Home Guy wrote:
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.
I'll disagree to the extent of scrapping the turbines. You are correct that
they don't work as efficiently when there's no wind - although some heat
escapes through those 18" holes - but when there IS a wind, they will move
an enormous amount of hot air. Plus, they do it at no electrical cost!
As for cosmetics, they can sometimes be installed below the ridge line so
they're not easily visible from the street.
And speaking of ridges, be sure to install a ridge vent. These are dirt
cheap and will probably give you the biggest bang for the buck.
Note: None of these suggestions are meant to be exclusionary. Do 'em ALL.
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.
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.
Again, I'll slightly disagree. You're correct that one can't have too much
soffit venting.
The usual standard is one sq ft of soffit venting for every 150 sq ft of
living space. If you've got a venting area 4' long and 6" wide on the
soffit, that's 2 sq ft. BUT, you've got to subtract the screening area. If
hardware cloth type screening, subtract maybe 10% of effective venting. If
it's that HardiPlank stuff with itty-bitty holes, subtract 98%.