The caption "Insulation R-Value vs Cost" in a yellow and blue graphic on a yellow insulation background

We all know that adding insulation to your home can help you save money in the long term on your heating and cooling bills. But with so many different types of insulation out there, it is hard to know what is going to give you the best energy savings for the least cost. 

We examined the R-value of five common types of insulation and compared that to their cost to help you decide which is the best to buy. What we found surprised us. Keep reading to learn more.

What Is Insulation R-Value And Why Does It Matter?

When purchasing insulation for your home, it is easy to feel overwhelmed. With so many products out there, how do you know which is going to be the best for your project? Besides cost, one of the first things to examine when considering insulation is R-value.

But if you don’t know what R-value means and why it matters, don’t panic! We’ll explain what R-value is and why it is an important factor when deciding on your insulation.

How R-value Is Determined

So let’s talk about how insulation works. Imagine a candle flame. When you hold your hand near the flame, you can feel the heat. Now let’s imagine there is something between the flame and your hand. That material is going to affect how much heat you feel. If the flame is enclosed in a glass candle holder, you feel less heat on your hand than the bare flame, but you will still feel it. But what if I were to put a piece of wood between your hand and the candle? Then you would hardly feel the heat. That’s what insulation does–it blocks the transfer of heat.

Scientists measure how good different materials are at blocking that heat transfer. Then, each material is given a value based on how well one inch of it blocks heat transfer. This number is the R-value. The higher the R-value, the better the material is at blocking heat. It’s that simple. Or is it?

Photo of a pair of hands cupping a white candle that is lit against a white background. Heat from a candle can illustrate insulation R-value to clarify the concept.
Suddenly, home insulation seems a lot less mysterious.

Factors That Can Affect R-value

The R-value you see when you look at insulation is based on laboratory conditions. But in the real world, a number of factors can affect your insulation’s performance and lower its actual R-value.

Installation choices can affect your insulation’s R-value. If your insulation gets compressed during installation, the R-value can be lowered. Where you are installing the insulation can affect its performance as well. According to the U.S. Department of Energy, studs, joists, and other building materials have unique R-values. These factors will all contribute to the final R-value of your wall or ceiling, too.

R-values Of Different Insulation

So what are the different R-values of insulation? Let’s take a closer look at five common insulation types, and talk about their installation and effectiveness.

Spray Foam

Spray foam insulation has the highest R-value of any insulation on the market, making it a popular choice for insulation in both homes and commercial buildings. Whether you choose open-cell or closed-cell insulation will determine your final R-value. (Closed-cell foam has the highest R-value at 6.50 per inch.)

Fiberglass

Fiberglass insulation is what usually comes to mind when people think about insulation. That’s because it is the most common insulation out there. It is sold in batts or can be blown in by a professional. The R-value of fiberglass is 3.14. Keep in mind, though, that batts are sold in thicknesses greater than 1 inch. So the R-value will increase with the thickness.

Cellulose

Cellulose insulation is a low-cost insulation method that is suitable for retrofitting older homes. It generally contains a high percentage of recycled materials, making it a popular choice for people looking for green insulation options. Blown-in cellulose has an R-value of 3.70. However, settling can occur over time that can leave gaps and lower the R-value.

Mineral/Rock Wool

Rock wool is similar in many ways to fiberglass insulation. Made from industrial slag or basalt rather than glass, the manufacturing process is the same, as are their R-values. You will find batts of mineral or rock wool also have an R-value of 3.14.

Rigid Foam Boards

You can use rigid foam boards to insulate just about any area of your home easily. Usually made out of polystyrene or polyurethane, they have great insulative qualities. Depending on which material you choose, the R-value can be as high as 5.

What R-Value Do I Need?

Now that we know what an R-value is and how the different materials add up, let’s talk about how to figure out what R-value you need. Several factors determine the R-value you need for your home.

You will find the R-value you need for your home depends on where you are located. Homes in colder regions, like Alaska, require higher R-values than homes in Florida. But where your home is located isn’t the only factor to consider.

You also need to consider where in your home you will be installing your insulation. Attics and basements require very different R-values than interior walls.

The U.S. Department of Energy has a great map showing R-value by zone and by part of the house.

US map showing recommended insulation levels for retrofitting existing wood-framed buildings
Map found at energystar.gov. Click through to see specific R-value recommendations for attics and walls.

Once you know your R-value, you can start to examine how much actual insulation you will need with the different materials. Let’s say, for example, you need insulation with an R-value of 30. To determine how many inches of insulation you need, take your desired R-value and divide that by the material’s R-value.

So, fiberglass has an R-value of 3.14. You would divide 30 (your desired R-value) by 3.14 (the R-value of fiberglass). I’m going to make the math easy and round 3.14 down to 3.

30/3= 10 So, you would need roughly 10 inches of fiberglass batt insulation to achieve an R-value of 30.

Let’s say instead of fiberglass you wanted to use closed-cell spray foam insulation. Its R-value is 6.5, nearly double that of fiberglass. So now we divide 30 by 6.5 and only need 4.6 inches of insulation.

Knowing how much insulation you need is essential to determining how much it will really cost to insulate your home. So now let’s talk about costs.

Insulation Cost

When it comes to insulation, I can’t say, “It will cost $X to insulate a 1500 square foot home.” There are a number of different factors that will affect exactly how much it will cost for you. So let’s examine those factors and talk about some averages.

Factors That Affect Costs

Insulation costs will vary depending on where you live and the type of insulation you choose. In general, you will find the higher the R-value, the more expensive the insulation. Also, while we don’t have any included in our list, you will find that natural insulation materials, like cotton batts, cost more.

Obviously, if you decided to install your insulation yourself it will cost less than paying for professional installation. But even professional installation costs can vary greatly depending on where you live.

Average Insulation Costs

Let’s take a look at some average costs for different insulation materials. Take note that some insulation costs are measured per square foot, while others are measured per board foot.

Spray Foam

While Spray Foam has the highest R-value, you will also find it is the most expensive insulation. Spray foam does require professional installation, which increases the cost. On average, spray foam costs between $1 to $1.50 per board foot.

Fiberglass

Fiberglass is a low-cost option for insulation. You can choose either to install it yourself or to have it professionally installed. Fiberglass batts are available in a variety of lengths and thicknesses, depending on your needs. They range in price from $0.50 to $1.50 per square foot.

Cellulose

Certain types of cellulose insulation you can install yourself, while others require professional installation. The type of cellulose insulation you choose, along with your installation method, will affect your final cost. On average, you can expect to pay between $0.60 to $2.30 per square foot for this type of insulation.

Mineral Wool

As we mentioned earlier, mineral wool is similar to fiberglass insulation in many ways. And that includes both installation methods and costs. You can expect to pay between $0.50 to $1.50 per square foot.

Rigid Foam Board

Like other insulation options, the price to install rigid foam boards is going to depend on where in your home you choose to install them. But you can figure on rigid foam boards costing between $0.25 to $0.50 per board foot.

Here’s a quick chart where you can see the R-value vs. cost

InsulationR-ValueAverage Cost 
Spray Foam (Closed-cell)6.5$1- $1.50 per board foot 
Fiberglass (batt)3.14$0.50 to $1.50 per square foot 
Cellulose (blown-in, attic)3.7$0.60 – $2.30 per sq foot 
Mineral Wool (batt)3.14$0.50 to $1.50 per sq foot 
Rigid Foam Boards (Polystyrene)4-5$0.25 to $0.50 per board foot 

R-Value Vs. Cost

Now we know the R-value of different types of insulation and their costs, so we are closer to deciding which to buy. With these numbers, you can make an educated estimate on how much it will cost for your insulation project. But oftentimes, more factors come into play than just dollars and cents.

Maybe you don’t want inches and inches of pink foam in your half-finished attic space. So, you decide you are willing to pay more to install spay foam into your attic simply because it requires less material than the less expensive fiberglass insulation. Or perhaps you are looking for the healthiest insulation for your home. As we mentioned, natural insulation can cost more for a comparable R-value.

Carefully consider all the factors that affect your family. Combine these factors with R-value and cost to decide which insulation is best for your home. 

Final Thoughts

When it comes to insulation, both R-values and costs can vary depending on installation choices. It is important to know what R-value your home needs and how much of each material you need to achieve your insulation goals. This can help you get a realistic idea of how much each material will cost to install.

Because your needs vary depending on where you live and where in your home you are insulating, it can be helpful to consult a professional. They will know what R-values are required in your region as well as what the current costs are for different materials. However, it is always useful to have a general idea of what it will cost before speaking with a contractor.

Don’t forget to consider other factors, like the quantity of material needed and your insulation’s environmental or health impact. These factors can help you decide if the increased cost for R-value is worth it for you.

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