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oktooma 10-28-2008 11:22 AM

Attic Insulation Installation
 
Hello All.....I've been doing all kinds of research on proper attic insulation installation and can't find my last answer. We live in northwest Ohio and have a two story house that I decided to add R-30 insulation to the existing R-19 in the attic. We don't have soffit vents but do have sufficient venting with gable vents, powered attic fan and an additional wall vent on the north side of the house for the 900 sq. foot attic area.

Here's my question.....down near where the roof attaches to the wall, should I insulate all the way out to the fascia? One factor is the R-30 (9.5" thick) will be laid perpindicular to the ceiling joists and the area near the roof/wall joint is pretty narrow. My concern is: can the insulation touch the roof or should it be trimmed down so it doesn't touch the roof or just leave that area as is (keeping the new insulation approximately 12" from the fascia)? There is R-19 in that area already but I want to be sure I'm doing the proper insulation job and get the most out of the additional insulation.

Your thoughts will be appreciated.

Marvin Gardens 10-28-2008 12:49 PM

Here is the issue with insulation.

There is such a thing as over insulating. There are also areas that shouldn't be insulated.

Every area is different and most depends on humidity and weather.

For high humidity areas there needs to be air movement to keep the humidity from precipitating out and causing rot in the wood. It can also get in the insulation which will compress and cut the R factor considerably.

Most precipitation happens in temperature differentials. This is why car windows fog up in cold weather. Hot moist air hits cold glass the the humidity saturated air cools down and can't hold as much water and it drips down the windows.

With that being said I am a big fan of ventilation in well insulated homes. I would not insulate up against anything that has the potential of large temperature differentials. Some ventilation over these areas is important.

While we don't use them here in the northwest there are plastic panels that are designed to allow air flow and will keep the insulation away from vents. It also keeps the wind from blowing loose insulation around the attic.

I know this doesn't give you the easy answer but even with the current standards there will be defects that are found out years from now. The latest thing is that over insulating is a bad thing. Building need to breath and vent out moisture.

Maintenance 6 10-28-2008 01:46 PM

In a nut shell: No you should not insulate against the fascia. You should leave a 1-1/2" gap for air flow between the bottom of the roof deck and the top of the insulation. Duro-vent panels installed between the rafters will insure air flow. Even though you don't have soffit vents, there is still some air migration along the underside of the roof. There are other companies that make similar products. Duro-vent is just one I'm familiar with. You can insulate out over the top plate of the wall. Any insulation beyond that point is doing nothing anyway.

joasis 10-29-2008 03:46 AM

You should give thought to cellulose instead of fiberglass, and that said, no point in blowing it out in the soffits. You can blow cellulose on top of the existing batts, and by adding 12 inches, you will have a solid R50+. Less expense also.


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