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WishIKnew 02-19-2009 08:26 AM

Yet Another Attic Insulation Advice
 
Could use a little help as I am about to blow in some more insulation into my home. My question concerns baffles and blowing the insulation as close to soffit area - where the roof meets the attic floor.

Right now when I am up there I can see daylight from my attic to the outside. I know proper ventalation is needed, but that much is silly.

There are not many of those styrofoam baffle things between the rafters, so I was going to put more of those up. Then I wanted to get the blown insulation and get it up as close to possible to those baffles.

Is that the right approach or dead wrong? I dont want to cause some sort of time vortex vacuum thing that causes moisture or heat issues. Just want to do it the right way, and from what i see up there now it was done half assed and wrong.

woodchuck 02-19-2009 11:27 AM

What you insulate is the heated space underneath. If there is no heated space under it then it doesn't need to be insulated except maybe a carport or garage to make it a little cooler in the summer.

AU_Prospector 02-19-2009 02:24 PM

From my experience, and I am not a PRO by any means... There is never TOO much ventilation in the attic. I dont think you want to interrupt in any way the air flow from the soffit vents through the attic and out your vent system at the crest whether it be ridge vent, attic fan, whirly bird, or side levours cut into the attic walls. If your soffits are wood, then you probably have vent grates in them every few feet. If you have vinyl or aluminum siding then the soffits might be perforated the whole way. If you block the soffits or even constrict the space from the soffit to your roof rafters, I believe you will be putting limits on the natural flow of cooling air up through the soffit vent to your ridge vents which traps heat. In the summer that may limit your insulation benefits.

Personally I have vinyl siding and a very high roof line with a cavernous attic. I can stand in the middle of the attic with the lights off and see a bright glow coming from the soffit area all around. I also can see light at the crest of my roof via the ridge vents. Also light comes in through my two attic roof fans. These areas do not leak in any way and the temp in my attic was only 108 F at eye level on a 98 F August day last summer with my roof in full sun.

jdougn 02-20-2009 07:43 AM

A pro would use the baffles at every rafter space then insulate fully to the baffle. As said above, do not decrease ventilation into your attic space. In fact, make sure you have soffit vents at regular intervals of not less than 4'. Then make sure there are vents up high towards the ridge, or at the ridge, at very regular intervals. The ventilation helps move excessive heat out in the summer that can overheat the house and causes shingles to wear out more quickly. In the winter ventilation removes damaging moisture that will cause your rafters and roof sheathing to rot.

Proper thickness of insulation is important. You should have at least 12-16" of insulation in your attic depending upon the insulation type. At 12-16" of properly installed insulation there is almost no heat transfer so adding more insulation is a waste.

hth, Doug

WishIKnew 02-20-2009 08:28 AM

Thanks jdougn. That is what I wanted to know. I am no where close to 12 - 16", so I need some.


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