Mixed construction types, adjacent buildings

[wilgrp]

proposed new freestanding buildings; a) 4 story courthouse (81,544 gsf type IIB (stick steel) - sprinkled) and b) open parking structure 4 stories (29,904 gsf type IIA (c.i.p concrete) - sprinkled). Distance to face of buildings 10 feet (same lot) - public streets surrounding. Desired option is to declare as single building of on single lot and thereby not requiring exterior walls to be rated. Thus I can connect the garage to the courthouse with open sky bridges (10 feet long) and not deal with penetrating rated exterior wall.
My question : is it valid to make assumptions as noted above under IBC 503.1.2 Buildings on same lot since the code is silent on mixed construction types.
IBC 2021:
503.1.2 Buildings on same lot. 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.

 

[steveray]

If combined they work as IIB it might work, but the connection thing gets a little weird...Your code path isn't correct I don't believe but it might still work...

 

[wilgrp]

If combined they work as IIB it might work, but the connection thing gets a little weird...Your code path isn't correct I don't believe but it might still work...

much appreciated...

 

[steveray]

much appreciated...

I've never done one of the skybridge things but I know we have discussed it here....Search for a thread or someone else might chime in...

 

[steveray]

Look here:

3104.1​

This section shall apply to connections between buildings such as pedestrian walkways or tunnels, located at, above or below grade level, that are used as a means of travel by persons. The pedestrian walkway shall not contribute to the building area or the number of stories or height of connected buildings.

 

[Sifu]

Can a 4 story, A3, IIB work? Separated or non-separated? Seems the 4 story A3 is a limiting factor. And, if not are any of the provisions in ch. 31 for walkways not available? Maybe make the distance 10'1" on the 3rd floor to meet 3104.5.3?

I think RLGA has experience with these.

 

[steveray]

Can a 4 story, A3, IIB work? Separated or non-separated? Seems the 4 story A3 is a limiting factor. And, if not are any of the provisions in ch. 31 for walkways not available? Maybe make the distance 10'1" on the 3rd floor to meet 3104.5.3?

I think RLGA has experience with these.

If all the offices are on the upper story maybe...Really tough without a plan...

 

[wilgrp]

IBC 3104 has me covered for pedestrian walkways from garage... another wrinkle is that I have 160 long walkway (40 feet above grade) connecting the jail (across public street) to the courthouse. This will serve as inmate transfer to court for trial (5 occupants per day/3 days/week. Texas jail standards are pretty silent on this issue. However, I plan to make this fully fire sprinkled with automatic smoke evacuation and 2 hour interior separations at each end (with man trap). The idea has not been vetted by the local code official, but i could envision having a rescue port in the side (inmate escape proof..famous last words).

 

[walker.t]

is it valid to make assumptions as noted above under IBC 503.1.2 Buildings on same lot since the code is silent on mixed construction types.

No, it is not valid. Though there is not a specific statement in 503.1.2 that says “the two buildings must use the same construction type,” there are other provisions that indicate that a building can only have one construction type.

2021 IBC 503.1 (partial quote, editorial note and emphasis added)
For the purposes of determining area limitations, height limitations and type [singular] of construction, each portion of a building separated by one or more fire walls complying with Section 706 shall be considered a separate building.

Think about it like this, if the space between the two buildings was filled in with Type IIB construction you would have a Type IIB building because the entire building doesn’t meet the requirements of Type IIA. Then if you removed the hypothetical Type IIB infill and still wanted to consider the two parts as one building they’d still be considered Type IIB because the lowest construction type of the aggregate area is Type IIB.