For many readers, ’tis the season to stay warm, and sometimes that means beefing up insulation. GBA-er “B3llo38” (B3) hails from Climate Zone 4A, specifically southern New Jersey. In this Q&A post, he writes that he’s in the process of insulating an existing vaulted ceiling. The roof is vented (soffits and ridge) and framed with 2×8 rafters. He doesn’t want to add rigid insulation to the roof’s exterior because the roof is only 6 years old, and he doesn’t want to spray the interior roof deck with closed-cell foam, as it would interfere with the venting.

He’s adding baffles to each bay for venting, and had planned a flash-and-batt strategy of 3 to 3-1/2 in. of spray foam and 3-1/2 in. of R-15 batts to achieve somewhere between R-35 and R-39. However, the baffles take up 2 in. of depth, leaving him with only 5 in. of space, so he needs to gain another 2 in. or so of space to get to the intended R-value.

Weighing his options, B3 says he doesn’t feel right about installing rigid insulation over the interior face of the rafters, as he thinks that will lead to nail pops in the drywall. He also wonders if he could use a shallower baffle—but that combined with 2 in. of spray foam and 3-1/2-in. batts, would only yield R-29.

His third idea is to add 2×2 furring strips to the bottom of the rafter, effectively increasing the depth by 1-1/2 in., but he’s not sure of the best way to install them, or if it would be better to run the strips perpendicular to the rafters.

So, what’s the best way for B3 to install the most insulation possible in his cathedral ceiling?

…