What is commercial-property coinsurance?

Key takeaways

• Use the policy's value definition and coinsurance percentage; do not substitute market value, tax value, loan balance, or purchase price.
• The formula can apply to a partial loss, not only a total loss, subject to the form and valuation terms.
• Agreed value may suspend coinsurance temporarily, but reporting and expiration conditions still matter.
• Review building, contents, tenant improvements, rental value, blanket limits, deductibles, and lender requirements separately.

Exception first: the policy—not a common percentage—controls

A coinsurance calculation applies only if the issued policy contains the relevant condition and the loss, property, value, and limit fall within it. The percentage can differ, and a policy may use agreed-value, reporting-form, stated-value, or other language. Do not assume that 80 percent, 90 percent, 100 percent, or any online example matches the declarations and endorsements.

In ISO's Building and Personal Property Coverage Form (CP 00 10 10 12), the Coinsurance Additional Condition applies only if a coinsurance percentage is shown in the Declarations, and the Agreed Value optional coverage suspends it for the scheduled property until the agreed-value expiration date, after which coinsurance is reinstated. IRMI's commentary on the condition explains that the 100, 90, or 80 percent choices are the basis for the rate credit and that the insurer compares the limit with the required amount at the time of loss. These are educational references; the issued policy, valuation evidence, and claim facts remain controlling.

• Locate the coinsurance percentage, value definition, limit, deductible, and valuation clause.
• Ask when an agreed-value or reporting requirement starts, expires, and must be renewed.
• Confirm whether the condition applies separately to building, contents, improvements, and income.

Sources for this section: Merlin Law Group, Property Insurance Coverage Law blog: CP 00 10 10 12, Building and Personal Property Coverage Form (reproduction of the ISO form); International Risk Management Institute (IRMI): Property Insurance: Coinsurance (William Austin, November 2018).

Whose value and whose property are being measured?

The owner may schedule the building and landlord-owned fixtures, while a tenant schedules contents, equipment, and improvements according to the lease and policy. A property-owning LLC, manager, lender, and tenant can have different interests at one address. A coinsurance issue can arise when one interest is accurately valued but another is omitted or uses a different valuation basis.

For a portfolio, determine whether limits are scheduled per location or shared under a blanket structure, then ask how coinsurance is calculated across locations. Do not assume unused limit at one building cures an underreported value at another without reading the form.

• Building: current reconstruction information and policy valuation basis.
• Contents and equipment: ownership, replacement cost, age, and location.
• Tenant improvements: lease allocation, ownership, and completion value.
• Rental value or business income: projected income, continuing expenses, and period of restoration.

How does the illustrative coinsurance formula work?

A common educational expression is: eligible limit carried divided by the limit required by the coinsurance percentage, multiplied by the covered loss, with the deductible then applied as the policy directs. ISO's CP 00 10 10 12 states the condition in four steps: multiply the value of the covered property at the time of loss by the coinsurance percentage, divide the limit by that figure, multiply the loss (before the deductible) by the result, and subtract the deductible; the insurer pays that amount or the limit, whichever is less, and when one limit applies to several items the condition uses their total value. Other forms change the inputs, valuation date, sublimits, and order of calculation. Treat every example below as hypothetical arithmetic, not a prediction of claim payment.

• Identify the value at the relevant date under the policy.
• Multiply that value by the policy's coinsurance percentage to find the required limit.
• Compare the carried limit with the required limit.
• Apply the policy's loss, deductible, sublimit, and other conditions in the stated order.
• Ask whether agreed value or another endorsement changes the calculation.

Sources for this section: Merlin Law Group, Property Insurance Coverage Law blog: CP 00 10 10 12, Building and Personal Property Coverage Form (reproduction of the ISO form); International Risk Management Institute (IRMI): Property Insurance: Coinsurance (William Austin, November 2018).

How does coinsurance fit into the rest of the property program?

Coinsurance is one limit and valuation condition—not a standalone coverage. Review it alongside replacement cost or actual cash value, agreed value, blanket limits, margin clauses, occurrence limits, ordinance or law, debris removal, equipment breakdown, catastrophe deductibles, and rental-value coverage. A policy can satisfy the coinsurance percentage yet still have an inadequate limit, exclusion, sublimit, deductible, or unaddressed peril.

A lender's required limit may be different from the policy's replacement-cost or coinsurance requirement. Meeting a loan number does not automatically establish adequate insurance to value. IRMI's commentary makes the same point from the claim side: a limit set below the required percentage of replacement cost produces a penalty on a partial loss, and the insurable value should rest on a replacement-cost estimate or appraisal rather than a guess. Ask for a written comparison of lender requirements, policy conditions, and the owner's risk tolerance.

• Valuation and limit: what amount is insured and how is it measured?
• Cause of loss: is the event covered, limited, or excluded?
• Deductible and sublimits: what is retained after the formula?
• Income and code costs: are rental value and ordinance-or-law limits sufficient?

Sources for this section: International Risk Management Institute (IRMI): Property Insurance: Coinsurance (William Austin, November 2018); Merlin Law Group, Property Insurance Coverage Law blog: CP 00 10 10 12, Building and Personal Property Coverage Form (reproduction of the ISO form).

Which restrictions and endorsements should be checked?

Check the property valuation definition, inflation guard, margin clause, reporting form, agreed-value condition, replacement-cost requirements, vacancy terms, protective safeguards, ordinance-or-law treatment, and catastrophe endorsements. An endorsement can modify one condition without removing all other limits. A current appraisal or valuation report is helpful evidence but does not rewrite the policy.

If the property is renovated, acquired, converted, or materially changed, update the values and ask how automatic additions or newly acquired property provisions work. A stale value statement can remain a problem even when the owner believes the building has been insured continuously. On CP 00 10 10 12, for example, the Agreed Value, Inflation Guard, and Replacement Cost optional coverages each apply only to the property for which they are shown in the Declarations, and the Valuation condition settles at actual cash value unless Replacement Cost is selected and the property is actually repaired or replaced.

• Read the declarations and every valuation or limit endorsement together.
• Confirm reporting dates and signatory responsibilities for agreed-value or reporting forms.
• Reconcile replacement-cost evidence to building systems, code assumptions, and current labor and material conditions.

Sources for this section: Merlin Law Group, Property Insurance Coverage Law blog: CP 00 10 10 12, Building and Personal Property Coverage Form (reproduction of the ISO form).

What do lenders, leases, and certificates prove?

A lender may request a limit, valuation, deductible, mortgagee clause, and evidence of coverage, but a certificate does not prove that the limit satisfies coinsurance or that a value estimate is correct. A lease can allocate tenant improvements and contents, yet the policy and endorsement must insure the party with the relevant interest.

Before closing, compare the lender's insurance exhibit with the policy's coinsurance, agreed-value, blanket, margin, and deductible language. If a certificate is issued, ensure its statements are accurate and avoid using it as a substitute for the declarations or forms.

• Identify the mortgagee and title entity exactly.
• Match required limits and deductibles to actual declarations and endorsements.
• Clarify who maintains values and who receives renewal or cancellation information.

How do values and coinsurance affect underwriting and cost?

Underwriters may consider construction, size, occupancy, location, catastrophe hazard, valuation method, loss history, protection, limits, deductibles, shared limits, and the quality of replacement-cost support. An accurate value can increase the limit and premium while reducing an underinsurance exposure; an artificially low value may produce a cheaper quote with a larger retained claim risk.

There is no responsible universal coinsurance savings figure. Compare the limit, condition, agreed-value cost, deductible, sublimits, and retained-loss scenarios on the same property facts. Better documentation supports a defensible quote but does not guarantee a rate or claim outcome.

• Ask for renewal options with current values and a clearly stated coinsurance condition.
• Model the cash exposure at partial loss, large loss, and multi-location loss.
• Treat the cost of a valuation or appraisal as part of total risk management, not a promise of broader coverage.

What documents support a coinsurance review?

A quote submission should show how each amount was developed and which party owns each item. Explain assumptions and date them. Do not copy the expiring statement of values without checking acquisitions, disposals, renovations, inflation, code requirements, and changed occupancy.

• Location-level statement of values with building, contents, improvements, equipment, and income fields.
• Replacement-cost estimate or appraisal with scope, date, assumptions, and exclusions.
• Construction, square footage, roof and system updates, photos, engineering, and code information.
• Lease, lender requirements, title entity, deductible structure, blanket or margin wording, and current policy.
• Loss runs and explanations for material losses, repairs, and unresolved recommendations.
• Requested valuation, coinsurance, agreed-value, reporting, ordinance-or-law, and catastrophe options.

Coinsurance decision table and renewal checklist

The goal is not merely to find a percentage; it is to understand what would be available after a covered loss. Use the table to identify the next question, then verify it in the actual policy.

• At renewal: update each value and identify changes in construction, use, systems, and code.
• Before binding: compare the lender's limit with the policy's required value and coinsurance percentage.
• At agreed-value election: confirm signed values, effective dates, reporting, and expiration.
• After acquisition or renovation: add the location or value promptly and ask how automatic coverage applies.
• At claim planning: calculate deductible, sublimits, coinsurance, and uninsured causes separately.

Valuation and limit conditions are not interchangeable

Sources for this section: Merlin Law Group, Property Insurance Coverage Law blog: CP 00 10 10 12, Building and Personal Property Coverage Form (reproduction of the ISO form); Independent Insurance Agents & Brokers of America (Big "I"): Margin Clauses and Blanket Insurance (Mike Edwards, Big "I" Virtual University, December 2013).

Hypothetical formula checklist

Sources for this section: Merlin Law Group, Property Insurance Coverage Law blog: CP 00 10 10 12, Building and Personal Property Coverage Form (reproduction of the ISO form); International Risk Management Institute (IRMI): Property Insurance: Coinsurance (William Austin, November 2018).

Hypothetical: Hypothetical coinsurance calculation

Assume, solely for illustration, a $1,000,000 policy value, an 80% coinsurance requirement, a $600,000 carried limit, and a $200,000 covered partial loss. The educational formula gives $200,000 × ($600,000 ÷ $800,000) = $150,000 before any deductible or other policy term. The actual policy and facts control.

Hypothetical: Hypothetical agreed-value renewal

Assume a portfolio has an agreed-value endorsement that expires at renewal and the owner does not submit the required updated values. The owner should ask whether coinsurance resumes, what deadline applies, and whether limits still reflect current reconstruction cost. No waiver should be inferred from last year's endorsement.

Hypothetical: Hypothetical tenant-improvement gap

Assume a tenant's equipment is valued correctly but a landlord's building limit omits recently completed improvements. A loss review would separate ownership, valuation, policy interest, coinsurance, deductible, and lease allocation. The example shows why one address can require more than one value schedule.

Sources

• Merlin Law Group, Property Insurance Coverage Law blog: CP 00 10 10 12, Building and Personal Property Coverage Form (reproduction of the ISO form) — accessed 2026-10-18; supports the October 2012 edition of CP 00 10: the Coinsurance Additional Condition (F.1), under which the insurer does not pay the full loss when the value of covered property at the time of loss times the coinsurance percentage exceeds the limit, computed by dividing the limit by the required amount, multiplying the loss by that fraction, and subtracting the deductible, with one limit over several items applied to their total value; the Agreed Value optional coverage (G.1), which suspends coinsurance for the scheduled property until the agreed-value expiration date, after which coinsurance is reinstated; the Increased Cost of Construction additional coverage (A.4.e), which pays the increased cost of complying with the minimum standards of an ordinance or law in the course of repairing or replacing the damaged parts of a building, limited to the lesser of $10,000 or 5 percent of the building limit and available only for buildings with the Replacement Cost optional coverage; and the Valuation loss condition (E.7), which settles at actual cash value unless the Replacement Cost optional coverage (G.3) is shown in the Declarations and pays replacement cost only once the property is actually repaired or replaced..
• International Risk Management Institute (IRMI): Property Insurance: Coinsurance (William Austin, November 2018) — accessed 2026-10-18; supports the commentary on the commercial property coinsurance condition: coinsurance percentages of 100, 90, or 80 percent are the basis for the rate credit; the insurer compares the policy limit with the minimum limit required by the coinsurance clause at the time of loss and reduces a partial-loss recovery proportionally when the limit falls short; worked scenarios in which a limit set below the required percentage of replacement cost produces a penalty on a partial loss but not more than the limit on a total loss; and the observation that a replacement-cost estimate or appraisal, not a guess, should establish the insurable value..
• Independent Insurance Agents & Brokers of America (Big "I"): Margin Clauses and Blanket Insurance (Mike Edwards, Big "I" Virtual University, December 2013) — accessed 2026-10-18; supports that a margin clause caps what a blanket property policy pays for an individual building or location at a percentage of the value reported for it on the statement of values; that the Agreed Value option on a blanket policy otherwise pays a building's full loss up to the blanket limit even when its statement-of-values entry was far too low; that ISO introduced the Limitation on Loss Settlement—Blanket Insurance (Margin Clause) endorsement CP 12 32 in its 2007 commercial property revision; that the ISO Commercial Lines Manual rule 34.B.6 provides rating factors for margin-clause percentages of 105, 110, 120, and 130 percent; and that many insurers use their own proprietary margin-clause wording..
• International Risk Management Institute (IRMI): Coinsurance provision — accessed 2026-09-13; supports Commercial-property definition and illustrative limit-to-value formula, including the possibility of an agreed-value provision; the issued policy remains controlling..
• Travelers Insurance: Commercial Property Insurance — accessed 2026-09-13; supports Insurer explanations of replacement cost, actual cash value, insurance-to-value assessment, lease and lender considerations, and business-income options..
• Federal Emergency Management Agency: Statement of Values and property program hazard context — accessed 2026-09-13; supports Official mapped flood-hazard source to include in location-level value and catastrophe review; it does not calculate replacement cost or determine coverage..