inside sheathing

drankinApril 16, 2009

I'm remodelling an 1882 summer kitchen which is attached to the back of my house. The addition is actually two rooms. I'm insulating and drywalling the room which is attached to the main house (so it is "sandwiched" between the main house and the second room of the summer kitchen). The room I'm doing had interior 1x8 sheathing, no insulation, then rosin paper and cedar siding nailed to the outside of the 2x4 studs. I'm planning on using bat insulation with paper to the inside and drywalling over. My question is, do I need to put plywood sheathing over the inside of the studs before drywalling? The two exterior walls (east and west) of the room are about 12' long and 8' high and buttressed between the sheathed back room and the main house. Are the 12' wide x 8' high walls strong enough to avoid racking without sheathing or diagonal bracing? There is a small unused loft above both summer kitchen rooms with a steeply pitched roof above. The roof rests directly on the east and west exterior walls of the summer kitchen. The gable ends are attached to the house on the south end and freestanding on the north end of the uninsulated room. Also, the original rosin paper is deteriorating in places. Would it be good or bad practice to put roofing felt on the back side of the cedar siding--noting that it could only be installed between the studs and not over them? Would that allow the new insulation to breathe? Should I leave the old rosin paper in place before insulating? I hope my descriptions of the situation are not too confusing. Thanks!

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theporchguy

drankin,
From my experience drywall over the existing inside 2 x 4 studs @ 16" O. C. on a 12' run is adequate, and the sheating would not be required.

On your second thought, I do not fully understand your
rosin paper description.
Can you give a clearer explanaton?

the porchguy

Here is a link that might be useful: My link

    Bookmark   April 17, 2009 at 7:18PM
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sombreuil_mongrel

The structure needs sheathing somewhere to stabilize the frame. The old interior sheathing which I assume is now gone, performed that function. Lap siding does not perform the function of sheathing. If you were to let in some rack bracing, that might do the trick. Plywood as interior sheathing is usually not a great idea, because there will be no acceptable place for the vapor barrier.
This being only a section of the wall span (I take it that the walls continue with interior sheathing in another room beyond this one) it just might be acceptable if the drywall itself is glued to the studs. whence it will become a structural element of the shear panel. But I'm not an engineer and I can't make that determination.
The best case would be to put the sheathing plywood where it belongs (in the modern insulated wall sense) which is under the lap siding on the outside. This would require removing all the siding and most likely the windows and doors.
One last thought: if you affixed 1/2" plywood interior sheathing, THEN used 1/2" spacers so as to provide an airspace between the ply and the drywall, and the vapor barrier resided on those spacers, that IMO would be acceptable. You just need to avoid exterior walls with plywood+drywall sandwiches. The spacers add to the wall thickness but provide the needed gap.
Casey

    Bookmark   April 18, 2009 at 8:36AM
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