Expert: Stephen Major (Owner--Major Design Group) - 3/21/2007

Question
Hi Stephen
Thanks for your time. I have built a 10' x 10' room in the attic to use as gun storage and reloading. My main concern is humidity & moisture. The room is elevateed to get above the duct work and the walls are freestanding. 2x4 frame and 2x6 for the ceiling. So far I have done 2 walls with R13, but could use R19 or more if needed. I also thought about running either plastic wrap around the inside after the insulation before the the sheet rock, or wrap the outside. I also debated putting up the 4x8 sheets of 1/2" foam board around the outterwalls & taping the seems, or combination of both. I have also considered doing paneling, instead of sheet rock on the walls, but I dont think paneling will give me as good a protection as the SR. I live in AL, so heat is the main factor in controlling the room temp. It will have a vent tied into the central heat/ac and a ceiling fan. There are some many choices I dont know which way to go. Thanks for your help!

Answer
Tim,
In an extreme cooling climate like Alabama, you need to keep "outdoor" warm moist air from infiltrating the wall and ceiling cavities from the outside, which in your case is the  attic space.  I think you are fine with R-13 fiberglass in the walls and R-19 on the ceiling.  The vapor retarder should be on the outside.  For this I would recommend using 1/2" or 1" foil-faced rigid foam panels, which will also add meaningful R-value.  Attach them with roof nails or plasti-cap nails, and tape the seams with 3" foil duct tape.  Along the framing perimeters (top, bottom), embed the panels in a continuous bead of caulk or construction adhesive, as some of these areas probably can't be easily taped.  

In addition, be sure that the attic space around the room is well ventilated, and that your construction doesn't interfere with proper and/or existing attic ventilation.

Drywall is fine for the interior finish.  Like any finished space, be sure to keep the room fairly well conditioned and comfortable as you would the rest of the house.  Funny thing about interior building and finish materials -- they tend to prefer the same climate as we do: moderate temperatures and humidity levels, and adequate air circulation.    

Inspect the exterior of the room occasionally, and keep the vapor retarder in good repair.  

Good luck.  Let me know how you decide to go.