Vapor Barrier for Ceiling?

[rmcfall]

I am redoing our kitchen ceiling with some knotty pine boards, and some of the knot holes in these boards are large enough for loose fill insulation to easily drop through. Consequently, I need to tack something to the ceiling joists before putting up the knotty pine boards. So I am wondering what to install? I am leaning toward a 5mm underlayment or 1/8" masonite? Any suggestions as to whether the underlayment or masonite would be better? And while I am at it, should I put up some plastic as a vapor barrier as well?
Thanks,
Rob

 

[beau5278]

Is this a single story?

 

[rmcfall]

yes, single story.

 

[webby3650]

I helped a friend do this on his ceiling and the knots became a problem for us to. We simply tacked a piece of scrap pine behind the knot as went across the ceiling.

 

[rmcfall]

That's a thought, but in my case the boards are pretty knotty, as well as have worm holes all over. I definitely need something continuous like 4x8 sheets of masonite or underlayment. While I am at it, I'm just wondering whether I should put up a vapor/air barrier as well?

 

[Hogwildz]

I have seen where vapor barrier was recommended. You could use tar paper, house wrap, etc.
I also put knotty pine up on my ceilings & walls of the addition. But it already had flake board up. So I installed over the flake board.
I have also read where roll plastic will work also.

 

[rmcfall]

this may be a dumb question, but what is "flake" board?

 

[webby3650]

this may be a dumb question, but what is "flake" board?

I believe he is referring to strand board or OSB ( Oriented-Strand Board)

 

[rmcfall]

I wondered that, but wasn't sure...