Sheathing plywood RTD or CDX

What's the difference between RTD and CDX plywood for sheathing (walls and roof) use? CDX appears to be twice as expensive as RTD. The walls sheathing will be covered by house wrap.
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If the vendor cannot tell you, the local building permits office can tell you whether either is specified in any part of the building code, and if so why.
--
Don Phillipson
Carlsbad Springs
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RTD is short for "Rated." Rated for what? Well, it should be written on the panel.
If it says "RTD SHTG", that means it's APA rated for use as sheathing, and would thus be approptiate for your use on walls and roof.
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On Oct 21, 10:08pm, snipped-for-privacy@invalid.invalid.com (Nails) wrote:

It is sold as "sheathing" so I assume it is rated for sheathing. My question is what the fundamental differences between RTD and CDX. I know what CDX means, I wonder why it is twice as expensive as RTD.
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ls02 wrote:

As was said before, the RTD isn't a grade; it's a conformance stamp that the material is up to the APA spec's for sheathing -- the actual product ratings is in the span and exposure data also stamped on the sheet.
The pricing will vary depending on the Span Rating w/ longer spans being more as well as which with exposure rating. I'd guess the panels you're comparing are towards the shorter spans and lower exposure range. I'm not sure where a standard CD-X would fall on the span rating; that would depend on the particular manufacturer to some degree which is the reason for the RTD system...
The APA site glossary has --
APA Rated Sheathing
An APA Performance Rated Panel designed and manufactured specifically for residential and other light frame wall sheathing, roof sheathing and subflooring applications. APA RATED SHEATHING can be manufactured with Span Ratings of 12/0, 16/0, 20/0, 24/0, 24/16, 32/16, 40/20 and 48/24, in thicknesses ranging from 5/16 to 3/4 inches, and in three exposure durability classifications-Exterior, Exposure 1 and Exposure 2.
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dpb wrote:

...
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One last note--whether the specific panel is appropriate depends on the actual ratings for the panel and the application details --
Here's the definition of "Span Rating" for sheathing and how to read/interpret the numbers (which is the actual rating, not the "RTD" which is simply a conformance certification).
Then, there's what the local Code, if applicable, requires but this is the basics of what the panel is designed/certified for in application.
Note that a panel can have the same Span Rating but be of varying thickness owing to differences in material and/or construction.
Span Rating
The number that appears in the trademark on APA RATED STURD-I-FLOOR, APA RATED SHEATHING and APA RATED SIDING panels. Two numbers separated by a slash (e.g., 24/0, 32/16, 48/24) appear on APA RATED SHEATHING. The left-hand number is the maximum recommended center-to-center spacing of supports in inches when the panel is used for roof sheathing with long dimension across supports (unless the strength axis is otherwise identified). The right-hand number is the maximum center-to-center spacing of supports in inches when the panel is used for subflooring with long dimension across supports. When a panel is applied as wall sheathing, the left-hand number applies to stud spacing. A rating of 24 oc or more means the panel can be applied to studs spaced 24 o.c. A rating less than 24 oc means the panel can be applied to studs spaced 16 o.c. APA RATED SHEATHING panels may be applied as wall sheathing either vertically or horizontally. In all cases the panel should be applied continuous over three or more supports.
And, I suppose since we're at it, might as well put out the Bond Classifications (glueline water resistance), too--
Bond Classification
Exposure ratings for APA structural wood panels designated in APA trademarks as Exterior, Exposure 1, Exposure 2, or Interior.
* Exterior panels have a fully waterproof bond and are designed for applications subject to permanent exposure to the weather or to moisture. * Exposure 1 panels have a fully waterproof bond and are designed for applications where long construction delays may be expected prior to providing protection, or where high moisture conditions may be encountered in service. Exposure 1 panels are made with the same exterior adhesives used in Exterior panels. However, because other compositional factors may affect bond performance, only Exterior panels should be used for permanent exposure to the weather. * Exposure 2 panels (identified as Interior type with intermediate glue under PS 1) are intended for protected construction applications where only moderate delays in providing protection from moisture may be expected.     * Interior panels or panels which lack further glueline information in their trademarks are manufactured with interior glue and are intended for interior applications only.
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