I’ve got a currently vented attic at my house (soffits + ridge vent).  Part of my attic is already finished by the builder, and there’s a door that leads to flat decking that’s already been insulated and air sealed into the unconditioned space.  The problem is, I have 2 hvac units here unfortunately – a heap pump for the 3rd floor space, and and a “standard” unit gas/ac unit feeding by 2nd floor space.  But yeah, they are both in the unconditioned vented attic sitting on some decking.  Since it’s already decked, I would like to be able to store a few things here as well.

The sloped sides of the roof here have an LP TechShield radiant barrier already.  This area faces North/South respectivly (top = north, bottom = south in the attachmet). The temp range was somewhere around 35 – 100-ish throughout the year, humidity all over the place as I’m in zone 4 (middle of NC).

I had the builder recommend someone to put in some insulation in the attic, and they did put r30 rockwool batts along the roof rafters after installing baffles that terminate up near the ridge. R30 is also along the ceiling plane at 9′, which is relatively narrow.  There’s still probaby a good 3-4′ of air to the ridge vent above this.  And they put r15 rockwool in the end-wall near the window.  See drawing for reference.  

I’ve watched this space for the last year after its been insulated, and it never really gets below I’d say 55 degrees (i keep temp/humidity/dew point sensors here with hard data), but it’s certainly not air sealed since it’s just batts in place.  The humidity is very well controlled in this area.  I think the hvacs here are marginally leaky, keeping it warm-ish in the winter (55-63-ish).  I also have a ventilating dehumidifier in this space connected to the 2nd floor AC unit, so that’s probably helping.

Anyway, the question I’ve mostly been concerned about is condensation.  It gets down sometimes to 10-15 farenheight here in the winter occasionally at night, even though the average temp in winter is somewhere around 38-40.  I’ve seen no evidence of condensation inside my little insulated bubble, but it’s hard to tell what’s happening outside or in the actual osb sheathing under my roof given the temp delta between inside my insulation bubble and outside it.  It is somewhat difficult to air seal this area due to all the ducting in the area.  

Roof is asphalt shingle with underlayment and then osb + radiant barrier.  From there, it’s 2×8 rafters on the interior.

Thoughts/concerns?

Blue = finished space
Pink = space insulated with r30 rockwool along roofline (with baffles) and r15 wall

The only reason I started thinking about this was I was showering one day and noticed condensation on my mirror.  Totally unrelated to my attic insulation per-se, but for whatever reason, I started thinking about the insulation I added last fall, and here we are!  Brains work in mysterious ways.