Techtalk 126 – Supplement A: Duradek Plywood Recommendations

Plywood Recommendations

Property	Recommended	Acceptable
Thickness	23/32” (18.5mm) over joists @ 16” (400mm) o.c.	19/32”(15.5mm) over joists @ 16” (400mm) o.c.
Grade	T&G—Floor, select tight face (SEL TF) B – C Grade	T&G—C-C Underlayment Plugged
Group/Species	Douglas Fir (Fir)	Canadian Softwood (SPF)
Exposure Durability	Exterior	Exterior

Property	Recommended	Acceptable	Acceptable
Thickness	23/32” (18.5mm) over joists @ 16” (400mm) o.c.	19/32”(15.5mm) over joists @ 16” (400mm) o.c.	19/32”(15.5mm) over joists @ 16” (400mm) o.c.
Grade	Sturd-I-Floor plywood(T&G), B – C Grade	C-C Underlayment Plugged: T&G 1 C-C Plugged: T&G	Sturd-I-Floor plywood
Group/Species	Group 1
Exposure Durability	Exterior	Exterior	Exposure 1 2

For APA Engineered Wood Specialists recommendations, see APA Technical Topic: Wood Structural Panels for Outdoor Decks, Form TT-008

Plywood for Outdoor Decks

Exterior-type plywood may be used in outdoor deck applications. Recommended grades include APA RATED STURD-I-FLOOR Exterior, C-C Plugged, Underlayment C-C Plugged, or Marine.

If there is a dry living area underneath the deck, apply a membrane roof covering or high-performance coating over the surface. The coating should be able to accommodate normal dimensional changes in the plywood without rupturing or cracking. Under these conditions, APA RATED STURD-I– FLOOR Exposure 1 may be used unless otherwise recommended by the coating manufacturer, and preservative treatment of the panels is not necessary.

Group/Species

A. Underlayment and C-C Plywood panels Performance Category 1/2 and larger are generally Span Rated and do not contain species group number in trademark. Designate Span Rating.

B. Most tongue-and-groove panels are manufactured with a 47-1/2 inch net face width, although manufacturing practices vary. Check with your supplier.

Exposure—Durability

Exterior panels have bonds capable of withstanding repeated wetting and redrying or long-term exposure to weather or other conditions of similar severity.

Exposure 1 panels are suitable for uses not involving long-term exposure to weather. Panels classified as Exposure 1 are intended to resist the effects of moisture due to construction delays or other conditions of similar severity.

C-D Exposure 1 APA Rated Plywood Sheathing, sometimes called “CDX” in the trade, is occasionally mistaken as an Exterior panel and erroneously used in applications for which it does not possess the required resistance to weather. “CDX” should only be used for applications as outlined under Exposure 1 above.

Veneer Grades

Sanded, Solid, Repaired Face Panels

A	Smooth, paintable. Not more than 18 neatly made repairs, boat, sled, or router type, and parallel to grain, permitted. Wood or synthetic repairs permitted. May be used for natural finish in less demanding applications.
B	Solid surface. Shims, sled, or router repairs, and tight knots to 1 inch across grain permitted. Wood or synthetic repairs permitted. Some minor splits permitted.
C	Improved C veneer with splits limited to 1/8 inch width and knotholes or other open defects limited to 1/4 x 1/2 inch. Wood or synthetic repairs permitted. Admits some broken grain.

Sheathing and Rough Surface Panels

C	Tight knots to 1-1/2 inches. Knotholes to 1 inch across grain and some to 1-1/2 inches if total width of knots and knotholes is within specified limits. Synthetic or wood repairs. Discoloration and sanding defects that do not impair strength permitted. Limited splits allowed. Stitching permitted.
D	Knots and knotholes to 2-1/2 inch width across grain and 1/2 inch larger within specified limits. Limited splits are permitted. Stitching permitted. Limited to Exposure 1.

For APA Recommendations, see APA Technical Topic: Wood Structural Panels for Outdoor Decks, Form TT-008