CMBS
Also known as: Commercial mortgage-backed security, Conduit CMBS
Securitised loans against offices, malls and hotels. Fewer, larger, lumpier loans than residential — which makes the analysis property-by-property and the tail much thicker.
1 · SnapshotThe one idea to remember
2 · BeginnerWhat is it, really?
A CMBS pools loans secured on commercial property — offices, shopping centres, hotels, warehouses, apartment blocks — and sells the cash flows as tranched bonds. The machinery is the same as residential MBS; almost everything else is different.
- Far fewer loans. A residential pool holds thousands of small mortgages; a CMBS deal might hold forty large ones, with the top ten dominating. Diversification is thin and one property can matter.
- Loans are usually non-recourse. The lender's claim is against the building and its rent, not against the borrower's other assets. If the property fails, the borrower can hand back the keys.
- Prepayment is mostly prohibited. Residential borrowers refinance freely; commercial loans carry lock-outs, yield maintenance and defeasance. The cash flows are far more predictable — but the credit risk is far more concentrated.
The result is a bond that behaves less like a mortgage portfolio and more like a leveraged claim on a small number of buildings.
Point at a line to read what it is doing.
How do I read this chart?
Losses on the underlying pool run across, losses taken by each slice up. Read it as three step functions rather than three lines: a tranche is untouched until the pool's losses reach its attachment point and then takes everything until its detachment point. The rating on a slice is a statement about where those two numbers sit, not about the borrowers.
Where this is explained properly:
The axes carry no scale on purpose. Every line here is a stylised shape drawn to show a mechanism, so there is no number to read off one — and any figure taken from it would be invented.
- Asset class
- Fixed income (securitisation)
- Instrument type
- Tranched, property-backed bond
- Traded
- OTC; deep US market, smaller in Europe
- Typical users
- Insurers, credit funds, banks, real-estate specialists
Which risks decide the outcome
Not how risky this is, and not a rating — there is deliberately no total. It says which of five failure modes drives what happens here, in the same order on all 129 products so they can be compared. This publication's own reading; see the notice below.
- Marketmatters
- Creditdecides it
- Liquiditydecides it
- Fundingbarely applies
- Operationalbarely applies
What decides it here. One large loan on one building with one tenant list. Diversification is thinner than the label suggests, and the exit depends on a refinancing market that can simply close.
3 · IntermediateHow it works in practice
The two numbers that decide everything
- LTV measures the equity cushion beneath the loan. A 60% LTV survives a 40% value decline before the lender is impaired.
- DSCR measures whether the rent covers the interest. Below 1.0 the property does not pay its own debt, and the borrower is funding it from elsewhere or not at all.
- These are the commercial-property cousins of the cap-rate arithmetic: net operating income over value is the cap rate, and when it falls below the loan rate the equity is being consumed.
The structure
| Tranche | Position |
|---|---|
| AAA (senior) | Paid first, protected by everything below |
| AA–BBB (mezzanine) | Where the risk and the analysis concentrate |
| B-piece (first loss) | Bought by specialists who underwrite every property |
The B-piece buyer is a genuine feature of this market: a specialist who takes first loss, does property-level diligence, and can typically kick loans out of the pool before closing. Their presence is a real alignment mechanism, and it is exactly what the 2008 residential machine lacked.
4 · AdvancedPricing & valuation
The maturity wall, not the default rate
Commercial mortgages are typically interest-only or lightly amortising with a large balloon at maturity, usually five to ten years in. The borrower never intends to repay from cash flow; they intend to refinance. That makes the credit event refinancing failure rather than missed payments:
- A loan can pay perfectly for its whole term and default at maturity because no lender will write a new loan at the property's current value and today's rates.
- This creates a dated, forecastable wall of risk — the maturity schedule is public — which is why CMBS analysts talk about vintages and maturity years rather than about default probabilities.
- Rate increases hit twice: they cut the property's value (a higher cap rate discounts the same rent to less) and raise the new loan's cost. Both squeeze the refinancing at once.
Special servicing and the extend-and-pretend question
- Troubled loans transfer to a special servicer, who can modify, extend or foreclose. Their incentives are set by the servicing agreement and rarely align perfectly with every tranche.
- Senior and junior holders want opposite things. A junior tranche prefers extension — time creates the chance of recovery. A senior tranche often prefers a prompt sale that returns principal. This conflict is structural and is fought in every distressed deal.
- Extensions delay loss recognition. Whether that is prudent workout or denial is only knowable afterwards, which is precisely why reported delinquency rates lag economic reality in this market.
Sector risk is the modern story
Property type dominates outcomes to a degree that surprises bond investors: post-2020, office and older retail have faced structural demand declines while industrial and apartments held up. A pool's property-type mix is a bigger driver of its risk than its average LTV, and single-asset single-borrower deals — increasingly common — remove diversification entirely in exchange for transparency about exactly which building you own.
The formulas above are standard textbook formulations, simplified for teaching. They explain the mechanism — they are not a valuation tool, and they will not reproduce a dealer’s price.
5 · Desk notesHow practitioners think about it
Now say it back
Close the page and give CMBS in four sentences. It takes a minute and it is the only way to find out whether reading it was enough.
- Who wants what — two parties wanted opposite things badly enough to write it down.
- What the contract obliges, and when — not the payoff; the obligation.
- Where the money comes from — name the source, or you have described a hope.
- What makes it lose — the ordinary way, not the dramatic one.
Put CMBS beside any other instrument →
Where this instrument shows up elsewhere
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