Mezzanine question

[Yankee Chronicler]

I'm involved in a urination contest with a civil engineer who fancies himself as a building designer over whether an upper level of offices in a new building for a moving and storage company is a second story or a mezzanine. The building was originally permitted as an empty shell, which was to consist of a 60'x100' pre-engineered steel building with exterior walls on all four sides. Eave height is, if I remember correctly, 22 feet. Tacked directly onto one end of that building (and shown in a separate set of drawings from the metal building supplier) is a 30'x60' annex, under the same roof, that was shown as future offices.

The shell is still under construction and they have now come back with an application to fit-out the office section. It's to be two levels, with each level completely filling the 30'x60' section of the structure. (See attached sketch.) The designer wants to classify the upper level of the offices as an enclosed mezzanine, which he says is part of the 6,000 s.f. warehouse.

I say it's a story. It's not "in" or any way part of the 6,000 s.f. warehouse. The warehouse is unconditioned, and the offices will obviously be conditioned space. But the designer sent me an e-mail on Wednesday claiming that the "mezzanine" and the warehouse will be the same atmosphere. One of the submittals (there have been multiple, as he continues trying to justify his classification) had a small window in one of the offices, overlooking the warehouse.

As far as I'm concerned, he has a two-story building attached to a one-story building ... but, because the separation isn't a firewall it therefore becomes one building, and IMHO that building is a two-story building.

Is it a mezzanine, or is it a story?

 

[Yankee Chronicler]

We've been scratching our heads in the office over why the designer is so hell-bent on making the upper level a mezzanine rather than a story. I'm getting slow in my old age -- or maybe he just fooled me. As I noted, the building was originally permitted as a shell, and the office fit-out came in as a separate permit application well after construction had begun.

And, to my shame, since we had issued a permit for the building and we knew there would be offices in the annex portion at some point -- when the drawings for the office came in, it didn't occur to me to review allowable height and area.

Until now. He's calling for the offices to be framed in wood, so the construction type will change from II-B to V-B. The warehouse is use group S-1, and it's not sprinklered. So it's limited in height to 1 story. I need to run the numbers on allowable area but I expect that if the upper level is a story it may also exceed the allowable area.

If I'm correct, his problems would go away if he just changed from wood studs to metal studs and kept the construction type as II-B.

 

[TheCommish]

is the office space thermally isolated from the warehouse? if it is, then same atmosphere does not cut it.

The section for 505.2 Mezzanines, is to much to past here, with a bunch of exceptions, I would walk through the section step by step and check the boxes and see if it comply with the section and exceptions, or not and justify from there.

 

[classicT]

I see no issue with classifying the story as a mezzanine, so long as it complies with IBC Section 505.

Given the description of what's provided, I would carefully review 505.2.1 (Area Limitation). Additionally, 505.2.3 (Openness) is worth a review; although, it seems Exception #1 or #2 would likely be the proposed.

Bigger issue I'd have is the change in construction type. I've had projects try to do this in the past and I've only allowed it on an ongoing permit if they submitted as a change to the original shell, which then brought about changes in the permit valuation and fees, plan review fees, etc. If it were an existing building with a closed permit, then it would be reviewed under the IEBC similar to a change of occupancy.

 

[steveray]

Do they meet egress and accessibility as an enclosed mezzanine?....I wouldn't have a huge issue, but I would definitely comb it all the way through.

 

[ICE]

How does it fit with the definition of a mezzanine?

MEZZANINE. An intermediate level or levels between the floor and ceiling of any story and in accordance with Section 505. [DSA-AC] An intermediate level or levels between the floor and ceiling of any story with an aggregate floor area of not more than one-third of the area of the room or space in which the level or levels are located. Mezzanines have sufficient elevation that space for human occupancy can be provided on the floor below.

 

[mtlogcabin]

A VA construction type allows 3 stories non sprinklered for an S-1.

 

[classicT]

A VA construction type allows 3 stories non sprinklered for an S-1.

Type V-A is pretty difficult with a PEMB.

 

[steveray]

is a 30'x60' annex, under the same roof, that was shown as future offices.

I'm not saying it's a mezzanine.....But this tells me it could be...

 

[Mech]

Perhaps they only need to downgrade to Type III construction. From the 2018 IBC:

602.3 Type III. Type III construction . . . Fire-retardant-treated wood framing and sheathing complying with Section 2303.2 shall be permitted within exterior wall assemblies of a 2-hour rating or less.

 

[classicT]

Perhaps they only need to downgrade to Type III construction. From the 2018 IBC:

602.3 Type III. Type III construction . . . Fire-retardant-treated wood framing and sheathing complying with Section 2303.2 shall be permitted within exterior wall assemblies of a 2-hour rating or less.

Again, difficult with an existing PEMB. 2-hr exterior walls comes into play with Type III.

 

[mtlogcabin]

Type V-A is pretty difficult with a PEMB.

I agree with you, so how about non separated uses. No separation required between a B and S-1.

 

[classicT]

I agree with you, so how about non separated uses. No separation required between a B and S-1.

Wouldn't solve the issue. If non-separated, the most restrictive requirements for area, height, and number of stories applies. The issue is that the project is limited to a single story.

The warehouse is use group S-1, and it's not sprinklered. So it's limited in height to 1 story.

2021 IBC 508.3 Nonseparated Occupancies​

508.3.2 Allowable Building Area, Height and Number of Stories​

The allowable building area, height and number of stories of the building or portion thereof shall be based on the most restrictive allowances for the occupancy groups under consideration for the type of construction of the building in accordance with Section 503.1.

 

[steveray]

Again, difficult with an existing PEMB. 2-hr exterior walls comes into play with Type III.

Yes and no.....IIIB requires 2hr exterior BEARING walls...A PEMB has no bearing walls...Typically....

 

[classicT]

Yes and no.....IIIB requires 2hr exterior BEARING walls...A PEMB has no bearing walls...Typically....

I seem to recall that the commentary to either Table 601 or to Sec. 602.3 has some guidance on this. And from what I recall, based upon a project that tried and failed to go that route, a PEMB is not exempted from the 2-hr fire resistance. I believe we were looking at having to wrap the columns, but the designer ultimately did not want to go the route of III-B due to the complexity of the 2-hr rating.

If anyone has the commentary, it may spark the memory.

 

[steveray]

I seem to recall that the commentary to either Table 601 or to Sec. 602.3 has some guidance on this. And from what I recall, based upon a project that tried and failed to go that route, a PEMB is not exempted from the 2-hr fire resistance. I believe we were looking at having to wrap the columns, but the designer ultimately did not want to go the route of III-B due to the complexity of the 2-hr rating.

If anyone has the commentary, it may spark the memory.

I don't think commentary says much and I agree it shouldn't be interpreted that way but...

❖ Buildings of Type III construction are typically constructed with both combustible and noncombustible materials. The exterior walls are required to be noncombustible with load-bearing exterior walls required to have a minimum 2-hour fire-resistance rating (see Table 601). Exterior nonload-bearing walls are not required by Table 601 to have a fire-resistance rating but must comply with the provisions of Table 705.5. The elements within the perimeter established by the exterior walls (i.e., floors, roofs and walls) are permitted to be of combustible materials. An example of a typical building of Type III construction is a structure having its exterior walls constructed of concrete, masonry or other approved noncombustible materials, but with wood-framed floor, interior wall and roof construction (see Commentary Figure 602.3). The structural members of a building of Type IIIB construction are not required to have a fire-resistance rating, with the exception of the exterior load-bearing walls.

 

[Mech]

Again, difficult with an existing PEMB. 2-hr exterior walls comes into play with Type III.

About 10 - 15 years ago, I think I considered a single story PEMB as having a structural frame, claimed the exterior walls as being non-load bearing, and said the fire resistance rating requirement was 0. I'm not saying this is right, but that is how I approached it back then.

 

[classicT]

I don't think commentary says much and I agree it shouldn't be interpreted that way but...

❖ Buildings of Type III construction are typically constructed with both combustible and noncombustible materials. The exterior walls are required to be noncombustible with load-bearing exterior walls required to have a minimum 2-hour fire-resistance rating (see Table 601). Exterior nonload-bearing walls are not required by Table 601 to have a fire-resistance rating but must comply with the provisions of Table 705.5. The elements within the perimeter established by the exterior walls (i.e., floors, roofs and walls) are permitted to be of combustible materials. An example of a typical building of Type III construction is a structure having its exterior walls constructed of concrete, masonry or other approved noncombustible materials, but with wood-framed floor, interior wall and roof construction (see Commentary Figure 602.3). The structural members of a building of Type IIIB construction are not required to have a fire-resistance rating, with the exception of the exterior load-bearing walls.

About 10 - 15 years ago, I think I considered a single story PEMB as having a structural frame, claimed the exterior walls as being non-load bearing, and said the fire resistance rating requirement was 0. I'm not saying this is right, but that is how I approached it back then.

It may has also been from the commentary to the following section.

2021 IBC 704.10 Exterior Structural Members​

Load-bearing structural members located within the exterior walls or on the outside of a building or structure shall be provided with the highest fire-resistance rating as determined in accordance with the following:

1. As required by Table 601 for the type of building element based on the type of construction of the building.
2. As required by Table 601 for exterior bearing walls based on the type of construction.
3. As required by Table 705.5 for exterior walls based on the fire separation distance.

 

[classicT]

It may has also been from the commentary to the following section.

2021 IBC 704.10 Exterior Structural Members​

Load-bearing structural members located within the exterior walls or on the outside of a building or structure shall be provided with the highest fire-resistance rating as determined in accordance with the following:

1. As required by Table 601 for the type of building element based on the type of construction of the building.
2. As required by Table 601 for exterior bearing walls based on the type of construction.
3. As required by Table 705.5 for exterior walls based on the fire separation distance.

I am actually quite sure that this addresses it fairly plainly; although my memory tells me the commentary nearly spelled it out for Type III-B.

It will still come to a matter of interpretation - - Is a PEMB column located within the exterior wall? I would say yes.

The exterior wall being an assembly of the cladding, purlins, and columns. If that is the case, per IBC 704.10, the load-bearing structural members (columns, purlins, diagonal braces, etc.) that make up the exterior wall assembly must be provided with a 2-hr fire-resistance rating as required for exterior bearing walls of a Type III-B exterior bearing wall.

 

[Mech]

Below is the 2018 IBC Section 704.10 Code Commentary.

704.10 Exterior structural members. [code omitted] Commentary-> Exterior load-bearing structural members, such as columns or girders, must have the same fire-resistance rating required for exterior load-bearing walls. As such, the required fire-resistance rating is the higher rating of that found in Table 601 for type of construction for structural elements or bearing walls or as required in Table 602 based on the fire separation distance.

 

[steveray]

I am actually quite sure that this addresses it fairly plainly; although my memory tells me the commentary nearly spelled it out for Type III-B.

It will still come to a matter of interpretation - - Is a PEMB column located within the exterior wall? I would say yes.

The exterior wall being an assembly of the cladding, purlins, and columns. If that is the case, per IBC 704.10, the load-bearing structural members (columns, purlins, diagonal braces, etc.) that make up the exterior wall assembly must be provided with a 2-hr fire-resistance rating as required for exterior bearing walls of a Type III-B exterior bearing wall.

Trying to not take this too far OT....But...If the purlins and insulation are on the outside of the frame, I would have a bit of hard time... but again..not trying to enforce it that way...

[BF] EXTERIOR WALL. A wall, bearing or nonbearing, that is used as an enclosing wall for a building, other than a fire wall, and that has a slope of 60 degrees (1.05 rad) or greater with the horizontal plane.

❖ An exterior wall is defined as an exterior element that encloses a structure and that has a slope equal to or greater than 60 degrees (1.05 rad) from the horizontal plane. Exterior enclosing elements with slopes less than this are generally subjected to more severe weather exposure than vertical surfaces and thus may experience a greater amount of water intrusion. These sloped surfaces, which may include elements such as inset windowsills, sloped parapets and other architectural elements, should be designed to resist water penetration in a manner similar to a roof.

 

[classicT]

Trying to not take this too far OT....But...If the purlins and insulation are on the outside of the frame, I would have a bit of hard time... but again..not trying to enforce it that way...

[BF] EXTERIOR WALL. A wall, bearing or nonbearing, that is used as an enclosing wall for a building, other than a fire wall, and that has a slope of 60 degrees (1.05 rad) or greater with the horizontal plane.

❖ An exterior wall is defined as an exterior element that encloses a structure and that has a slope equal to or greater than 60 degrees (1.05 rad) from the horizontal plane. Exterior enclosing elements with slopes less than this are generally subjected to more severe weather exposure than vertical surfaces and thus may experience a greater amount of water intrusion. These sloped surfaces, which may include elements such as inset windowsills, sloped parapets and other architectural elements, should be designed to resist water penetration in a manner similar to a roof.

I do agree. This section could benefit from a code change proposal to clarify how PEMB should be handled. In the case you indicate, if the exterior wall assembly (cladding, insulation and purlins) is the exterior wall and the PEMB columns are interior to the actual space, it would seem that the columns do not require a fire resistive rating. That said, the purlins would require protection (they are load bearing), and I am not sure how you would protect the purlins and not the columns. Columns support the purlins, so by principal, the columns would be protected as well as supporting construction.

 

[Yankee Chronicler]

Good discussion and I thank you for your input, but we are getting far away from the original question. I'm not the owner or the architect -- I'm the plan reviewer. It's not my job to tell the designer how to do his job. My job is to review what's put in front of me and determine whether or not it meets the code.

In this case, since the 60x100 portion is a complete building, with complete exterior walls on all four sides, and the office area is then tacked unto one end of the 60x100 warehouse, there is simply no way I'm willing to say that the upper level in the office portion is "within" the warehouse portion. We have rejected the application and told the designer if he still disagrees he can take the appeal route spelled out in Chapter 1.

 

[Mark K]

Could it be that the engineer is driven by structural issues while everybody is focusing on fire and occupancy issues.

The common analytical tools used may assume a complete diaphragm at each level but this does not exist. Maybe what is needed is another engineer to sit down with the engineer to understand his concerns.