Q&A Spotlight: Insulating Second-Floor Eaves and Attic in Duluth – GreenBuildingAdvisor

By Chuck Bickford | February 2, 2026

Ah, winter in northern Minnesota! One of the coldest places in the continental U.S.—a place where good insulation isn’t a luxury, it’s survival. Duluth resident and member “jh11850” (let’s call them “JH”) is in need of that insulation. The roof is framed with 2×6 rafters at 16-in. on-center, sheathed with 1×8 boards, and finished with asphalt shingles. It has a modest 5/12 pitch and two dormers on each side—classic early-20th-century construction with plenty of nooks where heat can escape.

Inside, the second-floor ceilings follow the roofline down to lower 5-ft. 2-in. exterior walls at the eaves. Above the flat ceiling area is a vented attic insulated with 14 to 16-in. of loose cellulose and ventilated with gable vents and a ridge vent. But the sloped rafter bays at the eaves have only 1 inch of wood-fiber batts. In a Duluth winter, that’s not nearly enough.

JH writes, “Ice dams are an issue. I have managed, via snow removal from the roof, since we moved in, but would like to insulate the roof.” The plan is to remove the drywall, open the sloped cavities, and fill the bays with mineral wool batts all the way past the ceiling line. They’re also considering strapping across the insulated bays with 2x6s, 24-in. on-center, to create more batt space to achieve something close to R-49. The batts would then be covered with 1-in. foil-faced polyiso, seams taped, then drywall.

“My thought is to stop warm interior vapor and allow it to dry up and out into the rest of the roof.”

Which raises the question: what about venting?

The conventional answer is to vent the rafter bays from soffit to ridge, to carry away any moisture that could condense on the underside of the roof deck and cause problems…