R-15 ComfortBatt Fire Resistant Stone Wool Insulation Batt 15 in. x 47 in.

NO....A vapor barrier is to prevent warm air from getting to a cold surface and condensing. That's it's main job ! Since you have foam insulation glued to your concrete walls, the air getting thru the Roxul will not see a surface cold enough to condense against. If you have foam board (properly sealed), when you install Roxul over that NO VAPOR BARRIER IS NEEDED.

You can use it in an attic, but I don't believe there is any real advantage to using this over other insulation types for an attic. One small advantage is that mice don't like it. The bales are large and heavy and might be hard to get up a typical attic hatch or stairway, although you could open the bale and take a few batts up at a time. Kind of a pain though. By far the most important thing to take care of if you are redoing the attic insulation is to do good air sealing. All cracks, joints and penetrations in the ceiling should be sealed with sealant or foam. Can lights should have insulated boxes built over them. Second most important thing is to ensure proper ventilation, with eave vents and ridge vents. If you take care of those items, then it almost doesn't matter what type of insulation you use as long as you use enough of it to get the recommended R-value for your area. I will say that working with Rockwool is less "itchy" than working with fiberglass.

We use Membrain plastic sheeting by Certainteed as a vapor barrier on interior walls (more about unheated spaces like yours, below). We have used Membrain for more than a decade as it is easy to work with and comes in a roll. It has tiny pinholes that allow for a bit of breathing within the wall structure itself. For vertical walls, we set Roxul to the exterior side, then attach entire swaths of the sheeting (takes two people; otherwise, you get bunching and folds) to the interior side of the studs, then sheetrock over that. For a cathedral ceiling, we leave a one-inch space between the Roxul and the roof's plywood underlayment, and then install Roxul to R-40 or so, and then staple sheeting to the ceiling joists over that, then sheetrock. For ceilings with sheetrock already, and just a crawlspace or attic above, it is our understanding from various research that there should be no vapor barrier on top of the Roxul batts laid on top of the sheetrocked ceiling. Roxul batts are made of mineral wool and don't support moisture like, say, recycled jeans (shredded cotton) can. You can do some more research on your own, but my carpenter would tell you not to use any vapor barrier in your situation as he told us not to use it when we insulated our unheated, open-to-the-elements-but-covered-by-a-roof front-porch ceiling which shares a few feet of the interior foyer space. PS Have never seen Membrain sold at Home Depot stores nor on its website; we bought it from a local distributor.

The R-15 Rockwool ComfortBatt bag measures 48 inches long, by 15.5 inches wide by 27" thick (or 27 inches tall when you look at this photo). (The 27 inches runs perpendicular to the printing on the bag). We have found that the bag can be somewhat compressed to fit into a space with tighter dimensions during transport. We managed to fit three across, inside an '87 Volvo station wagon, setting just like you see them in this photo. We fit six on top of the roof rack, using long straps to secure to the rack ends. (Note: The weight temporarily dented the roof metal in the middle, but it popped back out on its own because Volvo metal is like tank metal. I would not recommend putting more than the number of pounds your car's or SUV's manual says can go onto a roof rack.) We have rented a 15-foot trailer to haul bags of ComfortBatts, but I think we could only fit 8 bags into that trailer. If you use a trailer, you have to secure them with a tarp and rope. When we carry them on top of our Volvo wagon, only the strapping is needed to hold them securely in place, no tarp.