Cathedral Ceiling Woes – GreenBuildingAdvisor

Thanks for taking the time to read my question. My problem is as follows:

I purchased a small home in zone 5B this last December. I uncovered a significant amount of mold in our only bedroom, after smelling an intense mold/mildew scent upon our first thawing cycle. I pulled the ceiling (cathedral) and walls down to the studs and found that everything was insulated with R-19 fiberglass faced batt insulation. After remediating the mold, I am now in a position where I can start putting everything back together. My problem is the previous owner built the room as an addition, and built the room with a 2×8 ridge beam with 24″ OC 2×6 rafters. This does not allow me adequate space for appropriate insulation without spending an excessive (for my budget) amount of money on closed cell spray foam. In addition, rebuilding the roof and adding rigid insulation on the exterior sheathing is out of my budget, as well.

Current plan:

– My current plan is to keep this an unvented cathedral ceiling, with R-23 Rockwool insulation. Then an Intello Plus smart vapor retarder, 2×2 paralel furring strips, and finally tongue and groove for the ceiling.

– Walls will be virtually the same, with drywall instead of T&G.

– I happen to have an outlet near the ceiling of the closet and I am planning on putting a dehumidifier near the ceiling, and have the fan on for air movement.

My concerns:

– The roof is likely under built and I am not sure how much furring/strapping/scabbing onto the rafters I can safely do to make adequate depth for increased R-value batt insulation.

– Closed cell spray foam seems to be my only (that I know of) option to achieve adequate R value in the ceiling with current rafter depth. For me, this is cost prohibitive and I have concerns of longer term off-gassing.

– If I add a ridge vent and soffit vent system to this with inadequate insulation (R-23 Rockwool w/Intello Plus smart vapor retarder) am I going to improve the situation or just going to have continuous mold/other issues with the setup?

In closing, my question to the people here is: Is there any other budget friendly solution that you may have that you can share? What effect is my current plan going to have? Will having a dehumidifier going in the room, near the ceiling have a desirable impact?