T&G Kitchen Ceiling - Directly to Joists????

We're looking at putting up a tongue and groove ceiling in our kitchen to match the T&G we just finished in the porch (the kitchen opens into the porch) and we had a quick question. When we put the T&G up should we put it directly against the joists, should be use something like tar roofing paper first to seal the ceiling, or should we put it over sheetrock?
There is currently a dropped ceiling we are removing so if it's best to put it over sheetrock then we'd have to patch the ceiling where the drop is first. Just didn't know if there was something we should put up first before the T&G to be sure it's all sealed.
When we first did the porch we treated the top of the T&G with Thompson's Water Sealer to be sure that the roof side is protected. Didn't know if that was best to do here or if something else should be attached to the joists first.
Thanks!!!
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There are a number of different ways, some traditional in your area and some are legal building code. Much depends on where you are, warm climate, cold climate, Europe, North America, your local building department can give you the legal requirements and possibly some suggestions.
Personally, I would remove the old drywall and fix any electrical updates and insulation additions, add a 6 mil vapor barrier, 1/2 drywall with seams roughly finished then add your wood T&G strips.

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infiniteMPG wrote:

...
Interior there's really nothing to seal against--that's what the roof is for. If it's an attic above, the use of a barrier simply to stop any possible dust infiltration would be wise but that really would be its only function.
As for whether to use another layer, the key is how even the joists are--if they are close, directly to them is fine; otherwise you'll either want to shim or use furring strips to be able to even out the high/low spots. Of course, the joists need to be running perpendicular to the direction you want to run the ceiling or you'll need the furring strips to have a nailing surface the other direction.
I don't see any point in the sheetrock other than it could be the dust barrier spoken of athough it adds weight and is much more work to hang for to be simply covered up. And it surely wouldn't serve any purpose I can see to even tape it at all if did...
Well, I guess there might be one facet of sheetrock as a fire retardant barrier between floors, perhaps...
--
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On Tue, 15 Jul 2008 09:54:28 -0700 (PDT), infiniteMPG

I think I'd want sheetrock up first. Reason is that it is somewhat of a fire barrier, and is probably required by code.
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Found this in the Florida Building Code :
B3.3.2 Wood sheathing. Wood sheathing panels shall be considered air infiltration barriers when applied to a frame wall underneath an exterior finish and the following sealing requirements are met: 1. Joints formed by the square edges of adjoining panels shall be backed by a framing member. The joints between panels shall be sealed, or both adjoining panels sealed to the framing member using a mastic. For joints formed by tongue and groove edges, the groove of the panels shall be filled with mastic prior to mating the panels. 2. The panels shall be sealed to the top plate using a mastic. 3. The panels shall be sealed to the bottom plate, floor deck, or header and end joists using mastic. 4. The panels shall be sealed to the jambs or mounting fins of doors and windows using a mastic. Tapes of any type are not acceptable sealants for sealing wood sheathing to wood members, mounting fins, or masonry.
B3.3.3 Nonwood sheathing. Nonwood sheathing panels including foam insulation boards, and foil or plastic faced boards of other materials, shall be considered air infiltration barriers when applied to a frame wall under- neath an exterior finish and the following sealing requirements are met: 1. Joints between adjoining panels shall be sealed using one of the methods given for wood sheathing boards in Section B3.3.2, (1) above or, joints between adjoining panels shall be sealed by pressure sensitive tape with acrylic adhesive. Rubber-based adhesive tapes shall not be used for this purpose. 2. The panels shall be sealed to the top plate using a mastic. 3. The panels shall be sealed to the bottom plate, foundation wall, header and end joists, floor deck, or slab using mastic. 4. The panels shall be sealed to the jams or mounting fins of doors and windows using a mastic. Acrylic-based tape may be used to seal metal and plastic door and window mounting fins to the sheathing panels. Tapes of any type are not acceptable sealants for sealing nonwood sheathing to wood or masonry building components
Looks like a wood barrier is acceptable as long as there is a barrier sheet between it and the attic and mastic is used in the groves before assembly. Sound right?
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On Wed, 16 Jul 2008 09:55:17 -0700 (PDT), infiniteMPG

Looks like that they are talking exterior. I'd still put sheetrock behind it, it would keep a kitchen fire out of the attic for a few more minutes.
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infiniteMPG wrote: ...

No, that's sheathing...the application in question is _interior_ ceiling. Whether it's code or not, I'll agree the sheetrock would add a certain amount of fire retardation.
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