How close must notching be to the end of a supported beam for it to be permissible?

When it comes to notching a beam for plumbing or construction purposes, building codes typically allow notching only a limited distance from the end of a beam to maintain structural integrity. The permittable distance for notching is often specified in building codes and by engineering practices.

The correct answer states that notching must be no closer than one-fourth into the beam from the end. This means that at least one-fourth of the beam's total length should remain intact beyond the notch to ensure that the structural strength of the beam is not compromised. This one-fourth guideline is consistent with practices intended to minimize the risk of weakening the beam, which could lead to structural failures.

The other options suggest distances that are closer to the end of the beam, which could potentially undermine its support capabilities. Notching too close to the end of a beam can reduce its load-bearing capacity and may result in serious structural issues. Thus, adhering to the one-fourth guideline is critical in ensuring the safety and reliability of the beam in its application.