R19 vs R21 insulation ?

[naturalgas]

I'm getting ready to insulate the walls in my garage and looking for some advice. First of all it is a 36x40 x12 garage. The ceiling is already done with R38 batts and plastered. There is a lot of foundation in this as it is built into a banking. So 3/4 of my garage have roughly 5ft. Of concrete 12" thick. The upper walls are 2x6 and that's what I will be insulating. Here is the ?. Is it worth the extra cost to put R21 vs R19 in the walls? I will be heating this but not all the time, just when I'm out there working/ playing. I have good Anderson windows and good R value garage doors. Any thoughts on this? R19 or R21?


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[quattro_sinko]

My own garage? I'd probably go the R-19 and keep an eye out for salvage/cheap insulated panels on CL for the concrete. What are you going to use for heat?

FWIW, I think sloppy installation of fiberglass is it's biggest downfall. I try to be thorough.

 

[cowboy73]

You likely won't see the difference between R19 and R21. Most your heat loss will be from other areas.

 

[naturalgas]

That's my thinking save $400 bucks and go with R19 . I'm putting in a Rinnai 38k propane space heater.


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[hefnerconstructionlc]

You would be best off putting the extra money towards Air sealing the wall cavities with spray foam or caulking. R19 will be more than fine. Actually there isn't much difference to step from R 13 to R 19 if you look at the hard numbers. So I would spend more time air sealing and being careful with the installation to get the best result .

 

[The Cobbler]

negligible difference in r value. it's not like say r19 vs r30 (where there is 50% more r value)

 

[Firebrick43]

For occasional heat while occupied even r19 won't have a good ROI.

Are those concrete bank walls insulated on the inside? You may have some real issues warming up the shop with all that mass. A lots of sweating as well. I would insulate them with xps foam, even if it's just 3/4-1" thick.

 

[ItsNemo]

Up here we get R24 for almost the same price as the lesser 2x6 sized insulations...every little bit helps IMO and energy prices aren't going to get cheaper. Good sealing will make a huge difference too.

 

[Unhdsm]

I'm more worried about the bare concrete than the r19. Concrete has practically no r value so you'll be heating the ground outside in addition to your giant garage. Also that heater may be undersized for that cubic footage. Especially if you aren't heating it full time.

 

[Dragfluid]

Every little bit helps. But I would skip the batts and use dense pack cellulose. Cheaper, no gaps in coverage, and it inhibits air flow. And why only R38 up above? You're in Maine, you should have R60.
And please put some poly iso sheets on that concrete.

 

[Bamafan]

R19 in a 2x6 cavity isn't R19 since you will be compressing it. It will be more like R17. Still, I agree that you should spend the extra $$ on air sealing. That means caulking or foaming any air gaps.

Cellulose settles over time and will create a gap. If you want to dense pack, use loose fill fiberglass. Still, as said before, I'd use the extra $ on air sealing.

 

[Firebrick43]

R19 in a 2x6 cavity isn't R19 since you will be compressing it. It will be more like R17. Still, I agree that you should spend the extra $$ on air sealing. That means caulking or foaming any air gaps.

Cellulose settles over time and will create a gap. If you want to dense pack, use loose fill fiberglass. Still, as said before, I'd use the extra $ on air sealing.

Dense pack (and wet spray) cellulose (done to the correct density) can not settle. Also cellulose air flow resistance is a multitude times of fiberglass and will not form convection currents at higher temp differentials that effectively lower apparent r values like fiberglass. Cellulose is the most cost effective option to boot.

 

[Tj-gord]

The difference between 19 and 21 isnt enough to worry about. As said above, insulating rhat concrete and sealing the shop will be more important. Simple stuff like installing plastic boots behind the electical boxes, tuck taping all poly seams and joints.even throwing some r12 batts on top or your r30s in the attic will make a difference,

 

[pcmeiners]

Would stay with r-19 for the walls, hope you have a decent vapor barrier in the walls and below the slab. As others mention condensation will be a major issue if you do not, if you do, your present insulation should lessen the issue.
You state you have an r38 in ceiling. Unless you have something to stop air flow around the batts, as in a tight attic floor ,plastic above the batts or insulation is in the roof rafters, you do not have r38.
If I owned the garage I would go sprayed cellulose for the walls. As other mention it will stop air flow in the walls and provide great fire protection,( if rated could lower your insurance, per inch a higher r-rating). Had loose pack cellulose in my Mom hose, basement fire engulfed the entire basement but could not get to the first floor due to the cellulose.

 

[Dragfluid]

R19 in a 2x6 cavity isn't R19 since you will be compressing it. It will be more like R17. Still, I agree that you should spend the extra $$ on air sealing. That means caulking or foaming any air gaps.

Cellulose settles over time and will create a gap. If you want to dense pack, use loose fill fiberglass. Still, as said before, I'd use the extra $ on air sealing.

Dense pack cellulose doesn't settle. That's the point of doing it that way.

 

[naturalgas]

I spent a day foaming and caulking all gaps and went with the R21 dense batts with poly sheets vapor barrier. I figured I'm doing this once , worth the extra money to me


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[DC73]

I spent a day foaming and caulking all gaps and went with the R21 dense batts with poly sheets vapor barrier. I figured I'm doing this once , worth the extra money to me

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You did the right thing in my opinion. The investment in the extra R2 will eventually get paid back - especially if energy costs rise. I went with R15 in the walls of my shop instead of R13 and I'm glad I did. I've certainly spent money on less practical things.

DC

 

[Steevo]

Really?
A one-time cost of $0.27 per square foot to increase the level of insulation seems like a no brainer to me.
I went with R21 batts in the 2x6 walls of my shop, and have never regretted it.
Then again I foam sealed every wall cavity and between plates and stem walls, and made sure the soffits were properly configured to allow the 18" deep (R60) blown-in insulation would sit atop the wall top plates, too.

It's as tight as a nun's . . . . well, you get the idea.

 

[quattro_sinko]

I spent a day foaming and caulking all gaps and went with the R21 dense batts with poly sheets vapor barrier. I figured I'm doing this once , worth the extra money to me


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Sounds like a good start, any plans for the concrete walls?

 

[Dragfluid]

Really?
A one-time cost of $0.27 per square foot to increase the level of insulation seems like a no brainer to me.
I went with R21 batts in the 2x6 walls of my shop, and have never regretted it.
Then again I foam sealed every wall cavity and between plates and stem walls, and made sure the soffits were properly configured to allow the 18" deep (R60) blown-in insulation would sit atop the wall top plates, too.

It's as tight as a nun's . . . . well, you get the idea.

Nice to see someone else shares my thinking. I'm thankful every day when I'm out in the Shed and the furnace barely runs.

 

[Bamafan]

...and it's important to note again that R19 batts are not R19 when put in a 2x6 wall since they are 6.25" deep and the cavity is 5.5" deep. So you lose a lot of R value.

 

[Twodawgs]

R19 in a 2x6 wall will have a R18 rating. R21 in the same wall will have a R21 rating. Referenced from "Owens and Corning Building Insulation Compressed R-value Chart"

 

[Bamafan]

I've seen R17 calaculated, so close. The point is that R19 batts aren't really designed for 2x6 walls.

 

[DaveS53]

From the owens corning chart, you'll get 17% better insulation with the R21 product that is intended for 2x6 walls.

http://www2.owenscorning.com/litera...ul Compressed R-Value Chart Tech Bulletin.pdf

In 2012 when I built a new home, I had 2 inches of closed cell foam sprayed into the 2x6 walls first, then applied R13 fiberglass in the remaining space for a total of R26. The spray foam in not cheap though. R60 blow-in fiberglass was placed in the ceilings.

The basement walls have R10 foam sheets, plus R13 batts in the 2x4 interior studs, for R23.

I have a 36x50 shop with about 70' linear feet of wall with a stepped foundation. I first applied R10 foam sheets to the interior foundation walls, extended 4' below floor level, as required by code, then built 70' of 2x4 interior walls (12' tall), that left about a 14" thick space to fill with fiberglass batts. The remaining walls have ordinary R19 batts. The entire floor also has R10 foam insulation under the 6" concrete floor.

With the 3000 square foot ranch (with basement) and the 1800 square foot shop, my highest natural gas heating bill was about $100 per month (subtracting $20 per month that the hot water heater uses). The shop is heated full time to 68 degrees.

Both home and shop are air conditioned. The highest electric bill for cooling both buildings is only about $70 per month, usually in July or August. I figure that, based on the difference between my lowest bill in the late spring or early fall and the highest in the summer. In the summer, I'm also running a 3/4 hp irrigation booster pump, about 7 hours per day.

I may not live long enough to get any return on the investment, but the building both perform well.