Fixed Income 5: Securitisation and ABS

Securitized products — increasing complexity

Covered bonds: simplest structure — a pool of assets (e.g. mortgages) stays on the issuing bank's balance sheet as collateral; not a true securitization since assets aren't transferred to an SPE, and investors are paid by the bank, not the pool's cash flows. Pass-through securities: true securitizations — the asset pool is transferred to a separate SPE, which issues securities backed by it; principal/interest pass through to investors proportionally, with payments depending on the pool's credit risk and payment patterns. Bonds with structural enhancements: redistribute the pool's cash flows across tranches per a preset schedule, with lower tranches subordinated to absorb more default/prepayment risk, sometimes with added credit enhancements. MBS vs. non-mortgage ABS: MBS = ABS backed by mortgages (RMBS, CMBS, CMO); non-mortgage ABS includes CDOs, CLOs, CBOs, and CDO-squared.

Tranching and the benefits of securitization

Tranching (subordination) creates multiple bond classes — senior vs. subordinated/junior — from the same underlying cash flow pool, setting the order in which investors are paid and the order in which losses are absorbed. This lets securitization tailor risk-return profiles to investor needs, giving investors differing interest-rate and credit-risk exposures to suit their specific risk, return, and maturity preferences. Benefits to economies/financial markets: creates tradable securities more liquid than the original loans, improves price discovery and market efficiency, boosts overall system liquidity and reduces liquidity risk, and gives issuers an alternative (often cheaper) source of funding versus traditional debt/equity financing.

Parties to a securitization

Three main parties: (1) seller of the collateral / depositor — the original lender; (2) SPE — purchases the loans/receivables and issues the ABS backed by them (often called the "issuer" in the prospectus); (3) servicer — services the underlying loans, often an affiliate of the original seller. Third parties (distinct from the seller) include independent accountants, lawyers, trustees, underwriters, rating agencies, and sometimes financial guarantors.

Key securitization documents and the trustee's role

Purchase agreement: between the seller/original lender and the SPE — sets out the seller's representations and warranties about the quality of the assets sold. Prospectus: describes the securitization structure, including payment priority/amounts to the servicer, administrators, and ABS holders, and the credit enhancements used. Trustee ("disinterested trustee"), typically a financial institution: safeguards the assets once sold to the SPE, holds funds due to ABS holders until paid, and provides periodic cash flow reports — investors' only source of information to update the ABS's credit standing.

The SPE's role — bankruptcy remoteness and legal risk

The SPE's legal protection for originator and investors is what makes securitization possible, and can make it cheaper than a corporate bond secured by the same collateral, since the SPE is unaffected by the seller's bankruptcy. Courts generally can't change seniority in a securitization because removing assets into the bankruptcy-remote SPE decouples the funding entity's credit risk from the issued bonds' credit risk — so the only credit risk investors face is underlying borrower default. In many countries this relies on recognition as a "true sale" (assets irrevocably transferred and de-recognized from the seller's balance sheet), though such transfers can potentially be challenged in court as fraudulent conveyances and unwound. Legal frameworks (e.g. trust law) vary by country, so investors should evaluate the jurisdiction's legal considerations before purchasing ABS.

Covered bonds — definition, structure, and dual recourse

Covered bonds are senior debt obligations issued by a financial institution, backed by a segregated pool of assets (typically mortgages or public sector assets) that stays on the issuer's own balance sheet, ringfenced into a "cover pool" — unlike ABS, where assets are transferred to a separate SPE. This gives investors dual recourse in default: first a claim on the ringfenced cover pool, second recourse to the issuer's unencumbered assets. Because loans stay on the balance sheet, covered bonds don't free up regulatory capital for the bank the way true securitization does. Covered bonds carry less credit risk than ABS due to dual recourse

Covered bond risk-mitigation features

Dynamic cover pool: usually one bond class per pool; the issuer must replace any prepaid or non-performing assets to keep cash flows sufficient through maturity, and a third-party asset monitor reviews the pool. Overcollateralization: collateral in the transaction exceeds the bonds' face value (e.g. Germany requires at least 2% overcollateralization by economic value). LTV eligibility: mortgages must meet loan-to-value standards to stay in the pool, or are replaced with ones that do.

Covered bond redemption regimes

Hard-bullet: missed payments per the original schedule trigger default and accelerate bond payments. Soft-bullet: delay default/payment acceleration until a new final maturity date, usually up to one year after the original maturity date. Conditional pass-through: convert to pass-through securities after the original maturity date if all payments haven't yet been made.

Covered bonds vs. ABS — key differences

Covered bonds: loans stay on the issuer's balance sheet (ringfenced, not transferred to an SPE); pay a fixed rate and mature on a fixed date like an ordinary bond; collateral simply enhances the issuer's promise to repay, without giving investors direct exposure to the pool; lower credit risk/yield than similar ABS due to dual recourse, eligibility criteria, dynamic pool, and redemption regimes. ABS: loans are sold off-balance-sheet to an SPE (freeing up the originating bank's regulatory capital to support more lending); typically pay a floating rate and pass through early prepayments; give investors direct exposure to the underlying pool's credit risk, with correspondingly higher potential returns.

Credit enhancement — overcollateralization & excess spread

Credit enhancement = financial support that absorbs losses from defaults on the underlying loans in a securitization, improving credit worthiness. Overcollateralization: collateral value backing the transaction exceeds the face value of bonds issued; the excess cushion lets principal/interest keep being paid even if some loans default, making both senior and subordinated tranches more attractive. Excess spread: the difference between the coupon on the underlying collateral and the coupon paid on the securities; this spread can absorb collateral shortfalls or build reserves. Subordination: waterfall structure is also credit enhancing

Amortizing vs. non-amortizing collateral, and the lockout/revolving period

Amortizing loans (e.g. mortgages, auto loans): periodic payments include principal + interest; investors get scheduled principal repayments and any prepayments per the payment rule; the pool shrinks over time as loans mature. Non-amortizing loans (e.g. credit card debt): no scheduled principal repayments. During the lockout (revolving) period, principal repaid on non-amortizing loans is reinvested to acquire new loans, replenishing the pool; once the amortization period begins, repaid principal is instead distributed to ABS holders.

Credit card receivable ABS — cash flows

Pooled credit card receivables (the lender's claim on the cardholder's borrowed amount) back the ABS. Pool cash flows = finance charges collected (periodic rate on the unpaid balance, fixed or floating — floating rates are typically capped), fees (late payment, annual membership), and principal repayments. Since credit card debt is non-amortizing, during the revolving period security holders receive only finance charges and fees; once the amortization period begins, noteholders also receive principal repayments.

Rapid (early) amortization provisions

Included to protect credit quality, especially during the revolving period. Triggered if revolving-period repayments aren't enough to replenish the pool, or if defaults significantly change the pool's economics. This accelerates/alters principal cash flows so noteholders get their investment back earlier and can reallocate it to better risk/return opportunities — especially valuable during periods of macroeconomic uncertainty.

Solar ABS — structure, credit enhancement, and default risk

Solar loans (consumer borrows to buy the system) or solar leases (consumer rents the equipment) are securitized like other ABS: collateralized by the underlying debt, further secured by a lien on the installed systems, the property, or both — when structured as home improvement loans, this effectively securitizes a subordinated (junior) mortgage on the property. Many solar ABS include a pre-funding period, letting the trust acquire additional qualifying loans meeting eligibility criteria after closing. Investors look for prime borrowers (homeowners with good payment records) and are protected by credit enhancements: overcollateralization, subordination, a general reserve account, an inverter replacement reserve account, and excess spread. Default risk tends to stay low structurally too: solar payments often displace a consumer's former energy payment, so defaulting doesn't reduce their overall obligation to pay for energy — it just risks reverting them to higher utility bills.

Securitised Products Overview

CDO/CLO structure and economics\A collateral manager selects a collateral pool (loans/bonds/ABS), sold to an SPE that issues bond tranches backed by it. Senior/mezzanine tranches earn fixed returns; the equity tranche earns equity-like returns using the issued debt as leverage — so the pool's return must exceed the aggregate funding cost of the debt issued. Three CLO types: Cash Flow (interest/principal redistributed across tranches — most common), Market Value (tranche value tied to portfolio market value), Synthetic (collateral pool built via credit derivatives).

CLO overcollateralization test\OC ratio = principal value of collateral ÷ total principal value of CLO debt tranches. Keeps collateral value above the debt owed to noteholders. If the ratio falls below its trigger, cash is diverted away from equity/junior tranches toward senior tranche investors.

Prepayment risk, contraction risk, extension risk, and time tranching\Prepayment risk = principal is repaid at a different pace than the scheduled contractual payment plan. Contraction risk: principal repaid faster than scheduled (typically when rates fall and refinancing rises) — shortens maturity, forces reinvestment at lower rates, and limits price appreciation. Extension risk: principal repaid slower than scheduled (typically when rates rise and refinancing drops) — lengthens maturity and stretches out cash flows that are now discounted at a higher rate. Time tranching redistributes prepayment risk across bond classes with different expected maturities; in sequential tranching, principal repayments flow first to one tranche until it's fully repaid, then to the next.

Prime vs. subprime loans

Prime: high-credit-quality borrower, strong employment/credit history, low DTI, substantial equity, first lien. Subprime: lower credit quality, high DTI and/or higher LTV, can include loans secured by second liens subordinated to other loans.

Agency vs. non-agency RMBS

Agency RMBS = guaranteed by a federal agency (full faith and credit of the government) or a GSE (the GSE's own guarantee, for a fee). Non-agency RMBS = issued by private entities with no government guarantee; gain credit enhancement instead via pool insurance, letters of credit, guarantees, or subordination, and are typically backed by non-conforming or subprime mortgages.

Prepayment risk and the prepayment penalty

A prepayment/early repayment option lets the borrower pay more than the scheduled principal, creating uncertainty in cash flow timing/amount for the lender — this affects any mortgage that allows prepayment. A prepayment penalty compensates the lender for the gap between the contract rate and prevailing rates if the borrower prepays after rates fall, reducing the incentive to prepay (common in Europe, rare in the US).

Recourse vs. non-recourse loans, and strategic default

Recourse loan: lender can claim the shortfall between the outstanding balance and foreclosure sale proceeds from the borrower. Non-recourse loan: lender can only recover from the property itself. US residential mortgages are non-recourse in many states; most European residential mortgages are recourse. On an underwater mortgage (LTV > 100%), a non-recourse borrower has more incentive to strategically default, since the lender can't pursue their other assets — recourse loans make strategic default less likely.

Mortgage pass-through securities and the pass-through rate

Lenders pool mortgages and sell securities backed by them; the pool's principal, interest, and prepayments are "passed through" to holders, net of servicing/administrative charges. The pass-through rate (coupon) is lower than the pool's weighted average mortgage rate because of these charges — also called the "net interest"/"net coupon."

WAC and WAM

WAC (weighted average coupon rate) and WAM (weighted average maturity) each weight the individual mortgages in a pool — by rate, or by remaining months to maturity — using each mortgage's outstanding balance as a share of the total pool balance.

CMOs — purpose

CMOs securitize pass-through securities or loan pools, redistributing cash flows across tranches to create different exposures to prepayment risk. Tranching can't eliminate prepayment risk, only redistribute it — more senior tranches carry less prepayment and default risk.

Sequential-pay CMO

Time tranching: all principal goes to Tranche A until it's fully repaid, then to Tranche B, and so on. This protects the shorter tranche from extension risk (backed by the longer tranches) while protecting the longer tranches from contraction risk (since the shorter tranche absorbs early prepayments first) — letting investors pick a tranche matching their extension- or contraction-risk preference and desired average life.

Other CMO tranche structures

Z-tranche (accrual bond): no interest paid until a pre-set date, accruing at the coupon rate meanwhile; usually last in a sequential/PAC series; frees up cash for other tranches and carries no reinvestment risk, but long average life (20+ years) makes it risky/hard to value. Principal-Only (PO): receives only principal; value rises when rates fall or prepayments speed up. Interest-Only (IO): receives only interest, no par value; cash flows fall as prepayments rise — used to hedge interest rate risk (opposite exposure to a PO). Floating-rate tranche: rate tied to an index/reference rate with a cap and floor; can be structured as an inverse floater (moves opposite to rate changes); used to hedge interest rate risk. Residual tranche: collects leftover cash flow after all other tranches are paid; high risk/return, suited to hedge funds and long-term institutional investors (banks avoid it due to capital requirements). PAC/support tranches: PAC tranches get scheduled, fixed principal payments if prepayments stay within a set range; the support tranche absorbs all the prepayment risk in that case, giving PAC tranches more predictable, stable cash flows.

RMBS vs CMBS

CMBS — collateral and structure basics

Backed by a pool of commercial mortgages on income-producing property (multifamily, office, industrial/warehouse, retail, hotel, healthcare); repayment can come from leases and other property revenue. A single-asset deal securitizes one loan on one marquee property; a single-borrower deal securitizes multiple loans from one borrower. US CMBS pool more loans and are usually fixed rate; European CMBS often pool fewer loans (sometimes across countries, adding legal/foreclosure risk) and are usually floating rate, often capped.

Call protection

Distinguishes CMBS from RMBS — protects investors against early prepayment, making CMBS trade more like corporate bonds. Structural: sequential-pay tranches, where a lower-rated tranche can't be paid down until the higher-rated tranche is fully retired, and losses hit junior tranches first. Loan-level (via covenants): prepayment lockout (no prepayment allowed for a set period); prepayment penalty points (1 point = 1.00% of outstanding balance, paid to refinance); defeasance (borrower buys a government-securities portfolio replicating the loan's remaining scheduled cash flows instead of just repaying).

Balloon maturity provision and balloon risk

Commercial mortgages are typically not fully amortizing — interest and some principal are paid during the loan, with the unamortized balance due as a lump-sum "balloon" payment at maturity. Balloon risk = the risk the borrower can't make that payment (e.g. can't refinance, lender won't extend terms, or can't sell the property) and defaults; the lender may then extend the loan over a "workout period" — since this lengthens the loan's life, balloon risk is a type of extension risk.

CMBS concentration risk

RMBS pools hold thousands of small, homogeneous mortgages, so individual defaults barely affect holders. CMBS can consist of just a few large commercial mortgages, so a single default can significantly impact investors — requiring analysis of the individual loans/properties/owners, not just the CMBS structure.

Debt service coverage ratio (DSC)

DSC = Net Operating Income (NOI) ÷ Debt service. NOI = (rental income − cash operating expenses) − replacement reserves, excluding loan principal/interest, capex, depreciation, and amortization. Debt service = annual interest + principal payments. DSC > 1.0x means property cash flows cover debt service; higher is stronger. Commercial mortgages are generally non-recourse, so lenders rely on the property's own cash-generating capacity (LTV and DSC) rather than recourse to the borrower.