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Should I replace my insulation

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hdesert

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In the course of my home remodel I have discovered that my 2x4 exterior walls have been filled with R19 batt insulation from 30 years ago. I am concerned that I am losing insulating value due the compression of the batt. Since my walls are all exposed at this point is it worth replacing the R19 with R13-15? The R-19 fits and appears to be in pretty good condition but it is compressed when the wood T&G siding is put on. Any thoughts on the best course of action? The home is in a winter climate at 7000 ft elevation.

Thanks for your ideas
high desert
 
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volaredon

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nope its done its job this long/ put it back together and save your $$$$
 
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cowboyjosh

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Don't replace unless you intend on doing a closed cell spray foam (I don't recommend spray foam in walls for various reasons I still insulate my homes with batts; I do spray foam rim joist though).

One thing you MIGHT want to do with the walls open is take a can of Great Stuff and air seal any penetrations and the bottom and top plates of the wall.

Happy building.
 
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Kevin C

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I used R19 in the walls of my shop to get better sound deadening. You can put up to R21 to get the highest R value for that cavity depth (may bulge out thin sheet rock). R21 compressed down gets you ~ R15. R19 is probably a little bit better than R13 but not enough to call it R14.

Option 1: Put the siding back on and get approximately R13.4 from the batts.
Option 2: Run furring strips to space the wall out and get R19 from the batts.
Option 3: Buy new insulation, spend a bunch of cash and get the same or lower performance. :)
Option 4: Place a 1/2 to 1" foam under the plywood as a thermal break to increase the R value of the wall.

Effective R Wall Assembly R Values (16" OC, assumes 20 % of the wall is studs):

A few possible wall combinations.

1: No insulation is about ~ R4.6 (I put this in as a baseline for all of those that have sheet rocked, uninsulated walls.
2: R13 Batts ~ R12.7
3: R15 Batts ~ R13.7
4: Frame wall out to 2x6 equivalent with R 19 batts~ R17.4
5: 1/2 EPS Foam (R2) under plywood with r13 batts ~ 15.2
6: 1" EPS Foam (R4) under wood, R13 batts ~ R17.3
7: 2" XPS Foam under siding, R13 batts ~ R23.6


http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table

http://www.coloradoenergy.org/procorner/stuff/r-values.htm
 
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PAToyota

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Outlawmws said:
It won't be less that the R13/15, so no, don't replace, you just waste $$
Click to expand...

Tim The Tool Man said:
No leave it alone. compressed r-19 will give you a higher r-value than r-13. something in the neighborhood of r-15...
Click to expand...

Nope and nope. Batt insulation works on the principle of "trapping" air. When you compress it, it removes those air voids and lowers the R value. So compressed R19 can have less insulating capacity than R13.
 
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Tim The Tool Man

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PAToyota said:
Nope and nope. Batt insulation works on the principle of "trapping" air. When you compress it, it removes those air voids and lowers the R value. So compressed R19 can have less insulating capacity than R13.
Click to expand...

Yes and no. Compressing r-19 into a 2x4 cavity will yield a higher than r-13 r-value BUT less than an r-19 value. Compressing insulation and r-value are related to each other on a geometric bell curve. As you begin to compress the fiberglass your r-value per inch starts to increase but once you hit a point where there in no more captured (around 1/2" or less for r-19) air the r-value drops sharply.

The reason you don't see r-15 batts of insulation for a 2x4 wall cavity is simply a matter of diminishing returns on investment. It just isn't cost effective.

Here is a quote that I shamelessly stole from an energy auditor type website which explains what I was just saying much more eloquently (here is the link):


"How many of you have heard the statement, "compressing fiberglass insulation reduces it's r-value"? I'm going to assume everyone has, myself included. Well, the statement is correct, but the interpretation or application of it often leads to a wrong conclusion, for example: Stuffing extra fiberglass insulation into a wall cavity will reduce the walls r-value. That statement is most often wrong, here's why.

I found it confusing that compressing fiberglass insulation would reduce it's r-value, yet we could buy high density fiberglass at a higher r-value. So what is the difference between high density fiberglass and regular density that we compress into a tighter space? It turns out to be, not as much as we thought. The distinction is between the r-value of the fiberglass batt and its r-value per inch. Take for example, r-19 batts. They are nominally 6 1/4 " in thickness, thus an r-value of 3.04 per inch. Now, that's not the r-value our books give us, but it is what the numbers say and what the pink panther says. Now, install it in the normal 5 1/2" cavity and what do you get, 3.04 X 5 1/2" = 16.72, no. The panther says we get r-18, so what happened to the r per inch. It went up to 3.27.

So compressing the batts increased their r per inch, while reducing the total number of inches, resulting in a lower total r-value, and although the total went down, we can see that a limited amount of compression is not necessarily a bad thing. Where the turning point is, I haven't determined and obviously we can't squash the fiberglass flat and expect it to continue to increase its r per inch. But a little stuffing here and a little there can be a good thing.

Here is the panther's web page with the numbers I used and it does show that their high density for a a 5.5 inch cavity is actually R-21. Whether that's accomplished because they know how to increase the density better or because we need to add more insulation than the 6.25 in the example I started with, I don't know.
http://www.idimn.com/pdf/insulation/fiberglass/high-density/21149-D.pdf

I however do know I now understand the original statement better, I just hope my explanation helped you as well. Corrections welcome if I am wrong. -Bud"​
 
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Kevin C

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PAToyota

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bigbubba

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Randy in Maine said:
Would it be possible to install 1-2" of foam on the inside walls since they are all exposed?
Click to expand...

Off the top of my head I'd say it would be more of a pain than it's worth.1st you would have to reset all your electrical boxes so they sit flush with the new walls.And you will lose some inside sq. footage.
 
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Outlawmws

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Kevin C

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bigbubba said:
Off the top of my head I'd say it would be more of a pain than it's worth.1st you would have to reset all your electrical boxes so they sit flush with the new walls.And you will lose some inside sq. footage.
Click to expand...

You can use mud rings on the boxes... At least that my plan.
 
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