Is mineral wool worth the extra cost over fiberglass for an R60 attic?

The short answer is that for a 600-square-foot footprint, the price gap for mineral wool is negligible in the long run, but you have to get the **air sealing** right first. If you don't seal the top plates, light fixtures, and plumbing stacks with foam or caulk, the R-value of the insulation barely matters beacuse heat will just bypass it. Since you've alredy gutted the place, this is the best chance you'll ever have to get it airtight.

As for the weight, it is a valid concern but usally manageable. For R60 mineral wool, you’ll be stacking batts about 15 or 16 inches deep. If your ceiling joists are on 16-inch centers and you use 5/8-inch drywall or sag-resistant ceiling board, you won't have issues. Standard 1/2-inch GWB can sometimes bow over time under that kind of load if the humidity gets high, so upgrading the board is a smart move regardless of the insulation type. Mineral wool is definitely the better investment here. It doesn't slump or lose its effective R-value over decades like fiberglass can when it settles. Plus, the pest resistance isn't just a marketing gimmick. Mice genrally avoid it because the fibers are abrasive, whereas they love nesting in fiberglass. It also handles the occasional roof leak much better—it won't mat down and turn into a soggy, useless mess if it happens to get a little damp.

To save some cash, stop looking at Home Depot and Lowe's for bulk orders. Call up local insulation supply houses or industrial distributors. They usually have better stock of the thicker batts and lower prices than the big box stores, which mostly cater to DIYers buying a single bag. Ask about contractor pricing or overstock; for a 600-square-foot job, you might be surprised how much they'll wiggle on the price if you're hauling it yourself.

I'm relly worried about the 'itch factor' with fiberglass if I'm doing all this myself. I've heard mineral wool is way easier on the skin, but is that actualy true once you're up there in the dust? Also, since you mentioned stacking batts to R60, is it actually easier to cut around wires and stuff? I saw someone mention using a serrated bread knife for mineral wool, which sounds a lot less frustrating than dulling a dozen utility blades on fiberglass. If it saves me from a week of skin irritation, that might be the tie-breaker for me.

If you go with mineral wool, make sure you lay the top layer perpendicular to the joists. This breaks the thermal bridging thru the wood. Since rafters and joists have a much lower R-value than the insulation, covering them up properly is how you acutally hit that R60 performance. One thing people overlook is the acoustic benefit. If you’ve got a metal roof or live near a flight path, mineral wool is a game changer for noise reduction compared to the echo you get with fiberglass. Just make sure you still wear a high-quality respirator; even though it's not as itchy, the stone dust will still mess with your lungs in a cramped attic.