R-19 and R-21 Insulation?

Discussion in 'Homesteading Questions' started by SouthernThunder, Jan 2, 2008.

  1. SouthernThunder

    SouthernThunder Well-Known Member

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    I'm looking at insulating a house that has 2x6 studs. I am going to put R-board on the outiside with an r value of 5 and fiberglass on the inside. As far as fiberglass goes I have noticed that there is an R-19 that most people use around here and also an R-21. The R-19 is made to fit a 6 1/4" cavity. The R-21 is made to fit perfectly in a 5 1/2" cavity. My question is why does everyone use the R-19?
     
  2. Rod Torgeson

    Rod Torgeson Well-Known Member

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    When I had my house insulated in 2000, R-19 was the normal insulation. R-21 was an upgrade. I went with the R-21. I have 2 x 6 studs in the wall. It did cost a little more since it was an upgrade.

    Rod<---in Appleton, WA
     

  3. copperkid3

    copperkid3 Well-Known Member

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    Answer: Because it's cheaper???? :shrug:
     
  4. tamsam

    tamsam Well-Known Member

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    One reason that I can think of is a 2x6 doesn't measure 2x6 but closer to 1 1/2x 5 i/2. Just my thoughts. Sam
     
  5. Macybaby

    Macybaby I love South Dakota Supporter

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    My understanding is the R-21 is a higher density material that is a recent development.

    I don't remember seeing it in the store a few years ago.

    Our house is so much warmer now, but we had hard packed blown in insulation and no wind/vapor barrier. Now we have fiberglass with tyvek on the outside and plastic on the inside. We don't even have the heaters on in half the house and it is still staying warm. We also replaced all the leaky windows . . .

    The good part about doing the remodeling during the cold weather is you can walk around and feel for drafts and foam them before going farther.

    Cathy
     
  6. OntarioMan

    OntarioMan Rockin In The Free World

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    With things like insulation, it will get to a point of "diminishing return" - meaning that it will take much longer to recoup your additional investment. Is R19 the best value, R21? You'll have to figure out where that point is, because it depends on many factors.

    I was once considering a high efficiency furnace - at that time, I would have had to run the high efficiency furnace for 30+ years before I recovered my additional costs over a conventional unit. Saving energy does not always equate to saving money.
     
  7. The Paw

    The Paw Well-Known Member

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    don't know for sure, but I think the R-19 would fit into a 6 1/4 inch cavity, leave an inch for air space and it appears sized for use with 2x8 framing where you need to leave air circulating on the cold side (like cathedral ceiling).

    The R-21 fits into 5 1/2 inch cavity, perfect for 2x6 wall construction.
     
  8. SolarGary

    SolarGary Well-Known Member

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    Hi,
    You can figure out how much you will save for a given improvement in R value using this insulation upgrade calculator:

    http://www.builditsolar.com/References/Calculators/InsulUpgrd/InsulUpgrade.htm

    As an example, for my climate (cold) and fuel price ($2.20 propane), and 1500 sqft of wall area the savings is $43 per year for going from R19 to R21, or nearly $700 over 10 years with 10% per year fuel price inflation.
    Seems like a no-brainier to me :)

    Have you looked at cellulose?

    Gary
     
  9. Jim S.

    Jim S. Well-Known Member

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    Rising fuel costs are a given. The comparatively small added expense of more insulation at construction time will pay you back in future years. Get all you can afford, and as others have said, plug those air leaks. You'll be glad you did.

    My stone-sided house is one-half a 75-year-old uninsulated home and one-half newer construction with insulation. The new side is night and day warmer. Eventually, I will blow in insulation in the old half, but it will be much harder to add it now than it would have been at construction. The old part of the house was originally clapboard, and if they have even added the insulation when they added on and stoned it up in the '60s, it would have been cheaper. Sigh...oh well.
     
  10. ET1 SS

    ET1 SS zone 5 - riverfrontage Supporter

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    R-19 and R-21?

    I dont know.

    I just finished hanging a lot of R-30 fiberglass batting, you only get to insulate once.

    Do it right.
     
  11. SouthernThunder

    SouthernThunder Well-Known Member

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    Thanks for the replies guys. I did some checking an R19 is going for .383 cents a sq and R21 is .50 cents a sq. The price difference for doing this house in R21 instead of 19 is about $286.

    One other thing I found was that fiberglass insulation loses some R value when it is compressed. R19 will have to be compressed to fit into a 2x6 wall but R21 will not so the difference may be slightly better than I thought.

    Gary, your calculator says it would pay for itself in 5 years in this house. But if I'm not mistaken thats just for heating and not cooling which can be as big of a bill here in oklahoma as well. I havent realy looked into cellulose that you mentioned because I have heard it settles and leaves gaps at the top pf the walls? Is this true?

    Ditto the no brainer comment so long as I can find a supplier. I am having a real problem finding someone around here to sell it to me. The one place that quoted me a price couldn't sell it to me because I wasn't a contractor. :shrug:
     
  12. barelahh

    barelahh Well-Known Member

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    Depending on your location, the thickness of your studs, put the maximum recommended amount. It will save you more money in heating and cooling costs than you will spend on the insulation itself.
    That paper stuff aka cellulose sucks. It's ok for ceilings where you can get access to add more later on but as for walls, avoid it like the plague.
     
  13. SolarGary

    SolarGary Well-Known Member

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    Hi,
    Right, the calculator only does heating, so you might do a good deal better than it indicates.

    I'm a fan of cellulose.
    It will never settle if installed properly. It should be "dense packed" -- if the installer does not know what this means, I'd find another installer.

    It has a bit higher an R value per inch that FG, but the main thing is that it is dense enough not to allow air currents to form under cold conditions. Air currents in loose fill FG can reduce the effective R value by half under cold conditions. This should be less of a problem in walls, but (I think) would still be there.
    This is the ORNL test that shows this:
    http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/92/920510.html

    FG needs to be installed very carefully in walls to work well -- cut to fit carefully, fitted around wires and outlets, ...
    The insulation installers are usually the lowest paid guys on the site, and don't have a great reputation for taking a lot of pride in doing it right -- but, I'm there are are some exceptions -- maybe some free pizza would help :)
    But, if you are doing the work, probably either type of insulation can work well.

    You might check out the Taunton Fine Homebuilding forum -- there are tons of past discussion on insulation among the guys who do the installing -- very strong opinions :)

    There is some material on insulating here:
    http://www.builditsolar.com/Projects/Conservation/conservation.htm
    and here:
    http://www.builditsolar.com/Projects/SolarHomes/constructionps.htm

    This "Whole Wall" insulation calculator is also interesting -- it tells you how much R value you lose due to heat short circuiting through studs -- it will make you a believer in the insulating sheathing:
    http://www.ornl.gov/sci/roofs+walls/AWT/InteractiveCalculators/rvalueinfo.htm

    The book by Harley called "Insulate and Weatherize" is very good -- I've used it a lot.


    Gary