Under what condition must a truss be notched or grooved?

A truss must be notched or grooved if there is written approval from a certified engineer. This stipulation is crucial because trusses are engineered components designed to carry specific loads, and any modifications, such as notching or grooving, could potentially compromise their structural integrity. Therefore, obtaining preapproval ensures that such changes are safe and do not violate building codes or engineering principles. This process protects the overall stability of the structure and the safety of its occupants. Not having written approval could lead to significant issues down the road, including increased risk of failure or damage to the building.

Other options, while they present various conditions related to trusses, do not encompass the necessary engineering oversight that is critical for ensuring the truss's function and safety.