In which conditions can ducts that exhaust clothes dryers penetrate walls or ceilings?

Ducts that exhaust clothes dryers are required to meet specific construction criteria when they penetrate walls or ceilings. The answer is correct because these ducts must be constructed of materials that have been specified for their thickness to ensure safety and efficiency in operation. The reasoning behind this requirement is to minimize the risk of fire hazards, as well as to maintain the structural integrity and proper functioning of the duct system.

Properly sized and constructed ducts can significantly reduce the chance of lint buildup, which can lead to blockages and potential fire risks. Additionally, the thickness of the materials involved helps to contain the heat generated during operation, further reducing fire hazards while ensuring that the ducts can withstand the pressures from air movement.

While it is important to also consider insulation and material types, the primary focus in this question relates directly to the specified thickness of the materials used for the duct. Choosing the appropriate materials based on their thickness helps in adhering to the mechanical code requirements ensuring a safer installation.