Old 09-04-02, 10:06 AM
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Is it possible to have too much insulation. In my attic i replaced some insulation above a newly remodeled room. R-30 between the ceiling joists with paper towards the drywall. I then had some left over unfaced pink fiberglass which I laid perpendicular to the R-30. The total height is approx 20". I live in the NYC area. I only did this in areas well away from the edge so I would have ininterrupted airflow from my soffitt vents. Is this overkill? Any downsides here? Thanks.
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Old 09-05-02, 11:51 AM
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I do not see a problem with what you did and the term over-insulating refers to blocking vents. Which you specifically avoided.

The downside to this is really not the insulation fault. Insulation prohibits heat flow through it, by either not letting the heat leave the home during the winter and prohibiting the heat to enter the home during the summer. Part of this process is the insulation retains some of the heat that tries to pass through it.

The problem arises during the summer. Any object out in the sun will get warm and much warmer than the temperature outside. The warmer an object gets, the more heat that object will radiate. This is what happens with your roof in the summer. The heat from the roof radiates into the attic and raises the temperature in the attic. This heat tries to enter the home through the insulation but the insulation prohibits it from entering the home and at the same time retains some the heat that tries to go through it. Because the insulation is retaining the heat and releases the heat slowly, it will make the attic even warmer. This is especially important in warm climate areas, where large bulk insulation is not recommended because of it. This is also why light colored shingles do more in reducing attic temperature than anything else.

You could also provide more ventilation in your attic, like vents, turbine fans and/or power fans. Any average degree drop in attic temperature is advantageous to you.
Old 09-05-02, 01:15 PM
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Thank you for your response. I see the logic in your reply. I think I will leave what I did. Since it may cover less than 10% of the total attic space. I also put some around the supports for a cathedral ceiling, since this area had R-13 at best. I know my attic compared to outside ambient in the winter is within 5-6F degrees, which I believe (from what I read) is good. In the summer my attic does get quite hot and I will be lokking into installing a thermostatically controlled attic fan when funds allow. Thank you again for your expertise and any other comments you can provide.
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