My dad is converting the attached garage in his house into a den and washroom. He is framing the rooms off.
I noticed him putting up some drywall, but he feels that its not important to vapor-barrier the internal walls. He is going to insultate them.

I believe that since these internal walls aren’t really internal, garage isn’t insulated as well as the rest of the house, that these walls should have vapor barrier as well as insulation.

Could someone let me know whether is is best to include the vapour barrier, or if it is not needed?

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