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How Many Inches of Insulation Do I Need?

Insulation upgrades are an easy and affordable way to make your home more energy efficient. However, how much insulation you need depends on a number of factors.

Start by measuring the area you’re insulating. Use a tape measure to get the length and width of each wall or surface you’re measuring.

1. Measure the Area

If you’re remodeling or building a new house, consider advanced wall framing techniques that reduce thermal bridging through wood studs and maximize insulating area. These techniques will help you achieve the recommended R-value for your climate zone.

For existing homes, the easiest place to add insulation is in the attic. To find out how much space you have available for insulating your attic, measure the interior perimeter of your home and subtract the area of windows and doors, as well as any walls that you aren’t planning to insulate.

You can purchase fiberglass insulation in packages called batts, blankets or rolls. Rolls, like FAST ACTION Prodex Total 5M, are typically the more budget-friendly option and come in standard sizes that fit between standard dimension floor joists and wall studs.

You may need to cut insulation around electrical boxes, but it is better to notch the insulation rather than compress it, as this can decrease its R-value. Be sure to use a vapor retarder (also known as a vapor barrier) under insulation in northern climates to prevent moisture migrating into the insulation and reducing its R-value over time.

2. Multiply the Area by the R-Value

The R-Value of insulation is a number that indicates the material’s resistance to heat flow. The higher the R-Value, the better the insulation is at reducing energy consumption. Different climate zones have different R-Value recommendations. The Department of Energy has an easy-to-use map that breaks down the recommended R-Values by zone.

The type of insulation you choose will also have an impact on how much you need. Batts and rolls are best suited for regular spaces between studs and rafters, while blown-in insulation is ideal for hard-to-reach areas like attics or crawl spaces.

Foam boards and rigid foam panels are another popular form of insulation. These are often made of polystyrene or polyisocyanurate, and can be used in wall cavities as well as on foundation walls or floors. They have an R-Value of between R-4 and R-6 per inch, which means they can reduce energy consumption more than other types of insulation. Foam board insulation is usually covered with a vapor retarder on the surface, which helps prevent moisture from reducing its effectiveness. This type of insulation is less expensive than cellulose or spray foam.

3. Subtract the Areas of Windows and Doors

Before installing drywall, it’s best to measure the walls to see how much insulation is needed. Start by finding the area of each wall, then subtract the areas of windows and doors. This will give you the net area of the wall.

There are several different types of insulation to choose from:

Fiberglass batts cost about 40 cents a square foot, mineral wool costs 60 cents, and cellulose tops the list at $2.75 per square foot. All these options are available at home improvement centers and hardware stores.

Foam insulation comes in sheets or boards of either open- or closed-cell foam. Closed-cell insulation has a higher R-value and is more resistant to moisture than open-cell foam. It’s also more expensive, but it can plug air leaks more effectively than loose fill insulation.

Some insulation is available in boards made of extruded polystyrene or foil-faced polyisocyanurate. These can go on the exterior of a house, over the studs and under the siding, which is great in hot climates where the sheathing tends to absorb moisture.

4. Subtract the Areas of Framing

Taking the time to accurately measure and calculate insulation needs can help ensure you get the best results from your home’s energy efficiency project. This process will allow you to choose the right thickness or depth of insulation to achieve a desired R-value for each area or surface in your house.

The recommended R-value will vary depending on your climate and your energy efficiency goals. The higher the R-value, the greater the insulation’s thermal resistance and ability to regulate indoor temperature.

For walls, use the total square footage of the wall minus any areas that won’t require insulation (such as gable ends or above-grade foundation). For attics, measure from floor to ceiling.

You can use a variety of insulation materials, from basic fiberglass batts to high-density wool, cotton, or mineral fiber. For optimal energy efficiency and performance, your insulation should fit between the studs or joists in wall cavities and attics. These materials can be installed by professionals or do-it-yourselfers. Boards made from extruded polystyrene or polyisocyanurate foam (“iso board”) can be placed over the studs and joists but under the siding, a technique that works well in hot and humid climates.

5. Subtract the Areas of Walls

Homeowners can find the volume of insulation they need by dividing their desired R-value by the R-value per inch of the selected insulation material. They can then use this amount to calculate the thickness or depth of insulation they will need.

This calculation will help homeowners understand how much insulation they need, and it will also give them a good idea of which type of insulation would be best for their home. For example, fiberglass insulation is great for insulating homes in most climates because it prevents heat loss during colder winters and keeps indoor temperatures stable throughout the year.

It is also a great choice for insulating existing homes, and it is relatively inexpensive. It is available in several forms including rolls, batts, and bales. Rolls and batts are usually suited for insulating regular, sectioned-off spaces such as the space between studs and rafters in walls and ceilings. Blown-in insulation, on the other hand, is designed to fill hard-to-reach areas, and it is best for insulating attics and other open spaces. It is available in various types of foam, including open- and closed-cell polyurethane, and can be sprayed on the floor and into cracks and crevices.