Well, here's a link with a good explanation of how ventilation plays a part... But a previous answer recommending proper insulation and possibly a radiant barrier is key. But if you already have these, better ventilation will help. My neighbor's thermostat controlled fan would run all day before he added eyebrow vents and soffit vents; now it comes on only in the late afternoon. Also, if you re-roof, a light colored shingle will help a lot, if you can stand the look. I just went from wood shake to a black asphalt and my attic is now almost degrees hotter. Here is a link that might be useful: Summer Heat Build-up

First, you need to separate "attic ventilation" from your desire to "cool the attic air", then understand the purpose of each and then understand their effect on the roofing shingles. Attic ventilation is for the purpose of allowing moisture to escape from the attic space with an area ratio of 1:300 which involves very little air movement. Studies have shown that this level of ventilation has little if any meaningful effect on the temperature of the attic air or the temperature of asphalt shingles. But it does allow excess water vapor to escape and insulation to dry out if there is a leak or if water vapor has entered from bathrooms or rain and/or snow blowing through oversized vents. Don't try to make this system do more than that. If you want to cool the air in attic space you will need to move a great deal more air but there are two problems with doing that. First, that amount of air may draw moist air into the attic. Second, the major source of heat in an attic is the radiant energy (invisible infra red light) that is emitted from the hot back side of the roof sheathing. As radiant energy travels through air it does not raise the temperature of the air but when the radiant energy strikes the attic floor, it heats the floor and the floor then heats the attic air. Exchanging this hot air with less hot outside air by fan might lower the temperature of the attic air but it will do little to cool the hot attic floor and roof sheathing. Adding a radiant barrier under the rafters or on the attic floor will help to reduce the heat reaching the interior of the house by directing it back up toward the roof sheathing but that will not help cool the roofing shingles. Roofing shingles directly exposed to the sun are already as hot as they're going to get and there is little you can do inside the house that will reduce the shingle temperature by more than a degree or two. If you want to keep the hot attic air from increasing the cost of cooling the house add more insulation and move any AC ducting out of the attic. I prefer to include the attic space in the conditioned portion of the house by insulating between the rafters and installing an air vent path between the insulation and the roof sheathing. Aluminum foil on the back of the sheathing will help to reduce the heat that reaches the attic but this design will not reduce the temperature of the shingles. More effective ways to increase the life of your asphalt shingles are to use a lighter shingle color, trees, etc. for shading, face the smaller side of the house toward the south, or move farther north.

OMG...I'd have been concerned when they landed that massive pile of debris on my porch roof! That needed to go into a large dumpster!

It sounds like there may be a few different things going on, that are likely inter-related... Here is a good initial approach solving the issue: 1. Stop the source(s) of humidity - Attic ventilation is only a back-up system to exhaust any humidity from the attic. In cold climates, the home's inside air is warm and has a higher relative humidity than the unconditioned attic air. That warm/humid air wants to go to the cool/dry spaces, like the attic. Once it hits cool surfaces in the attic is condenses, leading to mold. Here are the most common causes I see during inspections: a.) Make sure the bath fan exhausts do not terminate in the attic space, they need to exhaust outside. b.) Seal any penetrations between the attic and living space. Chimney, flue and gas vent pipes should be sealed with special materials devices, by a professional. 2. Provide a balanced amount of lower to upper ventilation. If you do not have the proper amount or ratio of soffit to ridge ventilation, this can actually make problems worse by de-pressurizing the attic; and drawing more warm/moist air from the living space. Check out AirVent Inc., they have many resources for calculating the right amount of ventilation or finding a local pro to do that for you. It's hard to tell without seeing the space, but 3x 18x60 vents may not provide even ventilation and create dead air zones in the attic. Maybe you could post some pic's of the attic and roof and I can give you some more insights. (specifically attic overalls, around the HVAC unit, at the perimeter by the heels, exterior overall and by the snow fence) .