Understanding R-Value: What It Means for Insulation Performance

If you’re considering upgrading your home’s insulation, you’ve likely come across the term R-value. But what is R-value in insulation, and why does it matter so much when choosing the right material for your home?

At Complete Insulation, we help Tennessee homeowners make informed decisions about their insulation needs. Understanding R-value is a key part of getting the best performance, and the most energy savings, from your investment.

Let’s break it all down.

What Is R-Value in Insulation?

R-value measures how well insulation resists the flow of heat. The higher the R-value, the better the material insulates. It’s essentially a performance rating that helps you compare different insulation products.

R-value is determined by:

• Material type
• Thickness
• Density

In a climate like Tennessee’s—where hot, humid summers and chilly winters can push HVAC systems to their limits—choosing insulation with the right R-value is critical for both comfort and energy efficiency.

Insulation R-Value Explained: Why It Matters

To keep your indoor spaces comfortable year-round, your home needs a well-sealed building envelope that minimizes heat transfer. Insulation is one of the most important components of that envelope.

Here’s how R-value affects your home:

• High R-values reduce the amount of heat entering in the summer and escaping in the winter.
• Insufficient R-value leads to energy loss, temperature imbalances, and higher utility bills.
• Proper R-value improves indoor comfort, reduces HVAC strain, and supports better air quality.

In short, understanding insulation R-value allows you to make smarter choices for your home’s long-term performance.

R-Value by Insulation Type

Different insulation materials offer different R-values per inch, which directly impacts how well they perform. Here’s a breakdown of R-value by insulation type, so you can compare common materials:

• Closed cell spray foam has one of the highest R-values, ranging from 6.0 to 7.5 per inch. It’s ideal for areas that need both thermal resistance and moisture control, like crawl spaces and attics.
• Open cell spray foam typically offers around 3.5 to 3.8 per inch. While not as moisture resistant as closed cell, it still provides excellent air sealing and is a great option for interior walls and ceilings.
• Fiberglass batts, often used in walls and attics, have an R-value between 2.9 and 3.8 per inch. It’s one of the most affordable types of insulation but doesn’t seal air leaks on its own.
• Blown-in cellulose insulation comes in close with an R-value between 3.2 and 3.8 per inch. It’s effective in attics and wall cavities and offers some resistance to air movement.
• Rigid foam boards vary depending on the material, but most offer between 4.0 and 6.5 per inch, making them a solid choice for exterior walls and foundation insulation.

Of all these options, spray foam insulation, especially closed cell, is the top performer in terms of R-value per inch and overall durability, making it a smart choice for Tennessee homeowners seeking maximum energy efficiency.

Spray Foam Insulation R-Value: A Top Performer

At Complete Insulation, we recommend spray foam insulation for many homes across Middle Tennessee, not just because of its high R-value, but because of its added benefits.

Here’s why spray foam stands out:

• Seals air leaks – Spray foam expands to fill cracks and gaps, eliminating drafts.
• Moisture barrier – Closed cell spray foam resists water, helping prevent mold and rot.
• Structural support – Closed cell spray foam can add rigidity to your walls or subfloor.
• Long-lasting – Spray foam doesn’t settle or degrade like some traditional materials.

With a spray foam insulation R-value as high as 7.5 per inch, it outperforms fiberglass and cellulose by a wide margin. This makes it especially ideal for Tennessee homes battling both humidity and extreme seasonal temperatures.

What’s the Best R-Value for Attic Insulation?

If you’re focused on upgrading your attic, you’re not alone. Attics are one of the biggest sources of energy loss in most homes.

The best R-value for attic insulation depends on your location. In Tennessee (climate zone 4), the U.S. Department of Energy recommends:

• R-38 to R-60 for attics in homes with little to no existing insulation
• R-30 to R-49 if your attic already has some insulation

Here’s what that might look like in real-world terms:

• Closed cell spray foam: You can achieve R-38 with about 6 inches of foam.
• Fiberglass batts: You’ll need around 12 to 18 inches to reach R-38 to R-60.
• Blown-in cellulose: Typically 10 to 15 inches for a similar rating.

That’s another reason spray foam is so popular, it delivers high performance in a thinner profile, freeing up attic space while still hitting efficiency goals.

R-Value Isn’t Everything, But It’s a Good Start

While R-value is important, it’s not the only factor that determines how well your insulation performs. Other things to consider include:

• Air sealing – High R-value won’t matter if air is leaking around it.
• Moisture control – Insulation that traps water can lead to mold and rot.
• Installation quality – Even the best insulation can underperform if installed incorrectly.

That’s why working with experienced crawl space and attic insulation contractors, like the team at Complete Insulation, makes all the difference. We evaluate your whole space, address air leaks, and install insulation that meets or exceeds code requirements.

Choosing the Right Insulation for Your Home

When it comes to choosing insulation, it’s about more than just numbers on a chart. You need a material that suits your home’s structure, budget, and environmental conditions.

For Tennessee homeowners, we often recommend:

• Spray foam for crawl spaces, attics, rim joists, and walls
• Fiberglass batts for more cost-conscious attic upgrades in dry conditions
• Vapor barriers to pair with insulation in high-moisture areas

Not sure what’s right for your home? We’ll help you compare R-value by insulation type, assess your current setup, and create a custom plan based on your goals.

Schedule Your Free Insulation Assessment Today

Understanding what R-value in insulation means is the first step toward a more comfortable, efficient home. At Complete Insulation, we specialize in helping homeowners get the most from their insulation, whether you’re building new, upgrading old material, or sealing problem areas.

We proudly serve homeowners throughout Nashville, Franklin, Brentwood, and beyond with expert insulation services that emphasize performance, quality, and long-term savings. Ready to maximize your R-value and lower your utility bills? Reach out to Complete Insulation today for a free inspection and personalized recommendation.