Fire Separation Distance Definition

[cwe05]

I am new to the forum and have searched but haven't found a thread or advise on the following issue. I am a contractor building on a single municipal lot the following:

Existing building: S-2 Parking Garage, open or closed, Type IIB construction, 5,258 SF (basically an opened vehicle storage PEMB shed)
New Building: S-1 & B, Type IIB construction, 7,200 SF (PEMB light maintenance shop)
Total Area: 12,458 SF

I can't combine without sprinkling since I'm over 12,000 sf together. I currently have just over 10' between the two structures. There is no lot line, or alley/row between them which leaves me with the third FSD criteria " an imaginary line between the structures".
I am being told that based on this imaginary line I need to rate the wall of the new building to one hour. Is this correct? Can the imaginary line be at the building line of the existing structure or does "between" get interpreted to mean a midpoint dimension? That would require a 20' separation of building lines.
This seems illogical since, if there was a lot line and the existing building were 2-3' off the line and the new building were placed 10' off that lot line the distance would be less than the 20' for the two buildings owned by a single individual. If you have any advise or insight into this it would be greatly appreciated!

 

[classicT]

The imaginary lot line can be at any point between the two buildings. That said, if you place it immediately adjacent to the existing building, that building would necessitate the fire resistance-rated exterior wall.

With only ten feet between the buildings, one, if not both, will need FR construction.

 

[Yankee Chronicler]

classicT is correct. For a single building on a site, the fire separation distance is to the property line on all sides. When a second building is constructed on the same parcel, someone (usually the design professional who designs the new building) has to establish the location of the fire separation line between the two buildings. The fire separation distance for each of the buildings is then measured to this "imaginary property line" on the sides facing each other.

The problem you are facing is that you can't make the existing building less safe. Depending on where the line is drawn, you may have to rate the walls, doors, and windows of the existing building.

 

[mtlogcabin]

[F] 406.6.3 Automatic sprinkler system.
An enclosed parking garage shall be equipped with an automatic sprinkler system in accordance with Section 903.2.10.

An open parking garage is not required to be sprinkled until you exceed the fire area.
You mention a shed and a maintenance shop if they exceed 460 sq feet you can construct them as separate fire areas and not have to sprinkle.

[BF] FIRE AREA. The aggregate floor area enclosed and bounded by fire walls, fire barriers, exterior walls or horizontal assemblies of a building. Areas of the building not provided with surrounding walls shall be included in the fire area if such areas are included within the horizontal projection of the roof or floor next above.

 

[walker.t]

I can't combine without sprinkling since I'm over 12,000 sf together.

Is it not an option to combine the two buildings but separate the existing and new construction with a fire wall?

I am being told that based on this imaginary line I need to rate the wall of the new building to one hour. Is this correct?

Depends where the imaginary line is placed. Take a look at Table 603, if the fire separation distance is less than 5’ to the new building with the S-1 use then you need a 2-hour rating for the new building wall.

 

[Yankee Chronicler]

Is it not an option to combine the two buildings but separate the existing and new construction with a fire wall?

Certainly. In essence, the firewall becomes the imaginary property line, and the fire separation distance for each building then becomes zero.

Just be sure that the firewall is, in fact, a firewall. That means it has to be constructed such that, if the structure on either side collapses, the firewall will remain intact.

 

[steveray]

You can combine them with a 3hr wall between......one block wall solves all of your problems....