How much contingency should a window quote include for hidden rot?

I’m comparing quotes for replacing windows in an approximately 40-year-old wood-framed house with vinyl siding. There are 14 openings: mostly standard double-hungs, plus two larger picture windows. I can already see soft trim and staining around three openings, but I don’t know whether the damage is limited to the exterior trim or extends into the sill, studs, sheathing, or framing.

How are others handling the repair allowance for conditions discovered after removal?

I’m looking for quotes that clearly separate:

- Window and installation pricing
- Unit pricing for replacing rotten sill, jamb, framing, or sheathing
- Masonry or siding repair rates, if applicable
- A not-to-exceed allowance for concealed damage
- Photos and homeowner approval before work beyond the allowance

Would you expect a contractor to inspect with a probe or remove limited trim before finalizing the quote, or is a reasonable contingency the normal approach? I’m considering setting aside roughly 10% to 20% of the project budget, but I don’t want an allowance that becomes an automatic charge on every opening.

For anyone comparing bids, did your contractors list repair costs per linear foot, per opening, or by hourly labor plus materials? And did the quote identify which windows had visible damage versus applying one blanket allowance to all 14?