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I have an attic with a quite steep slope (maybe 8 vert by 12 hor) that has no eaves. The only vents are one gable vent at each end. I notices icicles during the winter and someone told me that asphalt shingles are cooked. This all sound like bad ventilati

LongfieldL | Posted in General Questions on

On one side of the house, I would put a fan in the gable vent blowing cold air in 1″ pipes that would outlet air at the bottom of each spaces between rafters (where soffit vent would be if there was eaves). In the gable vent of the other side of the attic, I would use a second ventilator blowing hot air out that would be collected from a perforated pipe running along the ridge beam. Both ventilators would be synchronized to run based on thermostat or humidistat. Does that sound crazy?

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  1. LongfieldL | | #1

    View schematic here.

  2. Jon_R | | #2

    Some thoughts:

    a) start monitoring attic temperature and humidity
    b) based on a), decide if you have a air/heat entering the attic from below problem or a solar heating problem. Also decide if doing nothing is OK.
    c) consider that total CFM might be much more important than where air flow is directed. Ie, might be better/easier to omit the pipes.

  3. LongfieldL | | #3

    Thank you Jon R.
    This is a good idea, I think that I will get a small Arduino data logger with few temp and humidity sensors hooked to it and monitor what is going on.
    The issue that I wanted to address with the above system is that (at least in Quebec building code), it is recommended to have 50% of vents area in the lower parts of the attic and 50% in the upper part with a bias favoring lower parts if 50/50 is not possible. I was also hoping that this would take care of the icicle problems that can evolve in an ice dam and water leakage.

  4. Jon_R | | #4

    You could also use the Arduino to be smart about when to run the fans - only when there is a risk of ice dams or condensation. Do that and some fairly large fans wouldn't use much energy. Or use solar fans.

    If you want to duplicate the slight negative pressure effect created by more upper vents, you can slightly restrict the intake fan. Perhaps monitor this issue too (BME280 is a very good sensor).

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