Attic roof vent and ventilation

I was thinking of installing some sort of roof vent directly over my unfinished attic to vent out some of the heat and moisture in summer. I live in NY. My house was originally a ranch and then the original owner had a second story put on the house (40 years ago). From what I can tell by living here for the past 15 years the upstairs level was not constructed very well with regards to energy efficiency and/or insulation. There does not seem to be any soffit vents, other than the few small ones I added myself in the past few years. The attic, which I can walk into as the previous owner put plywood down, has a small double-hung window at one end which I always leave open for ventilation. Above this window is the small typical louvered aluminum vent.
Two years ago I had a new roof (asphalt shingles) put on. There was a fair amount of water damage to the underlying exterior plywood which the roofers replaced as they went along. I have no doubt that part of the damage was caused by poor/no ventilation.
I should also note that the previous owner, for some reason although the attic is not finished, placed foil-faced insulation under all the roofing in the attic. Not sure why he did this and I also think that this is not a good idea in winter as it probably traps moisture right at the roof wood. I have seen some frosty areas on the attic roof wood on occasion.
In summer the upstairs living areas get really hot. I do have central a/c up there but it cannot keep pace with the afternoon heat of the sun and does not cool the upstairs until after the sun goes down. This leads me to believe that there is little, if any, remaining insulation under the roof but above the living areas.
I was originally thinking of installing a powered roof vent but I hear that sometimes the pressure from the vented air can suck air conditioned air from surrounding rooms and out the roof. So now I'm not sure about doing this. Perhaps installing some non-powered roof vents or a turbine would help but without soffit vents to allow air in under the eaves it would probably not help much.
I want to get a qualified energy audit person/company in to my house for additional ideas. Any thoughts on all this?
Thanks, Walter
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Walter Cohen wrote:

I'd get a lot more soffitting venting in place, preferably a continuous one. Then, I'd probably go with a ridge vent, which doesn't require any power and provides uniform air flow, as opposed to a point which is what you get with a gable, turbine, power fan, etc.
As to the foil faced insulation on the rafters, is it actual insulation or a radiant barrier, which is just an aluminum shield? If it has insulation, how much air space is open between the insulation and the roof? Is there a clear channel from soffit to peak and a way for the air to get in and out?
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Actually, when I had new roofing shingles put on I paid for and had them add a ridge vent the length of the roof. I have no idea if they put it on/in correctly as I understand they would need to cut out a portion of the very top wood along the ridge line for the length of the roof. Is there any way to tell from inside/outside? Still, even with a ridge vent there is no (or very few) soffit vents.
Who would put these soffit vents in - roofer or general contractor?
Thanks, Walter

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Walter Cohen wrote:

A general contractor should be fine. Or a roofer. You can even do it yourself, depending on how high they are and how easy to get to. Basicly you need to run a saw down the length of the house twice, set to a depth to just cut off the soffit material creating a channel the vent goes in.
You can see if you have a ridge vent by going in the attic. At the peak, there should be a piece of sheathing gone, about 2" on each side. And it should be covered by the ridge vent, the underside of which will be visible.
There are a wide range of ridge vents and I think considerable diff in how much air flow they allow, as some are more like foam filter material, others are more open.

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Walter Cohen wrote:

I agree with what trader wrote and was asking about.
You need to get air flow. Having just a outlet does not help, you need to have inlets as well. Usually the best inlets are low at the soffits. The exhaust vents should be high at the ridge. The difference in air temperature will move the air and the hotter it is the more air it will move.
I would avoid any kind of powered vents due to noise, maintenance and cost.
--
Joseph Meehan

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Along with what Joseph and Trader said, I would check/ improve insulation between living area and attic. If I'm understanding correctly, attic is above 2nd floor living area, not unfinished portion of same. Since you mention decking is in place, you would either have to pull it up or have insulation, such as cellulose, blown in.
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