How much can venting cool the top floors?

Question

I recently bought a house -- big, beautiful sucker built in 1900, with two full stories and a third that's essentially a very nicely finished attic.

I had a contractor give me an estimate for replacing some shingles that got blown off the roof. While he was up there, he told me that it looked like the venting was screwed-up, so in addition to the estimate for the shingle replacement, he also gave me an estimate for installing a ridge vent.

However, I just spoke with the inspector from my insurance company. Her guy was mostly there to estimate the repair work, but he knew about the ridge vent estimate, and he commented that he didn't think it was necessary; the roof wasn't boiling hot, and there are box vents in place.

Now, the topmost floor DOES get quite hot. It's our first summer in this house, but that top floor can easily get a good 20 degrees hotter than the floors underneath. And given that a lot of the work done to the house was a bit haphazard, it's plausible that the box vents are screwed-up in some way.

Nevertheless, I'm worried I'm being ripped-off.

What do people with more experience with roof vents think? Are there red flags here that I'm being taken advantage of? Or does the heat differential on the top floor suggest that perhaps some work does need to be done?

Answer 1

Ridge vent alone should cost at most a few hundred dollars on top of the roof repair. It's a matter of ripping a channel in the roof boards, laying down a mesh or molded plastic vent, and capping it with shingles.

However, if you already have other vents lower on the roof, you probably don't want to add ridge venting. Either add more box vents or close them up and do full ridge venting. By having vents at several levels you create a flow loop that mostly bypasses the outer areas of the roof. You want flow from the soffit to high on the roof in a single loop.