Garage Ceiling Insulation

[tearfromred]

Looking for some advice on cooling a 2 car detached garage in Chicago. Some backstory- I ran gas to it 2 years ago and use a 30k btu ventless infrared heater and it works wonderfully. In prep for this, I used R-14 batts on the walls and insulated the garage door as well in preparation. No issues with holding heat, it's been great.

The unexpected problem I'm having is that it now holds heat way too much in the summer, to the point where it's super uncomfortable to be in there. Last year I tried running a 10k btu portable A/C unit (there's 1 jalousie window) and it did nothing as it just couldn't keep up with the heat and it would still be 100+ in the garage. The only other ventilation is 2 mushroom vents in the ceiling.

I'm now looking to insulate the ceiling in hopes of keeping some of the heat out. First question- is this going to help keep the garage at somewhat of a lower temperature? Am I on the right track with this approach, or should it be something more like an attic fan?

2nd question- if I am insulating, what is the best approach to take. Here are the options I am considering.

1. Spray foam. This would be the easiest. I keep seeing conflicting opinions on whether spraying directly under the roof is okay. My understanding is that the foam makes a vapor barrier, so moisture being trapped isn't an issue. My concern is that you can't see anything from underneath, so if there was a roof leak/failure, that moisture would just sit there and there would be mold/rot. A positive of this would be that I could also retain the storage in the rafters. Most people seem to think this is the way to go, but it makes me nervous. Thoughts?

2. Netted cellulose. This is a cheaper option that was presented by a few companies. Some have told me that when it's netted, sometimes the cellulose settles after time and isn't quite as effective. The R-value on this is greater than the foam, albeit relatively similar. Does anyone have any experience with this and would it be effective in this situation?

3. Batts against the underside of the ceiling. This is originally what I was going to do myself, but hesitated as this isn't really a world I know well. My understanding is that you can't put the batts right up against the ceiling because they will allow moist air to pass through at some point and then it's trapped under the sheathing. Is the solution for that is using baffles something like this as they will keep a small air barrier between the roof and the insulation?

https://www.homedepot.com/p/Duroven...-Rafter-Vent-10-per-Carton-XUDV2248/205466794

There are no soffit vents, so the air would only be coming from inside the garage in this situation.

4. Hanging drywall for the ceiling and blowing cellulose on top of the sheetrock. I can hang the drywall myself, albeit very crudely, and just blow the cellulose on top of it. Is it appropriate to just blow it on top. I don't know if this is appropriate or how it's normally done, will the drywall support the weight of the cellulose?

Thanks in advance for reading. Is insulating the ceiling going to help with keeping the temperatures down or am I better off doing something like an attic fan and just dealing with it. If I insulate, I'm also open to doing a small a/c unit down the road.

If insulation is the way to go, which form it would work best? Pictures of the garage are attached for reference.

 

[mepstein]

I don’t know the percentage but ceiling insulation makes way more difference than wall insulation. I used rockwool in mine and even with the recently increased cost, I would absolutely do it again. Also, I’ll never touch fiberglass insulation again.

 

[thammel]

You definitely need to insulate the ceiling. What is happening in the summer is that heat is being transferred (radiated, conducted and convected) into the garage. In the winter, you were probably losing more heat out the ceiling than you realized. Insulating the ceiling will help immensely in the winter and will also keep the garage from experiencing large temperature swings in the summer.

 

[billconner]

Instead of drywall consider metal liner panel. Install and done - no tape or mud or paint. Much lighter so should be easier to install diy.

https://www.menards.com/main/buildi...panel/white1558085/p-1444448673649-c-5717.htm

And then cellulose blown in on top.

You should have venting - low and high - from exterior. This means vent baffles too. Depending on how much you heat and use it, you might get away with just a tight air/vapor barrier. Heavy poly attached to ceiling joists and seams taped before installing metal. Some eave and ridge or other high attic venting would be better.

 

[AC-WC]

What billconner said!

 

[jamesframes]

I installed white painted corrugated metal roofing on my rafters as a ceiling. Then had 30" of cellulose blown on top (truss roof - wasted attic space). Works great summer and winter.

 

[tearfromred]

Re-evaluating at this point because some costs are going to add up. The garage currently has zero soffit vents or a ridge vent, but there are 2 mushroom vents. I'm not comfortable venting the soffits on my own, so that is a cost that locally is around 700 (for 16 vents) after talking with a few companies.

By the time I have the venting expense and 500 worth of materials (this is w/ drywall, it would be more like 750 w/ metal) I'm looking at similar costs for foam and it would save me from doing the work.

If going the foam route, the vents would be sealed and it would be done quickly w/ minimal effort on my part. Does this approach sound like a reasonable solution? I don't know that I want to necessarily to the work myself for what is going to be a few hundred in cost savings with cellulose.

When foaming, should this be closed cell or open cell? My understanding is that open cell would allow water to come through it and be seen easily if there was a roof leak, which was part of my original concern. Closed cell is more expensive, albeit with a higher R- value per inch, but would make any water harder to detect in the future?

 

[tearfromred]

Anyone?

 

[billconner]

Can't help with open vs close cell, but did wonder if open cell also meant warmer and moister interior air could pass through and condense on colder surfaces nearer exterior.

If you want or need to meet code, you can't leave either foam exposed. I've read reports of coatings - paint - that solve this but I'd want that pre-approved by building department because installing drywall - the usual solution - would be a pita.

With a good air/vapor barrier under drywall or metal ceiling, I'd skip the soffit vents and just rely on existinges vents, maybe add a gable vent. They could be added later if needed. Somewhat predicated on never having washed a car in a garage. You'd want to not exacerbate humidity issues by washing etc. You could look into slab coatings intended to retard moisture passing through, and definitely avoid invented combustion heating - no salamanders.

I know the materials for a metal ceiling are more than drywall with tape and mud and maybe paint, but do you really want to stretch it out and invest so much labor? Just a thought. $250 seems like a bargain for the several days or more it would take me to finish the drywall, not to mention moving and lifting it.

 

[duneslider]

There is no turning back if you foam and any future work will be horrible. There are situations where it can be good but I would not do it here (my opinion).

If you have no soffit vents then seal up the roof vents and make it a sealed attic. You don't have to have a vented attic. If you do this, you need to have a vapor barrier on the ceiling, which could just be plastic before you put up drywall or metal liner pan. If you do a sealed attic you just need to keep the air from the garage going into the attic space.

 

[tearfromred]

Appreciate it everyone. Thanks!