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Old 11-07-2010, 08:47 AM  
smuttydog
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Default Venting and Insulation of a Gambrel Roof

I need to add more insulation in the attic crawl space in my attic. Presently I have about 4 inches of rolled faced pink insulation. I was going to blow in another 20 or so inches of cellulose. On the 2 gable ends of the attic I have ventilation louvers. Since this is a Gambrel I do not have soffit vents. What do i need to do to improve ventilation? Are the vents in the gables good enough?
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Old 11-07-2010, 09:16 AM  
oldognewtrick
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On the 2 gable ends of the attic I have ventilation louvers. Since this is a Gambrel I do not have soffit vents. What do i need to do to improve ventilation? Are the vents in the gables good enough?Thank you
No, gable end vents are not a good venting solution. They restrict to much air movement. Air will move upward, but will not cross-vent adequately. A better solution is to install shingle over ridge vent to allow for attic air exhaust and at the transition break on the roof install SV10 drip edge vent and be sure the area is free of insulation so as not to compromise air movement. Then take a heavy plastic or an insulation board and block off the gable vent. Introduction of different types of exhaust venting will short cycle the vent system.


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Old 11-11-2010, 08:38 PM  
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Before adding that much cellulose, check the drywall thickness and on center framing. 24"o.c. with 1/2" drywall= 1.6# total. 16"o.c. with 5/8 or 1/2"= 2.2#per sq.ft. If you blow-in at 2#per sq.ft., at 20" = 3.3#. http://gypsum.org/pdf/GA-216-2010.html
Chart #4.

Gary

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Old 11-12-2010, 06:01 PM  
smuttydog
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Thank you Gary. I think I have decided to use batts now instead of the blown in. I plan to lay them perpendicular to the ones already there. I am going to use unfaced ones. Good idea?

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Old 11-25-2010, 02:51 PM  
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F.g. would be my last choice unless the ceiling can only carry that. Check the density of fiberglass, blown-in or batt as it will get convective loops at low density. Testing at 0.5 and 0.97 density show c.l.'s. Buy a high density batt to run perpendicular as stated. Be sure all edges are touching and expect reduced R-value because it's not covered, but exposed to attic air for wind-washing. Air seal the attic first: How to Seal Attic Air Leaks | The Family Handyman

http://infrared-energy.com/files/SpecialReportAtticInsulationProblems.pdf

Energy Savers: Fiberglass Insulation Material

Gary



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