vapor barrier for interior walls?

[beckhamk]

I have a question here,  We have tyvek'd the outside of the cabin and its sealed up. We have also now gotten our insulation in. My question is should we be putting up some plastic vapor barrier on the walls before we put up our T&G paneling?   I am not sure if it would help with anything. We have spyder filled walls.

thanks in advance!

[Redoverfarm]

I have a question here,  We have tyvek'd the outside of the cabin and its sealed up. We have also now gotten our insulation in. My question is should we be putting up some plastic vapor barrier on the walls before we put up our T&G paneling?   I am not sure if it would help with anything. We have spyder filled walls.

thanks in advance!

Not real sure what you are calling "spyder filled walls" but if it is standard batt insulation that is "faced" then you do not need to add additional vapor barrier.  In doing so you will trap moisture between the two barriers.  If it is unfaced the vapor barrier goes to the warm side of the wall. 

[Alan Gage]

http://www.buildingscience.com/documents/reports/rr-0004-air-barriers-vs-vapor-barriers/view?searchterm=air%20barrier

http://www.buildingscience.com/documents/digests/bsd-104-understanding-air-barriers/?searchterm=air%20barrier

Alan

[rocking23nf]

its a code requirement in many areas.

[MountainDon]

Basic required info for a good answer is;
- type of insulation as John got into
and
- climate or general location
(all that may be mentioned somewhere else but I for one don't remember all the details)
- and it can be a code requirement as also was mentioned...


and I too haven't a clue as to what spyder filled means. Must be a local thing   

[MountainDon]

http://www.energybooks.com/pdf/D1142.pdf


http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11810

[Redoverfarm]

To answer your question yes you can use 6mil plastic.  But you should not have two barriers sandwiched.  So if the craft paper will not meet then remove it and use the plastic.  Use "grace tape" or other tape intended to seal the joints and cover any penetrations.

[Jeff922]

Key information is that 6mil poly is a "vapor barrier"  whereas kraft faced insulation is a "vapor retarder".  Don't use poly if you are going to have air conditioning in the summer.

[JRR]

The more I learn, the more I am confused!  The above list of permeability ratings shows "plywood with exterior glue" has a rating of .70 ... therefore is a "vapor barrier".  But does this mean exterior sheathing grade plywood  (exterior service glue) nailed to studs is a "vapor barrier" ... period?  Or does mean exterior grade plywood must be glued, as well as nailed, to studs ... to be rated as a "vapor barrier"?

[beckhamk]

thanks for the info.....   Sorry i forgot to tell you what spider was...  Its blown in sticky fiberglass insulation. made by john manville
http://www.specjm.com/products/sprayin2/spider.asp