climate zone 6 roof retrofit

This is a homeowner forum post, not a news story, so there's no program or policy update here — just one person thinking through a renovation and asking for advice from other builders and homeowners.

The homeowner is remodeling a 1986 house in a cold northern climate (climate zone 6). The house has a large central chimney with a single flue that currently helps support parts of the roof and floor, and it's being removed. Part of the roof over the kitchen and living room will become a clerestory — a raised section with its own row of windows near the roofline. The plan is to build a new, non-load-bearing roof over the existing one, adding two layers of fluffy insulation (rated R30 each) with a vented gap between them, sandwiching the original roof deck (the boards or panels under the shingles) in the middle. The question raised is whether that buried roof deck could become a spot where moisture condenses, since it sits between two permeable insulation layers. The homeowner also hasn't decided yet how to insulate the exterior walls, weighing a double-stud wall or a similar deep-cavity approach against the existing 2x6 framing.

For a homeowner reading this: it's a useful reminder that stacking insulation in unusual ways during a roof or wall upgrade can create hidden moisture risks, which is why these details usually get reviewed by someone familiar with building science before construction.