FRM Exam Part II · Structured Credit Risk

Securitization Structure: SPV, Tranches and Waterfall

Updated 11 October 2026 · Fact-checked

Securitization pools loans, sells them to a bankruptcy-remote SPV, and the SPV issues tranches of securities backed by the pool's cash flows. A waterfall pays senior tranches first and allocates losses to the equity tranche first. To solve questions, trace the cash, then the losses, tranche by tranche.

Understand Securitization Basics and Structure

Securitization turns a pool of illiquid loans into tradable securities. A bank (the originator) makes loans such as mortgages, auto loans or corporate loans. Instead of holding them, it sells the pool to a separate legal entity, the special purpose vehicle (SPV). The SPV pays for the pool by issuing bonds to investors.

The SPV is bankruptcy-remote. If the originator fails, creditors cannot claim the pool. If the SPV is not legally and economically separate, the structure loses its purpose. In a true sale, the assets legally move to the SPV and, if accounting and regulatory tests are met, leave the originator's balance sheet. In a synthetic securitization, the loans stay with the originator. Only the credit risk is transferred, using credit default swaps or credit-linked notes, so the funding benefit of a true sale is not obtained.

The SPV issues tranches, which are slices of the pool's credit risk. The equity (first-loss) tranche absorbs losses first. Mezzanine tranches absorb the next losses. Senior tranches are hit last. The portion of the pool's value that sits below a tranche is its subordination. A tranche is defined by its attachment point (where losses start to hit it) and detachment point (where it is wiped out).

The waterfall sets the order of payments. Cash collected from the pool first pays fees to the servicer and trustee, then interest to senior tranches, then interest to mezzanine, then principal in the order set out in the deal documents, with residual cash to the equity holder. Losses run in the reverse order, from the bottom up. Credit enhancement, such as subordination, excess spread and overcollateralization, protects the senior tranches.

Other parties matter too. The servicer collects payments and handles delinquencies. The trustee protects investors and enforces the documents. Rating agencies rate the tranches. Arrangers structure and sell the deal. Conflicts arise because the originator may keep little risk. This is the originate-to-distribute model and a key lesson of the subprime crisis.

Key formulas to remember

Tranche thickness: Thickness = Detachment point − Attachment point; Both points are percentages of the total pool. A tranche from 5% to 15% is 10% thick.
Tranche loss: Tranche loss = min(max(Pool loss − Attachment, 0), Detachment − Attachment); Expressed in the same units as the pool. Divide by thickness for the percentage loss on the tranche.
Subordination: Subordination of a tranche = Attachment point of that tranche; It is the share of the pool that absorbs losses before the tranche takes any.
Overcollateralization: OC = (Pool balance − Liabilities issued) ÷ Pool balance; Equivalent to extra collateral beyond what funds the notes. It is a form of credit enhancement.
Excess spread: Excess spread = Pool interest income − (Coupons + Fees + Losses); Positive excess spread is the first line of defence against losses before tranches are written down.
Waterfall order: Fees → Senior interest → Mezzanine interest → Principal per structure → Equity residual; Losses are allocated in the reverse order: equity first, senior last. Always check the deal's stated order.

How to solve Securitization Basics and Structure questions

Use this sequence for any securitization structure question, whether it asks about roles, cash flows or losses.

1Identify the parties: originator, SPV, servicer, trustee, arranger, rating agency, investors.
2Decide whether the deal is a true sale or synthetic. Ask whether assets legally move or only risk moves.
3List the tranches from senior to equity with their attachment and detachment points.
4For a cash question, apply the waterfall in order: fees, senior interest, mezzanine interest, principal, residual.
5For a loss question, apply the loss against the pool from the bottom: equity first, then mezzanine, then senior.
6Compute each tranche's loss using min and max against its attachment and detachment points.
7Convert to a percentage of tranche size if asked, then state what it means for risk or credit enhancement.

Quickest way: Layer-by-layer loss allocation

When to use it: Use when a question gives a pool loss and tranche sizes and asks for the loss on a tranche or which tranches survive.

Write attachment and detachment points for each tranche as percentages of the pool.
Compare the pool loss with each attachment point.
If the loss is below the attachment point, that tranche loses nothing.
If the loss is above the detachment point, the tranche is wiped out.
Otherwise tranche loss = pool loss − attachment point. Divide by thickness for a percentage.
Check that tranche losses add up to the pool loss.

Common mistakes in Securitization Basics and Structure

Treating a synthetic securitization as a true sale.
Both transfer credit risk, so they seem the same.
Fix: In a true sale the assets legally move to the SPV. In a synthetic deal the assets stay put and only credit risk moves, typically through credit derivatives.
Dividing a tranche loss by the pool size instead of the tranche size.
The pool loss is given as a percentage of the pool, so students stop there.
Fix: Subtract the attachment point, cap at thickness, then divide by thickness to get the percentage loss on the tranche.
Saying the senior tranche is risk-free.
It has the highest rating and last loss position.
Fix: Senior tranches lose money once losses exceed their attachment point. Correlated defaults make this more likely than models assume.
Mixing up the order of cash and the order of losses.
Both use the words senior and junior.
Fix: Cash goes to senior first. Losses go to equity first. They run in opposite directions.
Ignoring credit enhancement other than subordination.
Tranching gets most of the attention.
Fix: Remember excess spread, overcollateralization and reserve accounts. They absorb losses before tranches are written down.
Assuming the SPV is owned and controlled by the originator for all purposes.
The originator sets it up.
Fix: The SPV must be bankruptcy-remote and legally separate. Weak separation undermines the true sale and the capital relief.

Worked examples

Example 1

A pool of $500 million is securitized into a senior tranche of $400 million, a mezzanine tranche of $75 million and an equity tranche of $25 million. The pool suffers a loss of $60 million. Find the loss on each tranche.

Show the solution

Attachment points: equity 0%, mezzanine 5% ($25 million), senior 20% ($100 million).
Equity absorbs the first $25 million. It is wiped out.
Remaining loss = $60 million − $25 million = $35 million.
Mezzanine is $75 million thick, so it absorbs the next $35 million.
Remaining loss = $35 million − $35 million = $0. Senior loses nothing.
Mezzanine percentage loss = 35 ÷ 75 = 46.67%.

Answer: Equity loses $25 million (100%), mezzanine loses $35 million (46.67%), senior loses $0.

Example 2

A deal collects $12 million in interest in a period. Fees are $0.5 million. Senior coupons are $7 million and mezzanine coupons are $3 million. Pool losses in the period are $1 million. What is the excess spread, and where does it go?

Show the solution

Add the outflows: fees $0.5 million + senior coupons $7 million + mezzanine coupons $3 million = $10.5 million.
Add losses: $1 million, giving total uses of $11.5 million.
Excess spread = $12 million − $11.5 million = $0.5 million.
Under the waterfall, after senior and mezzanine interest and loss coverage, the remaining cash goes to the reserve or the equity holder per the deal terms.

Answer: Excess spread is $0.5 million. It is the first buffer against losses and is paid to the reserve account or equity holder as the documents specify.

Exam tips

Draw the tranche stack in your head from the bottom: equity, mezzanine, senior. Most loss questions are solved this way.
Read whether the deal is true sale or synthetic before answering any question on balance sheet or capital relief.
When an option says the senior tranche is immune to losses, treat it as wrong unless the loss is below its attachment point.
Link the originate-to-distribute model to weak underwriting incentives. This is a frequent conceptual question.
Check units: loss on a tranche as a percentage of the pool is not the percentage loss on the tranche.

Practice questions from Structured Credit Risk

Securitization Basics and Structure in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Securitization Basics and Structure: frequently asked questions

What is the role of an SPV in securitization?

The SPV buys the asset pool and issues securities against it. It is bankruptcy-remote, so the originator's failure should not affect investors. It also isolates the pool's cash flows for the tranche holders.

What is the difference between a true sale and a synthetic securitization?

In a true sale, the loans are legally transferred to the SPV. In a synthetic securitization, the originator keeps the loans and transfers only the credit risk, using credit default swaps or credit-linked notes. Synthetic deals give risk transfer but not cash funding from asset sale.

How does the securitization waterfall work?

Cash collected from the pool pays fees first, then senior interest, then mezzanine interest, then principal according to the deal's rules, with any residual to equity. Losses run the other way, hitting equity first and senior last.

What is attachment and detachment point?

The attachment point is the pool loss level at which a tranche starts to lose money. The detachment point is the level at which it is fully wiped out. The difference is the tranche thickness.