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Q: Help! My home feels cold in the winter and too hot in the summer, and I think I need to add insulation. But how much insulation do I need?
A: According to the Insulation Institute, around 90 percent of U.S. homes are underinsulated, so it’s no surprise to hear you need more in your home. Several factors affect the amount of insulation a home needs, including the areas that are being insulated, the type of insulation, and the home’s geographic location. While it may seem intimidating, there are several ways for homeowners to understand how much insulation is needed for their homes and when to contact an expert for assistance in installing or purchasing proper materials. But before heading to the home improvement store or looking up “insulation companies near me,” it’s a good idea for a homeowner to inspect the home and check to see what kind of insulation is already in place as well as its condition.
Determine what areas of the house you want to insulate.
Before learning how to install insulation, homeowners will want to first have a plan for where the insulation is being installed. The location will partly determine the amount of insulation that is needed. The most common areas where homeowners use insulation are attics, walls, and floors. Since it’s best to overfill attics with insulation to prevent an updraft that draws cooler air in, more insulation may be needed for an attic or roof than for flooring. When adding wall insulation to existing batting or adding blown-in insulation to an older home, it’s likely that more insulation will be needed than for insulation under flooring, but less than is required for attic insulation.
If cold air is getting sucked through gaps in the floorboards, it’s a good idea for the homeowner to add insulation to the floors to keep moisture from warping the wood or encouraging mold growth. A professional can install the insulation, or homeowners can glue or fasten rigid foam sheets to joists beneath the floor. Another option is for a homeowner to use spray foam from a can to fill small gaps. Since this requires special equipment, it may be worth them locating a professional who installs spray foam as opposed to DIY. The best spray foam insulation contractors (such as Dr. Energy Saver or USA Insulation) can ensure that the installation is done effectively.
Talk to a local contractor or building authority to learn the minimum required R-value for insulation in your area.
Homeowners who are not well acquainted with the basics of insulation installation may not have heard the term “R-value.” Put simply, the R-value of a material describes its capacity to insulate. The U.S. Department of Energy has recommendations for what R-value is needed in various regions of the country. Although it’s essential for a homeowner to have a basic understanding of what insulation does and what R-value means, one of the top insulation contractors in the area will have the expertise to confirm what R-value is required for a particular home based on its location.
For instance, in a Southern state, the R-value for the insulation needed will probably be around R-30, as opposed to homes in Northern areas, which need R-38 insulation for their attics, since winters are colder and summers can still get hot. After determining the R-value of the home’s insulation needs, homeowners will have a better idea of how much material is necessary to meet a professional’s recommendation for proper insulation.
| Zone | R-Value for Attic | R-Value for Wall | R-Value for Floor |
| 1 | R-30 to R-49 | N/A | R-13 |
| 2 | R-30 to R-60 | N/A | R-13 to R-19 |
| 3 | R-30 to R-60 | R-5 | R-19 to R-25 |
| 4 | R-38 to R-60 | R-5 | R-25 to R-30 |
| 5 | R-49 to R-60 | R-5 to R-6 | R-25 to R-30 |
| 6 | R-49 to R-60 | R-5 to R-6 | R-25 to R-30 |
| 7 | R-49 to R-60 | R-5 to R-6 | R-25 to R-30 |
| 8 | R-49 to R-60 | R-5 to R-6 | R-25 to R-30 |
For walls, measure the height and width of the wall and multiply the numbers together. Subtract the area of any windows or doors.
When calculating the amount of insulation a home needs, the first step is for the homeowner to find out the area of the space being insulated. Starting with one wall, they’ll want to measure the height and width of the wall, and then multiply those numbers to get the area. If there are any windows or doors in the wall, the homeowner will want to measure the height and width of those to calculate their areas. They’ll need to subtract the areas of any windows and doors from the entire wall’s area because they won’t need to be insulated. If the walls aren’t already filled with batt insulation, it’s also recommended for the homeowner to fill wall cavities with loose-fill insulation. An online insulation calculator can make it easier for homeowners to determine and keep track of the home’s measurements.
Older homes are likely to need more insulation than new builds. This is because insulation tends to settle in walls over time. For these situations, blown-in insulation through holes in the wall will be the best option to optimize the home’s comfort.
For floors, measure the length and width of the floor to get the area.
To know exactly how much insulation is needed for flooring, the first step is for a homeowner to calculate the length and width of the floor in the specific room or rooms where it will be installed. This will provide them with a better idea of how many rolls of insulation or insulation material are needed to ensure cold air and moisture don’t seep through any cracks or holes, which can cause issues with ventilation and also encourage mold growth.
In most cases, less insulation is necessary for flooring than for other areas of the home, such as interior walls or attics. For those who live in a Southern climate, an expert would probably recommend a value of R-13 for the home’s insulation. In the Northern region of the United States, that recommendation would likely be R-30. Homeowners will want to remember that if a professional will carry out the insulation installation, they will do all the calculations and determine the appropriate R-value.
For attics, measure the length and width as well as the height and width of any triangular areas.
Answering the question “How much insulation do I need in my attic?” may be more complex than for other parts of the home depending on the shape of the space. For attics that have a standard rectangular shape, finding the square footage will be as simple as multiplying the room’s length by its width. However, attic shapes are commonly irregular due to their proximity to the roof. Any portions of the attic that have a triangular shape will need to be measured using a slightly different method. The first step is for the homeowner to measure the height and width of the triangle. The measurement of the base can then be divided in half before being multiplied by the height.
If portions of the attic need to be calculated separately due to being different shapes, each section can be added together at the end to find the total square footage of the room. The larger the total square footage of the attic, the higher the attic insulation costs are likely to be.
Determine the best insulation material for your needs.
Not all insulation materials are suitable for every location or situation, so deciding on an insulation material might not be as simple as a homeowner comparing the cost of spray foam insulation vs. fiberglass. For example, in colder regions, materials with the highest R-values will be preferable over those with a relatively low insulation capacity. The location within the home where insulation is being installed can also dictate the best insulation material. For instance, cellulose is not commonly used in finished floors as it is a loose material and is usually blown in. Additionally, if homeowners are looking for soundproof insulation, some materials may be more effective than others. It’s also important for homeowners to understand the difference between faced vs. unfaced insulation. Insulation that is faced includes a layer of vapor barrier on one side of the material that can block out moisture and prevent mold growth. Faced insulation is also typically easier to handle and install than unfaced insulation.
According to the U.S. Department of Energy, there are many types of insulation materials for homeowners to choose from. If it is unclear which one is the best fit for a project, a professional can advise the homeowner on how to make the right selection.
- Cellulose is typically found in blown-in insulation and is made out of recycled paper. This type of insulation is used for attics and other tight spaces. To resist the potential for fire or pest problems, cellulose insulation is also typically treated with borate.
- Denim is a relatively pricey insulation material; however, it has the benefits of being both nontoxic as well as sustainable, as it saves used clothing from going to a landfill.
- Fiberglass is frequently found in blown-in or blanket insulation that is used for walls, ceilings, and floors. It’s advised to wear protective gear and clothing when handling fiberglass as it can be abrasive to the eyes, skin, and lungs.
- Foam comes in sprays or individual boards, meaning it can be used in most areas of the home in one form or another. Most often consisting of plastic, foam insulation can also be cement-based.
- Mineral wool refers to a fire-resistant man-made material that forms loose-fill or blanket insulation. One kind of mineral wool is Rockwool, which is a blend of natural fibers. Slag wool is a metal byproduct.
- Natural fibers that are used for blanket and batt insulation can include straw, wool, cotton, and more. Since these fibers are not naturally resistant to fire, pests, or mold, they are usually treated to combat these issues.
The amount of insulation you need will also depend on your existing insulation and the type of insulation you choose.
If there is already existing insulation in the home, less new insulation will need to be installed than is necessary when starting from scratch. Even if the insulation that is in place meets Department of Energy guidelines, it may need to be supplemented if the home is feeling cold in the winter and hot in the summer. Depending on where the extra insulation is being installed, a small amount of blown-in or spray insulation foam in a few areas may be sufficient, according to Energy Star.
How much insulation a home needs depends on the type of insulation being installed, as there are several options. Blanket batts and rolls are typically on the budget-friendly end and are designed to fit in between the width of standard wall studs, attic rafters, and floor joists. However, rolls of insulation are challenging to install in homes that are already constructed. On the other hand, many homeowners find spray foam insulation worth it for wall cavities as it can fill leaks and gaps. Blown-in insulation is one of the best attic insulation options since it is excellent for awkward-shaped spaces. Those wondering “How much blown insulation do I need?” will want to note that attics typically require more of this material than walls, so the cost of blown-in insulation might be slightly higher in an attic. Rigid foam panels are best for unfinished walls, floors, and ceilings. Radiant barrier insulation is most commonly used in attics, unfinished walls, ceilings, and floors in hot climates.
- Blanket insulation is typically considered to be the most DIY-friendly insulation as it comes in batts or rolls that are easy to install. Often used in walls and flooring, blanket insulation may be made of wool, fiberglass, cotton, plastic, or a variety of other materials.
- Concrete block insulation comes in the form of foam boards that can be placed on either the interior or exterior walls of a home. When installed over concrete, these boards can increase the insulation value of the wall by 10 times.
- Foam board is typically installed in unfinished indoor walls but can be weatherproofed for use as exterior wall insulation. It can also be placed in flooring and ceilings. A major advantage of this material is that it is relatively thin but has a high R-value.
- Insulating concrete forms, often referred to as ICFs, are integral to the structure of the wall. For this reason, they are most often used during a new construction rather than being installed retroactively.
- Loose-fill insulation (also called blown-in insulation) is made of cellulose, mineral wool, or fiberglass. Rather than being a type of board or cloth, this substance is blown into parts of the home that are oddly shaped or difficult to reach.
- Radiant barrier insulation is another DIY-friendly option that can be added to unfinished ceilings, flooring, and walls. It is made up of a foil or similar substance that reflects heat upward and is most useful in very warm climates.
- Rigid fiber insulation consists of mineral wool or fiberglass, and it is usually used in HVAC ducts because it can withstand extreme temperatures.
- Spray foam insulation, similar to loose-fill insulation, is piped into nooks and crannies that would be difficult to insulate using other materials. It’s commonly found inside walls and attics. Spray foam insulation costs around $2,492 to install on average.
- Structural insulated panels (SIPs) are installed as walls in new construction. They can be made of foam boards or filled with straw or liquid. SIPs are advantageous because they are simple and quick to install and have some of the highest R-values.
Understanding a home’s insulation needs can be intimidating, especially for those who have never undertaken a project of this kind before. Considerations such as R-value, striking a balance between insulation and ventilation, and getting the right materials for the job can create some understandable confusion. If any part of the insulation project feels unmanageable, it may make sense for the homeowner to search for “insulation company near me” for assistance. While taking on this project as a DIY may help homeowners save on the overall cost of insulation installation, professionals provide valuable expertise. For instance, they are sure to know what asbestos insulation looks like, whether it is present, and how to remove it safely. They’ll be able to calculate how much insulation is needed so homeowners don’t overbuy, and they’ll be able to advise homeowners on what the best type of insulation is for an individual home.
Sources: Energy.gov
