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  1. #1
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    insulation choice?

    Still trying to decide on the best insulation for my house. Some background to help in the process...
    Small paid off home,1000 square foot, with very cheap utilties. No plan on moving untill they wheel me off to the nursing home or mortician in 30 years. All ceiling penetrations have been sealed but there's still infiltration issues. New roof with ridge vent and soffit vent around entire house. Pitch is 4/12 with 3' overhangs so the max insulation over exterior walls is 2.5-3" without blocking roof ventilation. Existing insulation is 6" of 55 year old rock wool everywhere except the tight spots over the exterior walls. No vapor barrier. One gabel end and one hip end. Supply duct is in attic wrapped in 2" fiberglass with no vapor barrier. Design temps are 2 and 95, very humid in summer, heating hours are double cooling hours. Can be heavy snow loads on the roof,2x4 construction.

    Best application for this house would be?
    A) Spray foam underside of roof deck eliminating venting
    B) Remove rock wool and foam the ceiling
    C) Add a layer of batt over the rock wool
    D) other- please explain

  2. #2
    Join Date
    Jul 2004
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    Massachusetts
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    Quote Originally Posted by martyinlincoln View Post
    Still trying to decide on the best insulation for my house. Some background to help in the process...
    Small paid off home,1000 square foot, with very cheap utilties. No plan on moving untill they wheel me off to the nursing home or mortician in 30 years. All ceiling penetrations have been sealed but there's still infiltration issues. New roof with ridge vent and soffit vent around entire house. Pitch is 4/12 with 3' overhangs so the max insulation over exterior walls is 2.5-3" without blocking roof ventilation. Existing insulation is 6" of 55 year old rock wool everywhere except the tight spots over the exterior walls. No vapor barrier. One gabel end and one hip end. Supply duct is in attic wrapped in 2" fiberglass with no vapor barrier. Design temps are 2 and 95, very humid in summer, heating hours are double cooling hours. Can be heavy snow loads on the roof, 2x4 construction. I'll assume the 2x4 construction refers to the walls, not the roof joists with a heavy slowload??

    Best application for this house would be?
    A) Spray foam underside of roof deck eliminating venting I'm not a fan of unvented attics. JMO. Once the air exfiltrates from the treated envelope, let it go, as you've lost it.
    B) Remove rock wool and foam the ceiling You need a moisture barrier. I'd removed the rock wool, install a moisture barrier, then foam. I now dense foam is supposed to be a moisture barrier but somewhere in the thickness of that foam, the temperature reaches dew point and moisture that's penetrated the dense foam can condense, lowering the R-value. Again, I'm conservative. I like to see a solid moisture barrier, solidly sealed envelope and then insulation. Dense foam will seal and insulate.
    C) Add a layer of batt over the rock wool This is a waste of time and money if there is air movement. Loose rock wool and/or bats are useless against air movement, except to filter the air.
    D) other- please explain
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  3. #3
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    Thanks. Was leaning toward "B" from the start but then read some of the threads suggesting "A" on other homes. They were in warm weather zones though so I though the snow load info could be important . Joists are 2x4 but lots of support webbing which combined with a short roof makes attic work a real treat. Didn't know a vapor barrier was still needed with high density foam so will make sure it's installed.

  4. #4
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    Sep 2005
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    Atlanta GA area
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    My vote would be the foam under the roof. I have done HVAC on 'foamed' houses (both foam around the entire envelope and foam under the roof with bats in the walls). There is not denying the advantage to not having the attic an oven or refrigerator.

    Foaming a roof does raise other issues, a quality foam contractor can explain them and work out solutions.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  5. #5
    Join Date
    Nov 2009
    Location
    West Monroe, LA
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    If you go with foam under the roof you well need to seal off ridge vent & softfits for it to work right. I am not a fan of ventless attic to may variables plus your home was designed to be vented. What size hvac system do you have? Adding foam is going to decrease the load on your home even adding add fiberglass or cellulose well do as well. You don't want to have to big a system once insulation work is done!!! Just some thing to think about. Just wondering with good electric bills why add foam verus standard blowen insulation? I am sure you want to spend the less amount of money to get quick payback.

  6. #6
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    Mar 2008
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    Shelby Twp MI
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    I have to agree with skippedover. That dewpoint is a ***** and if it condenses on or in the wood your going to have problems. If you were in the extreme south I would go with it. Another thing you have to concern yourself with if your going to foam is the fact that if you develop a leak, it's going to saturate and hold that moisture in that foam and hold it on the wood, just rotting it away. You see alot of that in barns with the sprayed insulation. The only thing that holds the structure together is the foam itself.
    Jim

  7. #7
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    Jun 2010
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    How about a second opinion?
    Have you had any sweating duct problems to date? seems if you had you would have said something.
    The others advice is sound and a little pricey with the full foam treatment. Maybe some foam at the eaves would help the low rise space and do need to maintain the eave venting. Your ceiling as I understand has been sealed so there is your air barrier.
    The rest of your infiltration has got to be the walls, windows etc.
    You didn't say anything about your Bstm, crawl ?

    I think blowing in some added fiberglass would be quick, easy and economical. Perhaps change out your duct with 2" duct board that is sealed-insulated would help any infiltration that is due to the unit leakage (a big deal)

    The whole vapor barrier question depends on your experience to date
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  8. #8
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    Mar 2008
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    Shelby Twp MI
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    Quote Originally Posted by genduct View Post
    How about a second opinion?
    Have you had any sweating duct problems to date? seems if you had you would have said something.
    The others advice is sound and a little pricey with the full foam treatment. Maybe some foam at the eaves would help the low rise space and do need to maintain the eave venting. Your ceiling as I understand has been sealed so there is your air barrier.
    The rest of your infiltration has got to be the walls, windows etc.
    You didn't say anything about your Bstm, crawl ?

    I think blowing in some added fiberglass would be quick, easy and economical. Perhaps change out your duct with 2" duct board that is sealed-insulated would help any infiltration that is due to the unit leakage (a big deal)

    The whole vapor barrier question depends on your experience to date
    Don't take this the wrong way, but the guy is asking opinions on insulating his house and you suggest ripping his duct out and replace it with fuzzduct? Must every post be about ductboard?
    Jim

  9. #9
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    Hey Marine, no offense taken.
    The reason for the new duct suggestion is if it is leaking (probably) then the building science tells us the infiltration is especially bad. Agreed?

    Also chance are the existing duct is installed relatively low and the added insulation will bury it. Talk about sweating ducts, if they are not seating now then with it buried in more insulation and no vapor barrier, chances are even greater the duct surface will hit dewpoint. Agreed? You don't want to move/ reinstall an old duct system do you?

    So if the ceiling is the air barrier then the added insulation with a new sealed insulated duct system installed above the blow in makes the most sense to me. I know board is leak class 6 and sealed sheet metal according to Man J & D is 48 so sheet metal is 8 times more leakage than board.
    I fully understand that there are those who haven't seen it done right and think only hacks use it. Not my expierence

    Sound reasonable?
    Regards, Mike ( Army Artillery, the FO)
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  10. #10
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    Mar 2008
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    Shelby Twp MI
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    Quote Originally Posted by genduct View Post
    Hey Marine, no offense taken.
    The reason for the new duct suggestion is if it is leaking (probably) then the building science tells us the infiltration is especially bad. Agreed?

    Also chance are the existing duct is installed relatively low and the added insulation will bury it. Talk about sweating ducts, if they are not seating now then with it buried in more insulation and no vapor barrier, chances are even greater the duct surface will hit dewpoint. Agreed? You don't want to move/ reinstall an old duct system do you?

    So if the ceiling is the air barrier then the added insulation with a new sealed insulated duct system installed above the blow in makes the most sense to me. I know board is leak class 6 and sealed sheet metal according to Man J & D is 48 so sheet metal is 8 times more leakage than board.
    I fully understand that there are those who haven't seen it done right and think only hacks use it. Not my expierence

    Sound reasonable?
    Regards, Mike ( Army Artillery, the FO)
    I think we can both agree I'm not a fan of the stuff. I just think if the duct was sealed and properly insulated it would be better all around. I've seen it done the wrong way and the right way (I've installed it before, too much for my liking) and I (we) know the path of air isn't straight. It tears it up even done correctly. We both have our beliefs and I surely do not want to make this into a pissing match again. Particularlly with a former vet. I have too much respect for them, as I am one. So, you keep itching with your fuzzy stuff and I'll keep bending my metal and we'll both be happy. I just don't feel that making a completely new duct run will solve the insulation problem, it'll just cost more money to a project that will cost money and time and he can insulate the ducts and seal them the same time as the house insulation.
    Jim

  11. #11
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    Philadelphia PA
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    A million dollar experience I wouldn't give 2 cents to repeat (OOPS! shouldn't say that or another volley will follow the last one Artillary jokes are pretty lame)

    No Pissing contest, but The cost of wrapping it is almost equal to a new board system. And with wrap, it is almost impossible to maintain the vapor barrier with hangers sticking through it.

    Wish you could be converted, because it's guys like you who would do it right if you were given the right info. I think your past life may suggest you are trainable.
    You just need some more basic training is all.
    Drop and give me 20 for not agreeing!
    I'll go easy on you because you too are probably out of shape as well.
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  12. #12
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    Ductboard is a good product and has it's place.. I use it for some ductwork, however:

    It also has this issue of absorbing moisture... and in some places this just will happen regardless. I think it wise to evaluate the space before deciding which duct medium to use.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  13. #13
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    Jun 2010
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    Philadelphia PA
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    John, I agree with ductboard having a place. Most of the problems are from people using it where it doesn't belong, like the return 90 off the unit where it will get kicked and beat up.
    I am a little puzzled with your moisture comments simce all duct is delievering 98?% air. I think most of the moisture is sweating ducts that allow the liquid water to get into the duct. This can happen when the slips become a thermal bridge.
    But I like your comments John
    Regards, Mike
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

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