Insulation and Ventilation

patrioticSeptember 23, 2011

I am building an addition in Nebraska and need some advice on insulation and ventilation in the attic. I have closed cell foam in the walls (5 inches) and am scheduled for R38 batt (11.5 inches) with R19 batt (5.5 inches) on top of the R38, both over a 6 mil plastic vapor barrier. This is above a bathroom and closet on the hot (south) side of the house.

I have stapled styrofoam baffles 8 ft long in every rafter opening (14) to the underside of the roof that should help air flow from the eave vents to the ridge vent. The top of the openings on the baffles are more than 36 inches above the attic joists (attic floor). Roof slope is 5/12 and the distance from attic floor to ridge is 5 feet at the peak.

My concerns are:

1) Is a certain "volume" of air required in the attic to prevent condensation?

2) Is there something I am missing?

3) Can too much insulation cause havoc and how?

Thanks in advance for any advice.

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Ask the local building official.

    Bookmark   September 23, 2011 at 8:42PM
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snoonyb's somewhat terse reply is pretty accurate. There are so many variable factors involved - including but not limited to local climate, roof design and type, exterior treatment on the roof, insulation type - that you're going to need to seek out specific local advice. Even then, recommendations change with pretty consistent regularity.

    Bookmark   September 25, 2011 at 9:03AM
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