I built my current home 30 years ago, 2 story, crawlspace, zone 9B, stucco with tile roof in Northern California. Most of the roof is vaulted with about 20% attic space. I’ve had some issues with infiltration and leaks over the years, so am planning to enclose a balcony over living space and a terrace over a garage. My current roof, although mostly vaulted, has perimeter 2″ continuous venting under my 3″ overhang, and I have roof vents over my small attic area.

I’m considering extending my overhang to 3 ft, covering all vents and “conditioning” my attic, perhaps my crawlspace as well. My ductwork currently runs through these unconditioned spaces, but I’m also looking to replace HVAC and water systems with heat pump technology. If I can afford to outsulate my existing exterior stucco walls, I would replace windows and install a rainscreen to protect against moisture intrusion and wind-driven rain. I have a couple questions:

1.  Do you have to provide any venting to the interior or anywhere for conditioned attics or crawlspaces? Is it enough to just enclose the spaces and insulate above or around them, or do you have to provide “conditioning” of some sort? If so, what? I was planning to add 3″ of polyiso and a new WRB over everything, possibly even my exterior stucco exterior.

2.  I currently have Grace Ice and Water Shield over all my roof sheathing. Any problem installing 3″ of polyiso over the new insulation? This would in-effect create a sandwich between two roof membranes (one over the existing roof sheathing and one over the new insulation and sheathing above it.) I could still vent the soffit per the detail I sketched.

Thank you in advance for your advice!

Dan Burgoyne
Folsom, California