Notching Joists

Summary: How to notch a joist for pipes and cables if you need to run pipes or cables under a floor.

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Notches

(Also applies to wall studs for concealed showers etc)

Notches should only be made in the top edge of the joist.

Notches should be no deeper than 0.125 times the depth of the joist.

Notches should be no closer to the structure supporting them than 0.07 times the span of the joist and no further away than 0.25 (¼) times the span. This is to avoid the area of maximum shear force, and the area of maximum bending in the joist.

Holes

Holes should only be drilled on the centre line of the joist. This is where the compressive and tensile load distribution is neutralised.

Holes should have a diameter of no greater than 0.25 times the depth of the joist.

Holes should be no closer together than 3 times the largest diameter permitted.

Holes should be no closer to the support than 0.25 times the span and no further away than 0.40 times the span.

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