# Compressing Insulation Question



## HandyMat (Jan 22, 2018)

I have ran into a roadblock. I know all the data, specs and installation requirements however, I have a metal stud wall, 2.5" studs, 16"o.c. Has anyone used r13 unfaced ins. in these type of walls? I know roughly the R value decreases to r10 but what else can I do?

I have 2" XPS Foamular 150 behind studs against block wall.

This is a basement

thanks


----------



## Bud9051 (Nov 11, 2015)

The 2" of rigid probably meets your code requirements so whatever you put into the cavity is jut extra. Compressing insulation is a pain plus results in a poor install, meaning varied r-value from battling the installation.

Now, as to the compression myth. A mild amount of compression actually increases the r-value per inch but not enough to justify increased pain of the install. One of the insulation mfgs had (probably still out there) published the curves for r-value per inch as it is compressed. Note the distinction of "per inch". The actual loss of R-value results from fewer inches of depth and that brings us to your install.

At 2.5", if you installed 2.5 inches of fiberglass (no compression) you would have about R-8.75. That's r-3.5 per inch which varies a little with different mfgs and that amount is fine for your basement walls. Your options are to find a batt insulation the right size to fit or strip some off of the r-13.

Now, since you have steel studs (I'm assuming C shaped) you could fill the C with what you strip off. That will also satisfy your urge to compress some insulation.

Note, those metal studs will significantly bypass your fiberglass insulation giving you probably an R-5 layer inside your r-10 rigid. But again, that will work fine.

Bud


----------



## HandyMat (Jan 22, 2018)

@Bud9051 Thank you very much! Do you think I should frame the remainder of my basement walls with 3-5/8" steel studs or continue with 2.5?


----------



## HandyMat (Jan 22, 2018)

Here is what I am working with @Bud9051


----------



## Bud9051 (Nov 11, 2015)

Shifting to 3 5/8" is optional and others have commented on the reasoning. As far as insulation, I have stripped a lot of it for various reasons and it is no big deal. More of a concern for me would be getting the batts to stay in place. You really don't want Kraft faced so you need a friction fit between the studs. Metal doesn't provide a lot of friction so you will need something to hold the FG in place. Personally, I have never installed metal studs or had to insulate them.

Maybe some of the other helpers have some ideas.

Bud


----------



## DR P (Dec 16, 2017)

Hello - personally I would save my money and not use any batt insulation because your foam board installed has effectively created a vapor barrier at the masonry wall... & with metal studs that will not produce any R value but rather conduct & potentially allow a path for warmer air to permeate into the stud cavity & condense at the cooler foam barrier and get the insulation wet/mold/mildew...For that reason I also wouldn't install any vapor barrier on the house side of the metal studs and let your heat permeate into the metal stud cavities... unless you are certain there will be no moisture condensing / trapped inside between your vapor retarder & vapor barrier... I realize anyone can make any claim; therefore I have included literature from Corning as well as an Engineer's technotes on insulating steel stud walls... 



http://foamular.com/assets/0/144/172/174/3a1fa7fb-20e8-4169-980a-5a29c24c6612.pdf
From page 26

Vapor Retarder Performance

"*Vapor permeation is controlled by the careful analysis of location*, selection and installation of vapor retarding material in the wall system. *In heating driven regions the vapor retarding layer is typically near the interior surface with minimal perm resistance in the layers in the wall nearer the exterior. 
*
_*You have installed a vapor barrier nearer the exterior*_

Indoor air, warm, and seemingly dry, if sealed in a jar, taken outside and cooled, will condense liquid water or “excess moisture” on the inside walls of the jar. If the same warm air leaks through a hole into a wall, migrating until it reaches a surface colder than its dew point temperature, the same condensation will occur. If that condensation happens it will be in a location inside the wall that can’t be seen and where it eventually may cause damage. An air barrier can limit the flow of warm moist air into a wall. However, even if the wall is sealed with an air barrier, unless the wall is properly vapor protected, water vapor may still diffuse into the wall on the molecular level, where it may also encounter dew point temperature and condense with the same damaging result."

& on page 27

Design Strategies to Prevent Condensation

*In steel stud framed wall systems where materials are susceptible to damage from water vapor condensation, there are several design strategies often used in combination to minimize or prevent condensation: 
*
Install ci sheathing such as FOAMULAR® XPS to keep the materials in the wall above the dew point temperature. 

Install a properly placed vapor retarding layer to limit water vapor diffusion into the wall such as EcoTouch® FIBERGLAS™ Insulation with a variety of available facers and permeance ratings. 

Install air barriers such as FOAMULAR® XPS with JointSealR® Foam Joint Tape sealed joints to limit the amount of moisture laden air leakage into the wall. 

*Omit stud cavity batt insulation, thus placing the most vulnerable steel framing components at room temperature. 
*

Limit the accumulated condensation to an amount that can be safely absorbed, stored in reservoir materials, and reliably evaporated under summer conditions. (*An interior vapor retarder may inhibit the effectiveness of this design strategy by limiting drying capability.*)


by Joseph T. Kohler, Ph.D., P.E:

http://kohlerandlewis.com/pdf/SteelStuds.pdf

"What is a typical steel stud wall system and why doesn't it perform well? 

A typical wall assembly in common use consists of *6" steel studs with R-19 fiberglass batts*, with a polyethylene vapor barrier and sheetrock on the inside, and exterior sheetrock and siding or brick veneer on the outside. While this wall system appears to meet the code "on paper", it does not meet it in practice. The problem is that the steel studs conduct heat readily, short circuiting the insulation. *The American Iron and Steel Institute (Thermal Design Guide for Exterior Walls, 1995) rates the performance of this wall system as only R-10. Some building scientists rate it at closer to R-4, *which is only marginally better that an uninsulated wall.

How can we prevent "Short Circuiting"? 

The solution to this has been to add an inch thick layer of rigid foam to the exterior side of the steel studs to provide a thermal break. The American Iron and Steel Institute rates such an assembly at around R-16. 

What's wrong with this solution? 

*One problem with this approach is that it creates two vapor barriers - one at the foam and the other at the poly vapor barrier. Moisture that gets through the poly vapor barrier (which has a lot of penetrations due to fasteners and electrical wiring) may accumulate in the fiberglass and possibly condense.* 

Another problem is the use of fiberglass batt insulation. The batts release fiberglass particles which may present a health hazard to workers installing the fiberglass. In addition, *fiberglass can get wet from moisture entering from (in your case the heated) interior - it acts like a sponge and takes a long time to dry and provides an ideal environment for the growth of mold. Mold in fiberglass insulated walls and ceiling cavities is a frequent cause of indoor air quality problems."*

So all that said, if you do decide to install insulation batts, at least consider forgoing a second vapor barrier on the heated side of your wall.

Peace


----------



## Bud9051 (Nov 11, 2015)

I believe page 26 is discussing mostly above grade construction. I read some of that reference and didn't see the application for this wall assembly.

First, 2" of rigid foam is not a vapor barrier but a vapor diffusion retarder. Here is the data sheet for the 150
http://www.owenscorning.com/Network...LAR-150-XPS-Insulation-Product-Data-Sheet.pdf

Even at 2" it will provide some drying to the inside as compared to virtually zero drying to the outside (below grade). And it will definitely keep the inside surface of the rigid foam and stud cavities above the dew point, so no condensation issues.

Bud


----------



## DR P (Dec 16, 2017)

Bud9051 said:


> I believe page 26 is discussing mostly above grade construction. I read some of that reference and didn't see the application for this wall assembly.
> 
> First, 2" of rigid foam is not a vapor barrier but a vapor diffusion retarder. Here is the data sheet for the 150
> http://www.owenscorning.com/Network...LAR-150-XPS-Insulation-Product-Data-Sheet.pdf
> ...


"Like all FOAMULAR® XPS products, FOAMULAR® 150 XPS insulation is made with Owens Corning’s patented Hydrovac® process technology under strict quality control measures, which makes it highly resistant to moisture and permits the product to retain it’s high R-value year after year even after prolonged exposure" 

Even corning admits moisture is the enemy & I wonder 
why it needs to be so "highly resistant to moisture"
That said metal studs conduct - 
no real gain in R value anyway  with 2.5" studs
why risk it is all I'm getting at? Potato Potato
As long as hes happy; I'm happy too but
No way I'd put a 2nd barrier up in that scenario IMO

Peace


----------



## NotYerUncleBob2 (Dec 29, 2017)

DR P said:


> That said metal studs conduct -
> no real gain in R value anyway with 2.5" studs


The studs themselves will not provide any R value of course, but they're not the entire wall, just a small fraction of the surface area at what, 1.5" wide out of a 16" section? Or you could even count the thickness of the metal as the conductor and then it's like 1/16th" out of 16". 
With the foam being a very effective thermal break, I wouldn't worry about the R value (or lack thereof) of metal studs or even wood studs. 
That said, the fiberglass will supply some decent R value here compressed or not, but the question is whether it's enough to justify the expense here. If the basement is below ground I'm not sure I'd even use the fiberglass, but if it's above ground or has a good portion above ground then probably good to have that extra insulation, no?


----------



## Bud9051 (Nov 11, 2015)

Thanks NYUB, well said.

Bud


----------



## DR P (Dec 16, 2017)

NotYerUncleBob2 said:


> The studs themselves will not provide any R value of course, but they're not the entire wall, just a small fraction of the surface area at what, 1.5" wide out of a 16" section? Or you could even count the thickness of the metal as the conductor and then it's like 1/16th" out of 16".
> With the foam being a very effective thermal break, I wouldn't worry about the R value (or lack thereof) of metal studs or even wood studs.
> That said, the fiberglass will supply some decent R value here compressed or not, but the question is whether it's enough to justify the expense here. If the basement is below ground I'm not sure I'd even use the fiberglass, but if it's above ground or has a good portion above ground then probably good to have that extra insulation, no?


well IF walls are above grade then pages 26 & 27 definitely will apply...
BTW according to Corning's residential guide for formular:

http://foamular.com/assets/0/144/172/174/21072c44-af67-422a-8c47-452240d958fd.pdf
top of page 5:

General purpose

FOAMULAR® 150 

R-5.0 R-7.5 R-10
1" 1-1/2" 2"

Square, Scored Square and Tongue & Groove Edges 
24"x96", 48"x96" or 108"

For exterior sheathing insulation projects and 
*interior of basement walls in lieu of InsulPink® insulation*

If he wants the extra cost for little effect 
& is aware of the potential mold aspects, 
especially with a 2nd barrier in play then fine with me...
all I really wanted to do is make OP aware of a 
potential snafu in a cold climate such as Michigan... 
there are other issues in play such as did he protect metal base plate with barrier, 
no depth for electrical boxes, keeping FG insulation in place & from shifting...

The question is not only is the expense justified, 
but what is correct & what is incorrect procedure/process...
I believe FG insulation is not what he wants in that basement
if there is ever a potential of moisture collecting in cavities...

If OP is convinced he needs more R value, 
then glue/install section of XPS to fill stud channel, 
then also glue/install extra layer of XPS inside cavity, 
leave out 2nd vapor barrier to allow moisture to come & go... 
XPS wont wick/store moisture nor mold nearly as bad FG batts. 

Or save $ & effort and move forward with true R-10 & 
an all in one vapor barrier already placed inside basement... 
if new construction, is foam already placed on outside of foundation?
If so is any more R value truly needed inside basement?

Peace


----------



## SeniorSitizen (Sep 10, 2012)

Insulation value of wood.


----------



## HandyMat (Jan 22, 2018)

Thanks! What would you recommend for insulation?


----------



## HandyMat (Jan 22, 2018)

Thank you everyone for the recommendations. The only reason I was going to insulate the stud cavities is because that is what a friend/contractor did. With R-10 Foamular on the walls, a 2.5 stud with R13 FG Insulation (compressed 1"), Id still be getting at least an R value of 20. Or will R10 Foam on the walls be plenty and skip the FG insulation?


----------



## 123pugsy (Oct 6, 2012)

If it's a basement, use Roxul.

I'd try to get away with no VB. I had to spray foam my basement because inspector wouldn't allow doing foam/insulation without it.


----------



## user_12345a (Nov 23, 2014)

When you already have a good thermal break in a basement like 2" of foam, additional insulation doesn't need the barrier, there's no extra condensation risk.

They're behind the times, the whole putting a vapour barrier (and batts) in a basement thing never made any sense, given that moisture comes in from the foundation anyway.

Just need a good thermal break.


----------



## DR P (Dec 16, 2017)

user_12345a said:


> When you already have a good thermal break in a basement like 2" of foam, additional insulation doesn't need the barrier, there's no extra condensation risk.
> 
> They're behind the times, the whole putting a vapour barrier (and batts) in a basement thing never made any sense, given that moisture comes in from the foundation anyway.
> 
> Just need a good thermal break.


I agree - U nailed it.... 

basement are inherently cool and their walls are 
seasonally damp/wet from so many outside variables/potentials. 
& if/when the relative humidity rises in that basement 
its not going to smell pretty nor nice with FG batts involved...

There is bad code being enforced regarding insulating basements... 
one method does not fit all... 
each basement scenario is potentially different

Of course the insurance industry writes/involved with most code
& with their 1-time minimal coverages in play for mold/mildew
not certain there is an immediate & pressing goal anytime 
soon by them to solve this basement insulating science...
Then there is always the compounded problems of fire ratings

insulation industry is finding that best technique 
is an insulation barrier on outside of entire foundation 
(including sill & under basement floor if needed) 
that is the most logical app so far... 
(don't have to worry about what happens if it burns)
protecting that foam insulation & aesthetics 
are another issue all together...

If an inspector required me put up a plastic barrier 
between stud & finished wall of basement in Michigan; 
it would come back down after they left 
or have so many holes/slits in it 
before installing the finished wall... just saying

Peace


----------



## 123pugsy (Oct 6, 2012)

DR P said:


> I agree - U nailed it....
> 
> .............................
> If an inspector required me put up a plastic barrier
> ...


Doh! What was I thinking? I could have just ripped it down.

Actually, the spray foam saved a ton of work. :wink2:


----------



## ddsrph (Nov 23, 2013)

I would consider attaching flat wise two by fours to the metal studs. This would give you four inches and also isolate the metal from heated side. You could use metal decking screws to attach.


----------

