Roofs framed before 1900
This state has housing stock that predates building codes, dimensional lumber and the idea that a rafter should be sized from a table. Those roofs have stood for a century and a half, which is its own argument — but they behave differently from anything built after the war, and a quote written for a 1970s colonial does not apply to them.
How they were built, and what moves
Rafters were cut from what was available and sized by the builder’s judgement, often with no ridge beam and no collar ties, relying on the joists below to keep the walls from spreading. Sheathing was wide boards laid with gaps between them, which suited wood shingles that needed to breathe on both faces. Nothing about that assembly is wrong; it is simply a different system.
What shows after a hundred and fifty winters is deflection — a visible sag along the ridge or a dip between rafters, usually where the load has always been heaviest. Slow deflection is normal on these houses and is not the same thing as failure. What matters is whether it is still moving, and that is a question for someone qualified to assess structure, not for a roofer with a ladder.
What replacement actually involves
Two things a modern quote must address. The sheathing: a contemporary covering needs a continuous nailable surface, so the gapped boards get a layer of sheeting over them before anything else goes down. That is real material and real labour and it should be a stated line rather than a discovery. And the weight: three layers of asphalt weigh considerably more than the wood shingles the frame was built for, which is worth naming out loud before adding a second layer to an old roof.
One more consideration specific to old houses here: many sit in local historic districts where exterior work goes through review, and the timeline for that has nothing to do with weather. Confirm it with the town before booking a crew, not after.