Everyone needs insulation in their attic, but did you know there are lots of things to consider other than simply whether to blow it in (loose fill) or use batt (blanket) insulation? There are different recommended values depending upon where in the United States you live.

For example, those in the southernmost part of the US, attics should have from R30 to R60 (average is R38). Those up north will want anything from R49 to R60. The more you use, the better insulated your home will be. While there are also insulation recommendations for walls and floors, this article will deal mainly with the oft-overlooked attics. Here is a map of the different zones and corresponding R-value recommendations per the U.S. Department of Energy:

You'll find it hard to have too much insulation, though it is possible to simply overpay and reach a point of diminishing returns. Even though the chart above breaks down insulation ranges per climate zone, it's important to note that each zone has a range of possible R-values. That is partially due to the different heating systems in use across the united states.

Attic insulation can be blown in or laid down from rolls. Loose fill insulation is blown into the attic via a long tube and system that is fairly proprietary and often best left to the professionals. "Blanket" style insulation can be purchased as either batts (8' long rectangular pieces) or rolls (which come in 16 or 24 inch widths).

Insulation is typically made from fiberglass or mineral fibers, and with all the options, make sure you measure the spacing between the joists to ensure you grabbed the best kind for your needs. For example, unfaced insulation is great for adding to existing attic insulation, but paper-faced insulation is best for new spaces.

Calculating the amount of insulation you'll need isn't that hard, if you know the right formula. You'll want to measure the length of each row between the attic joists, and add that all up. If you then divide by the individual length of the bat or roll insulation you're buying, you'll have the quantity you need to purchase. Where it gets hard, is factoring in the required R-value.

If you are starting off fresh, and  have no attic insulation as of yet, start with an R value of at least 38 (you can check local codes and that Department of Energy chart above for specific recommendations). If you already have some insulation, simply subtract what you have from the desired value (R38 if you require a basic starting point). To find out if you have enough insulation in your attic, measure the thickness of the insulation from top to bottom using a ruler. If it is less than R-30 (which is to say, 11 inches of fiber glass/rock wool or 8 inches of cellulose) then you may want to add more. Check the chart below as a down and dirty guide of your existing R value:

For those blowing in insulation (our favorite choice) be sure to install some makeshift "depth gauges" in the attic from scrap lumber. You can mark them to indicate the desired finished thickness of insulation. It works and lets you know for certain that your contractors have indeed blown in the right amount of insulation.