Insulation / Metal Roof

[TX2021]

Good Evening,

Have a 24 x 24 detached garage, North Texas/Oklahoma border area. Roof is sheathed normally with a metal roof attached to the sheathing. There is currently no ventilation of any kind (no gable, ridge or other venting). The garage was wrapped with a Tyvek-type wrap.

I am going to insulate the interior garage portion (walls and flat ceiling) then cover the interior portion with plywood.

The questions are:

1. What type of insulation (faced or unfaced) and what direction for the facing if recommended?
2. Would it be recommended to add some kind of venting for the upper, uninsulated, portion of the garage to let air naturally migrate in and out? I don't want to go through the metal roof obviously so straight up isn't an option. If I don't vent I get the heat build up, if I do vent I let humidity in when it's humid.

The reason I'm doing this now is that I may in the future add a mini-split to put a little AC in the garage so I need to get the insulation in before covering the walls.

 

[AC-WC]

You will have to do a little research on which way to place the faced insulation. I'm much farther north than you and we need to have the facing towards our heated indoors. Because you're in Texas you may need to put the face on the outside and not inside. Some folks also like to do plastic vapor barrier in place of faced insulation.
There is no way I would not have some kind of ventilation in the unconditioned attic especially in your area. The heat build up would be horrible without some kind of venting. Gable vents would be relatively easy compared to cutting through your steel roof. You will need some kind of soffit vents to allow air into the attic, then the gables can exhale.
see link below.

Attic Ventilation Calculator: Proper Roof Ventilation | GAF

To calculate the amount of attic ventilation you need for your home, visit GAF's Ventilation Roofing Calculator now.

www.gaf.com

 

[billconner]

Metal liner panel ceiling, a foot or more cellulose, no vapor barrier, a vent in one gable and an exhaust fan ion a thermostat in other.

I've come to opinion vapor barriers are not helpful in climates with a lot of ac desired.