Spray Foam Insulation R-value & Thickness

This article discusses in detail the R-value of spray foam insulation and the thicknesses required to attain R-value thresholds.

There’s no doubt that spray foam brings forth a great deal of competition in the insulation market. The material is incredibly effective at minimizing heat conduction and has a high R-value for every inch if compared to other materials of similar standards. Though it brings several advantages to the table, all of these can go down the drain if the required R-value is not achieved. In this read, you’ll be learning about spray foam types, the recommended thickness, and everything related to its R-value.

Spray foam insulation R-value

The R-value of spray foam insulation ranges from 3.5 to 7 per inch thickness. For open-cell spray foam the R-value is approximately 3.5 whereas for closed-cell spray foam it is 6.

Spray foam insulation thickness

The thickness required for spray form insulation when insulating, for eg; an attic, depends on the R-value required for that place. The required spray foam insulation thickness is calculated by dividing the desired R-value with the R-value of the insulation.

For eg: For an attic that requires R-21, the spray foam insulation thickness is 21/3.5 if open-cell spray foam is used, and 21/6.5 for closed-cell spray foam.

So how thick does the spray foam insulation need to be to achieve commonly used R-value ratings? Given below is a table listing R-values and the corresponding thickness required for open-cell and closed-cell type spray foam insulations.

R-value RatingOpen-cell spray foam thicknessClosed-cell spray foam thickness
R-133.6 inches2.1 inches
R-195.2 inches3.1 inches
R-215.8 inches3.5 inches
R-308.3 inches5.0 inches
R-3810.5 inches6.3 inches
R-4913.6 inches8.1 inches
R-6016.6 inches10.0 inches
Spray foam insulation thickness chart

As you can see from the above table, the insulation thickness increases with the increase in R-value requirements. Not all thicknesses are practical though. I wouldn’t recommend using 16 inches of spray foam for R-60, instead, you could go for Rockwool or another insulation material that is easier to install.

These numbers shown above may slightly vary based upon the spray foam product you’re going for. You’re probably wondering why open-cell and closed-cell have different R-values despite both of them being spray foam. The answer for this lies in the composition of the material. Open-cell spray foam has a light and fluffy texture while closed-cell foam has more of a dense and tough one. Due to this difference, both open-cell and closed-cell have their own characteristics and R-value. You can check out our detailed comparison between the two types of spray foam here.

spray foam insulation

Spray foam insulation thickness for different US climate zones

The USA has seven climate zones, and the insulation R-value recommended for these climate zones varies. Given below is a table listing the recommended R-values for attic, floor and wall in those climate zones;

Climate ZoneFor AtticFor FloorFor Wooden Wall

Therefore, the spray foam insulation thickness needed varies with the climate zones. Given below is a table listing the thickness required for open-cell spray foam to achieve the desired R-values in different climate zones;

Climate ZoneFor AtticFor FloorFor Wooden Wall
13.6 inches3.6 inches3.6 inches
213.6 inches3.6 inches3.6 inches
313.6 inches5.2 inches5.2 inches
416.6 inches8.3 inches5.2 inches
516.6 inches8.3 inches5.8 inches
616.6 inches8.3 inches5.8 inches
716.6 inches10.5 inches5.8 inches
Open-cell spray foam insulation thickness for different US climate zones

The corresponding thicknesses required if closed-cell spray foam is used is listed below;

Climate ZoneFor AtticFor FloorFor Wooden Wall
15.0 inches2.1 inches2.1 inches
28.1 inches2.1 inches2.1 inches
38.1 inches3.1 inches3.1 inches
410.0 inches5.0 inches3.1 inches
510.0 inches5.0 inches3.5 inches
610.0 inches5.0 inches3.5 inches
710.0 inches6.3 inches3.5 inches
closed-cell spray foam insulation thickness for different US climate zones

These requirements are catered to the needs of every region in the US. Following them will help you ensure that your spray foam insulation is as effective as it can be. All you have to do is check which climate zone your region falls into. You can also look up the additional instructions regarding R-value requirements in your local residential code.

Comparing spray foam with other insulation materials

As it has already been established, spray foam is one of a kind in the insulation market. It provides an excellent air seal that retains heat energy within a structure. How well does it perform in competition with other popular insulation materials though? Let us find out.

Spray foam vs Fiberglass

Fiberglass remains unchallenged if we’re talking about popularity and use. Many factors have brought fiberglass where it is today, but how well does it stand in the ground against spray foam? Spray foam in its closed-cell form clearly outperforms fiberglass in terms of effectiveness. To achieve the basic rating of R-13, you’ll need just 2 inches of closed-cell spray foam insulation. For fiberglass, around 3.4 inches would be sufficient. This shows that a gap of 1.5 inches is the difference between both materials for achieving the same R-value.

Further reading: Spray foam vs Fiberglass

Spray foam vs Rigid foam

Spray foam and rigid foam insulation are quite similar in terms of R-value and composition. Both have many similarities but one thing that sets them apart is that spray foam is sprayed while rigid foam is not. Overall, spray foam takes the win here because it has one quality that rigid foam lacks, which is the ability to reach small spaces. Coming to the R-value, you’ll need around 2.6 inches of rigid foam insulation to get R-13. As for spray foam, we already mentioned that closed-cell can deliver the same results in just 2 inches. You can tell that there’s not much of a difference in R-value between the two since foam board is a brilliant insulator too.

Further reading: Spray foam vs foam board insulation

Spray foam vs Cellulose

Cellulose is up next for competing with spray foam. It is a material that comprises recycled paper and a few other chemicals. Cellulose is almost on the same level as open-cell spray foam but lacks way behind in relation to closed-cell. It needs around 3.8 inches of thickness to attain an R-13, which is the basic. Open-cell spray foam has approximately the same requirement but closed-cell needs just 2 inches. Furthermore, cellulose has some other benefits worth mentioning such as sound resistance and inexpensiveness which make it a worthy opponent for spray foam.  

Effect of temperature on spray foam’s R-value

When you choose spray foam as your insulation, you’re investing in a material that is well known for its durability. Extreme weather conditions will have no effect on the R-value of spray foam. The reason behind this is the material’s excellent moisture impermeability. Spray foam makes an air seal that resists moisture in all its forms to a great extent. Therefore, it remains firm and resilient throughout the years without compromising its R-value. However, you should try to have it sprayed during moderate weather otherwise extreme cold/hot weather might tamper with the application. 


Giving your insulation the proper strength in putting up the line of defense is essential. That is why homeowners should comply with the local R-value codes. We’ve given you an insight into the requirements needed for spray foam insulation. If installed correctly, it would last for a lifetime. 

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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