Insulating a Trussed Cathedral Ceiling

A homeowner in Rochester, NY is renting out a tricky insulation question for an advice forum, and it's worth knowing about if you have an older cathedral ceiling (one that follows the roofline, with no flat attic above). The house has a mid-1980s addition with a vented roof, meaning air is meant to flow from soffit vents at the eaves up to a ridge vent at the top, carrying moisture out. But the ceiling cavities were found packed tight with cellulose insulation sagging against stretched poly sheeting, with no baffles (channels that keep the airflow path open), so the venting likely hasn't worked properly in 40 years.

The deeper problem is the framing. The roof is built with trusses rather than solid rafters, leaving only about 5 inches of depth to insulate near the walls, not enough to hit the insulation levels recommended for this climate zone. The roof sheathing also needs replacing eventually, which rules out spraying foam directly under the roof deck for now. The homeowner is weighing a "cut and cobble" approach, which means hand-fitting rigid foam board pieces into each rafter bay, combined with mineral wool batts, while trying not to lower the ceiling height.

This is a niche, technical situation, but it's a useful reminder: vented cathedral ceilings depend on unobstructed airflow from soffit to ridge, and older homes often have that airflow blocked by insulation installed without baffles. If your home has a cathedral ceiling from this era, it may be worth having someone check whether the venting is actually working.