Under which condition must existing roof coverings be removed before installing new roof coverings?

The requirement to remove existing roof coverings before installing new ones is primarily mandated when the existing roof is water-soaked. This condition indicates that the roof has structural issues and potential damage that could compromise the integrity of the new roof. Water-soaked roofing materials can harbor moisture, leading to problems such as mold growth, deterioration, and decay of the underlying roofing structure.

Installing new roofing over an impaired surface can cause the new materials to fail prematurely and may not perform as intended, leading to costly repairs down the line. Therefore, to ensure the longevity and effectiveness of a new roofing system, it is crucial to start from a dry and stable surface, thus necessitating the removal of existing, water-damaged materials.

The other conditions mentioned, such as whether the roof is flat, has a slope greater than 4:12, or whether re-roofing is optional, do not inherently require roof covering removal in the same way as a water-soaked condition does.