The second layer
For decades it was normal in this state to lay a new roof directly over the old one. It saved a day of labor and a dumpster, it passed inspection, and on a great many houses here it is still up there, two coverings deep, with the original problem sealed underneath.
- 1 Ridge caps. Thin, exposed, and the first course to lift.
- 2 The field. The course you can see, over the underlayment you cannot.
- 3 Valleys. Leaf load mats where two slopes drain as one.
- 4 Flashing. Old masonry, and the wall an attached house shares.
- 5 Vent boots. The rubber cracks years before the shingles around it are done.
- 6 Eaves and ice dams. Where the melt runs out of warm roof and turns back into ice.
What the shortcut cost
Three things, all of them deferred rather than avoided. The deck was never seen, so any soft sheathing, old leak damage or missing nailing surface stayed hidden under the new work. The second layer runs hotter than the first, because it sits on asphalt rather than on wood and sheds heat more slowly, which shortens its own life. And the flashings were usually not replaced. New shingles were brought up to old metal and sealed, which is exactly the joint that freeze-thaw cycling opens first.
The bill arrives at the next replacement. Tearing off two layers is close to twice the labor and twice the disposal of one, and the deck underneath is an unknown until the moment it is uncovered. That is why the same house can receive two quotes thousands apart from bidders who are simply assuming different things.
Finding out before the quote does
You can often see it from the ground: look at the roof edge at a rake or gable end, where a double thickness shows as a step. A closer look at the eave from a ladder is more reliable.
Permit records for the property can tell you when the last work was done and whether it was a tear-off or a recover. Failing those, insist that every quote state the layer count it assumes and the price if there is another. That single sentence turns the biggest unknown in a north Jersey roofing job into a number you agreed to in advance.