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tjniemann 11-24-2012 08:54 PM

Insulation question
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 11-24-2012 09:36 PM

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.

jklingel 11-24-2012 11:21 PM

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 11-26-2012 07:06 PM

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

jklingel 11-26-2012 07:12 PM

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 11-27-2012 09:05 AM

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

Gary in WA 11-28-2012 05:57 PM

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.


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