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Community and Q&A

Advice on Smart Attached Garage Updates

pico_project | Posted in General Questions on
Working with a GC on a remodel project. Part of the work is to insulate and ‘finish’ the attached garage. Northern Michigan (Zone 6). Floorplan attached.
The garage has no insulation and is obviously very cold in the winter. It has some utilities than can freeze — and the garage got down to 28F this winter (monitored remotely). Since the house is built on a crawl space (near the lake) we want to be able to use the garage more as a basement and hope to keep it somewhat warmer.
So here is the current plan…
The garage exterior walls will be updated the same as the main houses’s exterior walls. This includes taking off the existing celotex sheathing, adding Rockwool batts (R15), adding 3/4″ plywood for sheating then putting Siga Majvest 500 SA over that for a WRB. The interior walls will be sheathed with 1/2″ BCX plywood.
The shared wall will have Rockwool batts (R15), then taped fire-rated drywall, then 1/2″ BCX plywood over that.
Ceiling done with same 1/2″ BCX plywood, vented attic, same ~R50 the house is getting.
There will be two 35×59 casement windows on the west end.
Garage door will be a simple insulated panel flush style door with no windows. Faces south.
There will be very little heat added. A small utility closet is being built against the shared wall. The utility closet will have a short section of hydronic baseboard heat (from same loop that heats the house) to keep the room above freezing. I’m thinking of adding some kind of simple vent to the closet to control heat a little.
Here are my questions so far:
– Re: Air quality. Should there be a better air barrier between the garage and house on the shared wall? Should we use the Mavjest 500 SA over the fire-rated drywall for example.
– Re: Airy quality. Importance of garage vent fan? My main concern is the car, obviously. My wife wants to park the car in there over the winter. Her car is a 2008 and our next car will be electric, so not a long-term issue. There will be an ERV exhaust somewhat near the door in the house side. Window in garage could remain cracked most of the year too.
– Can a garage be too tight for no planned HVAC, exhaust, fresh air? I’m assuming the 8×10 garage door will still leak more than a wall.
– Would it be wise to install some kind of interior vapor barrier (ex Majrex 200) behind the interior 1/2″ BCX plywood? I know it’s going to have some gaps that are not sealed. Or is the Rockwool, plywood, Majvest OK since it can dry to the outside?
– Any tips on sealing gaps on the attic side? Assuming I can caulk or tape any seams, gaps, etc… before insulation is blown in?
– Any other advice, suggestions, or feedback would be greatly appreciated.

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  1. mgensler | | #1

    We just did a garage remodel so to speak. is above the garage so we had ductwork and waterlines in the garage. Got rid of the ductwork, moved the water lines as close to the kitchen subfloor as possible, spray foamed between the joists, put 3 1/2" of poly iso on the shared wall, and covered everything with type x drywall.

    I'd recommend moving your utilities if you can. You are doing a lot and the door will never seal well.

    If you do want a heated closet, check into a hard wired resistance heater with thermostat. Only a couple hundred dollars. Putting hydronic in there is just over complicating things.

    1. pico_project | | #2

      The combi boiler and water lines will already be in the closet (building around existing stuff). Unless you mean other complications?

  2. canada_deck | | #3

    Have you been sure to carefully check the building code to establish your baseline requirements?

    For example, I believe this is the Ontario Building Code:
    (4) Where a storage garage is attached to or built into a building of residential occupancy,
    (a) an air barrier system conforming to Subsection 9.25.3. shall be installed between the garage and the remainder of the building to provide an effective barrier to gas and exhaust fumes,…
    (5) Where membrane materials are used to provide the required airtightness in the air barrier system, all joints shall be sealed and structurally supported."

    While you have everything open, seems like it would not be a bad idea to wire in some electric heat for the coldest days or at least run some wire so that you can add an electric heater (an in-wall unit or an overheat unit hanging from the ceiling) if you find the need. There is a good chance that you or someone else may decide at some point to use the garage as a workshop in which case it will be more valuable to heat it up quickly when needed.

    Are you putting in wiring for a future EV charger?

    I don't know how big of a concern air quality is if you are just driving in and out quickly and if the garage door is wide open while you are driving in and out. Obviously don't ever warm the car up inside the garage! That said, you might choose to install an exhaust fan if you have everything open anyway. Going back to future uses - it's a nice to have if you end up using the space as a workshop and do some painting and crafts in there in the future.

    1. pico_project | | #4

      Yes, wiring for future EV. Just looking into the details for that now. Any tips? Like how do I know which wall I want it on? Haha. Is there a default charger side for EVs?

      Regarding the air barrier. It seems like tapped drywall would meet code. I'm just wondering if the WRB would be better or overkill. Maybe it would be faster than taping drywall seams, but I doubt it. Certainly not cheaper.

      1. Andrew_C | | #5

        "Is there a default charger side for EVs?" I believe it's on the driver's side, often in front of the driver's door. If an EV were plugged in for a long-ish period of time (say, overnight) and a driver got into the vehicle, it'd be very easy to forget that it's plugged in if the connection was out of sight. My PHEV has both gas and electric charger ports on driver's side.

  3. mgensler | | #6

    Tesla charge port is driver's side in the rear corner panel. Chargers are wired to the wall shared with the garage door.

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