Table 602, this would require them to be fire rated. However, you could locate the imaginary line so that it is 10' from one building at 2' from the other; that would allow the building with the 10' FSD to have unlimited openings on that side.

Thanks for the quick response. Please elaborate on the fire rated requirement? If we are Type IIB / Business Occupancy and the exterior wall construction is 2.7 rated (masonry block)... wouldn't that meet the separation requirement?

Also, who determines where the imaginary line is placed?

 

[Yankee Chronicler]

Also, who determines where the imaginary line is placed?

The applicant decides, and it has to be shown on the site plan.

Once it has been established, permitted, and the building(s) built, that "imaginary lot line" is part of the permanent building record. It must be taken into account for any future alterations. This isn't an issue for buildings far enough apart that both can have unlimited unprotected openings but, in a case where in order to get 10 feet from one building the line has to be drawn 2 feet from the other building, that imposes severe constraints on future alterations to the second building.

In a future project the line can be moved and reestablished in a different location, but doing so requires reanalyzing both buildings and ensuring that openings in the walls of both buildings facing the imaginary lot line conform to whatever code is in effect at the time of the new project that seeks to relocate the fire separation line.

In fact, I would need to dig a bit to find the code section but I believe if an applicant just wants to move the fire separation line on a parcel (no physical alterations to either building) a new building permit is required.

 

[coolethan]

Also confused on 705.3 and Section 503.1.2.

The 12 buildings are paired up into three buildings per "cluster" (the site has a total of 4 total clusters).. so please imagine three buildings, same size, are 12 feet apart, comprising of the a "cluster". Each cluster is 73' apart, separated by a parking area.

If all buildings are on the same lot, same owner.. same type of construction and use.. Would the imaginary line still be required between the three buildings? Could the three buildings (aka cluster) be considered one building?

Few more things to add.. the windows are fixed storefront glazing, no doors between the buildings.

What were really confused about.. a very similar, recently project was constructed with the buildings 10 ft apart, same occupancy (not sure what type of construction) and non-sprinklered. They easily have 25% of storefront windows between each building (measured from their drawings).

 

[coolethan]

The applicant decides, and it has to be shown on the site plan.

Once it has been established, permitted, and the building(s) built, that "imaginary lot line" is part of the permanent building record. It must be taken into account for any future alterations. This isn't an issue for buildings far enough apart that both can have unlimited unprotected openings but, in a case where in order to get 10 feet from one building the line has to be drawn 2 feet from the other building, that imposes severe constraints on future alterations to the second building.

In a future project the line can be moved and reestablished in a different location, but doing so requires reanalyzing both buildings and ensuring that openings in the walls of both buildings facing the imaginary lot line conform to whatever code is in effect at the time of the new project that seeks to relocate the fire separation line.

In fact, I would need to dig a bit to find the code section but I believe if an applicant just wants to move the fire separation line on a parcel (no physical alterations to either building) a new building permit is required.

This makes since.. and I have seen the lines illustrated on other site plans. Thank you for clarifying the placement of the imaginary lines.

 

[coolethan]

What is the imaginary line shift to 10 ft and 2 ft. The 10 ft FSD building to have normal storefront glazing and the 2ft FSD to have 60 min rated assembly only on the wall facing the other 10 ft FSD building?

 

[steveray]

If all buildings are on the same lot, same owner.. same type of construction and use.. Would the imaginary line still be required between the three buildings? Could the three buildings (aka cluster) be considered one building?

503.1.2 Buildings on Same Lot​

Two or more buildings on the same lot shall be regulated as separate buildings or shall be considered as portions of one building where the building height, number of stories of each building and the aggregate building area of the buildings are within the limitations specified in Sections 504 and 506. The provisions of this code applicable to the aggregate building shall be applicable to each building.

 

[coolethan]

Its my understanding that 503.1.2. only applies to adding a building adjacent to an existing building? Sorry it's Friday and I'm pooped!

 

[Yankee Chronicler]

The 12 buildings are paired up into three buildings per "cluster" (the site has a total of 4 total clusters).. so please imagine three buildings, same size, are 12 feet apart, comprising of the a "cluster". Each cluster is 73' apart, separated by a parking area.

If all buildings are on the same lot, same owner.. same type of construction and use.. Would the imaginary line still be required between the three buildings? Could the three buildings (aka cluster) be considered one building?

The IBC has provisions for multiple buildings on a parcel to be considered as a single building. See IBC 705.3, Exception #1. Your call -- you get to choose which avenue to pursue.

Few more things to add.. the windows are fixed storefront glazing, no doors between the buildings.

What were really confused about.. a very similar, recently project was constructed with the buildings 10 ft apart, same occupancy (not sure what type of construction) and non-sprinklered. They easily have 25% of storefront windows between each building (measured from their drawings).

Windows are openings.

 

[RLGA]

503.1.2 Buildings on Same Lot​

Two or more buildings on the same lot shall be regulated as separate buildings or shall be considered as portions of one building where the building height, number of stories of each building and the aggregate building area of the buildings are within the limitations specified in Sections 504 and 506. The provisions of this code applicable to the aggregate building shall be applicable to each building.

I was going to suggest the same thing. Type IIB allows 23,000 sq. ft. for a nonsprinklered building, Twelve 1,900 sq. ft. spaces is 22,800 sq. ft., so all buildings can be considered as portions of one building.

Its my understanding that 503.1.2. only applies to adding a building adjacent to an existing building? Sorry it's Friday and I'm pooped!

The IBC does not say that. You can combine multiple new buildings and consider them as portions of one building (I am doing that as we speak for an apartment complex).

 

[coolethan]

I was going to suggest the same thing. Type IIB allows 23,000 sq. ft. for a nonsprinklered building, Twelve 1,900 sq. ft. spaces is 22,800 sq. ft., so all buildings can be considered as portions of one building.

The IBC does not say that. You can combine multiple new buildings and consider them as portions of one building (I am doing that as we speak for an apartment complex).

My actual total sqft is 23,652. But since each grouping of buildings is 73' apart.. Shall we consider the site to have 4 separate buildings? We're not aiming for a glass box.. just 24-25% of glazing between the buildings.


Please see the sketch attached and thank you all for helping out!

 

[Jay Smith]

Is there any reason not to propose a cluster of three as a single Type VB building? Allowable area is 9,000 plus the frontage increase.

 

[RLGA]

My actual total sqft is 23,652. But since each grouping of buildings is 73' apart.. Shall we consider the site to have 4 separate buildings? We're not aiming for a glass box.. just 24-25% of glazing between the buildings.


Please see the sketch attached and thank you all for helping out!

I am sure you could get at least 652 sq. ft. from a frontage increase.

 

[jar546]

Greetings. We are working on a design of a small office park (B Occupancy) and hung up on the following exemption.

705.8.1

1. In other than Group H occupancies, unlimited unprotected openings are permitted in the first story above grade plane where the wall faces one of the following:
   1. A street and has a fire separation distance of more than 15 feet (4572 mm).
   2. An unoccupied space. The unoccupied space shall be on the same lot or dedicated for public use, shall be not less than 30 feet (9144 mm) in width and shall have access from a street by a posted fire lane in accordance with the International Fire Code.
2. Buildings whose exterior bearing walls, exterior nonbearing walls and exterior primary structural frame are not required to be fire-resistance rated shall be permitted to have unlimited unprotected openings.

The current site plan places each rectangular shaped building (about 1,900 sqft each building) ,12' apart in a single row (no side soffits..). The project is comprised of an exterior insulated CMU block system (non-load bearing.. 2.7 hr rated), interior steel columns / wideflanges / steel joists / metal corrugated deck with standing seam roof system that is not dependent on the exterior walls. (Type II Construction - non-sprinkled).

Would these building meet this exemption and allow unlimited unprotected openings?

The client would like to place several windows on the side wall of the buildings (windows basically facing each other between each building) and we are wondering if we can exceed the 15% allowance (705.8).

Thank you for your feedback in advanced.

You don't meet either of the two exemptions and exceeding 15% is not allowed with the current condition.

 

[coolethan]

Wanted to circle back to this.. we did get a clarification from the local fire department.. if less than 10' apart, they are considered one bldg.

 

[RLGA]

That's not how it works. The code allows separate structures on the same lot to be classified as either portions of a single building or as separate buildings. The AHJ cannot dictate your compliance path; it is the designer's decision. However, whichever path you decide to take must be code-compliant.

 

[coolethan]

Yes I agree.. we had the option to select which direction to proceed with. Thank you for clarifying

 

[Yankee Chronicler]

Wanted to circle back to this.. we did get a clarification from the local fire department.. if less than 10' apart, they are considered one bldg.

The fire department is wrong. And why are you asking the fire department for clarification of the building code.

Several posts above I provided the code section for you to start with if you want to see IF you can consider multiple buildings on the same parcel as a single building. That is not the default. The default is that each building must meet the fire separation requirements on all sides.