Preservative-Treated Plywood

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Author Message Russell W. Wood, CSI, CCS Senior Member Username: woodr5678 Post Number: 35 Registered: 11-2003 Posted on Thursday, September 29, 2005 - 11:46 am:    Please settle an argument...Does plywood roof sheathing or wall sheathing need to be pressure treated? (conditions: south Florida, exterior grade plywood, both covered with building paper) Anne Whitacre, CCS CSI Senior Member Username: awhitacre Post Number: 254 Registered: 07-2002 Posted on Thursday, September 29, 2005 - 02:59 pm:    In our area (northwest, which means it can be wet for a while, and cool) we specify exterior grade plywood, but it is not pressure treated. we do typically use two layers of building paper, with staggered seams, so that one of them can rip apart in the wind before the roofing/siding is installed and the other layer stays more or less intact... David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 555 Registered: 03-2002 Posted on Thursday, September 29, 2005 - 05:30 pm:    Russell, I imagine the reason for your question has to do more with termites than with water/rot damage. Are the roof trusses and wall studs treated? John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 412 Registered: 03-2002 Posted on Thursday, September 29, 2005 - 07:15 pm:    I have observed that wood-framed buildings in Key West (where I spend winter vacations) are typically framed and sheathed entirely in PT materials for termite resistance. Russell W. Wood, CSI, CCS Senior Member Username: woodr5678 Post Number: 36 Registered: 11-2003 Posted on Friday, September 30, 2005 - 08:49 am:    David, For the most part the roof trusses and wall studs do not require to be PT except where in contact with concrete. Russell W. Wood, CSI, CCS Senior Member Username: woodr5678 Post Number: 37 Registered: 11-2003 Posted on Friday, September 30, 2005 - 10:46 am:    Part-2 of my question: When plywood roof sheathing is exposed to weather from the underside such as roof overhangs without soffits or dugout shed roofs, should the plywood be: 1.PT 2.CDX 3.Exterior Grade. David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 556 Registered: 03-2002 Posted on Friday, September 30, 2005 - 12:11 pm:    I used to work in Honolulu. Hawaii's is a paradise for humans.....and bugs. Termites are a HUGE problem. If possible we would preservative treat every stick of wood. I have personally seen termites eat carpet tack strips in an all concrete building. Wood furniture (especially particle board) also gets chewed to bits. I figure that south Florida has the same climate and would require that every piece of framing lumber be pressure treated. For wood items not exposed to direct rain, we used boric acid products such as HI-Bor (http://www.osmose.com/wood/usa/preserved/hi-bor/product/). Wayne Yancey Senior Member Username: wyancey Post Number: 77 Registered: 05-2005 Posted on Friday, September 30, 2005 - 03:55 pm:    David, Your HI termite buddies also ate through the expansion control sealant between concrete columns at Restaurant Row. Looked like swiss cheese. Urethane if memory serves me correctly. You may already know this; Steve Nash made principal at Durrant Media Five. Aloha and Mahalo John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 413 Registered: 03-2002 Posted on Monday, October 03, 2005 - 10:27 am:    CDX refers to the quality of the veneers, not the glue, and you would not be happy with seeing it exposed since knot holes are not required to be plugged. Exterior exposure would be required (the glue) and the PT question would go back to your first question about whether the project requires it in general. Remember that the treatment helps protect against insects, which exterior-exposure would not. Russell W. Wood, CSI, CCS Senior Member Username: woodr5678 Post Number: 38 Registered: 11-2003 Posted on Thursday, October 06, 2005 - 09:15 am:    Thanks for all your input. The point I was trying to make to some of my Architects is..... CDX Exposure-1 plywood is quite often mistakenly considered to be Exterior grade plywood and vice-versa. Pressure treated plywood is also mistakenly used on occassion in place of Exterior grade plywood and vice-versa. CDX Exposure-1 is suitable for roof & wall sheathing with temporary exposure to the weather. Exterior grade is suitable for permanent weather or moisture exposure. Pressure treated plywood is suitable to protect against decay, fungi, or termite and other insects. Mark Gilligan SE, CSI Senior Member Username: markgilligan Post Number: 38 Registered: 05-2005 Posted on Thursday, October 06, 2005 - 10:56 am:    I believe that we are mixing notation. CDX indicates C and D face veneers with exterior glue. This is equivalent to C-D Exposure 1. For an update on current plywood notation refer to APA's "Engineered Wood Construction Guide" which can be downloaded from www.apawood.org.