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Notches and holes

Notches

  • Should only be made in the top edge of the joist
  • Should be no deeper than 0.125 times the depth of the joists.
  • Should be no closer to the support than 0.07 times the span and no further away than 0.25 times the span.

Maximum notch depth

Joist depth  Notch depth
125mm 15mm
150mm 18mm
175mm 21mm
200mm 25mm
225mm 28mm

Location of notches and holes in simply supported floor and roof Joists

Holes

  • Should only be drilled on the centre line of the joist.
  • Should have a diameter no greater than 0.25 times the depth of the joist.
  • Should be no closer together than 3 times the larger diameter.
  • Should be no closer to the support than 0.25 times the span and no further away than 0.4 times the span.
  • If the above requirements cannot be met within the limitation shown, then increase the joist depth by the depth of notches or diameter of holes.