(Knotty Pine) Beadboard Ceiling in Kitchen .... (Q. Vapor Barrier Needed?)

[Frank Aaberg]

New construction. Two floor residence - kitchen/dining area on first floor. Plan on putting 3/4" beadboard on ceiling. Will spot prime "knots" with BIN2 to seal knots and then go back and apply BIN2 to the boards to completely seal. Then will paint the displayed side with final (latex) paint. I do have R13 in joists above. (Reason ... radiant floor above calls for it.) QUESTION ... Should I place a plastic (4mil) vapor barrier above beadboards? I would guess normally this wouldn't be needed (or even desired) but I'm thinking that a kitchen puts out a ton of moisture. (Also, there is no drywall - code does not require it.) THANKS!

[Sam Murdoch]

Your wisest investment- if you have not already planned for this - would be to include a vent fan over the cooktop.

[Frank Aaberg]

Thanks Sam ... Yep, have the vent covered. (no pun intended!!!)

[Sam Murdoch]

Thanks Sam ... Yep, have the vent covered. (no pun intended!!!)


Then if people use the vent fan you should be fine without the vapor barrier. Would have said so no matter but your phrase - a kitchen puts out a ton of moisture - suggested that you might be big pasta eaters with billowing clouds of moisture roiling around your kitchen ceiling and no escape plan. :)


The other thing that needs to be said - and forgive me if I am telling you something you already know - it is especially important if these ceiling boards are in fact boards and not bead board panels you will need to leave no less than 1/4" (preferably 3/8") of clearance to the side walls parallel to the run of the boards. That's clearance at both sides of the room to allow for expansion and contraction of the ceiling. It will certainly move and nothing looks more poorly planned than a wooden ceiling or floor that is all buckled in the middle. Plan on a crown molding of some sort to conceal the gap.

[Frank Aaberg]

Yep - 1/4" was my plan on each end plus the crown molding. Thanks for making sure. (I also plan on sealing the ends after any cuts are made.)

[Rich Engelhardt]

Either way you go, it appears you're going to be installing a "mold farm"....

If you put in a vapor barrier, you'll trap the moisture and it will drip onto the backs of the boards - where it will sit until it can evaporate. Who knows how long that's going to take.

OTOH - if you don't install a vapor barrier, then the insulation will hold moisture like a sponge and cause not only the backs of the ceiling to stay wet, but, the joists and the bottom of the 2nd level sub floor also.

You need some sort of ventilation between the vapor barrier and the ceiling planks.

Interesting problem.....

[Sam Murdoch]

Either way you go, it appears you're going to be installing a "mold farm"....

If you put in a vapor barrier, you'll trap the moisture and it will drip onto the backs of the boards - where it will sit until it can evaporate. Who knows how long that's going to take.

OTOH - if you don't install a vapor barrier, then the insulation will hold moisture like a sponge and cause not only the backs of the ceiling to stay wet, but, the joists and the bottom of the 2nd level sub floor also.

You need some sort of ventilation between the vapor barrier and the ceiling planks.

Interesting problem.....

I'm guessing that the boards will be applied to strapping which will keep them away from direct contact with the insulation. A good state of the art vent hood in the kitchen and a bathroom vent fan should more than adequately take care of removing moisture from the area if both are used conscientiously. Anyone who lives in a moderately cold climate (and even worse in really cold climates) and has sheetrock against outside or otherwise cold space insulated walls and/or ceilings would have mold growing in the corners of the walls and in the creases of the ceilings if normal household moisture was not somehow mitigated. I agree that a vapor barrier will not help the situation. I don't have the scientific data to back me up (don't even know the size of Frank's room) but I'm pretty comfortable that he will be fine with his planned ceiling.

[Jim Becker]

If you installed faced insulation, it already has a moisture barrier. It's not normal to install another moisture barrier over that and it can cause problems. I would just install the ceiling...you might consider priming the back of the boards, too, for good measure. If you do feel you need the additional barrier, then stand the boards off the natural ceiling line on wood strips to provide some breathing room and make sure it's vented in some way.

[Frank Aaberg]

Nope, no face insulation used. (I can imagine the problems of putting two barriers in and "trapping" the moisture.) No strapping either. These boards will be nailed directly to the floor joists above. These are 8 inch joists and the radiant only calls for R13. The boards have been completely (front, back, sides, and ends) with B-I-N. This is a shellac based primer.

[peter gagliardi]

The breadboard is being applied to the underside of "conditioned" space above it, no vapor barrier is needed or necessary.The amount of vapor from cooking getting into the space is negligible, especially if you have a vent hood and use it. Lot of worrying for nothing is my educated guess. I have been building houses for 25 or so years. Vapor barriers are so water vapor doesn't enter a cold cavity, and thus condense on the cold surfaces- makes sense once you puzzle it through for a minute.
Peter