Attic Temperature
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  1. #1
    Join Date
    Mar 2008
    Posts
    87

    Attic Temperature

    I was looking to add more insulation and had a roofing contractor up in the attic. He noticed I had inadequate ventilation and wants to add a ridge vent along the top off the roof. I measured the temp on the attic floor at 120F on a 80F day. For upstate NY is this a warm attic temperature?

    I had heard that in Manual J you can specify attic temperature. How does this affect the load during summertime?

    Thanks

    Teddy

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,271
    Some questions first:
    • Do you have ductwork in the attic?
    • Do you have heating and cooling equipment in the attic?
    • What level of insulation do you already have on the attic floor, if any?
    • Are the upstairs areas of your home difficult to keep cool in summer?
    Re: Manual J and specifying attic temperature. Not to my knowledge. Manual J accounts for degree of insulation on attic floor and roof shingle color. Manual J uses heat transfer multiples (HTM) to determine a weighted average expected heat gain or loss across a component of your home's "thermal boundary" (aka "envelope"), which is the shell of your home that acts as a barrier between you and exterior weather conditions.

    Ridge venting must have companion venting at the soffit level to be effective. Soffit venting must not be blocked by insulation, and must have sufficient free area (meaning free access to air between the grids of any insect/critter screening) to supply make-up air exhausted by the ridge vents.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #3
    Join Date
    Aug 2008
    Posts
    416
    Ditto - "Ridge venting must have companion venting at the soffit level to be effective."

    Is is a "complete system" and it is critical that you have both or you're wasting your money. Air comes in at the soffit and rises to the ridge vent.

    The "free" area at the soffit must be greater than or equal to the "free" area at the ridge. In others words, don't add a continuous ridge vent and then cut a few 1" holes with plugs in your soffit. It won't help.

  4. #4
    Join Date
    Apr 2002
    Posts
    11,808
    do you get a lot of icycles in the winter?
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  5. #5
    Join Date
    Mar 2008
    Posts
    87
    Thanks Shophound

    Do you have ductwork in the attic?
    No I do not.

    Do you have heating and cooling equipment in the attic?
    Nope. Its all in my basement.

    What level of insulation do you already have on the attic floor, if any?
    I have been told around R38 (12" Fiberglass Batts)

    Are the upstairs areas of your home difficult to keep cool in summer?
    Its just a 1 storey ranch.

    I do have quite a bit of sofit venting and it does not seem to be blocked.

    Thanks Carnak

    do you get a lot of icycles in the winter?
    Some but not any large ones that I can remember.

    Thanks

    Teddy

  6. #6
    Join Date
    Apr 2002
    Posts
    11,808
    The purpose of attic ventilation is to stop a problem with ice dams on your roof in the winter. Heat from the attic melts snow on the roof it starts running down hill. As it gets to the where the eaves overhang, there is no more heat coming up from the house and it starts to freeze. It can get bad enough to create standing water on your roof.

    So you ventilate to keep the attic space cold in the winter to stop melting snow.

    If you are going with a ridge vent, then you need sufficent soffit vents as others have mentioned.

    Sounds like you need a little more air in the winter time moving through your attic
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

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