Attic ventilation

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10,008
Location
Upstate NY
Question for all you more experienced homeowners: Do I need to vent every rafter bay in the attic? My house has a ridge vent and soffit vents. I peeked into the attic, and noted that about 10 of the rafter bays did not have any sort of ventilation. The insulation was in direct contact with the roof decking. The others have cardboard rafter vents. I'm thinking that those bays without rafter vents need to be vented, but just wanted more opinions before wrapping myself in Tyvek to play in the insulation.
 
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2,217
Location
socal
You want to check to see what the most updated bldg code says as you want to be in compliance. If it was me, I would vent it. U want enough air flow to get all the moisture, heat, etc out of the attic. I wish I could add another vent or 2 on my house to help the attic breath a little better.
 
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2,055
Location
North Carolina
For you the heat of the summer would not be as much of an issue like it is down here to have every rafter open to vent. I personally would make sure they are all vented. It helps with the entire attic to stay cool in the summer and keep moisture down all year long. Depending on how hard it is to get to those that need to be vented, to me it is worth it. I got rid of my power vents and just went with my ridge vent and made sure my soffet was open the entire length of the house all the way around. From what I read, that is the most efficient way to vent your attic.
 
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689
Location
us
The idea is that the insulation is responsible for keeping the heat in, not the roof. Imagine if you had a camping trailer, you could park it under a park shelter. The trailer would be the insulating shell and the park shelter would protect it from rain and sun. Ideally any moisture could easily blow away. But attics are often far from ideal. My house had the attic completely sealed up when I bought it. I corrected that, but it had been like that for probably 50 years. I'm not sure how much effort it will require to fix yours or whether it is going to worth the trouble. I guess this would be the time of year to do a job like that, though. Does it need any kind of upgrade or work up there that you could do at the same time and maybe make it a little more worthwhile?
 

JC1

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6,109
Location
Oshawa, Ontario Canada
Originally Posted By: sciphi
Question for all you more experienced homeowners: Do I need to vent every rafter bay in the attic? My house has a ridge vent and soffit vents. I peeked into the attic, and noted that about 10 of the rafter bays did not have any sort of ventilation. The insulation was in direct contact with the roof decking. The others have cardboard rafter vents. I'm thinking that those bays without rafter vents need to be vented, but just wanted more opinions before wrapping myself in Tyvek to play in the insulation.
You don't need to ventilate every bay, but I did when I added extra insulation. It's cheap and easy to do if you are doing it yourself and you can access every bay easily. After you vent every bay you'll see how much cooler it is in the attic since you'll have better air flow. Regards, JC.
 
Messages
6,174
Location
Illinois
You want to keep the underside of the roof as close to the outside temperature as you can get. In the winter this helps stop the ice dam formation, in the summer this helps keep the heat from radiating down in to the house. As long as there are no closed off areas in the attic then you don;e need a vent between every rafter.
 

JTK

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13,518
Location
Buffalo, NY
Sci- I know for my odd-ball 2900sq/ft 2-story built in 1973, one of the previous owners styrofoam baffled between every truss rafter and added a ridiculous amount of blown in. I can see light through every 'egg-carton'. Problem with all that blown-in is, I can't find my two upstairs bathroom fans or ducting. Ugh.. I have perforated aluminum on the underside of the exterior soffit and a full ridge vent up top.
 
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Messages
9,783
Location
Saskatoon canada
Attic venting is the most important part of a built home. Improper venting leads to a host of problems. If you've got a ridge vent and every second rafter space has an egg carton your fine,though I prefer no hinderance at all. I'm a journeyman carpenter,self employed with over 20 years building custom homes. It's not a bad idea to go up there and see if you can feel air moving. Because you have a ridge vent the hot air rises up out that vent which then sucks outside air from the soffit. A little wind increases this air movement. So climb up there and see if you can feel air movement. If you can feel it your good.
 

sciphi

Thread starter
Messages
10,008
Location
Upstate NY
I missed an important detail earlier today. The part that isn't vented is under a decorative dormer. How they constructed it was to deck the entire roof, and then build the dormer on top of the decking. The dormer is vented and non-insulated. So the area I was worried about doesn't need venting. D'oh! The attic was quite chilly, and I could feel a little bit of air movement during the windy day we had today. Likely updating the cardboard baffles to non-degradable ones and cleaning any drifted insulation out of the soffits would be beneficial. And re-fluffing the insulation with a carpet rake, since it doesn't look all that evenly distributed.
 
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