Residential underwriting, covered in Course 01, is fundamentally about a person: their income, their credit history, their debt-service ratios, their capacity to keep paying a mortgage for years into the future. Commercial underwriting asks a related but genuinely different question — can this property's own income support this debt? The borrower still matters, sometimes a great deal, but the property's cash flow is the primary evidence a commercial underwriter is looking for, not the borrower's pay stubs.
This shift changes almost every tool in the underwriting kit. Where a residential file leans on GDS and TDS ratios measured against a person's gross income, a commercial file leans on the debt service coverage ratio measured against the property's net operating income — concepts covered in modules 02 and 03. Where a residential appraisal compares a home to recent sales of similar homes, a commercial appraisal often values the property based on the income it produces. The vocabulary overlaps with residential lending in places, but the underlying logic does not transfer directly, and assuming it does is a common and costly mistake for brokers moving into this space.
Residential mortgage lending at federally regulated institutions is shaped heavily by OSFI's Guideline B-20, which sets out expectations for income verification, the minimum qualifying rate, and loan-to-value limits. Commercial mortgage lending has no equivalent single guideline setting national underwriting standards in the same way. Individual lenders, credit unions, insurance companies and private lenders each set their own commercial underwriting criteria, informed by their own risk appetite and by broader prudential principles rather than a single detailed rulebook.
Practically, this means the ranges quoted throughout this course — DSCR minimums, loan-to-value maximums, typical amortization periods — are genuinely ranges, reflecting real variation across the market, not a single number every lender applies. Where residential training material can quote OSFI's stress test with precision, commercial training has to speak in terms of what is typical and what varies, and a good commercial broker develops a feel for that range across several lenders rather than memorizing one fixed rule.
"Commercial mortgage" spans a wide range of property types: multi-unit residential rental buildings (five units and up, which is where CMHC's multi-unit insurance programs apply — see module 09), retail plazas, office buildings, industrial and warehouse space, and mixed-use properties combining several of these. The underwriting principles in this course — DSCR, NOI, cap rates, tenant quality, property class — apply across all of them, though the specific numbers a lender expects will vary meaningfully by property type. A well-leased grocery-anchored retail plaza and a half-vacant older office building are both "commercial," but they are not remotely the same risk.
This course does not cover raw land, construction or development lending in depth — construction financing generally, including builder-scale projects, is covered in Course 15 — nor does it cover very large institutional-grade transactions, which involve additional layers (syndication, mezzanine debt, capital markets) beyond this course's scope.
A commercial file typically involves more parties than a residential one: a commercial appraiser using an income approach, sometimes an environmental consultant, a lawyer or notary handling more complex security documents, and often an accountant reviewing the borrower's corporate financial statements alongside the property's own operating statements. The broker's role shifts accordingly — less about assembling a personal income file, more about assembling and interpreting a property's financial story, and understanding which of several very different lender types (bank, credit union, insurance company, private/alternative) is the right fit for a given deal. That fit question is picked up directly in the closing module of this course.
What is the primary question a commercial mortgage underwriter is trying to answer, as distinct from a residential underwriter?
Commercial underwriting centres on the property's cash flow because that income, not the borrower's personal paycheque, is what will actually service the debt in the normal course. Guideline B-20 is specifically a residential mortgage underwriting standard — it does not set commercial underwriting rules, which is one of the central differences this module establishes. Credit score and geography can be relevant inputs on some files but are not the defining question the way property income is.
