Which, if it was from water penetration from the outside it's on the owner.

I also agree with @Jay Hinrichs mold is usually created by a tenant, but also sometimes by an owner being neglectful, but whatever it is it is one of those issues for my renovation biz, even though I now know much more on mold (got great info from a mold removal guy here on BP too) and even though most mold is NOT the toxic strain, can be cleaned up relatively easily and IF the moisture source is eliminated, will not return.

Additionally, you will be creating more condensation in the attic than you want there which will lead to moisture damage and possibly (probably) mould.I would definitely plan to move the furnace into a conditioned space.

I would do whatever is necessary to get rid of your moisture problem.

I've installed laminates primarily for several years but am starting to lean towards vinyl plank flooring because I think it will hold up better to moisture and because it's easier to transport.

Well she left all the windows closed so the added moisture from the rain with no air flow caused mold/mildew to cover her stuff for the same reasons attics have soffits. 

It makes the two hours informative and fun.All of the documents and information booklets ("Mold, Moisture and Your Home", and "Protect Your Family From Lead In The Home", "Fire Safety", etc.) are given to the new tenant in a nice looking folder, along with our contact information and contact information for the utility companies.

Even in new construction while you may seal the roof deck from external sources of moisture, you are sealing in any moisture content in the new wood.When we spray the underside of a roof deck, we will typically plan to strap (sometimes with the application of an additional layer of {polyisocyanate} hardboard insulation) and over deck the existing roof (in the following 2 - 3 years) allowing a drainage plane between the original roof deck and the new one.  

There are acoustic dampening subfloor material that will seal the moisture and dampen noise. 

Also thinking of buying moisture meter to check reading.