Do I need to use 5/8″ drywall with 2×6 studs spaced 24″ O.C.
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I am constructing a home with 2×6 walls spaced 24″ O.C on the exterior walls to increase the insulation values as well cut down on the amount of lumber used. The building code as well the manufacture instructions say 1/2″ is o.k. to use with this type of stud spacing. My drywall contractor thinks there may be too much deflection at 24″ O.C.
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Replies
Bob, whether or not 1/2" drywall is adequate is up to you. I think it shows too much deflection. It should be perfectly fine for structural integrity however.
Rather than just go to 5/8" rock, have you considered other ideas that will save you money in the long run, such as 2x4 framing at 24" o.c. with 2x2's running horizontally inside (cavity filled with dense-pack cellulose) or 2x4's at 16" o.c. with exterior foam?
The first paragraph in my post above should have read:
Bob, whether or not 1/2" drywall is adequate is up to you. I think it shows too much deflection. 24" spacing should be perfectly fine for structural integrity however.
Bob, I would be interested in your location, there are a lot of sharp people who contribute to this site and could give far better advice if we know where you are. I am with Michael in considering an alternative to standard 2x6 construction. If you are thinking of OSB sheathing for instance this is a crappy wall in my opinion, way too much conductive heat loss through the framing.
Doug, I am in North Carolina. I don't doubt that there are more higher performing wall assemblies. I try to build the highest performing home I can on a limited budget. The average sales price of my homes is under $200K and most of them are speculative so there is a 50/50 shot that a buyer will actually see the value in the high performance deatils. My market is dominated by the use of 2x4 16" O.C. studs, with R-13 batt insulation, and OSB exteriors. In my cost analysis I have found that for less than $300 per home I can switch to 2x6 walls with 24" O.C. studs, with R-19 Batt, with OSB on the exterior. I am also doing 2 stud corners on the exterior, ladder frame details at intersecting walls, and packing out my window headers with 2" foam insulation. I have priced spray foam, Certain Teed Optima, as well as continuous foam sheathing on the exterior.
Bob,
For NC the wall you describe makes sense, R-19 is a lot of insulation for your climate and I think you are ok with the OSB sheathing as you border on a cooling climate. The primary air barrier should be on the warm side, in the north it's the room side, in the south, the outside. I suppose you go with ADA (airtight drywall approach) so the wall can dry to the inside, no poly or low perm paints
I wish Roxul was more readily available in the US, this might be a good insulation for you, You have specified fiberglass batt insulation and I am fine with it and have used it almost exclusively for 25 years with some impressive results, just keep air movement through the wall to a minimum. I think you should also add housewrap to your list and pay special attention to the exterior drainage plane details. OSB does not stand up to moisture near as well as plywood. My preferred sheathing is fiberboard but I can't say if this is appropriate for your area.
I've been building with 1/2" DW on 24 oc framing (walls & ceilings) for years and, even with dense-pack cellulose behind it, I've never noticed any bowing. As long as indoor humidity levels are controlled summer and winter, it should not be a problem. If DW is allowed to take on moisture, however, it loses its rigidity.