Insulation question

tjniemann

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!

joed

right over the plywood should be fine. The vapour barrier needs to be at the ceiling level. Unfaced. You do not want two vapour barriers.

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jklingel

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.

tjniemann

Appreciate the replies. Specifically, why would the blown work better than the rolled?

jklingel

blown cellulose will fill all voids and will slow down air movement better than fg. it also "crusts over" to further limit air movement through it.

ink

Where do you live? Local climate will change your vapor barrier needs.

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inK

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Gary in WA

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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