Sheathing plywood RTD or CDX

ls02

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Oct 21, 2010, 10:25:44 AM10/21/10

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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.

Don Phillipson

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Oct 21, 2010, 2:36:42 PM10/21/10

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"ls02" <aga...@audible.com> wrote in message
news:f4ce3087-2226-4c07...@n26g2000yqh.googlegroups.com...

> 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.

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
(Ottawa, Canada)

Nails

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Oct 21, 2010, 10:08:43 PM10/21/10

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ls02 <aga...@audible.com> wrote:

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.

ls02

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Oct 22, 2010, 8:58:34 AM10/22/10

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On Oct 21, 10:08 pm, hates...@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.

dpb

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Oct 22, 2010, 10:45:54 AM10/22/10

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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.

dpb

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Oct 22, 2010, 1:21:21 PM10/22/10

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dpb wrote:
> ls02 wrote:
>> On Oct 21, 10:08 pm, hates...@invalid.invalid.com (Nails) wrote:
>>> ls02 <agal...@audible.com> wrote:
>>>> What's the difference between RTD and CDX plywood for sheathing (walls

...

>>> 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.

...

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.

--

ges

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Apr 19, 2017, 1:44:07 PM4/19/17

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replying to dpb, ges wrote:
RTD refers to the method used to manufacture the plywood. This is,
essentially, next generation CDX plywood which is manufactured with a quality
control system using RTDs (Resistance Temperature Detectors) to maintain
correct temperature during the bonding process.

--
for full context, visit https://www.homeownershub.com/maintenance/sheathing-plywood-rtd-or-cdx-591793-.htm

P. Namio

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Jul 22, 2017, 3:44:11 PM7/22/17

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replying to Nails, P. Namio wrote:
RTD stands for Resistance Temperature Detectors, a method toe ensure the
plywood/adhesive is uniformly heated during bonding of the plies.
"The use of the in-process RTD sensors significantly reduced the delamination
caused by insufficient heating of the plywood during the press cycle. If the
plywood sheet is found to have delaminated areas, it is sold as a lower grade
plywood at a reduced market value. Each press handles 30 sheets of plywood per
two-minute press cycle, so the reduction in delamination has significant
economic impact."

ExpertBubba

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Sep 19, 2017, 10:14:10 PM9/19/17

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replying to Nails, ExpertBubba wrote:
RTD in this case does not mean "rated"...RTD refers to the method used to

manufacture the plywood. This is, essentially, next generation CDX plywood
which is manufactured with a quality control system using RTDs (Resistance
Temperature Detectors) to maintain correct temperature during the bonding
process.

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Apr 4, 2019, 1:14:06 PM4/4/19

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replying to ls02, Jason Brand wrote:
I physically loaded both onto a cart the other day. The RDT $13 was a little
uglier, flakier, than the CDX, $18 which was cleaner, harder/stronger, stain
grade even.

bcz...@gmail.com

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Jul 19, 2020, 10:39:01 AM7/19/20

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RTD is not short for "Rated", it is an abbreviation for Resistant Temperature Detector and refers to the manufacturing process for how the plywood was bonded. RTD is the newer and improved version of CDX.

Holzige Specht

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Sep 30, 2021, 3:15:08 PM9/30/21

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I suspect that twice-the-price you are referring to is Douglas Fir CDX, a hard "soft wood", as opposed to SYP, Southern Yellow Pine, an inferior wood for sheathing since it warps so much and is probably the reason for the development of the Resistant Temperature Detector tech used in the manufacture due to de-lamination. It is an improvement in the same way a "new-and-improved" Snickers bar is smaller and costs more. CDX simply means a C grade face and a D grade face on the other with exterior glue. Finding a complete and truthful material description from a big box store is a challenge nowdays.

--
For full context, visit https://www.homeownershub.com/maintenance/sheathing-plywood-rtd-or-cdx-591793-.htm