What Is Roof Insulation R-Value & Why Is It Important?

Sep 25, 2023


Moises V.




September 25, 2023


September 27, 2023

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Are you tired of high power bills? You’re not alone. The average American spends over $2,000 annually on energy costs, some of which are caused by poor insulation. However, you can lower your energy bills and save money by insulating your home, and we can help you with that. 

But how do you measure your home’s insulation levels? It’s through its R-value. We’ll guide you toward understanding roof insulation R-value and why it matters to help you keep your home warm in the winter and cool in the summer.


An Overview of Roof Insulation R-Value

Simply put, R-value means thermal resistance, which measures how well a material can keep heat in or out. It’s measured in BTU/ft²/h/°F, which shows how many British thermal units (BTU) of heat flow through one square foot of the material in one hour. 

The higher the R-value, the stronger the insulating power. 

How Do I Calculate the R-value of Insulation?

To calculate the R-value of a material, divide its thickness in inches by its k-value — the measure of how well heat flows through a material. The lower the k-value, the better the insulation. 

For instance, a piece of wood that’s 1 inch thick with a k-value of 0.1 has an R-value of 10 (1 ∕ 0.1 = 10). So, it’ll take 10 hours for 1 BTU of heat to flow through one square foot of the wood. 

Don’t worry; you’ll find the insulation R-values of different materials in the manufacturer’s specification or online. 


Why Does R-Value Matter?

Worker insulate the attic with mineral wool

The right insulation levels will make your home more energy efficient if you follow the minimum guidelines for your region’s R-values. 

Let’s take a look at why using the proper insulation R-values matters:

  • Lower Energy Costs: The U.S. Environmental Protection Agency (EPA) estimates that properly insulating your home can save up to 15% on heating and cooling costs. So, if your power bill is $100, you’ll save $15 monthly and $180 annually.
  • Higher Return On Investment (ROI): If you want to sell your home for more than it costs, ensure it’s properly insulated. Buyers are always looking for energy-efficient properties because it’ll save them money on their power bills. 
  • Pest Resistance: Insects and rodents will squeeze through gaps and holes in your attic, searching for food or shelter. A proper R-value seals up any cracks and gaps around windows, doors, and crawl spaces to keep pests out of your home.
  • Comfortable Living: The right R-value insulation will regulate temperatures effectively, keeping your home cool in the summer and warm in the winter. It’ll also reduce drafts, dust, and allergens that trigger allergies, making you comfortable in your living space. 
  • Extended Lifespan: In extreme temperatures, your drywall, flooring, and pipes may freeze and crack or overheat and warp. This is why you need to maintain the recommended R-values to keep your home’s interior and exterior in good condition, extending its longevity.


Types of Insulation Materials

spray polyurethane foam for roof

There are many types of insulation available, and the best option for your property will depend on your location, the recommended R-value, and your home’s features. 

Check out these types of insulation that you can consider:

  • Spray Foam: It has the highest R-value and is an effective air barrier, reducing heat gain and improving energy efficiency. This insulation suits interior and exterior walls, attics, and cold climates.
  • Closed Cell Foam: This is a type of spray foam insulation with closed cells filled with gas, making it water-resistant and durable. It has a higher R-value than open-cell foam, making it ideal for roofs in cold climates.
  • Rigid Foam: It has a high R-value and is a good air barrier. Also, the material is ideal for interior and exterior walls and roofs and is a suitable choice for all climate zones.
  • Mineral Wool: Mineral wool is a type of batt insulation made from spun fibers of rock, glass, or slag, reducing its thermal conductivity and increasing its insulating power. It’s common in exterior walls and is a good crawl space insulation.
  • Fiberglass: Another type of batt insulation manufactured from spun fibers with the same properties and applications as mineral wool. Although fiberglass applications are more affordable than mineral wool, you’ll find the material less fire-resistant. 
  • Cellulose: Loose-fill insulation is produced using recycled paper, making it one of the most inexpensive insulators. It’s applied to attics and other areas where you can blow it in place.

Here’s a table that includes the R-values and thermal conductivity for different insulation materials:

Insulation Material R-Value Thermal Conductivity
Spray Foam 3.5 – 6.0 0.022 – 0.026
Closed Cell Foam 3.2 – 6.0 0.022 – 0.026
Rigid Foam 2.5 – 4.5 0.033 – 0.035
Mineral Wool 2.6 – 3.8 0.038 – 0.045
Fiberglass 2.2 – 3.0 0.038 – 0.042
Cellulose 2.6 – 3.8 0.035 – 0.040


How Much Insulation Do You Need?

The level of insulation in your home varies depending on your insulation climate zone and property structure. Consider the following guidelines for insulation R-values in different parts of your house:


The minimum insulation R-value your attic needs depends on where you live. For instance, warm areas need at least R-30, while cold areas require at least R-49.2. The higher the R-value, the better because it’ll resist heat flow better than a low R-value. 

Remember that you can’t go wrong with more insulation, but it might not be worth the extra cost if you live in a warm climate. 


If you live in a cold climate and want to insulate your floors, an insulation R-value of R-25 will keep them warm in the winter. But if you’re in a mild climate, insulate your floors with R-19 to keep them comfortable in winter and summer. And if your climate is hot, an insulation of R-13 will ensure your floors stay cool in the summer. 

Exterior Walls

The insulation in your exterior walls is limited by the space between the wall studs — wood pieces that hold up the walls. Your insulation will have to fit between these studs, so an R-value between R-13 and R23 is ideal. 

Basements and Crawl Spaces

If you ignore the recommended insulation R-values in your basements and crawl spaces, you’ll lose a lot of heat through them, making your home less energy-efficient. 

So, as a rule of thumb, use R-25 to R-38 insulation in every climate and R-49 if you live in extremely cold climate zones. 



You need to consider many factors when insulating your home, and understanding its insulation R-value is an essential step. But even with this information, the practical work is more difficult than it seems. 

If you need to install quality insulation on your property, contact us today for a free estimate. We’ll ensure your home stays cozy in every season.

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