Insulation requirement for wall adjacent to expansion joint

I have a project with 2 blocks- the admin block (66,000SF) and housing block (68,000SF). They are separated by a 4” expansion joint and have a CMU wall on each side of it. The only way to access one block from the other is through a single corridor. For the purpose of modeling, since they have their own external wall, and different major occupancy type, I’ve treated them as 2 separate buildings. Now the wall adjacent to the expansion joint- does this wall require insulation like a normal exterior wall to comply with ASHRAE code? Or do I treat this as an interior wall? Any clue?

It is not clear from your description but if the expansion joint area is unenclosed and part of the ambient outside conditions (wind can blow through it) than I think it should be treated as an exterior surface and insulated following the nonresidential requirements on the admin block and the residential requirements on the housing block. This also applies if the space is more like a ventilated crawlspace area.

If on the other hand the space between the two blocks is fully enclosed but just not conditioned, it would be treated as semi-exterior envelope and then you would use the semi-heated requirements.

Unless the expansion joint area is fully enclosed and conditioned (which seems very unlikely) it will need some insulation based on 90.1.

Figure 5.5.2 from 90.1-2013 can help understand the interpretation.

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Please note this is just my personal unofficial interpretation and only represents my viewpoint and should not be viewed as an official statement from ASHRAE.