lev-os Structuring Abs Transactions
Designs asset-backed securitization structures with tranche hierarchy, credit enhancement, and cash flow allocation mechanics.
When To Use
- Designing a new ABS issuance and defining the capital structure (tranche count, sizing, and subordination levels)
- Evaluating credit enhancement adequacy for a given collateral pool and target ratings
- Building or reviewing a cash flow waterfall for principal and interest allocation across tranches
- Comparing structural alternatives (sequential pay vs. pro rata, turbo features, reserve account sizing)
- Stress-testing an existing structure against collateral performance scenarios (default, prepayment, recovery)
Inputs To Gather
- Collateral pool data: Asset type (auto loans, credit cards, trade receivables, RMBS, CLO), aggregate balance, weighted-average coupon, WAL, seasoning, geographic/obligor concentration
- Historical performance: Default rates, loss severity, prepayment speeds (CPR/ABS), delinquency migration curves, recovery timing
- Target capital structure: Number of tranches, target ratings per tranche (AAA through equity/residual), desired advance rate
- Credit enhancement parameters: Overcollateralization target, subordination levels, excess spread, reserve account initial deposit and floor, any third-party support (surety wrap, LOC) [VERIFY against current rating agency criteria]
- Waterfall rules: Payment priority (sequential vs. pro rata), interest-first vs. principal-first, trigger events (delinquency, cumulative loss, OC tests), turbo/catch-up mechanics
- Deal economics: Pricing assumptions per tranche, servicing fee, trustee fee, swap costs (if applicable), target equity yield
- Regulatory context: Risk retention requirements (5% vertical/horizontal/L-shaped), Reg AB II disclosure obligations, EU securitization regulation (STS eligibility if cross-border) [VERIFY jurisdiction-specific rules]
Workflow
Profile the collateral pool
- Stratify by key risk dimensions (FICO/credit score, LTV, loan age, geography, obligor size)
- Compute pool-level statistics: WAC, WAM, WAL, concentration limits
- Identify data gaps or quality flags that affect structural assumptions
Set base-case and stress scenarios
- Define base-case default curve, prepayment speed, and recovery assumptions from historical analogs
- Layer rating-agency stress multiples for each target tranche rating (e.g., Moody's Aaa stress = ~3.5x base loss for consumer ABS) [VERIFY current agency multiples]
- Include prepayment stress (fast/slow) and recovery lag stress
Design the tranche hierarchy
- Size senior tranche to survive the highest stress scenario with full principal recovery
- Size mezzanine tranches to meet intermediate rating targets with required coverage
- Residual/equity tranche absorbs first loss — size as the remaining balance after credit enhancement allocation
- Confirm subordination percentages align with precedent transactions and rating agency expectations
Build the cash flow waterfall
- Map interest waterfall: servicing fee → trustee/admin fees → senior interest → mezzanine interest (by seniority) → reserve account replenishment → excess spread to equity (or turbo principal)
- Map principal waterfall: sequential (senior first) until triggers are met, then potentially pro rata; define trigger reversion mechanics
- Model OC and IC trigger tests at each payment date — specify consequences of trigger breach (diversion of cash flow, trapping excess spread, acceleration of senior principal)
Size credit enhancement
- Overcollateralization: target and floor OC as percentage of pool balance
- Reserve account: initial deposit (typically 0.5%–2.0% of initial pool), floor amount, release conditions
- Excess spread: compute available excess spread under base and stress; determine if spread capture or turbo principal is needed
- Validate total credit enhancement (subordination + OC + reserve + excess spread) against rating agency required levels
Run scenario analysis
- Execute cash flow model under base, upside, and multiple downside scenarios
- Track key outputs per tranche: WAL, yield, principal window, break-even default rate, loss coverage ratio
- Identify the scenario at which each tranche experiences a principal shortfall (break-even analysis)
- Sensitivity analysis on key variables: default timing (front-loaded vs. back-loaded), recovery rate, prepayment speed
Document the structure
- Produce a structural summary with tranche table, waterfall diagram, and credit enhancement summary
- Highlight structural risks: concentration risk, commingling risk, servicer disruption, basis risk (fixed/floating mismatch)
- Note any deviations from market-standard terms and rationale
Output
- Tranche table: For each tranche — class name, rating, initial balance, percentage of deal, coupon type/rate, expected WAL, subordination level, payment window
- Waterfall diagram: Visual or tabular representation of interest and principal payment priority, trigger tests, and cash flow redirection logic
- Credit enhancement summary: Breakdown of total CE by component (subordination, OC, reserve, excess spread) with comparison to rating agency required levels
- Scenario results matrix: Tranche-level performance metrics (principal loss, WAL, yield) across base and stress scenarios
- Risk flags: Structural features that create tail risk, trigger volatility, or rating migration sensitivity
- Recommendation: Optimal structure with rationale, or comparison of 2–3 structural alternatives with trade-offs (advance rate vs. execution certainty, equity yield vs. rating stability)
Quality Checks
- Subordination levels for each tranche meet or exceed rating agency published benchmarks [VERIFY against current Moody's/S&P/Fitch/KBRA criteria for the specific asset class]
- Cash flow waterfall is internally consistent — all cash is allocated (no leakage), and priority of payments matches legal documentation intent
- OC and IC triggers are correctly modeled with breach-and-cure logic
- Stress scenarios cover both severity (high default) and timing (front-loaded loss) dimensions
- Risk retention slice (horizontal, vertical, or L-shaped) is correctly sized at minimum 5% of total issuance [VERIFY applicable jurisdiction — US Dodd-Frank vs. EU/UK rules]
- Excess spread calculations account for servicing fees, swap costs, and trustee fees before measuring available CE
- Break-even analysis confirms each rated tranche survives its corresponding rating stress with zero principal loss
- All collateral pool statistics reconcile to the actual tape (no stale or placeholder data)