Insulating Garage Ceiling R13 vs R19

[TrickVert]

I'm working on finishing my 2-car detached garage, and will be insulating the ceiling. Construction is 2x4 roof trusses 24" OC. The garage will only be heated when I'm working on projects, mostly automotive (evenings, weekends, etc.) Heat will likely be a tank-top propane heater or bullet heater if that proves insufficient.

I've finished an "attic" floor down the middle of the trusses on 2x4's that run perpendicular to the trusses. The right third has 7/16 ply right on top of the trusses, the other side is open. So, I go from having 3-1/2" of space to 5-1/2" down the middle (interrupted by the cross-laid 2x4's), to open area.

I'm stuck with using R-13 for one third (unless I remove the ply and jack it up on additional 2x4's), and would have a max of R19 in the middle. Given my occasional use, budget considerations, and "some insulation is a whole lot better than no insulation," I'm thinking of just using R-13 for the whole thing.

Any reason why I should rethink?

(And I do plan on using R-13 in the walls, as well).

Thanks in advance,

Andy

 

[JoeFin]

I only turned 1/2 of the attic into a loft but I have 2x6 for the bottom cord of the trusses. Under the plywood loft area I used R-19. Every where else I used R-30

Without air conditioning it stays a good 10 - 15 degs cooler in the summer

Your most important thought should be humidity control since an un-insulated garage with wild temperature swings will increases humidity in your garage and "Rust" will form on your stuff. With a good amount of insulation a small electric heat strip will provide "Frost Protection" during the period your not working in the shop

 

[TrickVert]

Thanks, Joe.

I generally don't need to worry about things getting too hot, and with our dry mountain air, rust seems to be a thing of the past, unlike NE Ohio where I ran a dehumidifier year-round.

THIS THREAD is an interesting read. I'm starting to think that for my intermittent heating needs, the R13 might be the best "bang for the buck?"

Andy

 

[fury9]

They make r-15 for use in a 2x4 cavity, might be another option.

 

[JoeFin]

Thanks, Joe.

I'm starting to think that for my intermittent heating needs, the R13 might be the best "bang for the buck?"

Andy

Perhaps solely on a cost analysis yes.

Depends on your habits and uses for the space too I think. I personally like Cad-designing in my underwear and loading programs into the CNC at 5:30 am. Easier to concentrate and far less distractions.

We had dual pane glass everywhere including the garage/shop when we bought the place. But the walls were un-insulated Cedar Shake which we've since replaced with 5/8" T-11 Dura-Board and R-19 insulation.

My electric dropped from an average $260 per mo. to $125 and we added a Hot tub at the same time

My wife being an architect and a stickler for detail, so I just bought her 3-4 can of expanding foam and let her go for it. We also insulated the garage door with foam insulation

 

[METALMOVER]

I recently researched this quite a bit and from what I found where all your infiltration of air is from where your trusses meet the walls(obviously when you think about it) I made little 2 in. thick plates out of pink panther Styrofoam, I made 1 template then made like 72, put em up in there then spray foamed around every one, then dry-walled the ceiling, each inch of dead air is 1 r value and I had 8 inches( thats what she said) sorry couldn't resist.... I put in a little wall heater I hooked to my propane tank and I can keep it 40 degrees above outside temp.... and since Im a driveway warrior....

 

[JoeFin]

I recently researched this quite a bit and from what I found where all your infiltration of air is from where your trusses meet the walls(obviously when you think about it) I made little 2 in. thick plates out of pink panther Styrofoam, I made 1 template then made like 72, put em up in there then spray foamed around every one, then dry-walled the ceiling,....

Not sure what your saying ... but the building codes require vents to promote air movement in the attic space to prevent the rafters from being destroyed by temps too much above 140 deg

 

[METALMOVER]

Sorry mines 2 stories with a full floor up above , however you tube it for insulting floor trusses.... MM

 

[TrickVert]

Thought I'd give an update.

I went ahead with the R-13 considering I will heat the garage only occasionally, and most/any cost of additional insulation would likely never be recouped. For the same reason, I didn't go crazy trying to seal up every gap and install a secondary vapor barrier, but was careful to staple the batts securely, and allow overlap to the sills on the ends without obstructing the soffit ventilation.

I've already seen a marked difference between evening temps above and below the ceiling with only stored ambient daytime heat. For my purposes, and with my limitations on space and budget, I think this was the way to go.

Andy