Vapor barrier in garage ceiling and walls or no? (Buffalo, NY)
Writing to ask if I should using a Kraft Paper Barrier, Plastic Vapor Barrier, or No Vapor in my garage insulation project..
Here’s the background:
I am starting the process of insulating my detached 23′ x 32′ Garage in Buffalo, NY (cold, lots of snow winters) with the secondary goal of having constant natural gas overhead heat keeping the ambient temperature between 40 and 50 degrees F in the winter.
However, the primary goal for the project is to reduce the humidity down from it’s current state which is 80 percent in the winter (according to hygrometer, and the air feels very cold and damp) down to 50 percent (normal for a house). I’d be willing to run a dehumidifier or powered vents to get the humidity down once the temp is high enough for the dehumidifier to run in the winter. During the winter the overhead door is never opened, and the garage is used as a hobby classic car workshop.
I did not build the garage, but the previous owner thought the slab was poured without a vapor barrier underneath when I asked him about it.
Currently bare steel, and some tools rust in my garage, and since I have classic cars, rust is the enemy!
The construction of the garage is pole barn style with 6×6 vertical poles, prefab 2×4 roofing trusses which are 24″ on center, osb sheeting, and vinyl siding. There is an overhead door on the 23′ side, two standard windows and a man door.
The ventilation is currently only in the soffits, but I would be interested in adding either a ridgevent, or whirlbird spinners when I get new shingles in the spring, if that would help with the humidity.
So, that brings me to the question if I should be installing a vapor barrier in the ceiling and walls?
My current plan was to use Kraft backed R38 fiberglass batts (with the Kraft as the vapor barrier) between the roofing trusses with taped seams for the ceiling, and luan plywood ceiling panels below that. For the walls, I am building 2×4 walls to hang 16″ on center R19 Kraft backed fiberglass batts, with the Kraft paper backing acting as the vapor barrier.
So my questions for the group are:
1. Is this style of insulation the right one if the goal is constant low heat and reducing humidity? If no, what style of insulation would you recommend? (vs. spray foam, or blown in, or other)
2. Knowing the goal is to reduce humidity, achieve dry air, and prevent rust, would you recommend a Kraft Paper vapor barrier, a plastic sheet vapor barrier? Or no vapor barrier?
Another note is that the overhead door is not used in the winter, so the only air exchange besides the building breathing at the seams, are the soffit vents and the man door.
I’ll post pics of the inside of the garage below:
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