Ornament is a component here
A cornice is a horizontal ledge that catches weather for a century; the parapet above it is a masonry wall with its cap exposed to everything. Open joints in the coping over a cornice is a classic Prospect Heights finding — small to see, expensive to ignore, because the water that enters there exits through the facade's best features.
Behind the parapet, the flat roof does its usual quiet work. Seams in aging coatings, flashings at every penetration, drainage that depends on pitch nobody can see from below — Lou photographs it all so the report shows you the roof you cannot otherwise look at.
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