Quote:
Originally Posted by rsmurano
If you are responding to my thread, no, we didn’t cool the attic. Our builder only used the spray foam that was over 10” thick on the attic roof. There are 2 kinds of this insulation: closed cell and open cell. We had friends that retrofitted their attics with the open cell spray foam at a cost of $8000 for a 2400 sq ft, and their attic in the middle of a GA summer was also 70 degrees. There is no magic to this. The other benefit to this in GA is your furnace lasts longer because they are located in the attic. A furnace running in a room at 70 degrees will last longer than a furnace running in an attic at 140 degrees
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My comment is based on your post:
When you walk in the attic, it looked like an igloo, but the attic was 70 degrees all year round, and that’s with 100 degree humid days or 15 degree nights. . That is impossible without using your HVAC to condition the attic temperature unless you had your house set at temperature much lower than 70F in the summer and much higher than 70F in the winter. The attic space which is between two very different temperatures zones will gradually change to a temperature somewhere between your conditioned house space and the outside air. Insulation slows down the temperature change but can not stop it. Since the outside temperatures keep changing, the attic space will continue to change but will remain between the two temperatures for typical temperature rate changes. This is fundamental Thermodynamics.
With 10 inch foam on the roof and no insulation in the ceiling of the home, heat transfer from the home will be greater than heat transfer through the roof insulation. You also stated that the attic was sealed with no ventilation so the heat transfer is basically across the insulation and ceiling. The attic temperature will tend to be closer to house temperature than the extreme outside ambient temperatures. If your 70F comment was "~70F in winter and ~79F in summer" I could see that happening. Your inside house space is cooling the attic somewhat in summer and heating the attic somewhat in winter. Again it depends on what your house temperature is.