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Insulating a Soffit-Vented Garage Roof

Kyle Laguns | Posted in General Questions on

I live an hour north of Toronto, I believe climate zone 5B?

We have a small single car garage, approx 21×12.  I was hoping to economically insulate the garage just enough so that we could run a small heater and use it as a workshop in the winter.

I insulated the 2×4 wall framing with R-14 fibreglass  Now it is time for the roof/ceiling and I am unsure how to proceed.  The garage has soffit vents around it but no other vents at the top of the roof.

Without any rooftop vents for the soffit airflow to escape, I’m afraid to insulate and trap moisture.  I was hoping to keep it an open cathedral type ceiling but realize I may have to turn it into an attic?  Is this even possible without any vents?

Any suggestions on how to proceed with this?

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Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    Kyle,

    Are your garage walls above grade? Did you insulate just the exterior walls?

  2. Kyle Laguns | | #2

    Hey Steve,

    Yes the walls are above grade and the 2x4 wall framing will be insulated with R-14 fibreglass batts. I've put them on pause to address the roof insulation.

    I've started to install 11' 2x4 across the top plates to secure drywall and create an insulated attic. My roofer pal is coming to install a roof vent in the next few days.

    Had to act quickly as it's unseasonably warm right now and wanted to capitalize.

    The goal is to have a workshop where we can maintain a temperature suitable for paint and wood glue to set.

    What do you think of this plan? Any suggestions?

  3. Steve Knapp CZ 3A Georgia | | #3

    Kyle,

    Much of the discussion on GBA centers on conditioned spaces. Workshops are different because they are not occupied in the same way. Fortunately, I was able to find an article on Fine Homebuilding that should be helpful. (See https://www.finehomebuilding.com/2021/11/16/insulating-a-workshop-in-vermont.) My takeaway from this piece is that you have lots of flexibility in how you approach your project as long as you pay attention to air sealing and install a vapor retarder.

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