Glossary
Positive drainage
A roof design condition in which slope is sufficient to drain all water from the roof surface within 48 hours of rainfall under normal conditions.
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Plain-English definition
A roof has positive drainage when water actually leaves it — flowing to drains, scuppers, or gutters — rather than collecting in low spots. It’s the design condition that prevents ponding water.
Why it matters to you
Placeholder: code minimum slope requirements, why “flat” roofs are never truly flat, and how drainage is evaluated in a condition assessment.