If a room is "unconditioned" it should be insulated from any "conditioned" space that is adjacent to it or above (as required by the building code for new construction). Adjacent conditioned spaces do not need insulation in the walls or the floor-ceiling assemblies that separate them. If the adjacent rooms are not conditioned to the same temperature then insulation might help but wouldn't be critical or required by code.

If you live up north maybe and maybe not. If the house has lasted that long with out any ice daming and roof rot I'd not be too concerned. I lived in a house that was built back in 1826 in Ct and it had no roof vents at all. There was never any kind of rot at all. We just opened the windows all summer and it was fine. I now live in Florida and have 2 solar vents in the roof and two 120v fans on either end of the gables one pulling air in and one out. I have no eve vents and I have insulation right up to the eves. This house has been here since 1923 and with all my improvements it should last till the next ice age. Your biggest concern is ice daming and eve rot from snow build up. If you have this problem you might wish to fix the problem but if not save your money

It would help to know the climate. If you add ventilation to the under floor space it should be dry/conditioned air. If you add insulation to the inside walls it must be covered with at least 1/2" gypsum board if it is plastic foam. There are fiber insulation boards that are pre-finished that are commonly used to finish basements. The most conventional method is vertical metal Z furring with foam board insulation and drywall over that.

Hello! My job is located inside a really old house. Recently, we’ve seen little bits of yellow insulation in the vents (they are on the ceiling). Nothing has come through the vents (that we’ve seen or noticed). Is this something we should be really concerned about? It was discovered in 3 of the 5 vents in the building. Just two or three pieces in each. Do we need to clean the ducts? I’ve found various things online…should we be concerned about the air quality in the house? Is it possible the entire place is contaminated with fiberglass? Do we need to clean the entire office space? Maintenance says that everything in the attic looks fine and is intact. Thanks for any help/insight.