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Detached Garage – Gable or Ridge Vents Needed If Future Insulation and HVAC

stuartd | Posted in General Questions on

Detached garage build, no insulation, no hvac, no plumbing
climate zone 6
slab on grade
footprint 28′ x 28′
6/12 pitch roof
asphalt shingles
zip sheathing
zip roof panel
2×6 wall framing
open truss ceiling

If ‘eventually’ I want to insulate this garage, and install mini split, builder suggested to install ridge vent, and 16″ x 24″ gable vents now, and do whatever necessary when time comes to insulate and climate control garage. What do you think?

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  1. matthew25 | | #1

    You need to decide if the air control layer will be on the Zip roof sheathing or the future ceiling drywall. If Zip, then you will have an unvented attic and until you add conditioning, you do have a chance of moisture condensation on the underside of the roof sheathing especially since you have no exterior insulation. Vented attics in your climate are usually the safer bet. Adding the vents now would be a good idea.

    Look at Steve Baczek or Jake Bruton videos showing how they extend the Zip sheathing into the ceiling drywall plane to make an air tight surface. This is a detail you may want to incorporate into your build now while you still can. Even if you don’t plan on installing drywall now.

  2. walta100 | | #2

    A agree with Matthew. You need to decide where the air barrier will be.

    I like the idea of a drywall ceiling cover with lot of cheap fluffy insulation under an attic with ridge and soffit vents.

    If you must have the conditioned attic space. You are stuck with poor choices all unvented roofs are risky at best. You will have almost no option but to use spray foam very ungreen and expensive making it very unlikely you will buy enough insulation to get a high R value.


  3. Expert Member


    There is no downside to venting the roof even if you later decide to condition the attic. Roof ventilation is most effective if located at the eaves and peak. So rather than ridge and gable vents, consider having at least half of it at the soffits.

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