Anomaly Density Index
Electronic leak detection reports conventionally state a raw anomaly count. A count alone tells an owner nothing about whether the result is ordinary or alarming: forty anomalies on a 60,000 square foot deck and forty on a 4,000 square foot deck describe entirely different buildings.
The Anomaly Density Index normalizes findings to anomalies per 1,000 square feet of tested membrane and places the result on a defined scale. It converts a number into a judgment that can be compared across projects, contractors, and years. ADI is derived from field data collected by Roof Analyzers across approximately 400 seamless membrane projects over eight years.
How ADI Is Calculated
ADI = (total anomalies ÷ square feet tested) × 1,000
Example: 42 anomalies over 8,000 square feet tested = ADI 5.25.
Square footage is the area actually tested, not the area of the roof. ADI is reported on any tested area; there is no minimum.
ADI Classification Scale
The ADI classification scale is non-linear. Each tier represents a multiple of the tier below it rather than a fixed numerical increment. This allows anomaly density to be evaluated in relation to the frequency and severity of observed membrane conditions.
| Tier | ADI | 1 Anomaly Per | Interpretation |
|---|---|---|---|
| Nominal | < 1 | > 1,000 sf | Isolated findings only. Membrane performing as intended. |
| Typical | 1 – 3.3 | 300 – 1,000 sf | Expected range for a competently installed and protected system. No systemic concern. |
| Elevated | 3.3 – 10 | 100 – 300 sf | Above expected range. Warrants review of installation practice, substrate condition, membrane protection, or post-installation trade traffic. |
| Severe | 10 – 67 | 15 – 100 sf | Widespread defect. Remediation review recommended before overburden. |
| Critical | 67 – 333 | 3 – 15 sf | Systemic defect indicated. Delamination possible. Membrane viability in question. |
| Fail | > 333 | < 3 sf | Delamination likely. Membrane does not perform as a water barrier. Replacement or comprehensive remediation indicated. |
| Continuous | n/a | n/a | Uniform conductance at all electrode contact. Attributable to either field delamination of the membrane or applied voltage exceeding the dielectric strength of the membrane. A condition, not a count. |
Tiers are lower-bound inclusive: an ADI of exactly 3.3 is Elevated, exactly 10 is Severe.
Full methodology, conditions of use, and limitations are set out in the standard.