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  1. #1
    Join Date
    Jul 2009

    Question Austin house had insulation in the rafters

    We live in Dallas, and the summers are hot. When the temperature is 102 outside, the attic is above 116 degrees. We want to put in a radiant barrier. Why did the Austin house have insulation in the rafters, did it have a radiant barrier between the insulation and roof? Regarding radiant barrier's a friend told me that I could not spray it in the the summer because it is too hot. I plan to do it at night when it is cooler. Is it true that I cannot spray it in in the summer, is there a heat maximum to consider? How much better is the aluminum foil radiant barrier? These questions all pertain to a house that is already built.

  2. #2
    Join Date
    Aug 2007

    Default Re: Austin house had insulation in the rafters

    The best radiant barrier is one that is already applied onto the bottom of the roof decking. It will not get dusty in that position. The next best is the high quality reinforced radiant barrier in rolls that can be stapled to the bottom of the rafters or trusses under the decking. The air space is the most important component in a radiant barrier. Aluminum will not easily transmit energy in radiant form but it will readily conduct heat in contact. Allow a slot at the bottom and top of the foil covered roof sections to allow the heated air to escape out of a ridge vent if possible.
    There are websites that show the effectiveness of various paintable radiant coatings. Some are very good. Some are worthless.
    The Austin project had most of the second floor roof as the vaulted ceiling also. There was no vented attic. The easiest manner to accomplish this is to use foam insulation under the decking to fill the cavity and prevent possible condensation where enclosed. Also the ductwork is in the insulated space of the leftover small attic and uses a furnace that draws in outside combustion air. We had over 8 inches of foam the attic and a "galvalume" (zinc and aluminum) metal roof that also has a radiant barrier effect as it was installed with a slight curve built in to raise the middle portion of each panel off the roof deck.
    The only reason I see to not work in a Texas attic in the Summer is that it is blazing hot. Drink lots of liquids.

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