Insulation questions

Cossack

I have gutted an area for a new bathroom in an old wood house built in 1863. The only thing between the exterior and the inside of the bath is thin clap board siding. I will be putting unfaced insulation up and covering it with plastic facing the interior of the bath. The wind can blow in between the clap board so I want to cover them with tar paper first as protection. Is tar paper considered a vapor barrier? I know you are not supposed to have facing on both sides of insulation.

Also, how does one secure unfaced insulation to walls without tabs?

Thanks in advance to all who help.

Gary in WA

Plastic and tar paper are vapor retarders with plastic being air-impermeable- a true vapor barrier. Plastic inside only in cold and very cold areas: http://www.buildingscience.com/docum...gs?full_view=1
http://www.buildingscience.com/docum...gs?full_view=1
Foam board would help unless cost is an issue. Tar paper and asphalt paper: http://www.fortifiber.com/pdf/fortif...sk_vs_felt.pdf Unfaced is factory cut larger than cavity width to self support. http://www.buildingscience.com/docum...archterm=insul

Gary

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