Coverage tower analysis is jurisdiction-sensitive, document- intensive, and frequently superficial. The single most under-flagged issue in tower exhaustion work is whether defense costs erode policy limits or sit outside them, layer by layer. Get that wrong and the entire allocation analysis is off. This article walks through the question and what a complete tower exhaustion brief covers.
The structure of a tower
A coverage tower has a primary layer, one or more excess layers, and often an umbrella layer above. Each layer carries its own attachment point, its own limit, its own policy period, and — this is the part that matters — its own answer to whether defense costs erode that layer's limits or sit outside them. The policy language varies by carrier, by layer, and by vintage. Reading "defense costs are paid in addition to limits" on the primary policy tells you nothing about the excess.
Why defense-cost erosion matters operationally
A $5M primary layer with eroding defense costs that has paid $1.5M in defense and $1M indemnity is at $2.5M exhausted, not $1M. The excess attaches when defense plus indemnity hits $5M, not when indemnity alone does. If the analysis assumes defense costs sit outside limits when they actually erode, the excess is expected to attach later than it actually will. The policyholder plans poorly; the excess carrier plans poorly; settlement negotiations happen on the wrong number.
The mirror error is also costly. If defense costs are assumed to erode when they actually sit outside, the policyholder under- utilizes primary defense and over-reserves on excess. Either direction, the wrong assumption produces wrong economic decisions.
What a complete tower exhaustion brief covers
SpotlightAICore builds D40, the Trial-tier Coverage Tower Exhaustion Brief, around seven components.
Tower structure. Each layer: carrier, policy number, layer position, attachment point, limit, policy period, gaps, sublimits-exhausted-first issues.
Exhaustion sequence. Under the operative policy terms and applicable law, whether the tower attaches horizontally (every primary exhausted before any excess attaches) or vertically (one primary then one excess). The rule is policy- and-jurisdiction-specific and the brief cites the source for whichever rule applies.
Allocation method. Pro rata by time-on-the-risk (the Owens-Illinois approach), all sums, joint-and- several, or something else. Jurisdiction-sensitive; cite the authority.
Payment history mapped to tower. Every payment made under each policy, applied against limits, with documentary basis. Double-payments, payments under reservation of rights, and payments that may have eroded limits incorrectly all get flagged.
Defense-cost erosion per layer. The decisive section. For each layer: yes / no / unclear on whether defense costs erode, with the policy-language citation and the implication for exhaustion. "Unclear" is a valid answer when the policy language is ambiguous; it triggers an open question for coverage counsel rather than a hidden assumption.
Leakage and disputes. Disputes between carriers (priority, horizontal vs. vertical, allocation) and disputes between carriers and the insured (denial, reservation, late notice). Both shape the operative number.
Exhaustion conclusion. The layer currently at risk, the amount remaining before the next layer attaches, what triggers the attachment, and the recommended next step.
Who buys this
Coverage counsel on both sides. Policyholder counsel needs the analysis to plan defense spend and settlement strategy. Carrier counsel needs it for reservation-of-rights posture and inter- carrier allocation disputes. In-house counsel at insureds with complex programs (D&O / E&O towers, environmental legacy programs, products-liability towers) often want the analysis quarterly as the matter develops.