Bert Hyman wrote:

We're re-roofing this spring and I'd like to replace the roof vents
at the same time. We currently have turbine-style vents which were
installed decades ago when the attic was insulated and vented.

The turbines have moving parts and I'm certain that they'll start to
fail soon, probably at the worst time. Last winter during a nasty
cold spell following a heavy snow, one did start screaming as it
turned, but quieted down as soon as the sun came out the next day.
We probably won't be so lucky next time.

On the other hand, the turbines are tall and stick out above the
snow on the roof. We often have a foot of snow on the roof for
months at a time.

Other than trying to avoid turbines, does the style matter, so
long as they're big enough and there's enough of them?

Bert Hyman St. Paul, MN

What kills your shingles is heat.

Heat happens in the summer - not winter.

The worst heat happens when there is no wind. If there is no wind, your
wind-powered vents will not turn, and the temperature in your attic will
rise - probably to 140f or more.

Do yourself a favor and scrap the wind-powered turbines and replace them
with electric fans controlled by a thermostat. You can have a powered
vent as well as a few passive vents. All these vents are low profile
and it's not uncommon for them to end up covered in snow by mid winter.
There's no real harm in that.

You should also have styrofoam baffles or shields placed under the roof
decking where the decking passes over your header plate and out over the
soffit. Most people jam insulation in that area leaving no air gap
where air can pass freely along the underside of the roof deck into the
soffit. Your shingles will deteriorate the most in that area, and you
will form an ice-dam in the winter because of heat conduction through
the insulation into the roof deck.

http://products.construction.com/swt...55/E715704.jpg

http://www.houserepairtalk.com/f106/...od-attic-9704/

You should also have a completely ventilated soffit along the entire
length of the soffit. If you have soffit clad with aluminum trim, the
soffit face should be the ventilated type (with small holes in it) and
it should be this way for the entire length of the soffit - not just
every 5 or 10 feet. If your soffit was originally wood then you will
have 1/4" plywood as the soffit underside and you will need to cut holes
in it between each rafter to allow for complete ventilation. A 6" hole
is all you need.

Depending on the past history of water penetration through your existing
shingles, age and weather conditions, it's not uncommon to have to
replace some (or many, or most) of the roof decking around the perimeter
of your roof during a re-roofing job.

And by the way, if you're planning to just lay a new set of shingles
over top your existing shingles, then you're a bone-head.