Metal and Shingle on the Same Roof, and the Underlayment That Has to Change
This Fatherland Street house in East Nashville has standing seam metal on some roof planes and asphalt shingle on the rest. That’s common on older homes in the neighborhood, usually a porch or addition that got a metal roof while the main house stayed shingle. It’s also a job most crews would rather not take, because it isn’t one roof. It’s two systems that have to meet cleanly.
Why the underlayment couldn’t be the same on both
Metal panels get considerably hotter than asphalt shingles. A standard self-adhered leak barrier under metal will soften over enough summers, and once the adhesive migrates it stops sealing around fasteners, which is the entire reason the membrane is there.
So the metal sections got 681 square feet of high temperature ice and water barrier rated for that application, rather than the standard product that went under the shingle planes. That distinction gets skipped constantly. Somebody buys one pallet of leak barrier for the whole roof, runs it everywhere, and the failure shows up in year eight as a stain nobody can trace.
What tear off turned up
Under the metal there were two layers of underlayment, one of them self-adhering. Neither belonged there, and both had to come off and go into the supplement, since removal and disposal of a second layer is real labor that nobody scopes until they find it.
That’s the general shape of a roof this age in East Nashville. Whatever the last three roofers did is still up there, and you don’t know what you’re dealing with until the shingles come off. Documenting it with photographs while the deck is open is the only way those line items get paid, which is most of what our insurance claims work involves.
Scope on this one:
- Tear off of existing shingle and metal roofing
- Removal and disposal of a second layer of underlayment found at metal (6.81 SQ)
- High temperature ice and water barrier at metal sections (681 SF)
- CertainTeed Landmark laminated shingles in Moire Black (25 SQ installed)
- CertainTeed Shadow Ridge hip and ridge accessory shingles, Moire Black (8 BDL)
- Standing seam metal roofing at porch and lower planes
- Shingle starter course (3 BDL)
- 6″ standard gauge aluminum eave drip, black (35 PC)
- Gutter and downspout detached and reset at metal sections (10 LF)
- Additional roofer hours for metal and shingle crew coordination (5 HR)
- Decking replacement as needed at tear off
Ordering for a roof you can’t measure cleanly
Thirty one squares of shingle were ordered, 93 bundles. Twenty five squares went on the roof including field waste, and 18 bundles came back to the supplier along with a bundle of starter, three bundles of ridge cap and a roll of leak barrier.
Over-ordering on a mixed roof is deliberate. When metal and shingle meet at angles, cut waste isn’t predictable from a measurement report, and running short mid-install stops the crew. Returning six squares costs a restocking trip. Running out costs a day. The CertainTeed Landmark in Moire Black was matched with Shadow Ridge accessory shingles in the same color, which keeps the manufacturer system intact rather than mixing a generic ridge cap onto a name-brand field shingle.
Where the two systems meet
Five additional roofer hours went into coordinating the metal crew and the shingle crew, which sounds like a line item and is actually the whole job. The transitions are where a mixed roof leaks. Panel terminations, the shingle courses that die into a standing seam edge, and the gutter sections that had to come off and go back on so the metal could be installed correctly underneath.
Work ran from the end of July into late August. That’s longer than a straight shingle replacement of the same size, and the reason is sequencing rather than square count. Metal fabrication and install don’t compress the way a shingle day does. Anyone quoting a mixed roof on a shingle timeline hasn’t done many.
East Nashville has a lot of houses in this condition, part metal and part shingle, with the two halves aging at different rates. If yours is one of them, price both systems honestly rather than shingling over the metal, which we see attempted more than we’d like. We handle roof replacement in Nashville across Davidson County, plus roof repair when a full replacement isn’t what the roof needs yet. More on our Nashville work.