Garage Ceiling Insulation for WIDE Spaced Rafters

[riverforester]

Hi Everyone -

Curious what the best methods are for garage ceiling insulation where my 2x8" ceiling joists are spaced 36" on center. I did a little hunting around at Home Depot and Menards and didn't find anything that wide. The only thing that wide was the pink foam board stuff that seems to top out around R-10. Was hoping I could use some kind of batt product with R-38+ since it's a ceiling surface

My setup:

Attached 2 car garage (separated by a cinder block wall), walls are framed 2x4" 16" on center and already insulated and vapor-barriered by previous owner. Ceiling/roof surface is completely open and bare with no insulation of any kind.

I'm looking to insulate the garage well enough to keep it at least 50ish degrees in there year-round (so my fridge and freezer keep working, and so that it's comfortable to wrench on some motorcycles) and, once insulated, plan to use a propane shop heater that's rated for indoor and outdoor use.

Is a batt product preferable for something like this, or are my options limited to foam board or blown-in? Thanks yall!

 

[Soccer918843]

I think your best bet is blown in or if the money allows spray foam

 

[dfiler2]

Does the building have a ceiling? If it does then the blow in would have the best coverage and probably be the cheapest.

 

[cpayne5]

Menards offers this on their website: https://www.menards.com/main/buildi...70-c-5780.htm?tid=-2615162383273795078&ipos=4

It's only R-19, though.

 

[Bert_]

Why do anything other than blown in cellulose?

 

[nadogail]

Why do anything other than blown in cellulose?

IMHO, blown in anything is an option. Cellulose may be your cheapest and best.

 

[riverforester]

Does the building have a ceiling? If it does then the blow in would have the best coverage and probably be the cheapest.

There is no ceiling at this time. It's just 2x8" joists going across horizontally and above those is clear up to the 2x6" rafters and plywood surface of the inside of the roof itself.

Here's a photo, hopefully it comes through as visible...

 

[riverforester]

 

[riverforester]

Menards offers this on their website:

It's only R-19, though.

Hadn't seen this - thanks! Could be a decent back up plan.

 

[riverforester]

IMHO, blown in anything is an option. Cellulose may be your cheapest and best.

Thanks for your help. One clarifying question since I'm such a novice at this kind of project. I imagine there are two ways to add blown in insulation in a place like this:

1) Blow the insulation directly onto the underside surface of the existing rafters and plywood roof surface, essentially coating the inside of the roof (leaving the space between the ceiling joists open if desired).

2) Affix drywall or some other barrier to the underside of the ceiling joists, creating a ceiling surface but also a "base" for the blowing in insulation, then adding the insulation on top of the drywall and between the ceiling joists.

Is one of these the preferred way?

 

[riverforester]

Here's that photo!

https://www.garagejournal.com/forum/picture.php?albumid=7628&pictureid=107910

View media item 107910

 

[Bert_]

Blow in is loose it doesn't stick to anything. You would need a ceiling. A ceiling helps keep the heat down were you are working anyway.

Cellulose does a better job of stopping air movement than fiberglass.

 

[cpayne5]

Hadn't seen this - thanks! Could be a decent back up plan.

You're welcome. Only reason I know about it is because I have a similar situation, but 48in OC trusses in my pole barn. It's a good solution to my problem (they make 4' wide rolls, too).

Unfortunately, we don't have any Menards in my area and I can't find anyone local who carries, or can get, the SilverCote products...or anything similar. The closest Menards is 250 miles away. Argh.

 

[harleybear66]

fill in the missing ceiling joists. then fiberglass batts would work. spacing that wide is too much for osb or even 5/8 drywall.

 

[Bert_]

fill in the missing ceiling joists. then fiberglass batts would work. spacing that wide is too much for osb or even 5/8 drywall.

Tin will span it without a problem and hold insulation.

 

[rd65]

I have seen bubble w/ foil backing insulation on a roll. something like this https://www.insulation4less.com/ins...aspx?msclkid=8148a956bdcf1c8425d5f6e66a7a96de

 

[JPinSTL]

Tin will span it without a problem and hold insulation.

Get the cheapest white 5 rib metal roofing you can find. Hang vapor barrier from the rafters. Run the metal perpendicular to the trusses/rafters. It will bridge 5ft, so your 3ft is no problem. Then blow in your insulation above it.