Thoughts on blowing new insulation over old loose-fill vs starting totally fresh?

I’d bite the bullet on the cleanout and air sealing. I took your buddy’s shortcut on my 1968 ranch about six years ago—rented a blower, dumped 14 inches of Greenfiber right over the old crusty rockwool, and called it good. My heating bills barely budged because warm air was still whistling straight up thru the top plates, plumbing stacks, and unsealed ceiling boxes.

Two years later, I finally rented an insulation vacuum, sucked all 1,100 square feet clean, and bought a contractor foam gun with a case of Great Stuff Pro. Sealing every single wire penetration and drywall seam took an entire Saturday, but the difference was immediate. The house stopped feeling drafty by that evening, and the furnace stopped short-cycling on windy 20-degree nights.

Plus, having the bays completly clear lets you staple down those floppy Romex runs properly so you aren't accidentally kicking live wire down the road. Insulation slows down conductive heat, but air sealing stops convective heat loss. Dumping a foot of cellulose over open holes just gives drafts a warmer blanket to blow right through.

You don't need to drop $3,000 on a vacuum truck to get effective air sealing. That all-or-nothing mindset is usually an upsell from remediation contractors. When I redid the attic in my 1964 split-level, I had the same spiderweb of haphazard Romex draped across the joists, and stripping the whole attic down to bare drywall just wasn't in the budget.

Instead of a full extraction, I took a garden rake, a shop vac for spot-cleaning, and a good respirator up there on a cool morning. I pushed the old gray rockwool aside only along the major leakage spots: the open chimney chase, the bathroom exhaust vents, plumbing stacks, and the drop-down ceiling above the hallway. I hit those primary holes with a Pro foam gun and Great Stuff, using pieces of rigid XPS board over the larger bypasses. Left the rest of the undisturbed fill right where it lay.

Once those major thermal bridges were plugged, I rented a hopper and blew 14 inches of cellulose right over the old dust and wiring. Loose-fill naturally settles around cables and irregular joist spaces without creating the voids you get with batts. My winter gas bills dropped around 25%, and I avoided spending thousands on waste disposal.

Before deciding on either route, have you ruled out open splices or hidden junction boxes buried under that gray fill? If previous owners were sloppy enought to drape live cables haphazardly over joists without protection, there's a fair chance they left flying wire nuts or abandoned fixtures under the fluff. Blowing a foot of cellulose right over uninspected, 60-year-old wiring connections coud just be insulating a fire hazard. Have you poked around the actual drywall plane yet to see what kind of electrical condition you're truly working with?

Whatever route you take, sort out your eaves before adding depth. A 1960s build almost never has baffles installed. If you blow 16 to 18 inches of loose-fill up to R-60 without protection, you’ll choke off the soffit intake completley and invite massive ice dams come January. Slap in some AccuVent baffles or standard Durovents stapled tight to the roof deck along the exterior top plates. While you're at the edges, check your bath fans—half the 60s ranches I've inspected had uninsulated vinyl flex hose venting warm moisture directly into the attic instead of terminating trough a dedicated 4-inch roof cap.

Man, reading trough all this makes me so pumped to finally fix my own drafty ceilings! But wait, quick question for you guys—if you blow 15 or 18 inches of loose fill over the joists, what do you do if you still need attic storage? Are people building raised platform decks on 2x4 stilts before blowing, or does that mess up the thermal barrier? I keep seeing those plastic attic loft legs online and I'm dying to know if anyone here has actualy tried them with blown-in!

Wait, what do you guys do about old ceiling lights or bathroom exhaust fans? I honestly don't know much about this stuff yet, but if you blow a massive pile of cellulose over everthing, isn't that a huge fire hazard with older fixtures?

Do you have to replace them with special airtight cans first, or do people just build little covers out of rigid foam board to bury under the fluff? Sorry if that's a dumb question, just terrified of burning my roof down.