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Hi, everyone - first post for me so I'll try to make it quick! We are moving to a new home - attic has a 3/4" plywood floor with (I assume but have not been able to check) insulation underneath. Inspector gave it a roughly R24 rating. We would like to add to this. From a moisture standpoint, can I just roll out some R30-something insulation right over the plywood or would the plywood need to be removed? Paper-faced for a vapor barrier or unfaced? Thanks in advance!
 

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Do any air sealing you can while anything might be exposed; around elect wires, pipes, ducts, etc. Spray foam and/or caulking should work well. Cellulose blown over the whole area will do much better than FG batts.
 

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The plywood is a vapor retarder. Any (1/8") gaps under the plywood will effective allow moving air to rob you of insulation R-value added on top the sheathing. Still air has R-1 for 1-4". You may grow mold under the sheathing, check annually, with insulation on top.

Gary
 
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