Downsides to insulation?

[Varinn]

Hey guys, new garage incoming and I'm debating pulling the existing drywall out to insulate.

Our new house is late 80's construction and may have asbestos to deal with in the existing drywall. Garage is 24x20, 9' ceilings with an attic space above, attached to the house across the rear wall and has one mandoor to the exterior, one window, and one single wide garage door which is currently un-insulated.

What are the ups and downs to putting insulation in? I'm thinking if I don't do it now I'll never get another opportunity as I tend to utilize the **** out of my wallspace.

Do I need to consider condensation or moisture?
Would i need to pull the drywall from the attached wall to add a vapor barrier or can it be left alone?
What about the ceiling/attic space? Can I spray in some foam up top or do I need to pull the gypsum to vapor barrier before insulating?

I don't have immediate plans to install any type of heater but who knows what the future might hold...

 

[Varinn]

I'm going to add to my original question with another question. If I only plan to heat the garage a few times a year (I don't really mind working in the colder seasons) is insulation less beneficial? My biggest concern is less the energy loss and more the risk of moisture problems

 

[PelicanPines]

You will need the correct moisture barrier.

 

[anythingyoucanimagine]

https://cellulose.org/Cellulose-Insulation-2nd.php?pagename=AirVaporBarriers&dirname=HomeOwners

What about cellulose? You get a free machine rental from HD/Lowes when you buy X amount of insulation. (and within reason, you can buy the minimum for free rental then return what you don't use and still get free rental)

When I did my garage I did walls first. It didn't make much difference with the heat. The roof was most important. I wanted the space up in the rafters (so I could pile a dangerous amount of car parts in a non-weight-bearing space). I did a small air gap under my roof-deck running from the soffit vents up to the ridge vent then I used rigid foam insulation. To do my air gap I bought 1x2 furring strips (actual = 3/4" by 1.5") and stapled them to the inside of each of the rafter bays. I did my garage roof in steps --so I bought a role of Tyvek and stapled that to the furring strips to make the air gap then did the rigid foam as time and finances allowed. In hindsight, with the rigid foam, I either didn't need the Tyvek --or I could have used the Tyvek and sprayed foam on top of that.


https://codes.iccsafe.org/content/iecc2018/chapter-4-re-residential-energy-efficiency


You are in same boat as I am (I'm in 5/4marine). Need R-49 for ceilings. Rigid/spray foam is R6.5 per inch which means you need 7.5" (8") of spray foam. Assuming 2x6 rafters, if you do 1.5" air gap (which is size of rafter baffles) you have 4" left... So you'd need to build out a mooney wall or some type of structure for the extra 4" of foam (then drywall). You don't want to do less than required with foam, people get lots of moisture issues from that.