The client
A self-build in Thetford Mines carried a $445,000 as-improved lending value, including a detached workshop appraised at $55,000 of contributory value.
As-improved lending value
$445,000
10% down, insured
Detached workshop
$55,000 appraised value
Counted in the lending value
Dwelling's own insured value
$320,000
Excluding the workshop
Other debt
$255/mo car loan
The problem
A standard homeowner insurance form automatically extends only a small percentage of the main dwelling's own coverage to a detached structure on the same property -- adequate for a garden shed, not for a purpose-built workshop the appraiser had already counted as real contributory value.
What the binder actually covered
- ▸The insurance binder extended a 10% automatic sublimit on the $320,000 dwelling coverage -- $32,000 -- to the detached workshop
- ▸The appraisal had already counted $55,000 of contributory value from that same workshop toward the lending value
- ▸The $23,000 gap between the two was invisible until the final draw's own review lined them up side by side
The workshop was real, built, and already counted toward what the lender had agreed to advance. The insurance binder, on its own default terms, had never actually caught up to it.
The numbers
Once the gap between the appraisal and the binder was identified, the fix was a straightforward insurance schedule addition -- the underlying mortgage math never changed.
| The insured construction takeout | Amount |
|---|---|
| Base mortgage (90% of as-improved value) | $400,500 |
| Default-insurance premium (3.10% at 90% LTV) | +$12,416 |
| Total insured mortgage | $412,916 |
| Ratio check at the qualifying rate | Figure |
|---|---|
| Payment at the qualifying rate (7.00%), 25 years | $2,892/mo |
| GDS (payment + $345 tax + $135 heat) ÷ $8,900 income | 37.9% |
| TDS (GDS numerator + $255 car loan) ÷ $8,900 income | 40.8% |
37.9% and 40.8% sit comfortably inside CMHC's 39% GDS and 44% TDS maximums -- self-build activity of exactly this scale is what Canadian housing starts data tracks nationally. The ratios were never the problem on this file; the insurance binder's own coverage gap on the detached workshop was.
The solution
A courtier hypothécaire licensed under Quebec's Act respecting the distribution of financial products and services treated the detached workshop as its own insurance-scheduling item, distinct from the construction holdback's own draw conditions.
First, compared the appraisal's own contributory-value breakdown against the insurance binder's coverage schedule line by line, rather than assuming a single overall binder number meant everything appraised was actually insured.
Second, had the insurance broker specifically schedule and insure the detached workshop at its own replacement cost, closing the $23,000 gap between the automatic sublimit and the structure's real value.
Third, supplied the updated binder to the solicitor before the final draw, so the lender's security matched what the appraisal had already relied on to set the lending value in the first place.
The outcome
The final draw released once the binder actually covered the workshop the appraisal had counted, with the completed takeout funding insured at 37.9% GDS and 40.8% TDS, and Quebec's welcome tax on the purchase coming to $4,786.
Both ratios sit comfortably inside CMHC's 39% GDS and 44% TDS maximums; the file was never close to either ceiling. The insurance binder's own coverage gap on the detached structure, not the mortgage math, was what needed fixing.
What to take from this file
- 01An insurance binder's automatic detached-structure sublimit is built for a shed, not a purpose-built workshop. Never assume a single overall coverage number means every structure on the property is actually insured to its own value.
- 02Compare the appraisal's contributory-value breakdown against the insurance binder's coverage schedule, structure by structure. The gap between the two is often invisible until someone lines them up side by side.
- 03A detached structure can be specifically scheduled and insured at its own replacement cost. It is a routine fix once the gap is identified -- the hard part is finding it before the final draw, not fixing it.
- 04The lender's security should match what the appraisal actually relied on. If a structure's value counted toward the lending value, it needs its own adequate coverage, not a default sublimit.
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.
- ▸Gouvernement du Québec — Droits sur les mutations immobilières — Quebec's transfer duties ('welcome tax') — 2026 indexed brackets.
Illustrative in this file — lender-specific, not rules:
- ▸5.00% contract rate — rates move daily; not a quote.
- ▸the 10% automatic detached-structure sublimit — each insurer publishes its own automatic sublimit for a detached structure; there is no universal percentage.
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.