Do I really need ventilation?
With all different types of ventilation what kind should you have. Well the answer isn't always as cut and dry as you may think, what may work for your house may not work for your neighbors. Overhangs with correct intake ventilation works best with ridge vent, but you want to make sure that you have a 50/50 ratio of intake vs exhaust. If you do not have over hangs, the only way to have a ridge vent work correctly is to install a intake at the eave (by the gutter) of your house. There are a couple different types of "intake ventilation" available, vented gutter apron could be installed but could also allow ice dams to enter. Another option would be Edge Vent which could be installed either at the very edge of your roof near the eave, or at the end of the ice and water shield which is usually 3 foot from the eave. Installing the Edge Vent at the top of the ice and water shield will prevent the chance of ice dams from entering threw the vent, and is the preferred install for Pittsburgh's climate zone. Another type of ventilation is an attic fan, installed on the rear of the house 2 foot down from the ridge. This will allow the fan to pull air in from the gable vents on a gable roof , or the soffit on a hipped roof. With an attic fan you must ensure that the fan cannot pull any air from your living space into the attic, so inspecting the steps or ladder you use to enter your attic is crucial. If your allowing the heat of your house to enter the cold area of the attic in the winter time you could create an area where cold air is meeting warm air. That will obviously create condensation, and you will see frost your attic.
In the photo above you see how soffit ventilation works ridge vent. The ridge vent pulls air from the soffit panels, and is actually the same principle that allows planes to fly. Adding the baffles will allow 1 sq inch of ventilation. It will allow the bottom of the roof decking to cool. This is the best type of ventilation by todays standards and is the preferred by all shingle manufactures.
The attic fan will turn on when temperatures reach a certain temp. It is usually set between 90-100 degrees. If you have overhangs like in the photo above the cool air will be pulled from your eaves just like a ridge vent, how ever if you do not it will pull from your gable vents that are located on either side of your house at the peak. This will allow the attic fan to pull cool air in from the outside, and with the hot air risen it will constantly be blowing out the hot air. This is the system that works best on hipped roofs, and house with no over hangs. The only thing you want to make sure of is that your shingle brand allows this for their warranty CertainTeed does allow this.
So to answer the question, YES you need ventilation on a house that doesn't have spray foam insulation. Make sure your Pittsburgh roofing company is going over the best option for your house and not just what they do on everyones house.