Proper Venting and Drainage Hole Placement and Dimensions for Box Sections

The figure shows the location of holes and clipped corners, which must be flush. Using the following formulas, the table shows typical sizes of holes.

Venting Box Sections for GalvanizingInternal Gussets

  • Space at minimum of 36” (91 cm)

Box Sections

  • If H + W = 24” (61 cm) or larger, the area of the hole, plus clips, should equal 25% of the cross-sectional area of the box (Area = H x W).
  • If H + W is between 16” and 24” (41-61 cm), the area of the hole, plus clips, should equal 30% of the cross-sectional area of the box.
  • If H + W is between 8” and 16” (20-41 cm), the area of the hole, plus clips, should equal 40% of the cross-sectional area of the box.
  • If H + W is less than 8” (20 cm), leave completely open, with no end-plate or internal gusset.

The table below is for square box-sections only. For rectangular sections, calculate the required area and check with the galvanizer for positioning of openings.

Box Size Holes A-Dim (H + W)
48” (122 cm) 8” (20 cm)
36” (19 cm) 6” (15 cm)
32” (81.3 cm) 6” (15 cm)
28” (71 cm) 6” (15 cm)
24” (61 cm) 5” (12.7 cm)
20” (50.8 cm) 4” (10.2 cm)
16” (40.6 cm) 4” (10.2 cm)
12” (30.5 cm) 3” ( 7.6 cm)