Mezzanine vs. 2nd floor

[Sifu]

This might get complicated, I will do my best. Mixed use, single occupant type V-B building, B and M, non-sprinklered, non-separated. (lots of assumptions based on observations because the architect didn't tell me)

I have a proposed mezzanine to be placed above an existing mixed use M-retail gun sales, and B-firing range. The plans presented some questions so I went to the site and found that there is no open space with which the proposed mezzanine would communicate, which I see as a non-starter. In order to be a mezzanine, the mezzanine needs to be open to the space below, and the size of the mezzanine is dependent on the area of the floor below it is open to. (Even an enclosed mezzanine, where permitted by exception must still be "within" the room below.) So IMHO, a mezzanine isn't going to work. I then considered it as a story. Nobody could seem to tell me the construction type, so with some destructive testing I found that it is a type V-B wood pole barn, with wood roof truss, wood interior framed floor and diaphragms. I was hoping to discover it was type III, but it was not. It is deceptive, because there have been multiple CMU walls built inside the pole barn for range enclosure and support structure for the range safety devices. As proposed, the mezzanine/story sits above the B-range and extends out and over the M-retail space, and would be used as offices in support of the operation and accessory storage. Without going too far into the weeds, the mezzanine/story will be constructed within the existing attic, incorporating the widely spaced trusses into the space plans.

Being of type V-B construction, non-suppressed, an M occupancy is limited to 1 story, and a B is limited to 2 stories per t504.4. On first glance I concluded that this would not fly as V-B, NS 2-story. BUT if the mezzanine/story is a B classification will this fly? B is allowed to be 2-story. The M is below on the first story, which is permitted. This is just me looking for possible solutions.

This building is old enough that no original core-shell documents have been found, I believe it may have been permitted originally by the county, before it was annexed. It has led many existences but was most recently permitted by my AHJ 9 years ago as the current B/M facility. That's why I had to look behind the walls.

Any thoughts are appreciated.

 

[steveray]

YOUR mezzanine may be required to be open....not all are:

505.2.3 Openness. A mezzanine shall be open and unobstructed
to the room in which such mezzanine is located
except for walls not more than 42 inches (1067 mm) in
height, columns and posts.
Exceptions:
1. Mezzanines or portions thereof are not required to
be open to the room in which the mezzanines are
located, provided that the occupant load of the
aggregate area of the enclosed space is not
greater than 10.
2. A mezzanine having two or more exits or access
to exits is not required to be open to the room in
which the mezzanine is located.
3. Mezzanines or portions thereof are not required to
be open to the room in which the mezzanines are
located, provided that the aggregate floor area of
the enclosed space is not greater than 10 percent
of the mezzanine area.
4. In industrial facilities, mezzanines used for control
equipment are permitted to be glazed on all
sides.
5. In occupancies other than Groups H and I, that
are no more than two stories above grade plane
and equipped throughout with an automatic
sprinkler system in accordance with Section
903.3.1.1, a mezzanine having two or more
means of egress shall not be required to be open
to the room in which the mezzanine is located.

 

[SH225]

Based on 2018 IBC 508, each occupancy in the mixed occupancy building is limited to the allowable height for that occupancy in that construction type. The B occupancy could go to the 2nd story of a mixed occupancy Type VB building, even though the M occupancy is limited to 1 story.

 

[Sifu]

So this is a point of discussion, and maybe I have it wrong.

You are correct, and this one is not required to be "open" by exception regarding occupant load. But I don't think that means the walls enclosing the mezzanine can be isolated from the space below. This building configuration is a single story with a trussed roof (not cathedral or otherwise open to the roof deck). There is a ceiling membrane across the bottom chords of the trusses. They propose a mezzanine above the bottom chord of the trusses. Think of a "story and a half house" where the second floor is entirely within the exterior geometry of the truss. My understanding of mezzanines is that they must be open to the floor below (but not necessarily "open" walled) in order to be considered as part of the story below. That even the enclosing walls are not required to be open, the wall itself must share the same atmosphere of the room below.

In addressing the mezzanine size restriction the code sates:
IBC 505.2.1...." the aggregate area of a mezzanine within a room shall not be greater than one-third of the floor area of that room or space in which they are located" indicates a mezzanine can't be outside of the room, which in this case, it is above the entire ceiling membrane and framing, and would no longer be within the room, and would be a story.

By definition the code states "an intermediate level or levels between the floor and ceiling of any story", again, this would be entirely above the ceiling as it is proposed.

 

[Sifu]

Based on 2018 IBC 508, each occupancy in the mixed occupancy building is limited to the allowable height for that occupancy in that construction type. The B occupancy could go to the 2nd story of a mixed occupancy Type VB building, even though the M occupancy is limited to 1 story.

That is the way I see it, but my brain may be confused since they are proposing it as a mezzanine. There may be limits that won't allow this to work as a story either, but I am trying to verify the concept first.

RLGA addresses this in his new book, which I bought but can never locate on my computer....still trying.

 

[RLGA]

Based on 2018 IBC 508, each occupancy in the mixed occupancy building is limited to the allowable height for that occupancy in that construction type. The B occupancy could go to the 2nd story of a mixed occupancy Type VB building, even though the M occupancy is limited to 1 story.

That is correct; however, the occupancies would need to be separated per Table 508.4.

Fortunately, in this case, Group B and Group M are in the same column in Table 508.4, so no separation is required, but you still consider the two occupancy groups as being separated using the sum of ratios per Section 508.4.

However, if the first story was a Group A-3, which is limited to one story in a nonsprinklered Type VB building, then a 2-hour horizontal assembly would be needed to separate the Group A-3 first story from the Group B second story. Without the separation, the most restrictive occupancy would apply to the entire building; thus, a Group A-3 (most restrictive) would not be permitted since the building is two stories.

 

[ADAguy]

Given the existing and proposed uses, wouldn't the addition of sprinklers help to resolve the issue?

 

[Sifu]

That is correct; however, the occupancies would need to be separated per Table 508.4.

Fortunately, in this case, Group B and Group M are in the same column in Table 508.4, so no separation is required, but you still consider the two occupancy groups as being separated using the sum of ratios per Section 508.4.

However, if the first story was a Group A-3, which is limited to one story in a nonsprinklered Type VB building, then a 2-hour horizontal assembly would be needed to separate the Group A-3 first story from the Group B second story. Without the separation, the most restrictive occupancy would apply to the entire building; thus, a Group A-3 (most restrictive) would not be permitted since the building is two stories.

Ok, so if I understand correctly, this non-separated building can house a two story group B, and a one-story group M without rated separations, and the 2nd story B can be over the M below. BUT per 504.2 IF it was an A3 on the first floor they would need to be separated because without that separation you would have a two-story A-3 space even if the upper floor wasn't being used as an A-3. I think I had it mostly right if so.

Would you agree with my assessment of the definition of the mezzanine? That whether "open" or not, the mezzanine must be within the story below to be considered a mezzanine and not a story?

And yes, sprinkling would solve some problems but it is not their preferred route.

 

[sergoodo]

Single story with an occupiable attic. Attic has specific code requirements. The area is within the exterior walls or within the horizontal projection of the roof.

 

[RLGA]

Ok, so if I understand correctly, this non-separated building can house a two story group B, and a one-story group M without rated separations, and the 2nd story B can be over the M below. BUT per 504.2 IF it was an A3 on the first floor they would need to be separated because without that separation you would have a two-story A-3 space even if the upper floor wasn't being used as an A-3. I think I had it mostly right if so.

Would you agree with my assessment of the definition of the mezzanine? That whether "open" or not, the mezzanine must be within the story below to be considered a mezzanine and not a story?

And yes, sprinkling would solve some problems but it is not their preferred route.

Yes. The mezzanine must be located within the room or contiguous open space below. I am going through this very same issue on a project.

 

[SH225]

Is this illustration on the left consistent with current code? I'm trying to understand the restriction to be within the contiguous open space below.

 

[RLGA]

Is this illustration on the left consistent with current code? I'm trying to understand the restriction to be within the contiguous open space below.

Yes.

 

[Sifu]

Perfect, that is the way I understand it.

 

[ADAguy]

Dwg is often worth more than words alone. Gets to the meat of the matter too.

 

[tonto961]

This might get complicated, I will do my best. Mixed use, single occupant type V-B building, B and M, non-sprinklered, non-separated. (lots of assumptions based on observations because the architect didn't tell me)

I have a proposed mezzanine to be placed above an existing mixed use M-retail gun sales, and B-firing range. The plans presented some questions so I went to the site and found that there is no open space with which the proposed mezzanine would communicate, which I see as a non-starter. In order to be a mezzanine, the mezzanine needs to be open to the space below, and the size of the mezzanine is dependent on the area of the floor below it is open to. (Even an enclosed mezzanine, where permitted by exception must still be "within" the room below.) So IMHO, a mezzanine isn't going to work. I then considered it as a story. Nobody could seem to tell me the construction type, so with some destructive testing I found that it is a type V-B wood pole barn, with wood roof truss, wood interior framed floor and diaphragms. I was hoping to discover it was type III, but it was not. It is deceptive, because there have been multiple CMU walls built inside the pole barn for range enclosure and support structure for the range safety devices. As proposed, the mezzanine/story sits above the B-range and extends out and over the M-retail space, and would be used as offices in support of the operation and accessory storage. Without going too far into the weeds, the mezzanine/story will be constructed within the existing attic, incorporating the widely spaced trusses into the space plans.

Being of type V-B construction, non-suppressed, an M occupancy is limited to 1 story, and a B is limited to 2 stories per t504.4. On first glance I concluded that this would not fly as V-B, NS 2-story. BUT if the mezzanine/story is a B classification will this fly? B is allowed to be 2-story. The M is below on the first story, which is permitted. This is just me looking for possible solutions.

This building is old enough that no original core-shell documents have been found, I believe it may have been permitted originally by the county, before it was annexed. It has led many existences but was most recently permitted by my AHJ 9 years ago as the current B/M facility. That's why I had to look behind the walls.

Any thoughts are appreciated.

So I have a project that is an A-3, gym. It has a second floor above the office that overlooks the gym. The second floor has treadmills and eliptical machines and is open to the gym with a 42 inch wall. Can I call this a mezanine to avoid adding sprinklers?

 

[steveray]

So I have a project that is an A-3, gym. It has a second floor above the office that overlooks the gym. The second floor has treadmills and eliptical machines and is open to the gym with a 42 inch wall. Can I call this a mezanine to avoid adding sprinklers?

Maybe....

 

[Yikes]

In order to be a mezzanine, the mezzanine needs to be open to the space below, and the size of the mezzanine is dependent on the area of the floor below it is open to. (Even an enclosed mezzanine, where permitted by exception must still be "within" the room below.)

My understanding of mezzanines is that they must be open to the floor below (but not necessarily "open" walled) in order to be considered as part of the story below

I too have an existing A-3 multipurpose building (church) that has a very tall A-3 multipurpose space at the second floor level.
The owner would like to add an A-3 fully enclosed mezzanine, but only has enough room for one stair, with <75' CPET.
Per CBC Table 1006.3, a story with only one exit access is not allowed at above the second level, so I really need this to qualify as a "second story mezzanine".

The yellow area below indicates the only wall face which "shares atmosphere" with the multipurpose room off to one side of it.

Question: is this single shared wall sufficient to have the 3rd level qualify as a second-story mezzanine?
Is this proposed mezzanine considered "within" the room below?

Keep in mind that the only opening on any wall of the mezzanine is the door that leads to the exit stairwell.

 

[classicT]

I too have an existing A-3 multipurpose building (church) that has a very tall A-3 multipurpose space at the second floor level.
The owner would like to add an A-3 fully enclosed mezzanine, but only has space for one stair. CBC T-1006.3 says that having a story with only one exit access is not allowed at above the second level, so I really need this to qualify as a "second story mezzanine".

The yellow area below indicates the only wall face which "shares atmosphere" with the multipurpose room off to one side of it.

Question: is this single shared wall sufficient to have the 3rd level qualify as a second-story mezzanine?

View attachment 11556

2022 CA-BC - 505.2.3 Openness​

A mezzanine shall be open and unobstructed to the room in which such mezzanine is located except for walls not more than 42 inches (1067 mm) in height, columns and posts.
Exceptions:

1. Mezzanines or portions thereof are not required to be open to the room in which the mezzanines are located, provided that the occupant load of the aggregate area of the enclosed space is not greater than 10.
2. A mezzanine having two or more exits or access to exits is not required to be open to the room in which the mezzanine is located.
3. Mezzanines or portions thereof are not required to be open to the room in which the mezzanines are located, provided that the aggregate floor area of the enclosed space is not greater than 10 percent of the mezzanine area.
4. In industrial facilities, mezzanines used for control equipment are permitted to be glazed on all sides.
5. In occupancies other than Groups H and I, which are no more than two stories above grade plane and equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1, a mezzanine having two or more exits or access to exits shall not be required to be open to the room in which the mezzanine is located.

Looks like...

• Exception #1 will not work; OL>10
• Exception #2 will not work; single exit
• Exception #3 will not work; whole room is enclosed and measurement of enclosed is 10% of the mezzanine area
• Exception #4 will not work; not an industrial facility
• Exception #5 will not work; single exit/exit access

 

[Yikes]

Looks like...

• Exception #3 will not work; whole room is enclosed and measurement of enclosed is 10% of the mezzanine area

Let me clarify: the aggregate floor area of the enclosed space of the 3rd level mezzanine is less than 10% of the floor area of the big multipurpose room on the 2nd level, so I think it qualifies for exception #3.

The things I'm not sure about are:
Does sharing one single wall (with no openings) with the floor below qualify it as "mezzanine"?
Note in the sketch that the footprint of the "mezz" space is not located directly over the footprint of the big multipurpose room. Does it still qualify as a mezzanine?

 

[classicT]

Let me clarify: the aggregate floor area of the enclosed space of the 3rd level mezzanine is less than 10% of the floor area of the big multipurpose room on the 2nd level, so I think it qualifies for exception #3.

The things I'm not sure about are:
Does sharing one single wall (with no openings) with the floor below qualify it as "mezzanine"?
Note in the sketch that the footprint of the "mezz" space is not located directly over the footprint of the big multipurpose room. Does it still qualify as a mezzanine?

Exception #3 specifies that the enclosed space is limited to 10% of the mezzaanine area. Meaning that you could have a room on the mezzanine that is enclosed, not the mezzanine itself.

Example - If the mezzanine area is 1000sf, you could have a single room of 100sf that is enclosed.

Mezzanines or portions thereof are not required to be open to the room in which the mezzanines are located, provided that the aggregate floor area of the enclosed space is not greater than 10 percent of the mezzanine area.

 

[Yikes]

Example - If the mezzanine area is 1000sf, you could have a single room of 100sf that is enclosed.

Ah, so with a 1000 SF mezzanine, I could have up to 10% of the space on the mezzanine level be enclosed.

Thanks for the clarification!

 

[Yikes]

2022 CA-BC - 505.2.3 Openness​

A mezzanine shall be open and unobstructed to the room in which such mezzanine is located except for walls not more than 42 inches (1067 mm) in height, columns and posts.
Exceptions:

2. A mezzanine having two or more exits or access to exits is not required to be open to the room in which the mezzanine is located.
5. In occupancies other than Groups H and I, which are no more than two stories above grade plane and equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1, a mezzanine having two or more exits or access to exits shall not be required to be open to the room in which the mezzanine is located.

As an aside, I do not see the need for exc. #5 in the code, given that exc. #2 is already even more permissive.