Too much insulation in attic?

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Old 12-03-13, 07:43 PM
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Too much insulation in attic?

How much blown in insulation in attic is too much? Or is there such a thing?

What problems, if any, can result from having too much?
 
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Old 12-03-13, 07:52 PM
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short answer --- No & none
 
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Old 12-04-13, 04:52 AM
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Expounding on the excellent short answer, just don't let any of it occlude any soffit venting. For insulation to work in conjunction with your house, you must have continuous air flow from the soffit vents to the ridge vents. The air in the attic should be as close to outside air as possible to prevent ice dams and moisture damage. Too much heat in the attic is not a good thing.
 
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Old 12-04-13, 06:34 PM
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Yes, you could overload the drywall for ceiling sag or worse; maximum weight with 1/2" drywall at 16"oc is 2.2# Max. with 5/8" at 24"oc is 2.2#. Cellulose at R-65 is over that; Step One - Calculate Your Need | GreenFiber.com

"air sealing is more important than the ventilation."; BSI-035: We Need To Do It Different This Time — Building Science Information

http://www.google.com/url?sa=t&sourc...wWATQw&cad=rja

"For insulation to work in conjunction with your house, you must have continuous air flow from the soffit vents to the ridge vents. " Chandler, do you mean ventilation?

Gary
 
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Old 12-04-13, 08:21 PM
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Different strokes, I guess. I consider the insulation as an integral part of the two envelopes....attic and living space. Ventilation is of utmost importance for the insulation to work properly and maintain a dry attic with air movement from the soffits to the ridge vent. Clearer?
 
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Old 12-05-13, 08:07 PM
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Yes, clearer, but I don't agree. Fiberglass insulation in an attic does not require ventilation to insulate properly. It works best by trapping air- the R-value rating it got was tested in a six-sided box- absolutely no air admitted to degrade the rating; https://docs.google.com/viewer?a=v&q...M8l_EeA2F-qvvA

The ceiling drywall is your air barrier- as per code to be in direct contact with the thermal barrier (insulation) but you still will never reach the rated R-value unless you cover the attic side with house wrap to stop wind-washing from the attic ventilation;
"Two general exceptions to the requirement for a six-sided air barrier with insulation are at band joist insulation and at the top of ceiling insulation. Although a significant performance advantage is realized where a six-sided assembly is provided (e.g. SIPs), band joist insulation is only required to be in contact with theexterior framing and any exposed edges, and ceiling insulation is only required to be in contact with the air-barrier below (e.g. the ceiling sheetrock) and at any exposed edges. This is due to current cost effectiveness concerns with traditional construction practices." From pp. 12; http://www.energystar.gov/ia/partner...ide_062507.pdf

Left uncovered, the R-value falls -- especially with the convective loops a gabled attic produces- in the top few inches of insulation;http://digitalcommons.unl.edu/cgi/vi...ventilation%22

That is the main reason to use baffles- direct the air up the sheathing to remove moisture there- not on the insulation (unless you forgot to air seal attic first). Ventilation is important to the attic but not to the insulation. Insulation will work just fine without ventilation in an open attic, IMO.

Gary
 
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Old 12-05-13, 08:23 PM
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Too much insulation

Thank you all for your feedback!
 
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Old 12-10-13, 03:09 PM
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But in all seriousness...good information.
 
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