A conduit CMBS is a bond backed by a diversified pool of commercial real estate loans that multiple lenders originated separately, sold to a sponsor, and combined into a single trust that issues securities to investors. The “conduit” label describes the assembly-line process: standardized loans flow in from various originators, get bundled by the dozen, and come out the other end as rated bonds. Investors end up with slices of the cash flow from office buildings, shopping centers, warehouses, and apartment complexes across different markets, without ever holding title to a property.
Conduit Deals Are Not the Whole CMBS Market
Commercial mortgage-backed securities come in two main flavors, and it’s worth separating them before going further. Conduit deals pool many loans from many borrowers. Single-asset, single-borrower (SASB) deals securitize one large loan against one property or portfolio controlled by a single borrower. In 2024, SASB issuance made up roughly 68% of the $125.6 billion in private-label CMBS issued that year, so conduit deals are actually the smaller share of the current market.1Trepp. Private-Label CMBS Market Issuance Increased 21% in 2025
The distinction matters because the risk profiles are different. A SASB deal concentrates everything in one borrower and one property; if that borrower defaults, there’s no cushion. A conduit deal spreads risk across dozens of properties, geographies, and borrowers, so a single default has a much smaller effect on the pool. That diversification is the whole appeal of conduit CMBS for investors who want commercial real estate exposure without concentrated bets.
What Loans End Up in a Conduit Pool
Loans that get packaged into a conduit deal have to meet standardized underwriting so rating agencies and investors can model how the pool should perform. Properties are typically stabilized, meaning they have a track record of occupancy and income. Loan sizes generally start at $2 million with no hard maximum, though most fall in the $2 million to $50 million range.
Three underwriting metrics drive eligibility:
- Loan-to-value is capped at 75% of the property’s appraised value, so the borrower keeps meaningful equity in the deal.2Trepp. CMBS 101: Trepp’s Essential Guide to the Life of A CMBS Loan Part 1
- Debt service coverage ratio must be at least 1.25, meaning net operating income covers annual debt payments 1.25 times over.2Trepp. CMBS 101: Trepp’s Essential Guide to the Life of A CMBS Loan Part 1
- Debt yield, calculated as net operating income divided by loan amount, typically has to clear 10%.2Trepp. CMBS 101: Trepp’s Essential Guide to the Life of A CMBS Loan Part 1
Almost every conduit loan is a ten-year fixed-rate instrument amortized over 25 to 30 years. That mismatch is deliberate, but it leaves a large balloon payment due at maturity. Borrowers usually refinance or sell to cover the balloon; if neither works, the loan defaults. This “balloon risk” is one of the defining features of conduit lending, and investors spend a lot of time modeling it.
Conduit loans are also non-recourse. If the borrower defaults, the lender can seize the collateral property but generally cannot pursue the borrower’s other assets. Limited “bad boy” carve-outs exist for fraud or intentional misconduct, but outside those, personal wealth is off the table. Non-recourse structure pushes more of the credit risk onto the trust and, ultimately, the bondholders.
Prepayment is heavily restricted. For at least the first two years after securitization, federal REMIC tax rules prohibit prepayment outright. After that, borrowers who want out generally have to go through defeasance (substituting a portfolio of government securities that replicates the remaining loan payments) or pay yield maintenance (a penalty equal to the present value of the remaining payments). A short open period near maturity usually allows penalty-free payoff, but for most of the loan’s life, exiting early is expensive by design because bondholders are counting on that predictable interest stream.
How the Securitization Gets Assembled
Turning a stack of individual commercial mortgages into tradable bonds is a structured process built to insulate the loan pool from everyone else’s financial trouble.
Various lenders originate conduit-eligible loans and sell them to a sponsor, usually a large investment bank. The sponsor aggregates the loans and creates a special purpose vehicle, a legal entity that exists only to hold the pool. Once the mortgages transfer into the SPV, they belong to the trust, not to the sponsor and not to the originating lenders. If the sponsor or any originator later goes bankrupt, creditors cannot reach into the SPV and seize the loans. That bankruptcy remoteness is the structural backbone of every CMBS deal.
For tax purposes, the SPV is almost always structured as a Real Estate Mortgage Investment Conduit (REMIC). A REMIC has to satisfy specific requirements under the Internal Revenue Code, including that substantially all of its assets consist of qualified mortgages, it has exactly one class of residual interests, and it uses a calendar taxable year.3Office of the Law Revision Counsel. 26 USC 860D – REMIC Defined The REMIC election lets the trust pass income through to bondholders without paying entity-level tax, which is what makes the economics work.
The SPV then issues bonds representing fractional ownership of the pool’s cash flow. Institutional investors buy the bonds, the sale proceeds flow back to the sponsor, and the sponsor repays the original lenders. Everything that happens after that is governed by the Pooling and Servicing Agreement (PSA), which sets out how cash gets collected, how it moves to different bond classes, who services the loans, and what happens when a loan goes bad.
Tranches and the Payment Waterfall
The signature feature of any CMBS deal is its waterfall. Cash flow from the loan pool gets split into layers, called tranches, each with its own credit rating, risk profile, and yield. This is how a single pool of mortgages can attract both conservative pension funds and aggressive hedge funds.
At the top sit the senior tranches, rated AAA. They get paid first from the pool’s cash flow and are last to absorb losses. Their protection comes from subordination: every tranche below them acts as a buffer, so losses have to eat through the bottom tranches before reaching AAA bonds. The tradeoff is that senior tranches pay the lowest yield.
In the middle sit mezzanine tranches, typically rated from AA down through BBB. They stand behind the senior bonds but ahead of the lowest-rated classes, and they pay higher yields to compensate for the thinner cushion beneath them.
At the bottom is the first-loss piece, often called the B-piece. If a loan defaults and produces a loss, the B-piece absorbs it first. Losses cascade upward sequentially: a higher-rated tranche only takes a loss after every tranche below it has been wiped out. The B-piece buyer earns the highest yield in the deal and takes the first hit when anything goes wrong.
Because they’re first in line for losses, B-piece buyers have every reason to scrutinize the pool before the deal closes. They conduct their own diligence on the underlying properties, including independent environmental reviews and property condition assessments, and they hold “kick-out” rights that let them force the sponsor to remove specific loans before securitization. Their influence continues after issuance: the B-piece buyer or an affiliate typically serves as the special servicer or holds the right to appoint and replace one. The most subordinate outstanding bond class, called the controlling class, gets detailed notifications about foreclosures, loan modifications, discounted payoffs, collateral releases, and property management changes, and can designate a representative to weigh in on workout decisions.
Who Manages the Loans After Issuance
Once the bonds are sold, the ongoing management of the loan pool falls to several specialized parties, each with a defined role under the PSA.
Master Servicer
The master servicer handles routine administration for performing loans: collecting monthly payments, managing tax and insurance escrows, monitoring covenants, and passing collected funds to the trustee. Compensation is a small percentage of outstanding loan balances. As long as a loan is current and behaving, the master servicer is the only party the borrower deals with.
Special Servicer
When a loan runs into trouble, it transfers to the special servicer, whose job is to maximize recovery on distressed assets. The triggers go well beyond missed payments. A loan can transfer for repeated late payments, unpaid taxes or insurance, occupancy falling below a specified threshold, the loss of an anchor tenant, approaching maturity with no refinancing lined up, or deterioration in the property’s physical condition. From there, the special servicer might restructure the loan, negotiate a discounted payoff, foreclose, or sell the property. Fees are higher than the master servicer’s and include workout fees tied to successful resolution, an incentive structure worth understanding if you’re a borrower headed into trouble.
Trustee
The trustee is the fiduciary for bondholders, holding legal title to the mortgages on their behalf. The trustee makes sure the servicers comply with the PSA, receives their reports, and distributes principal and interest payments according to the waterfall. The trustee doesn’t make loan-level decisions; it enforces the rules of the deal.
Risks Investors Actually Face
CMBS bonds carry several risks beyond ordinary credit risk, and which ones matter most depends on where you sit in the tranche stack.
- Balloon and extension risk is where most of the real trouble comes from in conduit CMBS. Because loans amortize over 25 to 30 years but mature in ten, every borrower faces a balloon payment. If refinancing or a sale doesn’t materialize, the loan defaults. The special servicer may extend or modify the loan, which delays payments to bondholders and stretches the bond’s life beyond expectations. As of December 2025, the overall CMBS delinquency rate stood at 7.30%, and the special servicing rate at 10.71%.4Trepp. CMBS Delinquency Rate
- Concentration risk shows up even in “diversified” pools. Some end up heavy in a particular property type or region. A pool overweight in office properties faces very different risks than one leaning toward industrial warehouses, and the AAA rating alone won’t tell you which is which.
- Interest rate risk works differently here than in most fixed income. Fixed-rate coupons make the bonds behave predictably in one direction, but prepayment restrictions prevent borrowers from refinancing when rates fall, so investors don’t get the reinvestment they’d see with callable bonds. When rates rise, prices drop like any fixed-rate instrument, and the call protection means the portfolio doesn’t naturally turn over into higher yields.
- Credit risk ultimately depends on the underlying properties. Tenants leave, markets soften, values fall. Subordination protects senior tranches from moderate losses, but a severe downturn can erode even highly rated bonds if losses run past the credit enhancement the lower tranches provide.
Post-Crisis Risk Retention
The 2008 financial crisis exposed how securitization could sever loan origination from the consequences of default. In response, Section 941 of the Dodd-Frank Act requires the sponsor of a CMBS securitization to retain at least 5% of the credit risk of the securitized assets, and prohibits hedging or selling that retained exposure.5SEC. Credit Risk Retention Final Rule
Sponsors can meet the requirement several ways. A vertical interest means holding at least 5% of every tranche. A horizontal interest means holding the most subordinate tranche in an amount equal to at least 5% of the fair value of all bonds issued. Combinations of the two are also permitted.6eCFR. 17 CFR Part 246 – Credit Risk Retention In practice, most conduit CMBS deals satisfy the rule through horizontal retention, with a third-party B-piece buyer holding the first-loss position for at least five years. The rule, first enforced in late 2016, has thinned the ranks of firms willing and able to sponsor conduit deals, because holding that retained risk requires meaningful capital.