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Every roof penetration for a furnace vent, water heater flue, or plumbing stack needs its own flashing, and while these components are individually inexpensive, they come up often enough in roof claims that it is worth understanding how they are built and evaluated. A metal furnace or B-vent flashing typically consists of a flat metal base plate integrated with shingles around it and a raised metal collar or storm collar fitted around the pipe itself, sometimes finished with a rain cap depending on the appliance being vented. Plumbing stack flashings, often called boots, are usually a metal or plastic base plate with a flexible rubber or thermoplastic collar molded to seal tightly around the pipe.
The rubber or thermoplastic collar on a plumbing boot is generally the weakest point of the assembly over time, since it is exposed to ultraviolet light and temperature swings and tends to crack or deteriorate years before the metal base plate or the surrounding shingles show comparable wear. This creates a recurring situation in roof inspections and claims: a roof damaged by hail may also have pipe boots that are cracked or split from ordinary aging, a condition unrelated to the storm event but discovered during the same inspection because the roofer or appraiser is on the roof examining every penetration.
Some manufacturers now offer boots with a lead or aluminum collar bent tightly around the pipe instead of a molded rubber gasket, a design intended to eliminate the rubber degradation problem entirely by relying on the malleability of soft metal to maintain a seal as the pipe and roof shift slightly over time. These metal collar boots are increasingly specified in colder climates where the freeze thaw cycling common across a Minnesota winter accelerates the aging of standard rubber compounds.
Metal furnace and stack flashings themselves can be dented by hail in the same way that other exposed metal roof components are, and denting on the collar or storm cap is one of the more reliable places to look for hail evidence, since these are among the softer, more exposed metal surfaces on the roof and often mark more clearly than shingles or step flashing. Comparing the pattern, size, and density of impacts on these flashings to impacts found elsewhere on the roof and on other metal surfaces around the property, such as gutters or window screens, is a standard technique used to help distinguish hail impact from other causes.
When a roof is replaced, standard practice calls for replacing pipe boots and furnace flashings along with the shingles, both because reusing an aged rubber collar under new shingles creates a near certain future leak and because most manufacturers do not warrant a new roof installed over old penetration flashings. Whether damaged or deteriorated boots and stack flashings found separately from the storm-related roof damage are addressed as part of the same claim, treated as routine maintenance, or handled some other way is a question that belongs to the policy and the parties, not to the physical inspection, which simply documents what condition each component is in.
This article is general education about how the appraisal process commonly works. It is not legal advice, and specific procedures can vary by state and policy.
Russ Lis is a working property insurance appraiser and umpire based in Minnesota, serving clients nationwide. Contact Appraisal Resolution.