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I have an attached garage I use as a workshop, and I'd like to insulate it since I plan on running water and sewer lines into the garage for a utility sink*. Right now, the garage is just studs and exterior wall. I don't plan on drywalling this garage. The ceiling is drywalled, since there is a bedroom above the garage.

I was thinking of just using fiberglass batt insulation. Would that be sufficient? If not, what is the best way to do this?

Edit: This house is located in Denver, CO. We get both warm summers and cold winters, but not a ton of humidity.

*Please note, I am going to have a shutoff valve and nipple drain on the line inside of the heated portion of the house. I don't plan on having this water line charged unless I need water in the shop.

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Fiberglass is an option. I would go roxul though with your climate.

However insulation is the least of your worry. If you want to run lines to an area of your house in your climate it must be a conditioned space - meaning it needs heat.

Really the only option you have in Denver is to run your lines to a shared wall with the inside of your house and install a shutoff on the other side that you can close up for a few of the coldest months (without a conditioned space). Would this get signed off by local inspector? Ask him. It wouldn't happen in my area but who knows in colder climates the allowances they make if you take precautions. Also make sure all plumbing after shut-off is heavily sloped down and out - I would say at least 10 degrees.

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  • Thanks for the insight. Yes, the line will be ran from inside the house (where a shutoff will be located). The lines will be coming up from a basement through a shared wall into the garage at ground level. One followup question: Would I need to put in a vapor barrier with roxul insulation, or would the insulation itself be enough?
    – Maxthecat
    Commented Dec 25, 2015 at 21:58
  • The vapor barrier needs to be pointing out meaning you would need to remove the siding to put it on. I guess I am not getting what you expect out of your garage. You are in a climate that gets cold as hell for 3-4 months. Insulation isn't going to help that much because the space isn't conditioned. I mean if you had 4-5 guys working in your garage and always kept it closed - then maybe you start preserving body heat but to me the insulation is a nice to have and matters pretty little. Is your garage door insulated and will you keep a car in the garage?
    – DMoore
    Commented Dec 26, 2015 at 5:00
  • @DMoore, The direction of the vapor barrier should depend on what he does the most of, heating or cooling the space. From the post, he stated he wanted to use it as a workshop. Insulating it makes sense since he'll have to heat it during those cold winters. A strong workshop heater can bring a two car garage up to temperature in minutes, and the insulation keeps it there. In the summer, insulated space with an exposed slab can keep comfortably cool. He doesn't have to condition the space.
    – ench
    Commented Dec 26, 2015 at 7:37
  • @ench - That is my point. He isn't talking about doing what you are saying - conditioning the space in any way. I don't see the point of talking insulation when we don't know if it will be cooled or heated at all. Also insulating the walls while having a "normal" garage door is a bit pointless.
    – DMoore
    Commented Dec 26, 2015 at 18:32
  • @DMoore, no, I believe you misunderstand. I will be using a space heater or garage heater (once I can afford one of those) in the shop as warranted by the weather. So, while the pipes are in use, the garage will have heat. When not in use, I intend to drain the pipes completely, since I don't want to heat the garage/shop 24x7.
    – Maxthecat
    Commented Dec 27, 2015 at 17:48
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If your budget permits, why not go with spray foam insulation? On top of that, you might also consider adding foam panel insulation to the garage door (if yours is not already a solid core garage door).

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  • Spray foam between studs is a waste of expensive foam; the whole-wall R-value you'll achieve is barely above what you could get by filling the cavities with Roxul mineral wool. In addition to high cost, spray foam is bad for the environment, must be covered with drywall because it's flammable, and a small percentage of spray foam jobs have the chemicals mixed wrong and smell bad for years.
    – iLikeDirt
    Commented Dec 31, 2015 at 19:04
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Ultimately, I decided to use Roxul for the exposed studs and then used 1" rigid foam insulation along with foil tape to insulate the garage door. The garage now held around 45 degrees with the outside temperature being around 7 degrees. There's a couple of spots I could add insulation, but I need to get the 24" batts for that.

I had decided against foam insulation, since I may want to run additional electrical circuits in the garage (where my main panel is). Foam would insulate wonderfully, but would be problematic if I need to run wire. I can just pull the Roxul right out, since it's a press-fit.

I think that with either an electric or gas garage heater, I could keep the garage constantly around 55 degrees without too much cost. This should keep the pipes from freezing and the inspectors happy.

Thanks for the suggestions, everyone.

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If you can put the utility sink against a shared wall, you can put your taps in with these:

Frost free sill cock.

This one shown has an anti-siphon valve on it. The valve seat is on the end opposite the valve handle. They run about 10-20 bucks depending on whether you want the anti-siphon valve or get threaded or solder (some are set up for both).

I recommend a threaded connection, as I find that faucets have to be replaced every 20 years or so.

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