Some homes don’t have attics, they are flat roofed, and some homes have 2-stories with floors in-between. In either case, this is a situation where there is usually 2×12 wood framing with drywall attached to the bottom and some plywood attached to the top. There is no crawl-space, it’s literally like a horizontal wall. In this case we treat it just like a wall: we drill holes and inject insulation into the empty cavities. We use cellulose because it has a higher R-value per inch and it’s the only material that can be effectively blown into a cavity.
Unfortunately, most places built in the 1970’s or newer tend to have fiberglass insulation installed in their ceiling and we can not inject additional insulation into these cavities. The best thing to do is check the ceiling to see if there is existing insulation. See How to Check for Existing Insulation