The Third Layer
A homeowner in a 1972 subdivision asks you to re-roof a 1,850-square-foot, 4/12 gable ranch. Two layers of three-tab shingles are already on the roof, the sheathing is 7/16-inch OSB, and the attic has continuous soffit venting but no ridge vent - only two small gable-end louvers. He wants to save $2,400 by having you install a third layer instead of tearing off, and says a cousin who "does roofs" told him it is legal. Your signed proposal assumed a full tear-off and he has paid a $2,000 deposit. The lowest competing bid is $1,100 under yours and, from what the homeowner describes, is also an overlay. Material delivery is Thursday.
1. How do you answer the homeowner, and what actually determines whether an overlay is permissible on this roof?
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Separate the two questions: what the code allows, and what the manufacturer allows.
- Layer count. Residential codes modeled on the IRC cap roof coverings at two layers over the original deck. Two layers already exist, so a third is out - the cousin's advice fails on the arithmetic alone.
- Local amendment. Layer limits and tear-off triggers are commonly amended at the local level in Michigan. Call the building department that will actually inspect this address and get the answer in writing before you promise anything.
- Fastening. Shingle fasteners must penetrate the deck. Driven through two old layers, nails are effectively short and the new field is fastened to whatever the aged layers will hold.
- Dead load and ventilation. A third layer adds roughly 200–250 lb per square, and this attic has two gable louvers and no ridge vent - the deck stays hot and wet regardless.
The honest answer is "I will not match that bid, and here is why," followed by real options: architectural shingles instead of three-tab, phased work, or a payment schedule. Do not solve a price gap with a code violation, and get the homeowner's decision in writing before the dumpster arrives.
2. Two-thirds through the tear-off you find three sheets of delaminated OSB at the valley and no ice barrier anywhere. The homeowner says to just "cover it back up" and argues the ice barrier was never there before. What do you do?
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Neither item is discretionary once the deck is open under permit.
- Stop and document. Photograph the delamination and the bare eave with a tape measure and a date stamp. A concealed defect that is covered without a record becomes your defect.
- Ice barrier. Michigan winters put the average January temperature at or below 25°F, so ice-barrier membrane at the eaves is a code item triggered by the permit - the fact that the original builder skipped it in 1972 is not a defense for you in 2024. The membrane normally extends from the eave edge to 24 inches inside the exterior wall line.
- Deck repair. Delaminated OSB will not hold fasteners. Replace it; price it at the unit rate in your contract, not as a surprise.
- Paper it. A written change order signed before the work continues, showing added cost and added days. If the homeowner refuses a code-required item, say in writing that you cannot deliver a code-compliant roof under those terms and let him decide - do not proceed and hope the inspector misses it.
The judgment being tested is that the contract price never authorizes a concealed code violation.
3. If the homeowner insists on the cheaper overlay and signs a waiver releasing you from all liability, are you protected?
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No. A homeowner's release does not bind the building department, the manufacturer, or a future buyer's inspector.
- The AHJ enforces the code, not the contract. A signed waiver is not a permit amendment. If the inspector red-tags a third layer, you pay to remove it.
- Warranty. Most shingle manufacturers void or limit coverage when their product goes over two existing layers or over an unknown substrate. You would be selling a roof whose paper warranty is already dead.
- Future liability. The waiver may be recharacterized as an adhesion contract or as your professional negligence in writing, and it will read badly in any later dispute.
Use the waiver conversation as a sales moment instead: explain the two-layer rule, show the dead load and ventilation numbers, and offer a scope that fits his budget honestly. If he still wants the third layer, decline the job. Losing a $14,000 roof is cheaper than removing one.