Should You Insulate the Attic Floor or Ceiling?

Should I insulate my attic floor or ceiling? If you're looking for the best way to make your home more efficient, you may be facing this dilemma. While there's no one-size-fits-all answer, the specifics of your home can help to determine which approach is best. This no-fluff guide to fluffing up your attic insulation will help you get the answers you need to move forward with this project.

Attic Floor vs. Ceiling Insulation: Key Differences

The main difference between attic floor and attic ceiling insulation is that attic floor insulation is placed on the floor of the attic, while attic ceiling insulation is placed on its ceiling. Attic floor insulation keeps the room beneath the attic comfortable, while attic ceiling insulation aims to control the attic temperature.

Insulating the Attic Floor

Insulating your attic floor is the standard practice for all residential unfinished attic spaces and costs about $1 to $3 per square foot, which comes out to $1,000 to $3,000 for a 1,000-square-foot attic. During this project, insulation should be applied to the attic floor, the attic subflooring, and any other flooring materials used. Why is insulating the attic floor considered the norm?

Generally, focusing on the attic floor is the best way to conserve energy. Insulation added to your attic floor can help to keep the main portion of your home protected against drafts and leaks. All you have to know for this to make sense is that heat rises. As heat rises, it finds its way to "icy" pockets of air. If your attic floor isn't insulated, heat will continue to rise away from your living area because there's no barrier to stop it. This creates higher demands for heating and cooling during hot and cold times of the year which will ultimately lead to higher energy bills.

Insulating the Attic Ceiling

The rules for where to apply insulation in your attic change a bit if you're talking about a finished attic that is used for additional living space. Once an attic becomes a living space, the goal of keeping warmed or cooled air out of the attic switches to keeping that "expensive" air within the confines of the attic instead of allowing it to fly out of the roof.

When attics are used as living spaces, it's necessary to insulate the inner surfaces of your roofing instead of your floor. The reason is that you don't want your insulation to prevent heat or cooled air from reaching your attic. Attics that go from frosty in the summertime to stiflingly hot in the summertime are unlivable.

Insulating your attic ceiling is far more complicated than insulating your attic floor and therefore costs more—between $3 and $7 per square foot—to install. First, you'll need to install an inner roof lining that keeps snow, rain, and debris out of your attic because moisture and debris particles can destroy insulation. Next, the installation process requires you to insert insulation between beams instead of simply lining them along the floor.

You should also consider adjusting your insulation plans away from standard floor insulation if you have future plans to turn a currently unfinished attic into a usable living space. However, you should do your research on the viability of actually turning an unfinished attic into an extra room before making a decision about your insulation based on a future plan. The reason is that local code requirements regarding attic conversions can be rigorous.

Generally, attics are required to have ceiling heights of 7 feet to 8 feet in order to be eligible for conversion. If your attic doesn't currently meet the local requirement for height, you may need to renovate your roof in order to get your home up to code. In many cases, homeowners end up lifting or extending their roofs by a few feet. If you add insulation to your attic ceiling before you know about these requirements, you may end up undoing all of the insulation work you just paid for when you alter your roof.

Insulating Both the Attic Floor and Ceiling

If you're looking to maximize energy efficiency, you can consider adding insulation to both the floor and ceiling. While this is more expensive, it will ensure that heat from the lower levels of your home stays in the home instead of "flying out" through the roof. Homeowners should also consider adding insulation to exterior walls for this reason.

Best Types of Attic Insulation

You can generally use the same insulation options for attic floors and ceilings. While blown-in insulation is becoming increasingly popular due to its affordability, the two most common choices recommended by local attic insulation companies are boards and mineral wool. Mineral wool offers the advantages of being inexpensive, resistant to moisture, and excellent for muffling sounds. You should have mineral wool on your radar if you're wondering how to soundproof a room after moving a bedroom to the attic. Mineral wool also provides excellent fire resistance.

While foam boards aren't as resistant to fire as mineral wool, they do offer many of the same benefits. Board insulation is excellent for regulating temperatures, combating moisture and mold, and preventing damage caused by pests. The dense, rigid qualities of foam board are also exceptional for preventing air leaks caused by gaps.