I worked summers with him, replacing roofs, insulating attics, and from scratch--building homes from the ground up.

Older tanks were not insulated well like the new ones today.

I was thinking of a spray foam insulation.  

But, if the property were owned by an LLC (properly filed and maintained), your risk exposure would be insulated by the protection of the entity, leaving only the assets owned by the LLC (as opposed to all of your personal assets) exposed to potential lawsuits and judgments.

Then I replaced all the windows, added r-6.5 insulation and vinyl sided them, and they all looked very good from outside.

Paid $5000 in heat last year in one house that well insulated.

I decided to move over to PLG because of the unpermitted work, wiring without junction boxes, lack of insulation and a whole host of shoddy quick flips. 

I did insulation for work, full time, when i was younger for a lot longer than I would have liked to....and there really is no magic cure.

Did the roofers/ contractors check that area to see if wet insulation needed to be replaced up there?

Only thing that might be missing is insulation in the walls.