1950s Los Angeles ranch style house with 32F lows in winter and 95-115F highs in summer. Ceiling above family room has exposed 6×6 wood beams with 1×6 pine tongue and groove slats resting on top. Above this ceiling is the bare wood slats with an inch or two of blown in insulation. No paper, no housewrap, no drywall, no other insulation, nothing but dust. Roof above barely-standing-room attic has turbines and ends of home have gable vents, no soffit vents where roof line meets walls.
Access to attic is through 30×30" entry.
How to insulate above slat ceiling?
After removing existing blown in insulation, I'm thinking:
(1) lay housewrap and use some kind of caulk/sealing around edges imperfect air seal
(2) drywall* screwed to slats with mortar between edges, expanded form all the way around to complete the air seal
(3) blown in insulation on top
Of course, I'll spend time looking for air gaps and use spray foam to seal those cracks.
Best Answer
Your goal here is a significant improvement in energy efficiency without causing any unwanted side effects, such as moisture buildup in the wrong places. With that in mind, I'd keep it simple.
That's pretty much it. You'll probably need to build a simple barrier around your access port to contain the insulation, and be sure any recessed light cans are rated for insulation contact. Otherwise, don't overthink it.