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Old 04-24-2014, 06:12 AM   #1
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3/12 attic insulation


Small 70x12, 3/12 pitch roof, summer home in ocean city, md.
6" soffit vent. And gable vents and 2 roof vents.

What batts insulation do you recommend?

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Old 04-24-2014, 07:06 AM   #2
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3/12 attic insulation


Do you have vent chute or baffles as the eaves?

Easier to loose fill blow it in there at that cramped quarters than it is to batt it in.

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Old 04-24-2014, 11:26 AM   #3
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3/12 attic insulation


I haven't done the soffit yet plan was to vent the entire soffit and put the baffle shoots.
I know blown insulation is possible but batts is easier for me at this time. Just wondering what batts I should use, r-38 faced down.
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Old 04-24-2014, 01:59 PM   #4
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3/12 attic insulation


Air Seal the attic floor at all the top plates and penetrations.

At that point, facing on the FG (as long as you have drywall that is air tight and has at least 2 layers of paint) is not required.

If you do put it in there with facing, facing goes towards the drywall.
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Old 04-24-2014, 02:59 PM   #5
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3/12 attic insulation


Thanks, I know not required just asking what you would do. I want to make it warm/cool according to season but not sure what r value I should use?
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Old 04-24-2014, 05:33 PM   #6
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3/12 attic insulation


Energy code requires R-38, minimum; http://energycode.pnl.gov/EnergyCode...state=Maryland

You are under IRC; http://www.reedconstructiondata.com/...odes/maryland/

Facing is required as an alternative to ventilation locations;http://publicecodes.cyberregs.com/ic...9_8_par091.htm

--unless special vapor barrier paint is used--, two or three coats of regular paint won't meet minimum code to reduce your attic ventilation requirements. Sorry, WoW, wrong class; http://publicecodes.cyberregs.com/ic...9_6_par006.htm

Using R-38 faced or unfaced, I would still add a housewrap over the insulation after air-sealing the attic, to prevent wind-washing in that low density batt insulation; Post #10; Which width for insulation rolls

IMO, use some rigid foam board at the exterior perimeter, in fact- forget the baffles altogether, make them using FB also; pp.5, "Site-built baffles"; http://www.buildingscience.com/docum...n-roof-venting

FB on wall plates, with safety note on using it for fire-prevention;http://bct.eco.umass.edu/publication...o-save-energy/

Gary
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Last edited by Gary in WA; 04-24-2014 at 05:33 PM. Reason: sp
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Old 04-24-2014, 11:35 PM   #7
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3/12 attic insulation


I was not comparing kraft facing to paint. I was saying it isn't required in their case if they have painted drywall.

Home is not likely used much in the winter and there are prevailing winds.

If no mold or mildew is noted yet, it will be exponentially less likely after air sealing and additional insulation.

At just over 840 sq/ft, the only require 5.6 sq/ft or 800 sq/in of NFA.

Depending on the vent size, they may already have that.

Last edited by Windows on Wash; 04-24-2014 at 11:41 PM.
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Old 04-26-2014, 03:49 PM   #8
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3/12 attic insulation


"At that point, facing on the FG (as long as you have drywall that is air tight and has at least 2 layers of paint) is not required.'----------- regular paint (Class 3)-- (unless it is a special low-perm vapor retarder/barrier paint -Class 2) has no value whatsoever as a vapor retarder per codes- to meet the ventilation rate. As that 4th link stated;


"R601.3.2 Material vapor retarder class. The vapor retarder class shall be based on the manufacturer's certified testing or a tested assembly.

The following shall be deemed to meet the class specified:


Class I: Sheet polyethylene, unperforated aluminum foil.


Class II: Kraft-faced fiberglass batts.


Class III: Latex or enamel paint."


So to meet code; either have vents (high/low)-- and sounds like you have-- per code OR faced batts for the 1/300, otherwise you need 1/150 as WoW figured for you. " As an alternative, the net free cross-ventilation area may be reduced to 1/300 when a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling."

Gary

PS. Just trying to show readers that regular paint won't meet the code requirements, only special low-perm paint.
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Last edited by Gary in WA; 04-26-2014 at 04:11 PM.
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Old 04-27-2014, 06:55 AM   #9
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3/12 attic insulation


Good enough and I know your aim is to educate and you do that amazing well.

I was speaking specifically to his situation and the lack of more than Class III vapor retarder given his ventilation schedule.

I would also point out that, and you know this as well, that air leaks carry exponentially more moisture than diffusion and the code is antiquated in that regard.

I would rather have a tight ceiling plane with a Class III than a bunch of can lights with a Class II. I will give you one guess as to which one will show mold and mildew in that case.

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