Our latest Question of the Week comes from a homeowner in New Jersey. Monica is uncertain of the best way to insulate the roof of a new second-story addition on her Cape Cod home. She wonders whether it's wise to insulate directly under the roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. — especially since the mounting system for her photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. array requires 54 holes to be drilled in her asphalt shingle roof.

Monica wrote, "Is spraying the roof deck with foam going to increase the possibility of a major problem down the road if a leak should develop? There will be 54 holes drilled for the solar mounting system, and even though the installer assures me they won't leak....well....of course they will say that!"

Robert Riversong pointed out that it makes sense to bring her attic inside the home's thermal envelope — especially since she has a furnace in the attic.

Martin Holladay pointed out that there are mounting systems available for standing-seam metal roofs that don't require roof penetrations.

John Brooks reminded Monica that it will be expensive to dismantle the solar array when her shingles wear out.

What do you think?

To read Monica's question and all of the responses it generated, see "Insulation options are of concern with solar panels."