Attic ventilation requirement

[lfoster]

How do you know the s/f amount for,,, say a turbine,, as opposed to a passive vent opening.?
Linda

[Joe Funderburk, CMI]

If I read the code correctly, "the total area is permitted to be reduced to 1 to 300" provided mechanical ventilation is provided. You don't measure the space provided by the mechanical ventilators--you measure the attic area and other ventilation openings and that ratio should be 1 to 300.

The best thing to do is not to do any calculations. Leave that to the contractor you refer the situation to.

[Mark A. Timpani, CMI]

O' hagen vents

[Roy D. Cooke, Sr]

Originally Posted by lfoster

How do you know the s/f amount for,,, say a turbine,, as opposed to a passive vent opening.?
Linda

We have found In Canada that turbines might not be the best way to remove air from the attic for many reason .
(I) They do leak snow under some conditions .
(2) They work no better the normally asperated vents in no breese.
(3) They some times work too well in a strong breese and pull air from the home even lifting the attic door some times .
(4) They always get noisy after a while
at 7:00 pm they sound like loud clock
At 10:00 pm they sound like a car idling ,
at 2:00 am they sound like a train sitting next door .
In many cases people remove them never to have a turbine again . That is my vote NO TURBINE.
Roy sr

[Christian F. Mettel]

Another problem that can occur with it is that a turbine vent can create a vortex in the attic space. If there is blown in or loose fill insulation, you should always check to make sure that it hasn't been blown around, or even sucked out.
Chris

[ccbrands1]

messed up
disregard

[ccbrands1]

I've always been told the general rule rule of thumb is 1/300 with a vapor barrier and 1/150 without.

[ccbrands1]

i give

disregard again

[ftingle]

Linda,
What I do (right or wrong) is look at the size of the opening in the roof sheathing from inside the attic, measure it and calculate mow many SF it is. They're usually about 1 SF.
ft

[ftingle]

Russ,
I use 1/150 when all the vents are low, that is, in the eaves, ie a hip roof. When the vents are high and low, that is, in the eaves and on the upper part of the roof and/or the gable ends, then I use 1/300, because the Gas Co considers that more effective ventilation.
(Why the Gas Co? Because I used to do attic inspections for them. New installations of insulation,and vents, in existing attics, so that low income people can save energy)
ft

[Jay Moge]

Originally Posted by mtimpani

O' hagen vents

how does this system NOT let water in?

[Russel Ray]

Yahoooooooooooooooooooo!

Here's one of them newfangled vents. They come in threes, meaning that three of our inspections yesterday had them.

P.S. I did not walk on the roof to get this picture.

[lewens]

Turbine vents are a waste of money. I have seen blown in insulation being sucked out by a turbine vent and being deposited in the neighbours yard, and as Roy said, they do get noisy when the bearings break down.
No attic ventilation means you are cooking asphalt shingles from both side, top and bottom. It is bad enough to have hot sun beating down on shinfles without having them cook from the underside by excessive temps in the attic.
Around here metal roofing installed over asphalt is a no no. There have been fires due to the heat build up between the asphalt and the metal. We used to be able to install metal over asphalt with the installation of strapping between layers but that too has been stopped.
Larry