unfinished building, mold on underside of roof plywood, is this a problem?

I live in the temperate rainforest, so it is cold and humid here all winter.  We're working on a strawbale+cob building.  The roof is done, made of plywood + ice&water shield underlayment + metal roofing.

Because it's so moist here, and perhaps also because the new plywood wasn't completely dry, the underside of the roof/ceiling plywood is growing mold on it.  It's ugly, but I'm only really worried about long term health implications.  When we insulate the ceiling this mold will be hidden anyway.

My question is, if we insulate this ceiling and then fire up a woodstove in the building so that it dries out thoroughly, is this mold a big problem?  My understanding of mold is that when it's completely dry it stops producing spores so it won't continue to impact the air quality in the building.

I could scrub the ceiling with vinegar too right before we run the woodstove, maybe the acidic vinegar will kill the mold so it's not simply dormant waiting for a hint of moisture to start growing again.  But I assume if we ever stop running the stove in there in winter, and it starts to get a little moist again, it will keep molding?

Type of mold matters and whether anyone living there is susceptible to it.  ALL lumber and straw have spores on them and will grow whenever the conditions allow.

There is a product called concrobium that is the gold standard that people who are sick from mold and are chemical sensitive use to treat black mold. It is pretty mild on the toxic meter. More toxic than vinegar, less toxic than the mycotoxin some molds release when you spray them with vinegar or bleach.

The product leaves a residue that helps prevent future growth.  I would treat the roof as soon as you can, using proper methods and safety gear.

treat it and clean off the mold before you seal up the area.  I have used this product,  https://moldzyme.com/ to clean off mold in a ceiling area, I ripped off the drywall, exposed the wood, and treated with this.  I am generally chemically sensitive, but had no problems with this product, and it worked.  

treat with the moldzyme once you can keep it from getting wet, so, do not seal up the area before drying it out, even if you have to move in, leave that area open ( no insulation or drywall yet).  Do not put in insulation and then run the wood stove to dry out.  Also, this way you can inspect the area and will know you have solved the problem.

As far as the future, you need to have a design so that moisture never builds up in areas of your house.  It will help  once the building is finished and dry .  People try and address this in different ways, and different ways depending on what part of the country.  I would find out what is code for roofs in your area, and what works for other peoples houses in your climate zone.  It doesnt matter that your walls are cob or straw bale and theirs is plywood, because it sounds like you are making a standard type roof.  Some people advocate alot of of air flow and venting, although to me in your area that seems like it would be counter productive, even though that is commonly done here.  The way I like to do it in my house is to insulate directly on the bottom of the roofing deck and not vent at all, and that way I do not have moist warm air hitting the cold underside of the roofing deck and condensing.  This means I use nasty foam and foam boards.  This foam is directly on the underside, on the plywood, with no air hitting the plywood, and there is no exterior venting to let in cold moist air, so the area on the house side of the foam is at house temperature and humidity.  So then it is no more likely to mold that the walls or other areas of the house. But, there are different trains of thought on how to solve this

R Scott wrote:Type of mold matters and whether anyone living there is susceptible to it.  ALL lumber and straw have spores on them and will grow whenever the conditions allow.

There is a product called concrobium that is the gold standard that people who are sick from mold and are chemical sensitive use to treat black mold. It is pretty mild on the toxic meter. More toxic than vinegar, less toxic than the mycotoxin some molds release when you spray them with vinegar or bleach.

The product leaves a residue that helps prevent future growth.  I would treat the roof as soon as you can, using proper methods and safety gear.

I use the same product here in Florida it works concrobium,   I also run 2 dehumidifiers to lower humidity which stops mold in it's tracks.     Another method is to kill the mold spores in the air with a treatment of ozone.     You must remove the moisture for the treatment to be effective.      If you read the ingreadients it is basically baking soda,   I add baking soda to my dish washer about 3 tbs per load to help kill the mold in the washer.    I find it effective.

     

Insulate the roofing material for a start with rockwool and silver paper. IN Australia its called building blanket.
Some moulds can cause respiratory issues in humans.

With ice and water shield on the roof, assuming a cathedral ceiling, the underside should be vented from eave to ridge, usually accomplished with ready made cardboard baffles installed before insulation and a path for air to enter the cavity at the eave and exit at the ridge, as under a metal ridge cap.
If there will be a normal ceiling and no insulation in rafter bays, you can vent through the gable ends.   Unvented roofs in cold climates with ice and water shield on top have rotted on many occasions.    However some mold on plywood or framing lumber is very common and generally no cause for concern.   Once a roof is on the materials dry out and the mold stops growing.

Sometimes structures are built with open soffits such that the roof plywood is exposed on the underside of the overhangs.  Certain winter conditions favor ice or condensation on this exposed plywood which leads to occasional mold growth and discoloring but I have never seen this alone lead to rot when the roof above is leak free.