Question-and-Answer Resource for the Building Energy Modeling Community
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Good question. The inheritance diagram for OpenStudio should help. Looking at it you can see 5 places where a surface or sub-surface can get a construction. The deepest assignment is hard assigning it to the surface directory. The shallowest is to assign a default construction at the building level. In your cases, the assessment was between those two, assigned to a space type.
If you have two conflicting surfaces OpenStudio tries to resolve them by applying the construction that has a deeper assignment. So if your hospital has a default interior wall of basic drywall, but you assign a construction set to the x-ray room that is lead lined. The lead wall will be win the tie breaker where there are interior walls for the x-ray room.
Now lets say you have another space type that has a unique interior wall. Lets say you have an un-conditioned space and you want it to have insulated interior walls. If a space using the unconditioned space type shares an interior wall with the a space using the x-ray space type OpenStudio an't break the tie. There is a warning on export to IDF, but that can often go unseen depending on how you run the simulation. In this situation you should hard assign the construction you want used (which may be a unique construction not seen in either space e.g. insulated and with lead) directly to one or the other of the two surfaces. You can assign a mirror of it to the other surface, but that isn't necessary.
