In the PNW/Zone 4 climate. The house I am purchasing built in 1942 with an addition added had an inspection performed and it was noted that some of the fiberglass insulation installed under the subfloor between the joists was falling down and/or showing signs of deterioration and/or missing in spots with the sheet vapor barrier missing in a few spots as well and no insulation/wrap on any of the ducting. No A/C just 80% gas furnace in the house with floor vents.
Researching adding insulation options, it seems like the new thought is that vented crawlspaces were done wrong and the new frame of thinking is to encapsulated the crawlspace into the building envelope/conditioned space. I plan to DIY this but a couple of things I had questions on:
Should I remove all the old batting and sheeting if the material is dry if I plan on encapsulating and insulating the walls of the crawlspace and close off the vents?
Mold does not appear to be a significant issue but would fogging the space while its still unoccupied be a good idea?
Is a vapor barrier with 10mil sheeting be sufficient and can I lay this on top of the old sheeting (basically addition underlayment) and up the walls? Is insulation necessary on the ground?
Once the space is encapsulated and insulated does the ducting also need to be insulated? I plan on beefing up the sealing with foil tape and mastic but do I need to wrap as well or would I be better off beefing up the wall/floor insulation?
Once this is all done in the next 5-years my furnace will likely need to be replaced and I would like to move it to the crawlspace with a 90% unit to free up space in the small house would that change much if any of the steps I outlined above in anticipation of this upgrade?