Insulating Detached Garage Question

[mikcool1080]

Hello members, let me start out by stating that I have a 22' by 23' detached garage and I live in southeast South Dakota.

I have spent a bunch of time trying to figure out the answer to my question and have read numerous articles and posts without coming away with a definitive answer. I am insulating and heating my garage. I already installed an electric heater, put in r15 faced insulation in the walls, r30 unfaced with 4 mil barrier in the ceiling, and purchased the drywall to cover everything. I also bought 4 mil plastic to install over the insulation, but after researching, will it cause me problems in the long run with moisture if I installed it?

 

[CombatNinja]

Where are you putting this plastic? Inside over the kraft facing? Or outside the framing (as in: house wrap)? Your question is not clear.

Your question makes it sound as if the garage is already built, so I would say just install the faced insulation as normal and forget about the plastic. FWIW, in S. Dakota, I would've pumped up those R values to R19 or even 21 in the walls and R38 or better in the ceiling. But if you don't mind paying the bill and your heater is powerful enough, you do you. With respect to a garage, so much is determined by how many overhead doors you have, door construction, what size(s) and how well they are sealed anyway.

 

[mikcool1080]

I apologize for not wording my question very well. The plastic in question would go over the the kraft faced insulation inside my detached double stall garage.

The garage was built in 2003 and was built with 2x4 framing on the side walls and ceiling joists. This is the first house that I have ever owned, and I had my uncle that has a little bit of experience help get me started. I honestly just purchased whatever he suggested.

 

[CombatNinja]

Not sure what the plastic is for in this application. Skip it.

 

[mikcool1080]

From my understanding, it would be used as a vapor barrier and installed over the kraft faced insulation in the side walls. I would think that it would provide another barrier from air leaking in from the outside. I am just trying to seal the garage as much I can to retain the heat, as I use the garage a lot during the winter.

 

[mikcool1080]

Can anyone please help me? I’m trying to get this done as soon as possible, and I don’t have much free time to spend on it.

 

[TurnipTruck]

In your climate, plastic vapor barrier is not needed if your insulation already has kraft paper.

 

[Loose Nut Buster]

U could always blow in more insulation in the attic after U drywall the ceiling just install soffet vents and chutes at the eves in the attic for air movement n not cause moisture problems. Hot air rises so that is where most of your heat loss is going to be.
If U have the space U could leave a section of wall area uninsulated, put some 1x4 shelves between the studs to store items on then frame W/2×4 or 6 and do the same to make a door or doors and in the recess hang your whatever in or more shelves doors closed... not much cool air infiltration.
My in wall tool closet in pic, 8' X 8' X 11" deep n its full, my wall are 2x6 studs as is the door framing.
Personally I'd use propane or natural gas B4 electric, my detached is 26x36, I heat it with a 35k BTU radiant heater set atop an empty 30# tank w/20' of hose to move where I'm working but have it connected/piped to a 100# tank (optional but less $$ to refill) outside. If i use it more than a couple hours it'll bring the temp from 28-30° to above 40° with a thermometer at opposite side of garage.
By moving the heater mounted atop the cylinder n with the hose... I'm never cold n shut it off when it reaches 50°.
I just leave the 30# tank on the floor, rotate it and the hose uncoil the length i need, when finished I just shut off wall valve and recoil the hose around the tank, works great n its neatly coiled back in place, heater n all.
Winter garage heat bill for me is about 150. here in Northern Michigan
Two 100# tanks generally is max for me, and my ceiling is 10' at walls, its a cathedral 15' in center, no fans.

Sent from my SM-A515U using Tapatalk

 

[bdbecker]

If you already have plastic on the ceiling (will be sandwiched between the drywall and insulation) a second layer of plastic over the top of the insulation is not needed or desirable.

Putting plastic over the kraft faced insulation on the walls for additional vapor barrier shouldn't hurt anything, but isn't really needed.

By the way - welcome to GJ! I lived in Vermilion from 2007-2012.

 

[see pictures]

The paper is the vapor barrier no need to put plastic over it. If it was unfaced insulation the plastic would be needed for vapor barrier.

 

[mikcool1080]

Thank you guys for the replies! It super eases my concerns and I won't use the plastic over the insulation. I have seen a lot of people highly recommend air sealing anywhere and everywhere that I can, but not a lot on what to use exactly. I have already installed the insulation, quite a few extra outlets, and spray foamed the door and windows. I am unsure what to use on the cracks (like where there is 2x4s doubled up, I apologize in advance for my lack of technical knowledge as to what they are called also), and I have seen people use spray foam to seal the outlets but I am not sure if I should spray it within the box or outside of the box?

Again, thank you guys immensely.

Bdbecker - I take it you did not enjoy the wonderful scenery in SD? Ha

 

[Higgins]

For what is worth, some contractors spend the $$$ and caulk the 2x4 plate to the subfloor, and every vertical space between studs.

AL

 

[bdbecker]

...Bdbecker - I take it you did not enjoy the wonderful scenery in SD? Ha

Work pulled me to Iowa - I loved living there and really miss it. Wife and I both agree that we'd move back if the right opportunity presented itself.

 

[Loose Nut Buster]

Do not spray foam inside the electrical boxs, u can buy foam gaskets to put under the covers
I'd caulk where the wires enter the boxs if you feel the need to prevent air infiltration.

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[CraigStu]

I am glad it was suggested to skip the plastic. I see so many contradicting recommendations for different climate areas etc that no way I'd ever use plastic anywhere. Also it seems to me that 'the plastic ought to be on X side of the Y' gets reversed in summer vs winter.

 

[Sawdust_]

Absolutely DO NOT use plastic unless you want to trap moisture and cause mold.
Use spray foam and any caulk you can lay your hands on to fill seams gaps/ openings wherever you see them. Especially around doors and windows.
Insulation doesn't do much of anything if you have air infiltrating it.

 

[mikcool1080]

It makes sense with plastic trapping moisture if sandwiched, it just seemed like a good way to stop air pockets/leaks from getting inside without having to hit every seam. I realize now that I should have had someone come in and shoot a sealing layer of spray foam before I put the insulation in, or just more sealing in general. I wish I had found this forum before I started the project. Ha

Work pulled me to Iowa - I loved living there and really miss it. Wife and I both agree that we'd move back if the right opportunity presented itself.

Well at least you are still close! Ha. I live in Sioux Falls myself.

 

[Ralbert]

I’m in Maine and I ran into the same question... If you have kraft faced batting, there is no need to add the plastic. In fact, if you add the plastic it could cause mold. The plastic does not allow the garage to breathe. Moisture from melting snow, etc. could cause problems.