Overlay Suitability Scoring
Overlay is not appropriate for all roofs. This scoring framework assesses substrate condition, moisture status, structural adequacy, drainage and detailing to determine whether overlay is suitable, requires remediation before overlay, or whether replacement is the only viable option.
Scoring Framework
Each category is scored from 0–10 and weighted by importance. Total score determines overlay suitability. Scores below 50 indicate replacement is required. Scores 50–70 indicate overlay is possible subject to remediation. Scores above 70 indicate overlay is suitable.
Substrate Condition
30%Sound structural deck, no cracking or deflection
Minor surface cracking (non-structural)
Moderate cracking requiring repair
Structural cracking or deflection present
Moisture Status
25%Moisture readings <10% across full area
Moisture readings 10–15% in isolated zones
Moisture readings 15–20% in multiple zones
Moisture readings >20% or widespread saturation
Existing Membrane Adhesion
20%Full adhesion to deck, no delamination
Minor delamination at edges (<10% area)
Moderate delamination (10–30% area)
Extensive delamination (>30% area)
Drainage Adequacy
15%Adequate falls, no ponding, outlets clear
Minor ponding zones (<5% area)
Moderate ponding (5–15% area)
Extensive ponding (>15% area) or blocked outlets
Detailing Condition
10%All details sound, upstands adequate
Minor detailing repairs required
Moderate detailing work required
Extensive detailing failure or inadequate upstands
Score Interpretation
Score 70–100
Overlay Suitable
Substrate condition is suitable for overlay. Proceed to specification with standard preparation requirements. All moisture readings must be confirmed on application day.
Score 50–69
Overlay Subject to Remediation
Overlay is possible but requires remediation work before specification. Common remediation: moisture drying, drainage correction, structural repair, or extensive preparation.
Score 0–49
Replacement Required
Overlay is not suitable. Structural defects, extensive moisture saturation, or widespread delamination require full strip-out and replacement. Overlay would fail prematurely.
Decision Tree
Is structural deck sound?
YES
Proceed to moisture assessment.
NO
Structural repair or replacement required before any overlay consideration.
Are moisture readings within threshold?
YES
Proceed to adhesion assessment.
NO
Substrate drying required. Retest. If drying not achievable, replacement required.
Is existing membrane adhered to deck?
YES
Proceed to drainage assessment.
NO
Delaminated sections must be removed. If delamination >30%, replacement required.
Is drainage adequate?
YES
Proceed to detailing assessment.
NO
Drainage correction required before overlay. If falls cannot be corrected, overlay not suitable.
Are upstands and details adequate?
YES
Overlay is suitable — proceed to specification.
NO
Detailing remediation required. Raise upstands, replace failed flashings.
Related Technical Reference
Inspection Checklist
Pre-specification survey requirements — visual, moisture, structural and access assessment.
Moisture Assessment Guide
Moisture meter methodology, calcium chloride testing, substrate drying requirements.
Why Overlay Cannot Fix Structural Failure
Structural assessment thresholds before any coating system.
Preparation Sequencing Guide
Cleaning, degreasing, repair, priming — the sequence that determines adhesion.