I forgot to mention in my three page thesis there, if you have any air ducts or pipe going through the attic, make sure they’re wrapped in some kind of insulation. The pipes will introduce condensation, and the ducts will ruin your heating efficiency. And it’s always good to put insulation over any place a wire or fixture is drilled through the drywall as well.

A ridge vent will help get rid of heat and moisture, and the soffit vents will help in cold weather. Don’t worry about insulating the back of the roof itself, you want to insulate the top of the ceiling. Paper or plastic backed insulation nailed to the joists backing side up is the standard, so the moisture and extreme temps go in and out of the vents and the house is protected. In that way, you would think of the attic being an exterior space.

If your venting is protected from bugs and animals with screens, you don’t HAVE to have backed fiberglass, and can just pile as much as you can get your hands on in the space, though every layer after two has diminished returns.

The old way to do it was to fill the spaces between the joists with shredded paper. It works, but it’s not great for moisture or fires. Filling those spaces with shredded polystyrene is more effective and less prone to problems, and can be free if you get packing peanuts or any kind of Styrofoam refuse.

If you use the standard backed insulation, or fill the gaps with paper/Styrofoam, a good way to make it even more effective is to also either use sheets of foam over the joists, or pile enough material to bury them, as the wood will transfer heat or cold right through the insulation directly to the ceiling, since the wood doesn’t have any air gaps in it to stop the transfer.

There are eave vents that open and close automatically at certain tempuratures, they’re reasonably effective, but can be expensive depending on how many/how big you need.

Depending how large your attic is, fans may be necessary to fight moisture lingering. The way I mitigated it in my crawlspace without having to buy a bunch of powered vents, was to attach repurposed cellphone solar panels to some old tool batteries wired to some old computer fans I had. It was just an expiriment, but it’s worked for at least a year, and I live in a wet area. Worth noting, that took some reading and help from a friend to figure out. You can’t just solder a fan to a solar cell, which was my first intention.

As for getting insulation, depending on where you live, Lowes often has partial returns from projects they sell really cheap. They offer them to employees first, but if you ask someone, they may help you. I got 15 full bats for like 65 dollars. Stupid cheap. If you live in a place that has a menards, they have an online section for each of their stores called ray’s list, that has returns and overstocks that are a lot cheaper and can be haggled for in person.

Want nearly free if not a lot more work? Rip up coats, blankets, furniture, and stuffed toys for the polyester wool. It’ll take a lot, and it’s not code, but it works and it’s great recycling. You could also theoretically spend a few months or years doing it, if you aren’t in a rush.

As for recycling old shit, anytime someone throws away a couch or chair, you can rip the foam out of the cushions. It’s usually open cell medium density petrolium foam, and is reasonably resistant to moisture. Old memory foamayresses can be cut or shredded similarly, and if you’ve ever slept on one, you know they trap heat like a motherfucker.