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Old 10-04-2013, 07:44 AM   #1
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Blow-in insulation or seal vents and spray?


We recently bought a mid-sixties ranch in southern Ohio. When we bought, the home inspector indicated that there was only 2-4 inches of blown-in insulation in the attic. Actually, there is less or none in some areas. So, I need to add to that, hopefully before the cold hits us.

The house has a hip roof with soffit and ridge vents. The soffit vents are spaced much farther apart than I think they should be and I am not sure that there is enough of a ridge vent given that it is a hip roof. In the attic, there are no baffles installed.

In addition, the house has radiant heat so there is no forced air ducts in the floor. The A/C unit is installed in the attic with ductwork thru the ceiling in each room.

So, I was looking at blowing in insulation but I have several concerns. One is that I would have to install baffles to keep the soffit vents open but access is difficult and I am not sure there are enough vents anyway. Plus, with the large A/C unit in the attic, I would still need access and have to keep from blowing the insulation too close to the unit. The ducts for the A/C are also a concern as even though they are insulated, there is a lot of heat there in the summer which I am sure has an effect on the air duct temp.

Spray foam sounded interesting. I could spray the underside of the roof and not have to worry about dealing with the A/C unit. This would create an insulated area and A/C ducts should perform better. BUT, I would have to seal the ridge vent and the soffit vents I GUESS?

What's the best answer?

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Old 10-06-2013, 12:43 PM   #2
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Blow-in insulation or seal vents and spray?


The best, IMO, is moving your thermal barrier to the roof from the ceiling because of HVAC; http://www.buildingscience.com/docum...r-all-climates

SPF is best with rigid XPS a second choice with much more work. Minimum foam to prevent condensation, plus cavity insulation to meet/exceed code minimum; http://www.buildingscience.com/docum...rchterm=attic+

Ceiling R-value required- this is minimum; http://energycode.pnl.gov/EnergyCode...jsp?state=Ohio

Then seal the intake/exhaust vents, but keep in mind the roof decking should have Grace I&W shield or similar to prevent solar drive before the shingles. Also expect a 10% less service life of shingles; http://www.buildingscience.com/docum...on?full_view=1

Gary

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Old 10-07-2013, 03:58 AM   #3
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Blow-in insulation or seal vents and spray?


Thanks Gary. After posting this, I realized another thing that will probably mean that I will have to forget about the foam. I have, and use, a whole house fan that of course vents in the attic. So, I can't seal it up.

Back to planning.


Quote:
Originally Posted by Gary in WA View Post
The best, IMO, is moving your thermal barrier to the roof from the ceiling because of HVAC; http://www.buildingscience.com/docum...r-all-climates

SPF is best with rigid XPS a second choice with much more work. Minimum foam to prevent condensation, plus cavity insulation to meet/exceed code minimum; http://www.buildingscience.com/docum...rchterm=attic+

Ceiling R-value required- this is minimum; http://energycode.pnl.gov/EnergyCode...jsp?state=Ohio

Then seal the intake/exhaust vents, but keep in mind the roof decking should have Grace I&W shield or similar to prevent solar drive before the shingles. Also expect a 10% less service life of shingles; http://www.buildingscience.com/docum...on?full_view=1

Gary
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Old 10-07-2013, 06:25 AM   #4
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Blow-in insulation or seal vents and spray?


The whole house fan could still be used with a simple change.
You build duct work from the fan to the outside making sure to leave access to the fan for service.
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