What is a key requirement for the installation of built-up roofs?

The requirement that built-up roofs must be installed on dry insulation is crucial for ensuring the longevity and performance of the roofing system. A dry substrate is necessary because moisture trapped beneath the roofing layers can lead to a host of issues, including mold growth, reduced insulation effectiveness, and premature deterioration of the roofing materials. By ensuring that the insulation is dry, the integrity of the built-up roof is maintained, leading to better energy efficiency and a longer lifespan for the roof.

While other options may present common practices or considerations regarding roofing, they do not align with the fundamental installation requirements specific to built-up roofs. Ensuring a dry installation surface is a principal aspect of proper roofing installation that cannot be overlooked.