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Attic ceiling insulation should have been taken out?

Attic ceiling insulation should have been taken out?

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  #1  
Old 09-05-14, 05:03 PM
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Attic ceiling insulation should have been taken out?

Hello all

I bought a tall double unit home that had very recently prior to my purchase had insulation blown into the attic floor. There is still the old fiberglass insulation in the attic ceiling (though parts of the insulation are in rough shape because the previous owners also re-did the roof and debris fell onto the insulation...)

My plumber said they should have removed the ceiling insulation and that it can actually build up moisture in the attic if both the floor and the ceiling of the attic are insulated. If there is floor insulation, there should not be ceiling insulation...

true or false?
 
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  #2  
Old 09-05-14, 05:57 PM
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Essentially your plumber is correct, but we would need to know more about how much insulation of what type is where.

In general, you want to go one way or the other. Insulate the rafters and ventilate above the insulation while the rest of the attic remains sealed from the outside (no ventilation) and it shares some of the heat from the conditioned space below. Sharing heat maintains the inside surface of the rafter insulation above the condensation point. Or, insulate the floor of the attic (ceiling from below) and ventilate the entire attic.

With either approach, of key importance is creating an air barrier in the same place as the thermal barrier. Air leakage carries moisture which can find a cool surface and become a problem.

Just adding Kraft faced fiberglass insulation between the rafters is not a good approach to start.

More details and we will go from there.

Bud
 
  #3  
Old 09-05-14, 06:15 PM
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Insulation in the floor will make the attic colder. If your roof deck has fibrous insulation against it with no air path for ventilation you will stand a better chance of forming condensation due to the colder space, a lack of airflow and a probable lackluster vapor diffusion retarder on the old insulation. If your roof deck is osb or plywood then the chances of condensation are greater than if solid wood.

You didn't mention what R-values are associated with the two installations but it would be best to have whatever is recommended for your area all installed in one plane.
 
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