What R rating for 2x4 contruction?

[JTSmithson]

Just like the title, looking for answer on both walls and ceiling, if they differ.

Thanks,

Joe

 

[bucs012]

my garage walls are built at 16" apart. R13 or r19 I beieve are your choices. Had my builder go r19 in the walls but r30 something in the ceiling rafters.

Here are pics
http://s104.photobucket.com/albums/m197/bucs012/Garage/?start=40

 

[benjamming]

You can fill the entire cavity with foam & achieve some very high real R values.

 

[mikeyr]

here in S. Cal, I did R13 in the walls and R30 in the ceilings, I think what you put in depends on where you live but that is pretty standard here.

 

[JCByrd24]

R13 is standard value for 3-1/2" fiberglass, you might be able to shove more in, R19 is normal for 5-1/2" cavity. Where you are in Minnesota, I'd go with the spray in foam recommendation, much higher value per inch than fiberglass, don't know the specifics but on the order of twice. In the ceiling, you probably have more physical space, blown in cellulose and fiberglass are similar in Rvalue and cost, cheaper than the spray in foam. Go 12" deep, should be near R38 or so.

 

[burleymike]

Spray foam is about R7 per inch. I know in Oregon they require 2x6 framing for extra insulation value. The price might be close to use spray foam with 2x4 framing vs 2x6 with fiberglass. If I could afford it I would go with foam in a heartbeat just because it is a perfect air barrier.

 

[director_gtr]

how do you buy the spray? gotta rent a sprayer or is it bottled or?? Get at menards/lows/HD or specialty place?

 

[jvitez]

You can't just arbitrarily pick any R value. A 2x4 wall had 3.5 inches of available space meaning nominal R12 fibreglass. Mineral wool can be a bit more, up to R15 is what I've seen. If you want anything higher use spray foam.

In Minnesota I'd use R40 minimum for the ceiling. I've got R60 in my house. R50 is the standard here now. You are a bit warmer, but not that much.

 

[benjamming]

how do you buy the spray? gotta rent a sprayer or is it bottled or?? Get at menards/lows/HD or specialty place?

Here's one place Tiger Foam

 

[GSSFC]

Here's one place Tiger Foam

I just looked at that site to re-confirm my thoughts.

You'll pay MORE for just the materials if you chose the DIY method, than materials AND labor combined to hire a pro to come out and do it.

Tim

 

[benjamming]

I just looked at that site to re-confirm my thoughts.

You'll pay MORE for just the materials if you chose the DIY method, than materials AND labor combined to hire a pro to come out and do it.

Tim

It was much cheaper for me to buy the materials & do it myself than to hire back in 2006/2007.

 

[Gary S]

If you are doing fiberglass, R13 is all that fits in a 4" wall. But, R13 is all you need. Do a search here. There was a great post not long ago that did the heat loss calculations for walls, ceilings, windows, and doors. Beyond R13 in a wall, the heat loss difference is hardly measureable.
If you put R13 in the walls, and R50 in the ceiling, almost all your heat loss will be the doors and windows. A 2 pane thermopane window is about R3. A 3 pane thermopane is about R5.
Simple math tells you where your heat loss is.

 

[belvedere]

I feel the same way, Gary. People get hung up on high R-values, but once you get past a certain point, you have greatly diminishing returns on your investment. IOW, for the real high R-values, you get little "bang for the buck".

 

[walrus]

Simple math tells you where your heat loss is.

What about conduction thru the studs?

 

[ripsnortMN]

Im up in MN as well. I did R13 in the walls and R49 in the ceiling. Your going to loose most of your heat in the ceiling anyway.

 

[Gary S]

What about conduction thru the studs?

As long as you have wood studs, I wouldn't worry about that. Wood is a good insulator, not a good conductor.
If you have metal studs, you have a problem.

The R value of most softwoods is 1.4-1.5 per inch, so 4 inches of wood gets you about R6 which still beats a very expensive window.

 

[wbclassics]

R-values of various construction materials

 

[Sawbladz]

R-values of various construction materials

That's an excellent link. Thanks