# Bang for buck ?



## Fix'n it (Mar 12, 2012)

i am doing all of the outside walls of my house with new insulation. were there had never been any insulation. while i would love to use mineral wool, that would cost my arm and leg. 

what are some options that still give acceptable results, so i can keep my arm and leg ? 

thanx


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## Pittsville (Jan 8, 2011)

If you're looking for the most bang for your buck, use Roxul.

If you're saying you want the most bang for your buck, but are really looking for the lowest cost option, use Fiberglass.

Sprayfoam is extremely efficient, but would probably be the most expensive option. I'm not a huge fan of cellulose, but I imagine the price to performance ratio would be close to the rock wool. Someone will chime in if I'm incorrect.


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## Windows on Wash (Aug 30, 2011)

Nothing wrong with fiberglass if the exterior wall is air tight.


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## Fix'n it (Mar 12, 2012)

Pittsville said:


> If you're looking for the most bang for your buck, use Roxul.
> 
> If you're saying you want the most bang for your buck, but are really looking for the lowest cost option, use Fiberglass.
> 
> Sprayfoam is extremely efficient, but would probably be the most expensive option. I'm not a huge fan of cellulose, but I imagine the price to performance ratio would be close to the rock wool. Someone will chime in if I'm incorrect.


no spray foam, too costly. no blow in, i want the insulation in before i put up the drywall. as far as bang for buck goes = if $100 gets me a 90% increase, and $200 gets me a 95% increase, i will go for the $100 option. on the other hand. if $100 gets me a %50 increase, and $200 gets me 90%. i will go with the $200 option. get what i am saying. 



Windows on Wash said:


> Nothing wrong with fiberglass if the exterior wall is air tight.


the outside wall will be air sealed. and if it isn't hard, or not recommended, in inside wall. 

now, i understand that fiberglass is frowned upon around here. so why do you say that it is ok ? only fiberglass in the attic is not good ?
i had a thread going about "thermal break walls". i am still thinking about doing that. so that would add about 2" more for insulation, if i do it.


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## Pittsville (Jan 8, 2011)

Fix'n it said:


> as far as bang for buck goes = if $100 gets me a 90% increase, and $200 gets me a 95% increase, i will go for the $100 option. on the other hand. if $100 gets me a %50 increase, and $200 gets me 90%. i will go with the $200 option. get what i am saying.


Here's some food for thought...

Roxul vs. Fiberglass - All pricing obtained from Lowes. Your mileage may vary.

Roxul: $0.62 per sqft R15 ($0.04 per R per sqft)

Fiberglass: $0.40 per sqft R13 ($0.03 per R per sqft)

Note: Both prices are for 3.5" batts. Note that the Roxul is already +2R over the Fiberglass at that thickness. The only way to do any better than R13 with the fiberglass would be to purchase a larger 6.5" R19 batt and compress it in the same 3.5" space. You obviously would not achieve R19, but you would do better than R13.

Roxul has better fire and water resistance than fiberglass, it doesn't sustain vermin and it doesn't sag or lose it's shape. It's much easier to cut in my opinion and makes insulating around obstructions a breeze. Shouldn't leave you all itchy and irritated afterwards like fiberglass either.

At only $0.01 per R per sqft more, the above mentioned benefits vs fiberglass make it the clear winner in my book of best bang for your buck.


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## Windows on Wash (Aug 30, 2011)

Fiberglass batting is different than blown in fiberglass (worthless crap).

It is much more high density and does not allow convection to the same extent.


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## Fix'n it (Mar 12, 2012)

thanx, fella's. 

one more question. that seems to have been answered. what is the standard R-value for walls ?


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## Pittsville (Jan 8, 2011)

Fix'n it said:


> thanx, fella's.
> 
> one more question. that seems to have been answered. what is the standard R-value for walls ?


Ideally, you want to get the highest R value that you can achieve. Using batt insulation and proper air sealing, you should be looking at:

2x4 walls = R13 to R15
2x6 walls = R19 to R22

The R value of the wall assembly can be increased by adding rigid insulation to the exterior of the wall. (Over the sheathing) This will reduce thermal bridging and improve efficiency.


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## Gary in WA (Mar 11, 2009)

Fiberglass is fine in a six-sided, closed, air-tight box as it is rated for the R-value, anything less than that is an R-value reduction. 2x4 wall use R-13- a medium density or R-15- high density with no convective loops. 2x6, R-21 is recommended with no convective loops. 

R-19 (6-1/4”) is made for 2x8 ceiling joists (7-1/4”) with a 1” air channel above for venting on a cathedral ceiling, not for 2x6 walls. Convective loops are inherent with it because of its low density, no matter how well or perfectly it is installed (you can’t win). http://findarticles.com/p/articles/mi_m0KWZ/is_3_6/ai_n8582994/
Just compressing it in a 5-1/2” wall reduces the R-value to R-17. If the wall gets wet from a siding/roof leak OR as little as 1/16” gap around an electrical outlet- or to the exterior air, you lose in another way. That cavity- top to bottom,* and* any connecting cavities (from the continuous “daisy-chained” wiring holes you never plugged in studs/plates) will wet the fiberglass reducing its effectiveness by 60-70%, from R-12 to R-4; or R-17 to R-11; http://www.nrc-cnrc.gc.ca/eng/ibp/irc/bsi/90-controlling-heat.html
Hence the reason to air-seal the drywall as well as the cavity sheathing from infiltration/exfiltration; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/

Caulk sheathing, foamboard on exterior (changes dew-point location), holes vs. diffusion (*90 times greater*), and “stack effect”; *pp. 15-22;* http://www.engr.psu.edu/phrc/training/understandingbarriers.pdf

There are many more places that air/heat/moisture can negate f.g. insulation: 
http://www.conservationtechnology.com/building_design.html#AirLeakagePathways

Less-than-perfect installation (insulation not in contact with drywall, side stapled facings, air leaks, etc.) of f.g. may result in major R-value losses- even in new, tighter construction, pp. 40, 41: http://www.buildingscience.com/docu...mance-residential-buildings-all-climate-zones

Add the thermal bridging; 2x4 wall = 11%, 2x6 wall = 28%- pp.40: http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/b-1239.2/b1239.2.pdf

Nothing wrong with JM’s Spider https://docs.google.com/viewer?a=v&...jzAbsc&sig=AHIEtbS8nArkYPqlpNc-XWVzO6aRj-hhwg insulation in walls or attic, other than the cost, notice the densities- 1.8----2.6#cubic ft. compared to R-19 at 0.55#cu.ft: compare them in a “How to” I made a while ago: http://www.diychatroom.com/f98/biggest-loser-fiberglass-insulation-90438/

Gary


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