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  1. #1
    Join Date
    Jul 2003
    Location
    Rochester NY
    Posts
    160

    Spray foamed attic and duct work question.

    1800's old House total remodel. Third floor attic is all new spray foamed roof, soffit , walls. NO ROOF VENTS at all now.
    Large staircase leading to this attic space. There will be a horizontal 95% gas furnace and ac system up there.
    Does duct need to be insulated ? The ceilings below will not be insulated just drywall.
    The staircase door leading to this area will be undercut. Builder wants a return in attic duct to draw air from under cut door up into attic for air change.

  2. #2
    Join Date
    Apr 2004
    Location
    MN
    Posts
    1,838
    I can't answer with 100% certainty, but I would think that if you had a supply on one end and return on the other end the space would be conditioned enough to prevent sweating during cooling season. Technically, the attic is now inside the building envelope. It shouldn't be a whole lot different than a unit in a basement.
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  3. #3
    Join Date
    Aug 2008
    Location
    Charlotte, NC
    Posts
    216
    Usually, at least an R-4 is required in an encapsulated attic.
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  4. #4
    Join Date
    Apr 2006
    Location
    Houston, Texas
    Posts
    40
    you will need to verify with residential & energy codes for your climate region. Most are minimum of R6 within the building envelope. I am in the southern region, R4 maybe suitable for up north

    To get air changes a small tap for both supply and return will work. Make sure that there is a balancing damper on the supply collar if you are not using a grill with adjustable louvers. That is code. On the return I use a small 4"x4" or 6"x6" louver with screen.

  5. #5
    Join Date
    Feb 2011
    Location
    Georgia
    Posts
    280
    Minimum r-6 is code on any duct other that vented attic r-8

  6. #6
    Join Date
    Jan 2011
    Location
    Highland Park, CA
    Posts
    89
    Duct work should still be insulated. As doc havoc said it's now in the envelope. Is the combustion air piped from outside? Does undercutting the door give you enough free space for air changes?

  7. #7
    Join Date
    Jul 2003
    Location
    Rochester NY
    Posts
    160
    yes two pipe vented. Combustion from outside. Well the undercut door will be around 3 inches. One supply and one return in attic would be a better air change.

  8. #8
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Closed cell or open? drywall under foam? If open and no vapor barrier, it could end up being very humid in the
    attic. Even with r20, itf can still be almost 90f up there in mid summer on a sunny day. I know from experience. I added a small register in the attic to dehumidify it a little.

    Be sure to have line the supply plenum to reduce condensation.



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  9. #9
    Join Date
    Jan 2013
    Location
    Dyersburg, TN
    Posts
    230
    Just finished a job like this spray foam on attic on rafters. 1 in of foam is R-8 no insulation in ceiling the Sheetrock will have enough infiltation to keep the attic within a four to five degree difference from the downstairs. The walls are foam and blown in we had to add a outside air damper that takes air samples every 2 hours. Equipment is 90 % dual fuel and the duct is insulated it is working better than great. Anxious to see about this summer with our high humidy here in west tn

  10. #10
    Join Date
    Jul 2012
    Location
    CT
    Posts
    232
    We do alot of jobs like this and most of the areas dont bust on us for using unwrapped duct. There is a town that requires the duct to be wrapped no mater where your putting it but thats about it.

  11. #11
    Join Date
    Feb 2013
    Location
    north georiga
    Posts
    652
    here in north carolina it's not required (yet) to insulate duct installed in that manner but we do because to offen it does sweat if the system is running for a period of time longer than a "normal" cycle

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