Help with my Half-Assed Attic – GreenBuildingAdvisor

GBA enabled me to GC the energy aspects of the gut-renovation of my 1960s ranch (Maine coast, zone 6a) to a Pretty Good House level- completed in 2022.  I thought I could live with the attic I knew I was half-assing- it was fatigue, budget, schedule, etc.  But I have a bad summer attic overheating situation (a near-constant “heat blanket” that can reach 130 many afternoons) that I believe compromises indoor comfort for the 4-5 weeks of our peak summer. I am seeking suggestions for relief.

The attic ended up a mongrel, for sure, with very little ventilation and (only) decent floor insulation. I had a contractor spray foam the long overhanging soffits to eliminate thermal bridging to the living space- too bad, it’s done, can’t bear to think of excavating any for venting. Besides, I have inadequate ridge venting from the roof contractor’s metal-bending and installation.  There’s a new carpenter-built vent in each gable, about 2 x 2ft sq,  but free space is reduced by screening and slanted weather baffles.

The roof has 3/4 ply deck, full-cover stick-on membrane, medium gray metal roof on horizontal sleepers (very little air movement btwn them).  The roof gets direct sun all day long.  No insulation currently in the 2×6 rafter bays.  The attic floor got R-60 blown-in cellulose (has settled a bit since install) on top of a well-detailed poly vapor barrier. The one blower door test we did, after completion, was 1.53 ACH50.  Ducts for kitchen, baths, and HRV sit on attic joists and are covered by the cellulose. I haven’t measured attic humidity at all, but I expect the good vapor barrier keeps that to a minimum year-round. Assumption??!

On warm or hot days I manage the windows (but most are awnings, so limited air change), screen doors, and two floor fans to help reduce interior temperatures and cool off somewhat overnight.  But then the cycle begins again.

I’ve read what I can find on both GBA and BSC, but because it’s a mongrel, I turn to the Forum for help.  Access to the attic is limited to a 2×2 hatch and the gable vent spaces via ladders.  Improvement options seem to include:

– Least expensive and least intrusive, simply add to the existing attic cellulose (can easily add 5” more) and continue experiments with windows and fans in the living space

– Spray foam the 2×6 rafter bays. If so, open, closed-cell, or a combo?

– Netted loose-fill fiberglass or cellulose in the rafter bays.  If so, most suitable netting type?

– Installing one or two powered gable vent fans (the air-tightness at attic floor probably makes this ‘safe’?)

– Something else? Rigid foamboard installed across the rafter faces?

In all cases except powered gable fans, should I cover the gable vents and try to seal the ridge to make it unvented? Also, I really fear a contractor puncturing the vapor barrier and not repairing it, so I’ll have to manage that.

Thanks for knowledge and viewpoints!