by Aaron Simac

Why do I need proper attic ventilation?
Attics can reach a stifling 165 degrees in the Midwest summers and even higher temperatures in the south. Ventilation exhausts this hot air to the outside and serves to keep the home more comfortable. Also, ventilation helps to protect other parts of the structure such as roof framing and sheeting.
I’ve found that standard passive ventilation like ridge vents and punched aluminum soffit vents do not work well. I’ve cut into enough roofs and felt the hot air rush out.
What about insulation?
Insulation prevents the conduction of heat from warmer to cooler areas. The thicker the insulation, the longer it takes to equalize the temperature on both sides. In a 150 degree attic with a 70 degree second floor, the insulation will be somewhere between this. At night as the attic begins to cool, the insulation will hold the heat and therefore will even be hotter that the attic air.
Ductwork in attic?
If you have a 2 story house, odds are you have ductwork somewhere in your attic buried beneath the insulation.
If your air conditioning is properly tuned, there will be a 20 degree drop against the A-coil. Meaning if the air returning to the blower compartment is 72 degrees then the air above the coil should be 52. Just a side note: having a 20 degree drop doesn’t mean your system is dialed in, but not having the drop confirms it. Losing just 5 degrees of heat from the plenum (top of furnace) to the upstairs vents cuts your effective capacity 25%. The hotter the attic means the larger amount of temperature loss, leaving the insulation even hotter. A 12 degree temperature loss is not uncommon, meaning a loss of 60% of capacity.
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