New Type 1V HT Addition to an Existing H-3 Building

[123james321]

Hey all. Long time listener, first time caller.

We're using the 2018 IBC.
Our firm is beginning some programming work for an addition to an existing higher-education lab building.
The existing building is two-story, fully-sprinkled, Type IIB construction, with B and H-3 occupancies.
The existing and new buildings will be on the same lot.

Our new building will also house higher-education laboratory spaces. We're currently working within the provisions of Section 428, which I believe gives us a B Occupancy. We're exploring fully-sprinkled, Type IV, heavy timber construction for the addition. The new building will be two-stories and will connect to the existing by a smallish, ground floor corridor area. We're not planning on a large shared-wall scenario.

My questions are:
1) Assuming we meet the requirements of both options in 503.1.2, would it be better to classify the project as one or two buildings?
2) If we classify the buildings as a single structure, we wouldn't need a fire wall where new and old construction meet, right? Assuming we don't exceed the maximum area for which ever occupancy is most restrictive.
3) If we consider them separate structures, I believe we would need a firewall separation. In that case, locating the firewall where the connecting corridor meets the non-rated Type IIB walls seems problematic.

Thanks!

 

[Yankee Chronicler]

A building can only be one type of construction. If you add a section of type IV construction to a building that was originally type II-B, the overall building height and area will then be governed by the more restrictive of the two types. If I'm reading the tables correctly, it looks like type IV actually allows greater height in both feet and stories, but type II-B allows greater area. If that's correct, I don't know how you would determine which type is the lowest common denominator for classification purposes.