The client
A buyer in Cobourg purchased a $390,000 legal duplex with a basement bachelor secondary suite, at 10% down, on $7,200/month of their own income -- income that alone could not clear CMHC’s GDS ceiling without help from the suite’s rent.
Purchase price
$390,000, Cobourg
10% down, insured, legal duplex
Rent schedule's own figure
$1,450/month
Priced against one-bedroom comparables, in error
Corrected market rent
$1,050/month
Priced against bachelor-unit comparables matching the suite as built
Buyer's own income
$7,200/month
Not enough alone to clear GDS
The problem
A lender’s appraisal for a property with a secondary suite typically includes a rent-schedule addendum estimating the suite’s market rent from comparable rentals nearby -- and that addendum is only as reliable as the comparables the appraiser actually selected.
What the appraisal contradicted about itself
- ▸The report's own unit-description field correctly identified the basement suite as a bachelor unit -- no separate bedroom
- ▸The same report's rent-schedule addendum selected one-bedroom comparables to estimate the suite's market rent anyway
- ▸The resulting $1,450/month figure was well above what a genuine bachelor unit in that building actually commands, and nobody had reconciled the two fields against each other before the file was submitted
The buyer's own income never cleared the GDS ceiling on its own. Whether the file could close at all depended entirely on which of the appraisal's own two contradicting numbers the lender actually used.
The numbers
Correcting the rent schedule -- not any change to the mortgage itself -- is what decided whether this file could close.
| Qualifying with the suite's rent, correctly priced | Amount |
|---|---|
| Base mortgage (90% of purchase price) | $351,000 |
| CMHC premium (3.10% at 85.01-90% LTV) | +$10,881 |
| Total insured mortgage | $361,881 |
| GDS, buyer's income plus 50% rent add-back | Mispriced one-bedroom comparable | Corrected bachelor comparable |
|---|---|---|
| Rent schedule's own figure | $1,450/mo | $1,050/mo |
| 50% add-back to qualifying income | +$725/mo | +$525/mo |
| GDS on income plus add-back | 36.7% | 37.7% |
On the buyer's own $7,200/month income alone, GDS runs 40.4% -- above CMHC's 39% ceiling. The mispriced one-bedroom comparable's add-back would have shown a comfortable 36.7%; the corrected bachelor comparable shows 37.7% -- both clear the ceiling, consistent with how thin these margins can run per rental vacancy rate data, but only one of them describes the suite actually built.
The solution
A mortgage agent licensed under Ontario’s Mortgage Brokerages, Lenders and Administrators Act read the appraisal as one document that had to agree with itself, not two independent numbers to pick between.
First, flagged the internal contradiction directly to the appraiser -- the unit-description field's own "bachelor" finding against the rent schedule's own one-bedroom comparable set -- rather than accepting the higher figure because it helped the file.
Second, requested a revised rent-schedule addendum using bachelor-unit comparables actually matching the suite as built, drawn from the same immediate market.
Third, resubmitted the file on the corrected rent, showing the lender both the original and revised addenda side by side so the correction was transparent rather than quietly substituted -- one of several rental income offset methods a lender may apply, and each depends on the underlying rent figure actually being right.
The outcome
The purchase funded insured at 37.7% GDS and 40.6% TDS on the corrected, bachelor-comparable rent -- a real approval, but a noticeably tighter one than the mispriced $1,450/month comparable would have shown.
Both corrected ratios sit inside CMHC's 39% GDS and 44% TDS maximums; the buyer's own income alone, at 40.4% GDS, did not.
What to take from this file
- 01A single appraisal report can contradict itself. Check a rent-schedule addendum's comparables against the same report's own unit description before relying on either.
- 02An add-back convention is only as accurate as the rent it's applied to. A mispriced comparable can make a file look safely inside a ratio ceiling it is actually much closer to.
- 03Flag an internal inconsistency to the appraiser directly, in writing. A revised addendum is faster, and more defensible, than choosing between two numbers on the same report.
- 04A tighter, correct approval is a real approval. A wider-looking margin built on a mispriced comparable is not actually safer -- it is simply wrong.
Sources
Every regulatory figure in this file traces to one of these primary sources. Client details and anything that varies by lender are illustrative, as flagged below.
- ▸CMHC — Purchase (Mortgage Loan Insurance) — default-insurance premium schedule by LTV band (25-year amortization).
- ▸CMHC — CMHC Home Start — minimum down payment tiers (5%/10%) and the $1.5M insured price cap.
- ▸OSFI — Minimum qualifying rate for uninsured mortgages — the minimum qualifying rate — greater of contract rate + 2% or 5.25%.
- ▸CMHC — CMHC Reviews Underwriting Criteria — GDS 39% / TDS 44% maximums and the 600 credit-score floor for insured files.
- ▸Provincial/territorial mortgage-broker legislation fetched directly (bclaws.gov.bc.ca, legisquebec.gouv.qc.ca, fcaa.gov.sk.ca, web2.gov.mb.ca, nslegislature.ca, assembly.nl.ca) plus FCNB's own site for NB and CanLII's index for PE — see notes for per-province method — provincial mortgage regulators and licence titles.
Illustrative in this file — lender-specific, not rules:
- ▸4.90% contract rate — rates move daily; not a quote.
- ▸the 50% rental add-back convention — each lender publishes its own treatment for a secondary suite; there is no universal rule.
Authority & provenance
How this case file was built
We publish the origin, the verification method and the reviewer for every case file, so you can judge how far to trust it before you rely on it with a client.
Where it comes from
Derived from files handled by Treadstone’s fulfillment desk and from scenarios contributed by partner brokerages. Names, employers, exact amounts and dates are changed so no client or file is identifiable.
Provenance: Composite — a pattern seen repeatedly on fulfilled files, not a single transaction.
What is verified
Every regulatory figure traces to a primary source listed above and was checked against it on the date shown. The arithmetic is recomputed by machine on every rebuild.
Anything that varies by lender is labelled illustrative rather than stated as a rule.
Who reviewed it
Reviewed for Canadian regulatory accuracy before publication, and re-checked whenever a cited rule changes.
Reviewed by: Nicholas Parson, Treadstone Associates — reviews every case file before publication.
This case file is professional reference material for licensed mortgage professionals. It is not advice to a borrower, and it is not a lender commitment. Insurer rules, qualifying rates and provincial taxes change — confirm the current position with the insurer, regulator or lender before you rely on any figure here in a live file.