Is it really true you can't get R-19 with 2x4s (walls)?

[dominog]

Someone told me this before that you can only have R-13 in exterior walls with 2x4s, R-19 requires 2x6s?

Then someone else said I have close to R-19 anyway when you add up the R-13 insulation + drywall + plywood + tyvex + brick or Hardiboard.

[TnAndy]

An inch of polyurathane foam ( not the blue or pink styrofoam ) board is good for R-8 I think I recall.....

Or you could do what I did to get about an R-30 in a 2x4 wall......just build two of them....ahahahahaaaaa.....


My inside wall is 2x4's set on 16" centers and the outside wall is 2x4s on 24" center.......inch space between them, and a 9" 3/4 plywood plate on the top. Outside sheathed with 1/2 plywood and 1/2" of the blue foam board......I think it's in the R-30 range.



PS....don't use Tyvek....it is CRAP.

[giddonah]

Andy, I've seen you mention double 2x4 walls, did you ever give your theory why instead of 2x6 or even 2x8? Is it for sound?

[TnAndy]

I just had a BUNCH of sawmill 2x4's, so I went that route at the time.

The 2x4s were sawed on a circle mill and weren't all that accurate as to size ( some would go 3 3/4" on the '4' inch , and some would go 4 1/4" or so ), and by building a double wall, I could set the "uneveness" to the inside cavity of the wall, leaving a smooth plane on the outside and inside.

I also had a source of cheap fiberglass insulation......there is a water heater manufacturer over in town, and they used to take the old heaters back on warranty failures.....they had a whole department that stripped them down, recyled the metal, wire, thermostats, etc, and the fiberglass insulation was bagged in big plastic bags that anyone could stop by and get. Everytime I was by there, I'd stop and get a pickup load. Sorta messy to work with, but my whole house is stuffed full of used insulation.....ahahahahaaa......am I cheap or what ?

[giddonah]

Ah, I gotcha. I was thinking it was some master plan to make the house soundproof to the outside. That's how soundproof rooms are built, double walls with a space between them. Have you noticed that they're extra quiet? Then again, how do you measure extra quiet in the hills of TN?

[VALENT]

Tnandy, thats not cheap, thats responsible.

[TnAndy]

Then again, how do you measure extra quiet in the hills of TN?


Man....you've got THAT right......I can lay here with the doors and windows open and hear nothing but the occassional bird or cow.......I can't stand to spend a night in a motel.....never do get any sleep.

[rabadger]

Yep it's true. Use R-15 and foam board on the outside. My software doesn't even have a R-19 insulation and 2X4 listed.

2X6 has the R-19.

[danh]

a) You can get an R-19 wall in a 2x4 with spray-applied closed-cell polyurethane foam.

b) This house will have substantially lower energy bills than TnAndy's.

c) Tyvek is not actually crap - I've never ever seen it come out the back end of any type of farm animal. Nor have I ever met anyone who could excrete spun bonded polyolefin.

[giddonah]

Nor have I ever met anyone who could excrete spun bonded polyolefin.
you just need to get out more :lol:

[rabadger]

True, you can get an r19 wall with the spray stuff.

It won't happen with the pink panther.

[dominog]

Does anyone have the R-Values of basic building materials such as MDF / plywood, drywall, brick, and tyvex?

[TnAndy]

c) "Tyvek is not actually crap"


If you had seen the condition my Tyvek, installed under white pine siding in 1984, when I removed the siding this year, you'd call it CRAP too. It was shedded and falling to pieces....tore like tissue paper, not the tough stuff it was to start with.

I'll never use it again.

[rabadger]

dominog,

Exactly what are you trying to do?

[danh]

c) "Tyvek is not actually crap"


If you had seen the condition my Tyvek, installed under white pine siding in 1984, when I removed the siding this year, you'd call it CRAP too. It was shedded and falling to pieces....tore like tissue paper, not the tough stuff it was to start with.

I'll never use it again.

That's like saying "I took my CD player from 1984 out of storage when I wanted to listen to a CD this year, and it didn't work. CD Players are crap; I'm never buying one again."

Products change. Most get better.

[dominog]

I built a house with a GC, he only offered R-13 for walls. But next time I build I wanted to have a clear understanding of this.

Someone told me that even though I have R-13 insulation in the walls, I have close to R-19 anyway when you add up the R-13 insulation + R values of drywall + plywood + tyvex + brick(or hardiboard).

[rabadger]

It's not easy to explain.

When running load calculations the J manual takes the entire wall construction into account.

Code 13 - 2X4 walls with R-13 then you pick out the other materials. The software figures it into the wall and gives a U value for the structure as built.

with metal studs
with wood studs
with brick
with any exterior finish
with R-5 sheathing on the outside and dark brick.

What you need to be concerned about is the R factor of the insulation and ouside sheathing. Let the software do the rest. I have figured it by long have before. It's a pain.

[TnAndy]

Fine danh....you buy all the Tyvek you want. I doubt you've examined too much of it after 20 years down the road to see what shape it's in.....and I'm sure Dupont counts on that.

Personally, I'M NOT USING THE STUFF AGAIN since it didn't hold up worth a flip.

Your analogy using CD player isn't even close.

By the way, I've found quite a few discussions on various boards since finding this about mine where Tyvek has done the same thing.....so it's NOT just an isolated case.

[rookie]

I got a R19 on mine by using the blow in blanket system and 3/4 inch foam. The blow in blanket is supposed to give a r15 and the foam r4. I don't know what you get with the sheetrock, OSB sheathing and brick. The blow in blanket system is much more economical than the spray foam although if money was no object I would have went with the spray foam.

[rabadger]

You can get R-15 for 2X4 frame walls.

[danh]

I built a house with a GC, he only offered R-13 for walls. But next time I build I wanted to have a clear understanding of this.

Someone told me that even though I have R-13 insulation in the walls, I have close to R-19 anyway when you add up the R-13 insulation + R values of drywall + plywood + tyvex + brick(or hardiboard).
Nope.
Now exterior continuous insulation can get you up to R-19.

What's more important is that R-Value is only a component of heat loss / heat gain. And even infinite R-Values won't make a lick of difference against a good portion of the heat loss / heat gain.

Radiant heat & air leakage are the other half. Cover those bases and your R-13 house will crush any R-19 or R-22 behemoth.

Fine danh....you buy all the Tyvek you want. I doubt you've examined too much of it after 20 years down the road to see what shape it's in.....and I'm sure Dupont counts on that.
Done. My stock portfolio now includes DuPont.

PS as houses get tighter, high perm materials become more valuable, and low perm materials become more useless.

[Tom R]

I find a lot of today's products are based much more on 'hype' than performance.

That's one of the reasons I never even switched over to Tyvek, - - felt paper has already stood the test of time.

[dominog]

Thank you all for the information.

[patrick.ogrady]

Good thread, thanks for all the info. I'd like to add a question. Since I am down to the wall studs on my renovation, would it be a bad idea to add 2x2 all around and cover the existing fibreglass batt with foam? I will be adding 1" to the exterior, just thought this would be a good way to get the most insulation in while I have it this far.

[Rich]

You would be better off putting the sealing layer (the foam) to the cold side of your wall. Not sure if I would put too much money into spray foam if you are planning on putting something to the exterior as well.

[JPolito830]

I wouldnt spend much at all on the foam.

[rabadger]

When this thread started it was not available. That was in 2005.

[Construction15]

If I understood you correctly and your asking if you should put foam over your Batts the answer is no... Someone resurrected an oldie but a goodie =)