A Note about Attic Ventilation
At first it may seem odd to add insulation for warmth and then purposely allow cold air to enter the attic through vents, but this combination is key to a durable and energy-efficient home. Here's why: In the winter, proper ventilation helps maintain a cold attic which reduces the potential for ice damming (snow that melts off a roof from an attic that is too warm and then re-freezes at the gutters causing an ice dam that can damage the roof). Proper insulation and air sealing also keeps attics cold in winter by blocking the entry of warm, moist air from below.
In the summer months, well-vented attics help move super-heated air out of the attic, protecting roof shingles. Well-insulated attics keep the heat in the attic and cooler air in your living space. The most common mistake homeowners make when installing insulation is to block the flow of air at the eaves. NEVER COVER ATTIC SOFFIT VENTS WITH INSULATION.
A Note about Attic Fans
Attic fans are inteneded to cool hot attics by drawing in cooler outside air from attic vents (soffit and gable) and pushing hot air out through the fan. However, if your attic is poorly ventilated and not well-sealed, attic fans can draw conditioned air up from below, making your air conditioner work harder and increasing your energy bill. You don't want your unfinished attic cooled by your air conditioner. To prevent this effect, follow the air sealing and insualation strategies and make sure the attic is well-ventilated using passive vents and natural air flow.
Clean the gutters! Seriously, it might be a bigger problem than you think.