Our 70 year old house is located in a cold northern climate and this is our first winter in it.. While there is no insulation in the attic/roof rafters, fiberglass batting has been placed under the attic floorboards. Earlier this week after retrieving some items from the walk-up attic I noticed one of the cardboard boxes seemed slightly damp. Today while back in the attic I noticed little balls of frost/ice in the tips of the roofing nails that protruded slightly through the roof sheeting. In addition, frost had formed on the inside of one of the gable windows as well as on the underside of some of the sheeting that extends out over the soffit enclosed overhang.

Obviously I’ve got some sort of problem with venting and excess humidity. I’ve partially opened one of the gable end windows and made sure that there’s no insulation blocking the soffit vents. How do I know if this is enough ventilation?

As for the excess humidity, I suspect it’s coming from the second floor bathroom. When the previous owner remodeled this bath, he put ½" drywall over the old plaster ceiling (which I would think would act as an added vapor barrier), but the added vent/heater fan assembly has some gaps around it. What is the best way to make a better seal - can I use expandable foam (e.g. Great Stuff)? Also, should I place some sort of plastic vapor barrier around fan assembly box before laying the fiberglass batting back on top? - (Although it’s a combination heater and vent fan, the metal assembly box doesn’t seem to get hot). Finally, should I replace the plastic flexible 4" vent hose with an insulated vent hose?

Any other things I should do to reduce the attic humidity?

I’m open for any/all ideas.

Thanks!

You did not mention it, but I hope the exhaust is vented outside. The problem with expandable foam is that is somewhat permanent and you will have to replace that fan in time. It can be a bear to break it loose to remove the existing fan. All of the gaps should be sealed since a shower emits a tremendous amount of moisture. Use a product that remains flexible, something akin to Mortite. You can try a vapor barrier but it may trap the moisture and cause some water spots on your ceiling. A better solution may be to build a false box around and over the exhaust fan with a hole large enough for the vent hose. You can seal this gap with the expandable foam. also use it around all of your vent stacks, electrical wire holes and any other gaos you may run across. An insulated or vinyl duct will also help eliminate the transmission of moisture. It is safe to put insulation around the box itself.