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Fire Separation Distance Between New and Existing Building with Windows

M

mahrelizabeth

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Joined
Feb 7, 2024
Messages
7
Location
Cedar Rapids, Iowa
Hi there! Recent grad, intern architect and second time poster. I'm working on a project in Cedar Rapids, Iowa and am using the 2021 IBC and commentary. To say I'm a bit overwhelmed is an understatement. I have a conundrum (at least for me, hopefully not for you all). I've attached a picture to explain some of the options I've been exploring.

I have a site that has a 0'-0" grade at the entrance on one side of an existing building, and a 17'-6" grade at the entrance on the opposite side of the building - essentially creating two first floors in a two-story building. The existing building is EIFS over fluted CMU with no projections. It is also sprinkled. On the second story it has windows that are 2'-4" above grade. The upper story is B Occupancy, while the lower story is an M occupancy. I have been tasked with putting a similar building next to it. The existing wall was the separation between an anchor building and a mall. The new building is essentially a continuation of the existing building in size, material, and occupancy type.

I have done some digging into the IBC and am attaching my understandings of Chapter 7 in how it relates to this.

First - my understanding is that this would need to be a fire wall rather than a fire barrier because both sides of the wall need to act and collapse independently from each other. The new wall would have no openings, penetrations or projections.

Section 705.8.1, Exception 1.2 says that unprotected openings would be allowed where the wall faces an unoccupied space. That unoccupied space shall be on the same lot or dedicated for public use, shall not be less than 30 feet wide and has access from a street. Does my new roof count as an unoccupied space? If not, what if I were to turn it into some sort of pocket park or patio rather than a blank roof? Would this change it?

Section 706.1.1 says that party walls located on the lot line should be a fire wall without openings, which my new one would be. The openings in the existing wall are my concern.

Table 706.4 requires a 3-hour fire-resistance rating for M type buildings.

706.6.1 requires the wall to extend a minimum of 30" past the lower roof. The exception mentions that one of the provisions to meet is that the entire length and span of roof and supporting elements be 1-Hour rated. Would this help my case?

Options A and B were preliminary explorations when there was a chance this new building would also be 2 stories. Now we have knocked it down to one story so ideally, I want option C to work - where there is no separation between the buildings and the existing windows would be looking over the roof of the new building. I'm hoping this is allowed because the buildings only meet on the first floor. The new building is assumed to be IIB but that is flexible and I am open to other options as well if it will help me achieve butting these buildings up to each other. Am I reading into this correctly and if not, what am I missing or where can I find more information?

Additionally, both the existing and the new building were both designed by our firm and have the same contractor/owner. Would it be a possibility to suggest upgrading the existing windows in that building (even though it isn't technically part of this project) to a different glazing system that would allow this (i.e. proving that they are fire-rated glazing)?

Thanks in advance!
 

Attachments

  • Fire Seperation Opt 2.jpg
    Fire Seperation Opt 2.jpg
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What's the construction type and fire-resistance rating on the existing wall that will be facing the proposed building? Your attached analysis seems to only consider the new building, but you can't do anything with the new building that will create a non-compliant condition in the existing building.

Your sketches show the new building as a separate building. Therefore, the term ":fire wall" does not apply. What you are concerned about is the fire separation distance between two independent buildings, and the resultant requirements for fire-resistance rating of exterior walls and percentage of openings (protected or unprotected) based on the fire separation distance.
 
Are both buildings sprinklered? Treat them as one building?

503.1.2​

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.
 
Yankee Chronicler said:
What's the construction type and fire-resistance rating on the existing wall that will be facing the proposed building? Your attached analysis seems to only consider the new building, but you can't do anything with the new building that will create a non-compliant condition in the existing building.

Your sketches show the new building as a separate building. Therefore, the term ":fire wall" does not apply. What you are concerned about is the fire separation distance between two independent buildings, and the resultant requirements for fire-resistance rating of exterior walls and percentage of openings (protected or unprotected) based on the fire separation distance.
Click to expand...
The construction type is IIB and the existing wall is not fire rated.

Good point - you are correct. So I guess then my question is how can I approach this so that my fire separation distance is 0? Maybe that's not even feasible.
 
steveray said:
Are both buildings sprinklered? Treat them as one building?

503.1.2​

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.
Click to expand...

Both buildings are sprinkled but I believe it is two different lots. Additionally, the two combined square footages would be more than the allowed area.
 
mahrelizabeth said:
The construction type is IIB and the existing wall is not fire rated.

Good point - you are correct. So I guess then my question is how can I approach this so that my fire separation distance is 0? Maybe that's not even feasible.
Click to expand...

I was going to write that to plunk another building adjacent to the existing, with either a zero or very small fire separation distance, you would have to upgrade the exterior wall of the existing building. HOWEVER:

Are you certain the two buildings are on separate lots? If so, and the existing building doesn't have a rated exterior wall and the existing opening s are unprotected, that building was probably constructed in violation of the code. That said, when dealing with separate parcels my understanding is that the code only regulates you as far as the property line. If a neighboring building is in violation, essentially that's not your problem. You just have to make your [new] building conform.

This suggests that before pursuing this any further you NEED to conform whether or not the proposed building is on a separate lot and, if so, exactly where the property line falls.

In the case of two buildings on one lot, the fire separation line ("imaginary property line") can be moved pursuant to a building permit and satisfying all the requirements for fire separation distances. An actual property line isn't as easy to move, because it's not just moving a line on a piece of paper, it's actually transferring property from one owner to another, or at least from one parcel to another. If they are separate parcels, that makes your analysis much easier. If it's all one parcel, your job will be more difficult.
 
steveray said:
It is a little confusing between lot line and FSD line......It's one or the other....
Click to expand...

It's not confusing at all. For buildings facing an actual property line, the fire separation distance is measured from the face of the building to the property line (measured perpendicular to the face of the building).

For multiple buildings on the same lot (parcel/property), someone has to draw a line (I prefer to call it the fire separation line, the definition in the IBC refers to it as an "imaginary lot line") somewhere between the two buildings. Once that line has been established, the fire ratings and exterior openings of the two buildings are determined based on the distance from that line. It doesn't have to be mid-way between the buildings -- it can be 1 inch away from one building and 23 feet away from the other, but the building with the 1-inch fire separation distance then has to get rated walls and no openings.

1730848382476.png

From the 2021 IBC Commentary:

1730848492134.png

The Commentary says:

Fire separation distance is the distance from the exterior
wall of the building to one of the three following
locations, measured perpendicular to the exterior wall
face: an interior lot line [see Commentary Figure
202(19)]; the centerline of a street or public way [see
Commentary Figure 202(20)]; or an imaginary line
between two buildings on the same property [see
Commentary Figure 202(21)]. The imaginary line can
be located anywhere between the two buildings; it is
the designer’s choice, but, once established, the location
of the line applies to both buildings and cannot be
revised.

The distance can vary with irregular-shaped lots and
buildings, as shown in Commentary Figures 202(19)
and 202(20). When applying the exterior wall require-
ments of Table 602, the required exterior wall fireresistance
rating might vary along a building side; for
example, where the lot line is not parallel to the exterior
wall.
Click to expand...

The figure calls it an imaginary line, but it's not imaginary. It's only "imaginary" with respect to being a lot line, because it's not a lot line. But the distance that determines exterior wall fire-resistance ratings and allowable opening percentages is based on the distance to this line, as if it were an actual property line, rather than the distance from one building to the other building.

When we have multiple buildings on one site, we require the construction drawings to show the location of the fire separation line. This then becomes part of the record for that property. Any time in the future when work is proposed that might change the required fire separation distance for either building (or, if within the regulated distance, the rating or percentage of unprotected openings), we require the designer to provide an analysis of how the changes address the fire separation distance. On a couple of occasions, new projects have required relocating the "imaginary lot line" to accommodate more openings in the face of one building, at the expense of imposing additional restrictions on the other building.
 
Yankee Chronicler said:
It's not confusing at all. For buildings facing an actual property line, the fire separation distance is measured from the face of the building to the property line (measured perpendicular to the face of the building).

For multiple buildings on the same lot (parcel/property), someone has to draw a line (I prefer to call it the fire separation line, the definition in the IBC refers to it as an "imaginary lot line") somewhere between the two buildings. Once that line has been established, the fire ratings and exterior openings of the two buildings are determined based on the distance from that line. It doesn't have to be mid-way between the buildings -- it can be 1 inch away from one building and 23 feet away from the other, but the building with the 1-inch fire separation distance then has to get rated walls and no openings.

View attachment 14614

From the 2021 IBC Commentary:

View attachment 14615

The Commentary says:



The figure calls it an imaginary line, but it's not imaginary. It's only "imaginary" with respect to being a lot line, because it's not a lot line. But the distance that determines exterior wall fire-resistance ratings and allowable opening percentages is based on the distance to this line, as if it were an actual property line, rather than the distance from one building to the other building.

When we have multiple buildings on one site, we require the construction drawings to show the location of the fire separation line. This then becomes part of the record for that property. Any time in the future when work is proposed that might change the required fire separation distance for either building (or, if within the regulated distance, the rating or percentage of unprotected openings), we require the designer to provide an analysis of how the changes address the fire separation distance. On a couple of occasions, new projects have required relocating the "imaginary lot line" to accommodate more openings in the face of one building, at the expense of imposing additional restrictions on the other building.
Click to expand...
But the OP seems to be moving it.....Which really matters when it is a lot line......And not "imaginary" FSD line....
 
steveray said:
But the OP seems to be moving it.....Which really matters when it is a lot line......And not "imaginary" FSD line....
Click to expand...

I didn't see anything in the OP that suggested moving the line. If it is one parcel and the line is the proverbial "imaginary lot line," it can be moved at any time by making an application under the building code and submitting documentation showing that buildings on both sides of the proposed new location will be in compliance for exterior wall fire-resistance rating and openings percentage and protection.

If it is an actual property line, it can be "moved" only by an actual land transfer, accompanied by a survey establishing the new metes and bounds of both parcels involved in the swap. The sticky wicket is that I can sell a slice of my property to anyone, at any time. I have to get zoning approval, but if the zoning setbacks are met there's nothing in the laws regarding selling property that requires getting building department approval before selling some or all of your side yard or rear yard.

I think the OP needs to determine whether this is one parcel or two parcels. Come back with that information, and we can proceed accordingly.
 
mahrelizabeth said:
First - my understanding is that this would need to be a fire wall rather than a fire barrier because both sides of the wall need to act and collapse independently from each other. The new wall would have no openings, penetrations or projections.
Click to expand...

I just noticed this, and I think it requires correction.

As I re-read this post, it seems to imply that a firewall can be two walls. That's not the case. A firewall is a single wall. The requirement is that in the event of a fire, the structure supported by the firewall can collapse on one side without causing the wall itself or the structure on the other side to collapse. It's generally difficult to make an existing exterior wall into a firewall, because typical exterior walls aren't usually constructed in ways that would allow whatever the wall supprts to collapse and leave the wall intact.
 
Yankee Chronicler said:
I didn't see anything in the OP that suggested moving the line. If it is one parcel and the line is the proverbial "imaginary lot line," it can be moved at any time by making an application under the building code and submitting documentation showing that buildings on both sides of the proposed new location will be in compliance for exterior wall fire-resistance rating and openings percentage and protection.

If it is an actual property line, it can be "moved" only by an actual land transfer, accompanied by a survey establishing the new metes and bounds of both parcels involved in the swap. The sticky wicket is that I can sell a slice of my property to anyone, at any time. I have to get zoning approval, but if the zoning setbacks are met there's nothing in the laws regarding selling property that requires getting building department approval before selling some or all of your side yard or rear yard.

I think the OP needs to determine whether this is one parcel or two parcels. Come back with that information, and we can proceed accordingly.
Click to expand...
In Los Angeles, the building department supplies you with a form called a "Covenant and Agreement to Hold As One Parcel". If you can convince your neighbor to agree to a lot tie that gets recorded with the county, you can essentially treat a real property line like an imaginary property line.
https://www.ladbs.org/docs/default-...ie-affidavit)-pc-str-aff22-2014.pdf?sfvrsn=12

The form has you state the purpose of the lot tie, so that in the future if they try to eliminate the lot tie, they first have to mitigate the condition that created it.
 
One other thought regarding those windows on the property line.
I once had this exact same situation on a site , except that the tall building was the one undergoing remodel. It had a one hour property line wall with no openings, facing a multimillion dollar ocean view. Their lower next door neighbor was a car dealership building.
We designed Firelite ceramic glazing into hollow metal frames in the wall. It looks just like a fixed window, but it is UL tested as a fire rated "transparent" wall, so it is not considered an opening in the fire wall.
That Firelite is expensive - - several hundred dollars per square foot - - but the view was worth it for the property owner.
 
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