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  1. #14
    Join Date
    Jun 2010
    Location
    Philadelphia PA
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    2,190
    I am sorry Marty, I should have read this more carefully:
    Can be heavy snow loads on the roof,2x4 construction.
    Even though your 2x4's were really 2x4 You may have to "sister" those roof rafters because now the snow won't immediately melt.

    You probably thought that so you mentioned it. Check your local code for snow load and pick the right rafter.

    PS Your North Latitude and those 3 ft overhangs really cut your cooling load from what you report.
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  2. #15
    Join Date
    Jul 2010
    Location
    nebraska
    Posts
    1,629
    Good stuff guys. Knowing what to do, and what not do is step #1.

  3. #16
    Join Date
    Jun 2010
    Location
    Philadelphia PA
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    2,190
    Marty, don't get me wrong, I think that closed cell foam on the roof rafters is a great way to do it. Puts the duct INSIDE of the building.
    For your job and description, I think that maybe a little foam at the low eaves and rest traditional fiberglass is the way to go
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  4. #17
    Join Date
    Mar 2008
    Location
    Shelby Twp MI
    Posts
    820
    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

  5. #18
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190
    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 !!!!!!!!

  6. #19
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,020
    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

  7. #20
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190
    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 !!!!!!!!

  8. #21
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,020
    Quote Originally Posted by genduct View Post
    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
    Hey Mike,

    In my neck of the woods, we have mild winters and hot humid summers. We also have very damp crawl spaces, some of which have water puddles in them. IMO these damp crawls are not a good place for ductboard. (Yes, a damp or puddled crawl is the exception to the rule). I have taken out a number of ductboard/flex systems in damp to wet crawl; and replaced them with metal plenums and hanged off the joist flex. Then carefully sealed it all up so the indoor air and the crawl air never cross.

    Now if it were an attic, ductboard is fine IMO. I thnk the key is to go the extra mile to be sure it is well sealed when one gets done.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  9. #22
    Join Date
    Jul 2009
    Location
    Lizella, GA
    Posts
    139
    Seal the floor of the attic with a small layer of foam and the pump in the correct amount of insulation.

  10. #23
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    Quote Originally Posted by HSI View Post
    Seal the floor of the attic with a small layer of foam and the pump in the correct amount of insulation.
    Good less expensive, effective approach. 1" spray to attic floor and 16" cellulose over top. Thats if no hvac in attic, and you don't live in stormy areas. Otherwise option a- directly to roof deck.

    Btw. Condensation does not occur within a solid, it occurs when surface temperature is below dew point. Spray foam is a solid.

    That's why beer cozy's prevent wet rings on the counter, dew point temperature is within the foam.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  11. #24
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190
    How do you control RH with standing water in your crawl?
    No answer req'd
    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. #25
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,190
    Kidd, 55 year old home, old wires no doubt, my reading says cellulose and old wires don't mix. The weatherization guidelines for our State of PA says same thing or even more broadly, when chance of moisture then don't use cellulose. THink they will NEVER ever have even a minor roof leak?

    My understanding is that open cell foam can have RH condense inside of product just like any batt when conditions are met. Is this not true?
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  13. #26
    Join Date
    Mar 2008
    Location
    Shelby Twp MI
    Posts
    820
    Quote Originally Posted by tedkidd View Post
    Good less expensive, effective approach. 1" spray to attic floor and 16" cellulose over top. Thats if no hvac in attic, and you don't live in stormy areas. Otherwise option a- directly to roof deck.

    Btw. Condensation does not occur within a solid, it occurs when surface temperature is below dew point. Spray foam is a solid.

    That's why beer cozy's prevent wet rings on the counter, dew point temperature is within the foam.
    Spray foam holds water. Look at long term effects and how it rots wood. It gets saturated, just how it is. You see it in homes, barns and marine applications where everyone claims it's a great barrier, it wicks moisture, blah, blah, blah. It's not given the climate it's used in. For the record (if we're using a beer for comparison) there is moisture involved and is formed. Where does it form? Between the foam and the source. What would be in between the foam and the source in the home? The roof deck. Without air flow in between the two, there is no way to remove that condensation. The wood rots. Just the way it is and I've seen it happen on more than one occasion.
    Jim

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