Below grade fire rating?

[Sifu]

I have a group H building that requires 2-hr rated exterior walls per t602. The exterior wall is a concrete stem wall where below grade with PEMB on top, so the exterior wall is partially below grade (8') with earth behind it. On one of the walls that require the rating there is a 3' wide x 4'10" tall tunnel used for process piping and equipment run between the new building and an existing building. By definition, the exterior wall is both the concrete below grade portion and the PEMB above grade portion of the wall. The above grade is appropriately rated, but per plan the below grade portion is not (aside from the inherent qualities of the construction). I wouldn't think to require a rating for the below grade portion except now there is a tunnel opening providing a direct path to the adjacent building so my thinking is that any process piping or other elements passing down this tunnel would be required to pass through appropriately rated through penetrations. Anyone seen anything like this or have contrary thoughts?

 

[steveray]

You could use 721 or 722 for the rating on the concrete if you need to, but if the buildings are "connected" underground there should absolutely be a rating somewhere....?

 

[Sifu]

You could use 721 or 722 for the rating on the concrete if you need to, but if the buildings are "connected" underground there should absolutely be a rating somewhere....?

Yeah, not worried about how to rate the wall, but right now there is not even the wall, just the 3' x 4'10" opening. My thinking is they will need to continue the wall and then provide rated penetration assemblies.

 

[Sifu]

But...there is no scoping for penetrations in 705, and 714.4 does not include exterior walls as assemblies that require rated through penetrations.

 

[steveray]

Property line?

 

[Sifu]

Thinking about this a little more....I don't think penetrations in an exterior wall are regulated, BUT, since the tunnel connects two buildings, and they are treating them as separate buildings, in order for them to be two separate buildings they need a fire wall at the point of connection. Easy since the wall is 12" concrete for the first 8' and a 2-hr assembly above and structurally independent. Fire wall penetrations are scoped to 714. So they will need to continue the wall construction across the tunnel opening, and provide through penetration systems for any of the process piping being run in the tunnel. Continuity is ok since the walls and roof assembly are all non-com. That is my thinking anyway.

 

[steveray]

Exactly....

 

[Sifu]

I have another utility access tunnel. This one runs across 3 buildings separated by fire walls due to allowable area limitation at each building line. It has access openings in the floor of the first building and the 3rd building, crossing underneath the building in the middle. There is no access from the middle building, so access to the section in the middle is only possible from building 1 and/or building 3.

Fire walls are required to provide complete separation per 706.1.
Fire walls are required to extend from the foundation per 706.6.
Fire walls are required to have protected openings per IBC 716.

The architect has specified a rated access hatch at each floor opening, instead of a rated hatch and penetration systems at each fire wall line with just an open tunnel where it crosses the fire walls. This seems to provide the required separation. If fire erupted in either of the buildings with hatches it would be limited by the access hatch and if fire erupted under any of the buildings it could not spread to any area inside any of the other building. This way no penetrations would be needed and the tunnel could remain open at the line of each fire wall. Way better for maintenance and access and I think easier from a maintenance and inspection standpoint for the penetrations. Would you accept this? Would you consider it a modification per 104.10?

 

[Yankee Chronicler]

Thinking about this a little more....I don't think penetrations in an exterior wall are regulated, BUT, since the tunnel connects two buildings, and they are treating them as separate buildings, in order for them to be two separate buildings they need a fire wall at the point of connection. Easy since the wall is 12" concrete for the first 8' and a 2-hr assembly above and structurally independent. Fire wall penetrations are scoped to 714. So they will need to continue the wall construction across the tunnel opening, and provide through penetration systems for any of the process piping being run in the tunnel. Continuity is ok since the walls and roof assembly are all non-com. That is my thinking anyway.

If they are treating it as two buildings, which building does the tunnel belong to?

 

[Sifu]

They have three buildings, but entry into the tunnel is from 2 of them, the middle has no entry, nor penetration that I have found so far. It is a passageway under the middle building. So I guess it belongs to 2 of them, each with a rated floor hatch. The weird thing is the passage appears to be for piping that could just as well be buried. Their appears to be no good reason for it.

 

[Yankee Chronicler]

Multiple buildings on a single parcel either have to have fire separation distance, or be treated as a single building. Which way has this property been handled?

If they are multiple buildings, where is the fire separation line? (The "imaginary property line" the code talks about.) Wherever that line falls is where the firewall should be located, because that's where one building ends and the next building begins.

Remember, a basement is still a story -- it's just a story below grade.

Perhaps the tunnel could be regarded as not part of either building, under IBC 3104. Check that out for required fire separation assemblies.

 

[Sifu]

Separate buildings. 3104 as a pedestrian tunnel doesn't seem applicable but if it could be used the tunneled walkway would still require the 2-hr wall at the connection to each building with the rated opening. No gain as far as I can see. The fire separation line exists at the fire walls for each building. I dealt with this last year but the tunnel terminated at the fire wall on the inside and connected 2 buildings separated by open space. This one connects two buildings with a 3rd building filling the gap. This one keeps going, turns a corner until it reaches a lockable room where it turns up and comes through the floor. This happens in each of the two buildings with the tunnel terminations. They apparently want the tunnel as one continuous tunnel instead of the 3 segments it would create.

 

[Yankee Chronicler]

Separate buildings. 3104 as a pedestrian tunnel doesn't seem applicable but if it could be used the tunneled walkway would still require the 2-hr wall at the connection to each building with the rated opening. No gain as far as I can see. The fire separation line exists at the fire walls for each building. I dealt with this last year but the tunnel terminated at the fire wall on the inside and connected 2 buildings separated by open space. This one connects two buildings with a 3rd building filling the gap. This one keeps going, turns a corner until it reaches a lockable room where it turns up and comes through the floor. This happens in each of the two buildings with the tunnel terminations. They apparently want the tunnel as one continuous tunnel instead of the 3 segments it would create.

Sorry, but this makes no sense. If the buildings are separated by open space, there can't be any fire walls.

[BF] FIRE WALL. A fire-resistance-rated wall having
protected openings, which restricts the spread of fire and
extends continuously from the foundation to or through the
roof, with sufficient structural stability under fire conditions
to allow collapse of construction on either side without
collapse of the wall.

You may have 2-hour rated exterior walls, but that doesn't make them fire walls. And you can't have two fire separation lines separating two facing buildings. There's only one "imaginary property line," and someone should have decided where it occurs at the time the second building was designed.

It seems to me that you are trying to do the job of the design professionals. IMHO, all you need to do is tell them they have a problem, and require them to provide a solution.

 

[Sifu]

The current building is 3 buildings separated by fire walls. Think of them from left to right as #1,#2,#3. The tunnel begins in #1, travels under #2, and terminates in #3. The fire walls are internal.

The previous building I spoke of was one building, constructed close to another structure such that it required a 2-hr rated exterior wall. That tunnel began in the existing building, ran underground to the new building and terminated on the inside of the exterior wall below grade. It's termination was in the 2-hr exterior wall. I only brought it up to demonstrate that it was simpler than the one I am working on now because the point at which protection was provided was already in the plane of the wall. Forget that building, it was just an example.

Here is the tunnel under the floor. The issue is they don't propose protection of the openings in the fire wall in the plane of the walls, rather they propose the rated hatches at each end.

 

[Yankee Chronicler]

The tunnel compromises the fire walls at buildings 1/2 and 2/3. The definition is clear that a fire wall has to extend from the foundation through to or through the roof. They need to provide continuity of the fire walls through the tunnel at both building interfaces.