Cost: $300 (attic insulation), $23 per 4' x 8' board (solar sheathing), $4,000 (new roof), $600 (whole-house fan), $570 (whole-house heater), $1,450 (two skylights) After $18,500 in rebates and ...

Cons: Foam board insulation can be harder to install snugly in unusually shaped spaces, leaving gaps for air to flow. To create an effective air and moisture seal, you need to tape all seams ...