Ridge Vents Versus Mushroom Vents

I have scanned messages in this forum and have found differences of opinion about ridge vents.

I am having a new roof put on an older home in Northern Illinois. Both layers of the existing roof will be removed and some plywood will have to be replaced. Several roofers say they will install ridge vents; one experienced roofer says that ridge vents have problems and he will put in 4 – 6 mushroom vents. He also recommend installing a power roof vent since we have a whole house fan that is ineffective because, I believe, the attic ventilation is inadequate. There are no gable vents; we do not have cathedral ceilings.

Additionally new siding and soffits will be installed as part of our remodeling.

Any suggestions as to whether I should have a ridge vent installed?

Thank you for your response.

 

I would opt to have new soffitt vents installed along with new gable end vents. It should be pretty inexpensive and easy if done during the siding work. There are lots of options for attractive gable end vents to match your siding. Properly sized gable, soffitt and ridge ventilation should take care of your attic vent problems without adding one of those ugly mushrooms.

 

Ill go the other way. Some codes now outlaw ridge vents. The wind can blow heavy rain back up in to them as it runs along the whole ridge. Then the ones that come with a filter like it gets dirt in it and air cant get out. If you have the gables put vents in them for sure. Can also put a attic vent fan in. And still put button vents near the ridge
You need 1sq ft vent for every 150 sq ft of attic.
Thats 1/2 in and 1/2 out. For a attic vent fan sq ft of attic X 0.7=== the CFM of the fan.

ED

 

I was looking at adding another electric roof vent.

the guy at the home center said the mushroom vents were better and I should just add one of those.

Is there an appreciable difference between the two options?

 

Is there any rule of thumb about how far apart the mushroom vents shou be placed and how far from the peak?

 

Regarding venting, a lot depends on your location: are you in the snow-belt or sunbelt, and what is the direction of prevailing winds.
In the snow-belt, mushroom vents are often covered up by snow accumulation, so there is a move to larger vents that stay clear even with heavy snow. Also, in the snow-belt, using power fans is usually NOT a good idea, as there is a danger of sucking warm moist air from the house into the cold attic where it can cause condensation. In the sun-belt, that's not an issue, so power fans are generally good for evacuating excess heat.
The weakness of many (not all) ridge-vent designs is that snow and water CAN be blown in. They are usually used for esthetic reasons, but the installer must be aware of contra-indications. If a roofer cannot tell you how they prevent entry of water into ridge vents (other than telling you 'trust me'), then they shouldn't be doing the roof.
The goal of all venting to get a steady, laminar flow of air from the base of the roof (the soffits) to the ridge of the roof. The vents along the ridge should be placed to give the most effective distribution of air flow. Assuming there are no obstructed locations, this can be achieved by separating them about equal distances from each other. In terms of location relative to the ridge, as high as possible is the usual rule.

 

your local building code will specify the amount of vents rewuired