Ceiling tongue and groove 1×6 pine over 1×3 cross strapping
cabinflyer
| Posted in Energy Efficiency and Durability on
Are there any issues with this? The 6 mil air barrier is up under roof trusses 24″ OC.
Due to the material I have on hand I need run the tongue and groove boards the same direction as the roof truss. If I install cross strapping I can do this.
Question: Will cross strapping screwed to the truss provide a sturdy nailing base between the truss bottom cord, or should I put something between the roof truss and strapping like drywall?
Steve
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Replies
Steve,
You seem to be worried about fastening issues, but I think you should be more worried about the lack of a rigid, permanent air barrier.
Six-mil polyethylene is fragile. Once installed, it usually ends up with holes or poorly sealed seams. I don't think polyethylene is robust enough to act as a ceiling air barrier. And since a board ceiling is notoriously leaky, you need to think this issue through.
I usually advise builders in your position to install taped drywall as an air barrier before installing ceiling boards.
If you are worried that the 1x3s aren't thick enough to hold your fasteners, the obvious solution is to install 2x4 strapping.
Martin,
What I'm hearing you say is drywall is a better air barrier than 6-mil poly. Isn't 6-mil poly code now? I understand most ceilings are rocked in new homes, but that's just because they are. I am building a rustic lake home with T&G red pine on the ceiling and most walls.. The walls are dense packed double studded (10" total) and there is going to be 24+"of loose packed cellulose in the ceiling. The taping of the poly was professionally done.
Is there anything needed other than taping the drywall? What thickness...1/2" or 5/8"? It will be covered with the strapping and T&G so is bare drywall good enough?
I'm not opposed to doing this and it should be an easy task to do since I have a drywall crew coming out to do a few interior walls anyway.
Steve
Steve,
Half-inch drywall is fine. A single coat of paper drywall tape and mud is all you need -- no sanding required.
The point is to create a durable air barrier. In addition to taping the drywall seams, you want to makes sure that all electrical boxes and ceiling penetrations are detailed for airtightness.
There is no code requirement for 6 mil poly in the U.S., although some U.S. code officials (and many Canadian code officials) insist on it. Vapor-retarder primer (paint) satisfies code requirements for a vapor retarder (where such code requirements exist). For more information on this issue, see Do I Need a Vapor Retarder?
By the way, a durable air barrier is desirable on walls as well as ceilings. So if you plan to finish your walls with 1x6 pine boards, it's a good idea to install drywall on your walls, too.
Even rustic lake homes need an air barrier.
Martin,
I was planning on using a smart membrane like Intello Plus on the walls. We have been very careful to place the minimum of electrical on exterior walls and in the ceiling.
So one last time, just so I'm correct, I do not need to paint or otherwise treat the drywall? Some sites call for latex.
I had been looking into drywall for this application before at the advice of the insulation folks went the poly route. I've seen videos where they use acoustic sealant on all the truss bottoms and in the corners in addition to screwing the drywall in place. I suppose it couldn't hurt.
Steve
Steve,
The way most codes are written, there is no code requirement for a vapor barrier on a ceiling, as long as there is a ventilation channel above the insulation layer -- as is typical in a vented attic or a vented cathedral ceiling. So you don't need vapor-retarder paint on your ceiling drywall.
What really matters is airtightness. Limiting air leakage is much more important than limiting vapor diffusion.
Just out of curiosity, if you already have 6 mil poly installed why couldn't you use 1/2" OSD (with caulked seams) in stead of Dry wall? The OSB would give you a surface that you could attach your T&G to without batten strips.
In climate zones 7 & higher it's prudent to go with a true vapor barrier on the ceiling, especially if the attic or cathedralized ceiling venting is at code-minimum levels. But in zone 6 or further south it's really not necessary.
DLAUFFENBURGER's recommendation for OSB detailed as an air barrier & ample nailer for the t & g at random locations (they don't need to be cut to length since the butt ends don't need to land on the strapping) works. If the inherent ~1-perm vapor retardency (when dry) makes you nervous, painting it with "vapor barrier latex" should bring it to the 0.5 perm range.