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303 Siding

Selecting Siding (Cladding) Panels

APA 303 Siding panels are manufactured specifically for use as external cladding on a variety of building types from domestic homes to garden sheds.  They can also be used to completely clad larger buildings or as part of a specific feature.

The 303 Siding Grade indicates the number and type of repairs on the face of APA 303 Siding (external cladding).

303 grade
APA’s Siding Manufacturing Specification
-6- maximum number of repairs allowed on the face of a 2440mm (96″) by 1220mm (48″) panel. The allowable number of repairs is proportional for other sizes
S/W indicates the type of material used for the repair
‘S’ synthetic repair
Choosing Face Grades
  • 303 Siding is available in 13 different face grades grouped into 4 appearance classifications (Special Series 303, 303-6, 303-18 and 303-30) that are primarily differentiated by the number, size and type of repairs.  Each of these classifications is subdivided according to the face grade as shown in the table below.
  • Special Series 303 is unusual as it does not allow any repairs except for small colour-matched wood shims.
  • 303-OL is plywood overlaid with resin-impregnated paper which is available with smooth surfaces.  This provides a stable, check-free surface with excellent finishing ability.
  • 303-NR provides a more rustic appearance, allowing knots and knotholes in the face veneer (patches are not permitted).
  • 303-SR is similar to 303-NR, but it allows synthetic repairs in the shape of natural characteristics such as knot holes.
Other Siding classifications
  • The other three classifications (303-6, -18 and -30), are graded according to the number or repairs and their type i.e. wood or synthetic.  The number immediately after the 303 designation refers to the maximum quantity of repairs allowed in the face (6, 18 or 30).  The letters S (synthetic) and W (wood) indicate the material from which the repair is made.
  • There is no colour matching of the repairs in classes 303-6-S or any of the classification types under 303-18 and 303-30.  The one exception is 303-6-W, where the wood patches and wood shims are colour matched.  There is also greater restriction on the size of the repairs.
  • When 303 Rated Siding is used outdoors it should be correctly finished to protect the surface from weather degrading. Various proprietary brands of finish are available for wood exposed to the elements such as oil-based, semi-transparent stains, solid colour stains and house paints.  Advice on the advantages and disadvantages of these various types can be found in the APA Technical Note – Finishing APA rated Siding for Protection and Appearance – Form No. M335C.
List of 303 Siding Face Grades
303 Face Classification
Knots / Knot Holes
Special Series 303 303-OC (Clear) Tight: Not permitted Not permitted

Not permitted

Pin: Not permitted
K. Holes: Not permitted
303 OL (Overlaid e.g. MDO Siding) Tight: Max. 25.4mm (1”) Not permitted

Not permitted

Pin: Same as tight

Not applicable for overlays

K. Holes: Not permitted
303-NR (Natural Rustic) Tight: Max. 38.1mm (1-1/2”)2. No limit Not permitted

Not permitted

Pin: Same as for tight
K. Holes: 25.4mm (1”). Occasional 38.1mm (1-1/2”)3
303-SR (Synthetic Rustic) Tight: Max. 38.1mm (1-1/2”). No limit Not permitted

Permitted as natural characteristic shape only

Pin: Same as for tight
K. Holes: 9.5mm (3/8”). Occasional 38.1mm (1-1/2”)3
303-6 303-6-W, 303-6-S, 303-6-S/W Tight: Not permitted Limit 6 Not permitted

Not permitted Limit 6

Pin: Max. 9.5mm (3/8”). No limit

Limit 6 – Any combination

K. Holes: Not permitted
303-18 303-18-W, 303-18-S, 303-18-S/W Tight: Not permitted Limit 18 Not permitted

Not permitted Limit 18

Pin: Max. 9.5mm (3/8”). No limit

Limit 18 – Any combination

K. Holes: Not permitted
303-30 303-30-W, 303-30-S, 303-30-S/W Tight: Not permitted Limit 30 Not permitted

Not permitted Limit 30

Pin: Max. 9.5mm (3/8”). No limit

Limit 30 – Any combination

K. Holes : Max. 6.4mm (1/4”) by 12.7mm (1/2”).
Glue line exposed limit 3 Max. 6.4mm (1/4”) by 6.4 (1/4”).
Glue line not exposed no limit
Notes: W – wood patches; S – synthetic patches; S/W – both wood and synthetic patches.  Number indicates maximum number of patches allowed.2 Unless otherwise noted, least grade characteristic dimension is across the grain measurement.3 6.4mm (1/4”) by 12.7mm (1/2”) maximum in 3- and 4-ply panels.