Min R-value for ceiling (between joists)?

[TheRealMcCory1]

I'm building a 16'x22' detached garage in Alabama. The contractor installed R-13 in the walls which is definitely acceptable.

Any advice on a minimum R-value for between the ceiling joints?

Thanks,
Cory

 

[ADSR]

Not sure on your building code there. But R-40 is standard in my parts.

 

[TheRealMcCory1]

Good point. Thought about that but having trouble finding code online. I'll try to get it Monday.

Thanks.

 

[TheRealMcCory1]

I found codes for residential that say R-30 in my area. Does this apply to a detached garage as well?

 

[Cobra6]

I found codes for residential that say R-30 in my area. Does this apply to a detached garage as well?

In this neck of the woods R-30 is usually standard for the ceiling.

 

[GYPSY400]

Code may not apply to a garage as it's not a dwelling..

You should do double of whatever you did in the walls.. So 2 layers of R13.. Staggered joints. I'm actually surprised the ceiling didn't get done first..

And how is the vapour barrier done? That is as important as the insulation itself... I'm not going to comment on how to do VB, as I'm in a different climate ( I live in an igloo)


Sent from my iPhone using Tapatalk

 

[TheRealMcCory1]

In this neck of the woods R-30 is usually standard for the ceiling.

Thanks Cobra. Do you know if that pertains to uninhabited spaces as well?

I live in Madison, by the way.

Cory

 

[METALMOVER]

I doubt if theres code for a detatched garage, theres not in my county and I just got done building it, they did require me however to have all my electrical covered before I passed inspection, wasnt planning on that. Are you sheating the top side of the rafters so you have attic storage?

 

[volleyball]

Is this just parking or a work area? And why go with minimum if it's your work space. If you can afford to pay someone to build it, you can pay someone to put in lots of insulation. Costs once, pays you back forever.
Putting down a couple of inches of hi density foil faced insulation under or preferably over the roof deck and then adding bats will go a long way

 

[aar0s]

If your going to pay to heat it then put the highest r value you can find in it. Most homes here are r38 in the ceiling. I went cheep on mine and wish I'd put more.

 

[hippie2cams]

On my pole barn I had 2x6 purlins between trusses so I used r19 batts to insulate my ceiling, that plus builder installed reflective barrier that was iirc r7 rated under the metal on the roof. I also did the r19 in all the walls and I can say it does a wonderful job here in texas. Of course the 4t ac/heatpump doesn't hurt either.

 

[ADSR]

The difference between cheaping out on insulation and doing a good job isn't many dollars.
Find out what will FIT up there, and do it.

This! Suff R-40 up there and never worry about it again.

 

[TheRealMcCory1]

The difference between cheaping out on insulation and doing a good job isn't many dollars.
Find out what will FIT up there, and do it.

This is the key. I did some research. They used 2x8s for ceiling joists so r30 won't fit. Barring some of the high density r22, r19 is the best that will fit in this cavity.

Turning my attention to doing the best possible job, I have thought about doing the spray foam under the roof line. Don't know the r-value but that stuff is incredible. (but very expensive) Blown in fiberglass is not an option as the entire attic space is decked for storage. I could also do batt or rigid foam under the roof but I'm not at all familiar with those options.

What do you guys think?

Thanks for all the advice so far guys. I want to make this the best, most comfortable work space possible.

Cory

 

[Gator01]

What ever you do, put in reflective foil first! I'm in SUNNY Florida and heat build up from radiate heat is the biggest problem here. The foil alone made a HUGE difference in my garage. Foil by itself has NO R-value but it definietely blocks the radiate heat. It was the first thing that I put into my new metal building and it alone dropped the temperature from close to 100d inside to about 85d. You're supposed to leave a gap between the outside wall and the foil. I don't know if it's really necessary but I couldn't really attach anything to the the existing steel frame (5 foot spacing!) so I put in a inside wall made with standard 2x4 constraction (24" centers) and lined it with standard 3 1/2" thick fiberglass insulation. (I don't recall R-value but it was standard.) My building is made of 2" square steel tubing and I attached (taped) the reflective foil to that then build the inside frame wall right up against the steel one and added FG insulation and then covered everything with peg board. The steel building is strong but impossible to attach things to (AND voids the warranty!) But the 24" oc wooden studs makes it easy to hang shelves, etc. I never have to use heat and seldom have to run the AC. The empty 2" gap between the outside wall and the foil is nice for running wiring and pipes through! And no, there's no real danger of freezing pipes here!

 

[TheRealMcCory1]

Thanks Gator. I'll do more research on the foil. I don't know how that works exactly but sounds like a DIY type thing.

Thanks again
Cory

 

[LB-1911]

Thanks Gator. I'll do more research on the foil. I don't know how that works exactly but sounds like a DIY type thing.

Thanks again
Cory

Here is a start - TekFoil Buyer's Guide

https://www.farmtek.com/farm/supplies/ExternalPageView?pageKey=EXTERNAL_PAGE_3005

 

[volleyball]

The foil faced foam is much better as it does both radiant and convective heat. The foam is rigid to keep it from sagging and collecting debris that critters like to call home. You should have a 1" or so gap for it to be most effective. That is why I said foil foam over foil wrap.
The foil wrap is great if you insulate your ceiling and attach the foil to the bottom of the rafters. Work great in the house too.

 

[The Cobbler]

This is the key. I did some research. They used 2x8s for ceiling joists so r30 won't fit. Barring some of the high density r22, r19 is the best that will fit in this cavity.

......
Cory

R20 fits into a 2x6, R28 /30 into 2x8

 

[ADSR]

This is the key. I did some research. They used 2x8s for ceiling joists so r30 won't fit.

Cory

Are you saying it's only 7 1/4 to the bottom of the roof sheeting?

 

[ADSR]

R20 fits into a 2x6, R28 /30 into 2x8

Correct!

 

[LB-1911]

This is the key. I did some research. They used 2x8s for ceiling joists so r30 won't fit. Barring some of the high density r22, r19 is the best that will fit in this cavity.

Turning my attention to doing the best possible job, I have thought about doing the spray foam under the roof line. Don't know the r-value but that stuff is incredible. (but very expensive) Blown in fiberglass is not an option as the entire attic space is decked for storage. I could also do batt or rigid foam under the roof but I'm not at all familiar with those options.

What do you guys think?
Thanks for all the advice so far guys. I want to make this the best, most comfortable work space possible.

Cory

Are you saying it's only 7 1/4 to the bottom of the roof sheeting?

He left out the part about the floor till post #14....

 

[TheRealMcCory1]

He left out the part about the floor till post #14....

Sorry guys. Yes this is correct.

Cobbler and Diesel, I looked at different websites that showed r-19 for a 2x8 cavity but after reading your posts I found where the Roxul website lists r-28 and -30 for 2x8s. Thank you.

Cory

 

[John in OH]

When I built my new shop in VA (NE of Richmond) I used Kraft faced R30 fiberglass batts in the ceiling between 2x8 bottom truss chords. Since there is no floor on 2/3 of the second floor, there is no compression of most of the insulation. R30 fits satisfactorily between 2x8 joists and has worked out great for me as the shop holds heat well in the winter and stays cool in the summer. You can sort of see how if fits by viewing the pics attached to post #78 of my build thread: http://www.garagejournal.com/forum/showthread.php?t=98038&page=4

In 'Bama you're going to be more concerned with keeping the shop cool rather than warm so I wouldn't use anything less that R30. I suppose you could use more insulation, but I don't think it will be of much benefit between 2x8 joists. The previous suggestions regarding the use of reflective material under the roof sheathing are good as this material will make a notable difference in keeping the attic space cooler.

 

[ADSR]

Sorry guys. Yes this is correct.

Cobbler and Diesel, I looked at different websites that showed r-19 for a 2x8 cavity but after reading your posts I found where the Roxul website lists r-28 and -30 for 2x8s. Thank you.

Cory

Good deal! Try and look for the roxul on sale. The stuff isn't cheap up front, but you'll save in the long run.

 

[TheRealMcCory1]

Hey folks. Wanted to give you a quick update and a big thanks for all your advice and info. I'm having R-30 put in the ceiling tomorrow and will plan to put foil under the roof in the near future.

GJ is great, especially you all!

 

[ADSR]

Hey folks. Wanted to give you a quick update and a big thanks for all your advice and info. I'm having R-30 put in the ceiling tomorrow and will plan to put foil under the roof in the near future.

GJ is great, especially you all!

glad to hear you worked it all out.

 

[volleyball]

Hey folks. Wanted to give you a quick update and a big thanks for all your advice and info. I'm having R-30 put in the ceiling tomorrow and will plan to put foil under the roof in the near future.

GJ is great, especially you all!

I would have done it the opposite way. The bats may get in your way.