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novice adding insulation to attic...venting question


wags1970's Avatar
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09-28-08, 09:42 AM   #1  
novice adding insulation to attic...venting question

I've got an attic in my house in which I am going to add some blown in insulation. Currently there is only 6" of the original rolled insulation that was put in when the house was built in the mid 70's. I'm going to be using the blown in cellulose insulation and I'm going to do it myself.

My question is regarding venting. Where do I install these "venting baffles" I keep hearing about? The eaves of the house are where the current insulation stops, leaving a gap of about 16". This covers the entire length of the house on the front and back. There is also an insulation vent on each side of the house up near the pitch of the roof. I'm assuming it is in the eaves where I am not supposed to blow in the new insulation, but I'm unsure how a baffle works. I've never seen one, but read they are easy to install. But wouldn't I have to install a baffle the entire length of my house, both front and back if I wanted to keep the new blown in insulation from blocking the venting? That sounds like a huge undertaking? I know I am novice, obviously, and should hire a pro, but I can't afford it, so I'm doing it myself, just don't want to mess it up. Can someone explain to me what I need to do as far as the eaves go?

 
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09-28-08, 06:17 PM   #2  
The baffles are to stop the cellulose from blocking the soffit vents. Do you have soffit vents in the eves of your house? If you dont have any then you dont need the baffles. If they are present, the baffles only need to be installed so they reach about a foot or so above whatever depth of cellulose you will blow in there not all the way to the peak. Usually this means installing just one baffle, no more than 2 per rafter bay in the eves.

 
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09-29-08, 08:16 AM   #3  
not 100% sure what sofit vents are, but under my eaves the whole length of the house on the front and back is a beadboard looking material with little holes all through it. So I'm assuming this is what you mean, please confirm. And thanks for your reply.

 
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09-29-08, 08:30 AM   #4  
yes, thats what soffit vents are...


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10-01-08, 12:55 PM   #5  
in order to establish the thermal boundary, you must fill in the eaves with the blown in cellulose. If not , then you are wasting your time by adding more to the rolled fiberglass that is existing. Venting in an attic becomes obsolete, once you have established a thermal boundary between your conditioned space and the unconditioned attic space. If I should explain further, let me know.

 
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10-02-08, 06:46 AM   #6  
If you would not mind explaining that further, I'd appreciate it. I don't quite understand and I want to make sure I do this right. If I'm understanding correctly, if I go to the trouble of installing vent baffles, then I must make sure I blow the loose fill insulation into the eaves, while making sure none goes down into the vents?

If I'm careful where I blow the insulation, do I even need to worry about vent baffles? I've never used this insulation blower so I don't know if it would be easy to avoid blowing into the eaves, if you can recommend one method over the other that would be great. I was going to go to the hardware store tomorrow, so I'd like to find out whether or not I need them or not.

Also, do I need to create a barrier around my lighting fixtures? I've seen warnings to do this if using recessed lighting, but all my lighting is traditional lights that are not recessed. What's the best thing/material to use if I do need to isolate these from the insulation?

Appreciate the help!

 
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10-02-08, 10:29 AM   #7  
wags...I'm not sure what db is saying about "venting becomes obsolete" either. The best venting would flow from the very edge of the roof, traveling up between the rafters/trusses and out at the very peak of the roof. This helps with roof temp differences that can cause ice dams if you live in a part of the country where its an issue. Better venting can also lower the overall temps in the attic, reducing the load on A/C in the summer time. Will also improve the lifetime of shingles.

No amount of residential insulation can completely stop heat transfer, it only slows it to a more acceptable level. Just like a Thermos vacuum flask, it keeps things hot or cold much longer than something like a cheap styrofoam insulated coffee mug, but the contents still eventually come back to ambient temps.

Anyway, as to your lights, if you don't have any "can" or recessed lighting, then you don't need to worry about any isolation. As a matter of fact, if you have the access and time, you should seal any penetrations between the attic and the living space with caulk or low expansion foam. Look especially where wiring runs up through the top plates on interior walls. This can be a huge source of air leakage and thus heat loss.


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