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Detached Garage with Shared Wall & Partially Heated Shop

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  • Detached Garage with Shared Wall & Partially Heated Shop

    It's been a busy past couple years. Between working in the US for a year, and just welcoming our newborn son into the world a short while ago (our first), I haven't been on here in a long time.

    Well, win-win, along with the new guy we moved to a bigger house, with a bigger garage! Still not huge, but 20x20 is far better than what we used to have, and I will have one bay dedicated as a wood shop (no plans to park in the other bay permanently, but want to have it mostly clear so that it's always a possibility - I'll have a rolling workbench to serve as an outfeed table and layout space, that can be moved in and out of the other bay).

    It's a typical Calgary-area semi-detached home (we share 1 wall with our neighbour), with the detached garage that also has a shared party wall with the neighbour (facing the alley-way). The only garage wall that's insulated is the one shared with the neighbour, the other 3 walls and the ceiling are uninsulated. I'm in the process of insulating and finishing the rest and have 2 questions:

    1) From what I can tell, the insulated shared wall (fiberglass bats) does not have a vapour barrier (I can't see one). If I will be partially heating my side of the garage, and the neighbours is unheated, will I need to put up a vapour barrier on the shared wall? I know it's always supposed to go on the warm side, but I only plan to partially heat the garage - please no cookie-cutter answers here. It's Calgary so we're very dry here - summer there would be no issue without the vapour barrier, winter is the only question really. I'm going to take a look myself at some psychometric charts because I think just heating it to 5°C (even to 10°C) wouldn't create any moisture problems if there is no vapour barrier (as I won't be adding any humidity aside from my breath - there won't be melting cars in there). But I want to be certain and check what others have done. I think there is a similar duplex down the street that is brand new, and was finished with a fully insulated and finished garage - I might check to see what that builder did as well (if I can track them down).

    2) We don't have NG in our garage, so I was just planning to use a 4.8 kW 240v construction heater and only heat it when I'm going to work out there, which would likely only be a couple times a week. This would only be to take the edge off the -20°C outside, ideally I would still wear a couple layers and only heat it to 2-5°C. Are there any potential problems with temporarily heating the space like this, and the resulting temperature swings? I know that if I go warmer, I could see condensation on tolls & metal surfaces as they take longer to warm up, which is why I only plan to partially heat it.
    Last edited by czechm8; 06-12-2018, 12:07 PM. Reason: Typos
    John in Calgary
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  • #2

    Re: Detached Garage with Shared Wall & Partially Heated Shop

    VB should be placed on the warm side as you say. The only issue you may have is knowing the construction of the dividing wall. Find out how it was built. What is on either side and what is in between both sides.
    "Do it Right!"

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    • #3

      Re: Detached Garage with Shared Wall & Partially Heated Shop

      The common wall is already covered with drywall, right? Rather than tear that off to install vapor barrier, how about a few coats of oil based paint. It is very resistant to vapor transmission. I think there are actually paints sold as vapor barrier paint. Even if it doesn't meet code, practically speaking, it will do the job.

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      • #4

        Re: Detached Garage with Shared Wall & Partially Heated Shop

        All depends on the construction and fire barrier between units. Basically what you have is an interior partition wall. No real need for a vapour barrier. The insulation is a sound barrier and usually a firebreak is provided for with drywall in between two walls. Like i said try to check it out with builder and or other neighbours etc.
        "Do it Right!"

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        • #5

          Re: Detached Garage with Shared Wall & Partially Heated Shop

          Originally posted by drzaius View Post
          The common wall is already covered with drywall, right? Rather than tear that off to install vapor barrier, how about a few coats of oil based paint. It is very resistant to vapor transmission. I think there are actually paints sold as vapor barrier paint. Even if it doesn't meet code, practically speaking, it will do the job.
          Correct, it's drywalled already, but not taped & mudded or painted, so it would be rather easy to back the screws out and reuse the sheets after. I'm kind of leaning towards that, as then I can add concealed electrical along that 20' wall and then do the poly (was going to do all surface mount electrical along that wall if I left the original drywall).

          The paint would probably be more than enough for a VB, but I wasn't thinking of ever finishing the drywall - no tape and mud just hang it and paint it - so I'm not sure whether the paint would work as well in that case as there would be gaps between each sheet. My original thinking was that this way I can always unscrew a board if I need to change something (though I'm adding more than enough 120v electrical beforehand, plus will be doing all 240v from a surface-mount sub-panel), so maybe that's overkill and I don't need any more flexibility. Is there any other downside to not finishing the drywall with tape & mud other than it won't look as nice? (I guess if I paint it all now, it may be impossible to mud at a later time?)

          On a side note, I had a friend give me a bunch of vapour barrier for free, but it feels much thinner than what I've typically seen used in residential, it might be a 3 or a 4 mil? Looks like I can get a roll of 9' 6 mil fairly nearby (kijiji) for $30. Is it better to just go with the 6 mil, or will 3 or 4 do just as good of a job?
          John in Calgary

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          • #6

            Re: Detached Garage with Shared Wall & Partially Heated Shop

            Originally posted by czechm8 View Post

            Correct, it's drywalled already, but not taped & mudded or painted, so it would be rather easy to back the screws out and reuse the sheets after. I'm kind of leaning towards that, as then I can add concealed electrical along that 20' wall and then do the poly (was going to do all surface mount electrical along that wall if I left the original drywall).

            The paint would probably be more than enough for a VB, but I wasn't thinking of ever finishing the drywall - no tape and mud just hang it and paint it - so I'm not sure whether the paint would work as well in that case as there would be gaps between each sheet. My original thinking was that this way I can always unscrew a board if I need to change something (though I'm adding more than enough 120v electrical beforehand, plus will be doing all 240v from a surface-mount sub-panel), so maybe that's overkill and I don't need any more flexibility. Is there any other downside to not finishing the drywall with tape & mud other than it won't look as nice? (I guess if I paint it all now, it may be impossible to mud at a later time?)

            On a side note, I had a friend give me a bunch of vapour barrier for free, but it feels much thinner than what I've typically seen used in residential, it might be a 3 or a 4 mil? Looks like I can get a roll of 9' 6 mil fairly nearby (kijiji) for $30. Is it better to just go with the 6 mil, or will 3 or 4 do just as good of a job?
            3 or 4 mil is used as drop clothes for painters.
            Use the 6 mil.

            I would just do 1 coat of mud and tape, use durobond or Sheetrock 90 and mesh tape.

            Then prime and paint.

            Nathan

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            • #7

              Re: Detached Garage with Shared Wall & Partially Heated Shop

              The construction heater will do a fair job in a 20 by 20 space with some decent insulation. It won't be tropical but 10 C should be achievable on most days. You can do a calculation using this site https://www.simplex.ca/en-CA/tips-advice/btu-calculator
              I have not had a problem with tools heating my shop in winter then letting it go cold.
              Last edited by dwoody; 06-14-2018, 07:19 PM. Reason: Added not to correct last sentence

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              • #8

                Re: Detached Garage with Shared Wall & Partially Heated Shop

                At minus 30 the heater will not keep up and will take hours to do much of anything.
                "Do it Right!"

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                • #9

                  Re: Detached Garage with Shared Wall & Partially Heated Shop

                  Originally posted by Rusty View Post
                  At minus 30 the heater will not keep up and will take hours to do much of anything.
                  Correct starting from -30. From -10 to go to 15 requires about 4500 BTU's which the heater will provide. Assuming 3,200 cubic feet and insulated walls and ceiling.

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                  • #10

                    Re: Detached Garage with Shared Wall & Partially Heated Shop

                    Dennis I can't see any comment on how long it will take to go from - 10 to 15. if that's what you're saying. What I'm saying is I'm not sure exactly what you're saying. I was starting at minus 30. I have one of those heaters and I know what they will do and what they won't do.
                    "Do it Right!"

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                    • #11

                      Re: Detached Garage with Shared Wall & Partially Heated Shop

                      Originally posted by Rusty View Post
                      Dennis I can't see any comment on how long it will take to go from - 10 to 15. if that's what you're saying. What I'm saying is I'm not sure exactly what you're saying. I was starting at minus 30. I have one of those heaters and I know what they will do and what they won't do.
                      I'm with Dennis - my 2 bay attached garage with only partially insulated ceiling (but all the walls are insulated) only gets down to -5 to -10C in the winter time during our coldest temps in Calgary, my electric cube heater will raise the temperature up to the 10C range after a couple of hours of continuous heating. Its definitely cooler by the garage door, and the floor doesn't ever get above +5C (nor does it drop below +5C through the winter), but I do eventually peel off my flannel jacket once its warmed up.

                      John
                      Wally in Calgary likes this.
                      Shut up, wretched cricket of doom...

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                      • #12

                        Re: Detached Garage with Shared Wall & Partially Heated Shop

                        Thanks John for the 2 hour input. Dennis didn't mention time. 2 hours is fairly reasonable for a hobby shop. If you start at minus 30 you're going to be waiting a tad longer and that's where I was starting from. I guarantee though I never got to plus 15 with my cube heater,,,,,, and I tried,,,,, because working in the shop with or without that temperature meant light, food and water to me. Good luck to all of you!
                        "Do it Right!"

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                        • #13

                          Re: Detached Garage with Shared Wall & Partially Heated Shop

                          Originally posted by Rusty View Post
                          ... If you start at minus 30 ...
                          But I think that's the key - I've never seen -30 in our garage, at worst its gotten down to -10 C in there when I go to start the car up and pull it out in the morning, but never colder than that, and that's with two vehicles stored inside (so at least 4+ garage door openings during the day) and the ceiling ~1/3 - 1/2 uninsulated (and with two roof vents open to atmosphere up there in the uninsulated part).

                          John
                          Shut up, wretched cricket of doom...

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                          • #14

                            Re: Detached Garage with Shared Wall & Partially Heated Shop

                            John you may never get to minus 30 in your enclosed garage and I'm not trying to be the heavy here but usually when thinking about things like this people miss the obvious cause they don't want to think about it. Calgary on a whole can be a lot warmer than Edmonton on any given day but I know for certain you get days of minus 30. If your garage is minus 10 inside and it's minus 30 outside you're probably going to have at least Mommy's car in there. When you open that overhead door to let her car out what temperature will you achieve inside the garage? Yep! It's going to be a little colder than minus 10 as the arctic front moves in through the 7x16 hole in the wall and your open ceiling is going to be an exhaust chimney for any air warmer than minus 30. Now your insulated garage has just become a freezer and your insulation will hold the cold in just exactly the same as a walk in freezer does. I know it sounds brutal but I've been there and an electric cube heater of that size is going to work for a long time to raise the temp to any degree of satisfaction.

                            Post a pic of the heater you have. We may be able to help. BTW the other issue you have if you pour heat up into that uninsulated portion of the roof is ice on the underside of the roof and possibly the creation of a huge ice dam at your eaves. Now picture a Calgary chinook and sunshine beating down on that roof with ice and water dropping on you, the cars, and/or your tools.
                            "Do it Right!"

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                            • #15

                              Re: Detached Garage with Shared Wall & Partially Heated Shop

                              The cement floor certainly stabilizes the temperature, both in winter and summer. Based on my experience in a larger space all should be fine if the expectation is 10 or so with an outside temp of no less than minus 10.

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