Q My blown-in insulation -- Owens Corning, installed in 1993 -- is 12 inches deep. Can I roll blanket insulation over the existing insulation, rolled out perpendicular to the ceiling joists? Should the blanket insulation be faced or unfaced? How thick should the blanket insulation be? And would the savings justify the expense?

A The loose-fill insulation works because of all the air pockets between the fibers of the material. If you compact the material, you will lose some of the R-value -- the measure of the material's thermal resistance to heat flow. (The higher the R-value, the greater its insulating ability.) Twelve inches of loose-fill fiberglass has around an R-30. Go to the Department of Energy's insulation calculator (www.startribune.com/a121) to see how much you need for your area. I think you will find you are close enough that adding more insulation might not be cost-effective.

If you do add more, use the same loose-fill fiberglass. Consumers who have loose-fill cellulose might want to add blankets of fiberglass over the material. Cellulose has an estimated R-value of 3.1 to 3.8 per inch of fill. Do the math to see if you need more.

When adding blanket insulation, do not use a kraft-faced or foil-faced material on top of the existing insulation. The blanket facing is a vapor barrier, and it will trap moisture in the underlying insulation. Wet or damp insulation not only loses most of its R-value, but it can support the growth of mold often seen in poorly vented attics.

The savings derived from adding insulation depends on how much insulation is needed, what your current and future energy costs will be, and the variations of the weather. There are just too many variables to approximate what savings there might be. If your attic is properly insulated and ventilated, you might want to consider a reflective barrier. (See www.startribune.com/a123.)

The barrier can be laid atop any existing insulation. Because it is made of such a lightweight material, it will not overly compress loose-filled fiberglass insulation. Some reflective barriers have thousands of tiny holes to allow for moisture transfer so that moisture does not work as a vapor barrier. Other reflective barriers are made of materials that allow moisture to pass through the barrier. In either case, a buildup of dust and debris over many years will reduce the barrier's effectiveness and its transfer of moisture. To avoid dusting, hanging the barrier from the rafters might be a better choice -- but, of course, that would cost more.

According to the Department of Energy, a typical contractor installation is 15 to 30 cents per square foot of attic floor space when installed on top of existing insulation. Hanging the materials from rafters is 20 to 45 cents per square foot. The DOE suggests getting prices and then shopping around. Depending on your attic space, this could be a simple do-it-yourself project.

DWIGHT BARNETT, SCRIPPS HOWARD NEWS SERVICE

Plaster poses problem Q In our dining room, there is something that I think is called rough plaster -- it looks as though there are small nonpareils under the plaster. What is the best way to cover over this and make it smooth? We thought about using wallpaper liner, then covering it in paint.

A This is a messy, painstaking job, and I wonder whether it wouldn't be worth it to just pull out the old surface and then drywall. That's what I ended up doing after trying it your way.

Let's look at covering over the "stucco-ish" wall. It could be stucco or swirled spackle, which I've seen people do to hide cracks in plaster ceilings.

Use spackling compound that tends not to shrink much as it dries; otherwise, you'll be filling it in for the rest of your life. Remember: Apply, dry, sand, apply, dry, sand, ad infinitum.

Now, the wallpaper-liner plan. Liner paper is a heavyweight paper with a smooth surface. It is typically applied over Masonite to hide shallow grooves in the surface, although you might have to use drywall compound (two or three applications probably, depending again on level of shrinkage).

It can be applied over textured walls before you apply regular wallpaper or paint. Always prime first, and sand between coats for better adhesion and to get rid of lumps and bumps. Liner is available in several weights, usually 36 inches wide.

If you want to try wallpaper liner in both places, it might be less labor-intensive than filling in swirls with spackle.

AL HEAVENS, PHILADELPHIA INQUIRER