Insulation questions, answered

R-value measures how well a material resists heat flow. The higher the number, the better it insulates. R-values of layers add up, so an R-15 layer with R-30 on top gives you R-45.

It depends on your climate zone and the part of the house. For attics, ENERGY STAR recommends R-30 in zone 1, R-49 in zones 2 and 3, and R-60 in zones 4 through 8. Walls, floors and basement walls have their own levels. Enter your ZIP code in the calculator to see yours.

Deep enough to reach your zone's target. For R-49, blown cellulose goes in at 14.3 in and settles to 13.3 in, or you need 16.4 in of blown fiberglass. For R-60, it's 17.3 in of cellulose (settling to 16.1 in) or 19.8 in of blown fiberglass.

Look across your attic floor. ENERGY STAR's rule of thumb is that if the insulation is level with or below the tops of the floor joists, you probably need more. Measure the depth and the calculator will tell you how far you are from the target.

Neither is better in itself; both reach the same R-value. Blown-in flows around wiring and framing in an attic and came out cheaper than batts in our attic examples. Batts are the usual DIY choice for open walls and floors, and they don't need a blowing machine.

Usually, yes. If the old insulation is dry, free of mold and isn't vermiculite, you can add loose-fill or unfaced batts on top. Don't put a kraft facing or vapor barrier between the old and new layers.

It depends on your climate and what you're insulating. As a general rule, a vapor retarder such as the kraft facing on a batt goes on the side that's warm in winter, and you should never trap insulation between two vapor barriers. Codes set the rules by climate zone, so check locally before adding plastic sheeting.

For materials only, our 1,200 sq ft example in zone 5A, topping up 3.5 in of old batts to R-60, came to $1,503–$1,689 for blown cellulose or $2,996 for fiberglass batts. Labor, tools and blower rental are extra. Run the calculator for your own attic.

Yes, if you are comfortable working in the attic. Laying batts and blowing loose-fill are both realistic DIY jobs, and home centers often lend a blower free with a minimum bag purchase. Spray foam is different: it's a job for a certified installer.

Take precautions. Attics get very hot, so work early on a cool day and take breaks. Step only on joists or boards laid across them, watch for roofing nails overhead, and don't disturb wiring. Wear an N95 mask, goggles, gloves and long sleeves.

It can be. Vermiculite is a pebbly, gray-brown or silvery-gold loose fill, and the EPA warns it may contain asbestos. Leave it undisturbed and have a trained, accredited asbestos professional deal with it before any work in that attic.

In walls, basement walls and sloped roofs, insulation between studs or rafters can't be deeper than the framing. A 2×4 wall holds about R-13 to R-15 of batts and a 2×6 about R-21. To go further, you need continuous foam board over the framing or a different material.

It uses the same coverage charts and product data you'd use by hand, so the math is exact for the inputs you give it. Real homes have framing, obstructions and uneven depths, so treat the result as a planning estimate and check the coverage chart on the product you buy.