What limit is placed on re-roofing an existing roof?

The correct answer highlights the regulation concerning the maximum number of roofing layers permitted on a structure. Building codes often establish limits to ensure the integrity of the roof, to reduce excessive weight, and to facilitate proper drainage and ventilation. In most jurisdictions, building codes stipulate that if a roof already has two layers of roofing material, adding a third layer is not allowed. This is primarily for safety reasons, as additional layers can increase the load on the structure and potentially lead to failure or other issues.

The other options do not align with standard building practice and codes. Permitting a second layer regardless of the existing roofing contradicts the restrictions typically placed on layering. Allowing only one layer for the entire roof life is also uncommon, as most places permit a replacement after removal of existing materials. Lastly, while a structural engineer may be consulted for special cases, the baseline code typically restricts roofing to a maximum of two layers without special permission.