R13 vs R15 Insulation: Detailed Comparison

Picking out which insulation to use in your home is one of the most important decisions to make. The biggest indication of how great your insulation will work is the R-value. R-value depicts thermal insulation performance; hence, the higher the value, the better the performance. Nonetheless, homeowners can often debate between R13 and R15-rated insulation. It’s imperative to remember that each has its gains – you need to know which benefit will fulfill your requirement more efficiently and effectively. The two don’t have many significant differences, but they’re just enough to know which one suits you. 

Differences and similarities between R13 and R15

To help you reach a safer conclusion, look at the table below giving insight into the differences between R13 and R15: 

R13 insulationR15 insulation
Relatively lower performanceBetter insulating ability 
More suitable for narrow areasOften too thick to be placed in narrow areas
Cheaper Can be cost slightly higher
3.57 inches of fiberglass batt needed4.12 inches of fiberglass batt needed
R13 vs R15 insulation

Despite some of their differences, R13 and R15 also hold similarities. These similarities include their capacity to control moisture, prevent pests, reduce noise, and usage in 2×4 walls. When it comes to moisture control, it’s worth knowing that if the insulation gets wet, its R-value will naturally decrease. In terms of pest prevention, insulation materials can be treated with pesticides regardless of their R-value, making no obvious difference at all. Noise, both indoors and outdoors, seems to be equally reduced with either of the two insulations. 

R15 offers higher energy efficiency compared to R13 due to the ability to provide insulation that improves with raised R-values. On the surface, it may seem obvious to choose R15, but, when facing the selection between R15 and R13 – you need more information, so here’s your chance. 


Naturally, if you live in a colder climate, you’ll need more insulation to retain heat inside the house. If you live in a hotter climate, you need the right amount of insulation to restrict heat transference into your house. Keeping that in mind, if you’re a homeowner in colder regions, then install R15 insulation as it’ll give you the ideal results. On the other hand, if you’re a homeowner in hotter regions where the weather remains warm throughout the year, then R15 and R13 both, can work for you. R13 seems more suitable for places with mild to moderate temperatures. 

The cost difference between R13 and R15

As per general rule – as the R-value increases, so does the cost. When the R-value raises, the thickness of the materials required to achieve a certain value increases. Therefore, when the thickness increases, so do the material and cost. In this case, R15 is relatively more expensive to install than R13. R15 will provide you with raised quality and outcomes, but it’ll cost you more. If you’re on a tight budget, then R13 will grant you what you’re looking for at the price you’re willing to pay. 

Where to install R13 or R15?

R13 insulation is typically used in the cavities of inner walls due to its noise reduction power, with the added advantage of lesser cost and material. R15 is more commonly seen in basements, attics, floors, and external walls, giving R15 greater versatility compared to its competitor. In fact, R13 is more applicable for cramped spaces with a limited surface area, such as your loft. 

Thickness needed to achieve R13 and R15

The point of the insulation is to provide resistance to heat; thus, the depth of the material alters the insulation’s performance. Higher R-values need more material to attain that value. Normally, R13 and R15 use fiberglass, spray foam, cellulose, foam board, and Rockwool. To reach the values of R13 and R15, you’ll need to go for a certain amount of insulation thickness, as shown below: 

MaterialR13 Thickness (inches)R15 Thickness (inches)
Fiberglass (batt)3.574.12
Fiberglass (loose-fill)4.335.00
Spray Foam (closed-cell)2.172.50
Spray Foam (open-cell)3.614.17
Foam Board2.603.00
Cellulose (loose-fill)3.824.41
Rockwool (batt)3.614.17
Rockwool (loose-fill)4.335.00


R13 and R15 are somewhat similar, but they are adjustable given your budget, residence, and requirements. If used correctly, they both will be worth your money. All you have to do is figure out which one makes it off your checklist using this guide.

Additional Reading:

Charles John

Experienced HVAC technician with 8 years of experience in the industry. Capable of handling all sorts of heating and cooling equipment as well as proficient in operational management, construction-related techniques such as preventative maintenance, electrical troubleshooting and AutoCAD

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