Hey All-
I am installing a 6 inch tongue and groove red cedar ceiling in my new master bath. I have craft faced R-13 insulation with a ton of blown in on top of that. I am wondering about the moisture situation in the 10X12 space (with fan). Should I, or should I not install a vapor barrier upon the craft paper prior to the tongue and groove ?? Would this trap moisture between the wood and barrier?? The wife is freaking about mold. This is new construction. Any input? From Michigan currently @ 25 degrees.
Thanks, from a new comer.
Mark, nailer01
Edited 1/16/2006 12:57 am ET by nailer01
Replies
Seems like you want the continuity of a continious VB cause the kraft is really most effective in conjuction with a sheet covering like DW, and in the light of you using T&G which is far from solid.
I would use the poly VB. If the thought of trapping vapor between the two gets to you then slice the heck out of the paper.
In the finishing dept. I would protect the back of you T&G with some kind of sealer cause with the grooves ever 6" you know the wood is going to absorb moisture if giving the chance.
Welcome aboard Mark,
Mike
" I reject your reality and substitute my own"
Adam Savage---Mythbusters
Mike:
Thanks for your reply. I am thinking the same thing.. The T&G just invites leaks as opposed to DW. Again, however, is moisture going to get up between the wood and the barrier and create a mold problem?? I am staining and sealing both sides of the t &g, but mold could still grow?? If you slice the craft paper is it helping? ie heat loss, etc. Should I sheet with dw and then apply the t& g ??? My main fear is the moisture from a bath situation. Thanks Mike. Glad to hear from MN> Hope your weather is better than mine. 55 one day, 25 the next!!!!!!!!!
Mark, nailer01
I would leave the DW out---If you seal the back of the wood and the next surface is poly there is nothing to support the mold--unlike the paper on DW.If you want the DW , which is fine with me , just be sure to prime and paint to seal the paper face against the mosture.Might as well paint it black if there are any voids in the cedar and avoid the peek through of the poly.As for sliceing up the Kraft paper--it is only there for VB purposes and to stop air movement, a real r value killer, both of which will be effectivily replaced by the poly.BTW don't scimp on the mil rateing. 4 is min. but 6 is way better in staple holding power and tear resisitance, both a bonus in polying ceilings.Don't tell anyone but it has been in the high 20 and even mid 30 for a while--most of the snow banks are gone and I might have to mow soon.That is the beauty of Mn. There is always a 100% chance of weather.Mike" I reject your reality and substitute my own"
Adam Savage---Mythbusters
That's a tough situation. A lot of moisture load in a bathroom.
In the conventional case we rely upon the inherent airtightness of drywall to prevent moist air from escaping into the ceiling. Still, mold and mildew on ceilings is common, due to condensation.
You have to assume that the T&G provides essentially no air barrier, since the cumulative gaps will amount to a large hole in the ceiling. I would not be comfortable with a poly VB with hundreds of nail holes poked through it either.
In a cold climate, there is also the likelyhood that condensation will occur behind the T&G, and will be trapped there. In direct contact with the poly, it will not readily dry out.
I would want a complete standalone air barrier behind the T&G, then the T&G is just decorative.
For me, this would mean foam board, since that would keep the substrate warm enough to keep it above the dew point (most of the time).
Couple of ideas:
Drywall (at least greenboard, sealed seams) over 2 inches (ok, at least 1") of foam board with sealed seams (gun or can foam). Glue T&G to drywall, or apply strapping and nail to that (better).
or
Plywood primed on all sides, sealed seams (foam or caulk) over 2 inches of foam as above. Then you could nail wherever you like. Very convenient.
Also, you will want to seal the T&G with some sort of coating on all sides.
That's a great sounding solution. Another approach might be foam board directly on the rafters, with the seams sealed. Then furring strips running continuously below the rafters for nailers.Andy
Never try to teach a pig to sing. It wastes your time and annoys the pig.
"That's a great sounding solution. Another approach might be foam board directly on the rafters, with the seams sealed. Then furring strips running continuously below the rafters for nailers."
My thinking here was fire resistance. May not matter.
Hey Guys
All great input. I appreciate it. Adding foam board, fir strips or anything else will screw up my can lights, fan, etc.. I would have to tear all of it out and lower to accomodate the Material added. I'm still pondering, but leaning towards going with the barrier (4 mil poly), seal any joints and squirt on some sealant to seal finish nails through the t&g. As my father would have said, "do something even if it' s wrong!".
Thanks again, Mark
Yeah, can lights are trouble in a bathroom. At least make sure they are IC sealed cans. Otherwise they are little chimneys pumping hot moist air into your ceiling.
You may want to review both sides of the poly vapor barrier issue. See the site below. This guy sees a lot of poly barriers that result in mold. He claims the only place for poly in a home is on the floor of the crawl space.
http://www.energydesignedhomes.com/papers.htm
Marc
Vapour Barrier is an absolute must, and I'd do the walls, taping or using acoustic sealant to all joints. I might suggest strapping - either along the joists, or at right angles (depending on which way you want the t&g to run) , again with acoustic sealant where the strapping touches the joists - this will seal any punctures from nails. Apply t&g. Now you've a space behind where air may even circulate (albeit slightly), and also will become closer to the ambient temp of the room. This will reduce the likelihood of condensation IMHO
All the best...
To those who know - this may be obvious. To those who don't - I hope I've helped.
Well, no, it's not. The need for a vb depends on climate. In the land of Nanook, sure, use one. But in any mixed climate, where it gets both hot and cold, there is no good place to put them, because sometimes it's hotter outside, sometimes inside. In the deep south, vb should go on the outside, not the inside. Air barriers are far more important than vapor barriers in just about every case.Andy
Never try to teach a pig to sing. It wastes your time and annoys the pig.
Thanks - I guess I'm a bit parochial...All the best...
To those who know - this may be obvious. To those who don't - I hope I've helped.
Parochial? Are you in the north? Believe me, I don't argue against competently installed vbs in very cold climates.
Fun stuff, this building science. Andy
Never try to teach a pig to sing. It wastes your time and annoys the pig.
Would you two quit agrueing!! I made a decision. Today I hung black 4 mil poly on the darn ceiling. I have stained ( with exterior Cabot stain) both sides of the t&g. I now will seal both sides with ceramithane (Graham, water born urethane) and then hang the t & g blind nailing with 2 1/2" trim gun nails. Hopefully I can squirt some sealant at the nail points ( 24" OC modified scissor trusses). Right or wrong?? Don't know. " do something, even if it's wrong".
Thank's to all for input.
nailer01, Mark
Mark, you haven't been here long enough to remember the great vapor barrier wars of '98. Why, we went on for months until the mounting casualties brought about a cease fire!
One of my favorite things about this site is how regional practices are discussed, and how we all learn from each other. And by the way, iirc, you're in Michigan? You're probably OK with a vapor barrier. And welcome to Breaktime, where building minutiae ascends to religious heights.Andy
Never try to teach a pig to sing. It wastes your time and annoys the pig.