Insulation Selection Guide for 2×4 Walls

Picking out insulation can be a lengthy task with the many brands, types, and thicknesses of insulation out there. Adding the complexities of how much space your home’s walls have and recommended R-values for your climate zone makes the process even lengthier.

Knowing the innate R-values of certain kinds of insulation as well as how much space you have between your 2×4 walls is essential for picking out insulation for your home. Each insulation option fits some climate zones better than others and has other pros and cons to consider.

What to Consider When Selecting Insulation

Where Do You Live?

Although insulation is important in all homes regardless of where you live, not all homes will need the same kind of insulation. 

This is because climates vary across continents, countries, and even states. 

Insulation made for a place with warm winters will not work for a place with freezing winters. 

Because of this fact, different levels of insulation have varying R-values. 

An R-Value is meant to measure how much the insulation material can resist the conductive flow of heat through the material. 

In general, a higher R-Value means that the insulation material resists the flow of heat more.

Recommended R-Values can vary by latitude, elevation, and how close the area is to a body of water. 

Most countries have different climatic zones laid out that show which R-Value of insulation is best for the area.  

Climate Zone	Wood Frame Wall R-Value	Mass Wall R-Value	Basement Wall R-Value	Crawl Space Wall R-Value
0	13 or 0 and 10ci*	3/4	0	0
1	13 or 0 and 10ci	3/4	0	0
2	13 or 0 and 10ci	4/6	0	0
3	20 or 13 and 10ci or 0 and 15ci	8/13	5ci or 13	5ci or 13
4 except Marine	30 or 20 and 5ci or 13 and 10ci or 0 and 20ci	8/13	10ci or 13	10ci or 13
5 and Marine 4	30 or 20 and 5ci or 13 and 10ci or 0 and 20ci	13/17	15ci or 19 or 13 and 5ci	15ci or 19 or 13 and 5ci
6	30 or 20 and 5ci or 13 and 10ci or 0 and 20ci	15/20	15ci or 19 or 13 and 5ci	15ci or 19 or 13 and 5ci
7 and 8	30 or 20 and 5ci or 13 and 10ci or 0 and 20ci	19/21	15ci or 19 or 13 and 5ci	15ci or 19 or 13 and 5ci

What Is the Innate R-Value of the Insulation

There are a variety of ways to achieve the recommended R-value for your location.  

First off, the thicker your insulation is, the higher the R-value will be, so you can just install thicker layers.

Additionally, each insulation material has a different innate R-value (usually a range), so you can choose insulation materials with higher innate R-values.

Then you would either need less insulation or the amount of insulation you have will do a better job.

You can see which approach would be more cost-effective.

Common insulation materials include loose-fill and batt fiberglass, loose-fill and batt mineral wool, loose-fill cellulose, plastic fiber batt, open-cell and closed-cell polyurethane, and foam boards.

Innate R-values of these are:

• Loose-fill fiberglass = 2.2 to 3.4 per inch.
• Fiberglass batt = 4.3 per inch.
• Loose-fill mineral wool = 2.8 to 4 per inch.
• Mineral wool batt = 3 to 4.3 per inch.
• Loose-fill cellulose = 3.2 to 3.8 per inch. 
• Plastic fiber batt = 4 to 7.2 per inch.
• Open-cell polyurethane = 3.5 to 7.0 per inch.
• Closed-cell polyurethane = 3.6 to 7.0 per inch.
• Foam board insulation = 3.6 to 8 per inch. 

How Much Space Is There in 2×4 Walls?

Knowing these innate values is important because 2×4 walls only have so much space for insulation.

If an insulation material’s R-Value is too high or low, this can make getting the necessary R-Values for your location harder. 

While insulation can be cut and shaped to fit a variety of shapes within your walls, its thickness cannot be changed. You also don’t want it to be too thin or it will move in the space and become less effective.

That being said, the space allotted for insulation between 2×4 walls is about three and a half inches. 

Knowing this, we can figure out what our insulation options are for 2×4 walls.

2×6 Insulation in 2×4 Walls | 6 Reasons Why It’s a Bad Idea

Insulation Options for 2×4 Walls

Loose-Fill Fiberglass

Climate Zone	Loose-fill Fiberglass for Wood Frame Wall	Loose-fill Fiberglass for Mass Wall	Loose-fill Fiberglass for Basement Wall	Loose-fill Fiberglass for Crawl Space Wall
0	Only if it is in the higher range of innate R-value and only if ci.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
1	Only if it is in the higher range of innate R-value and only if ci.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
2	Only if it is in the higher range of innate R-value and only if ci.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
3	n/a*	Only if it is in the higher range of innate R-value.	Only if it is ci.	Only if it is ci.
4 except Marine	n/a	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value and only if ci.	Only if it is in the higher range of innate R-value and only if ci.
5 and Marine 4	n/a	n/a	n/a	n/a
6	n/a	n/a	n/a	n/a
7 and 8	n/a	n/a	n/a	n/a

This material is often more cost-effective than other options and fairly easy to install.

However, blown in insulation is not always the best option for walls because it can compress due to gravity and expose some portions of the wall.

Fiberglass Batt

Climate Zone	Batt Fiberglass for Wood Frame Wall	Batt Fiberglass for Mass Wall	Batt Fiberglass for Basement Wall	Batt Fiberglass for Crawl Space Wall
0	Appropriate for use.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
1	Appropriate for use.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
2	Appropriate for use.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
3	Only if 15ci	Appropriate for use. Will over-insulate.	Appropriate for use.	Appropriate for use.
4 except Marine	n/a*	Appropriate for use. Will over-insulate.	Appropriate for use.	Appropriate for use.
5 and Marine 4	n/a	Only for R13	Only for R15ci or R13 and R5ci	Only for R15ci or R13 and R5ci
6	n/a	n/a	Only for R15ci or R13 and R5ci	Only for R15ci or R13 and R5ci
7 and 8	n/a	n/a	Only for R15ci or R13 and R5ci	Only for R15ci or R13 and R5ci

Batts work well in walls and this material can easily be equipped with a vapor barrier for even better insulating properties.

Loose-Fill Mineral Wool

Climate Zone	Loose-fill Mineral Wool for Wood Frame Wall	Loose-fill Mineral Wool for Mass Wall	Loose-fill Mineral Wool for Basement Wall	Loose-fill Mineral Wool for Crawl Space Wall
0	Only if it is in the higher range of innate R-value.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
1	Only if it is in the higher range of innate R-value.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
2	Only if it is in the higher range of innate R-value.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
3	n/a*	Only if it is in the higher range of innate R-value.	Appropriate for 5ci. Appropriate for R13 at higher range of innate R-value.	Appropriate for 5ci. Appropriate for R13 at higher range of innate R-value.
4 except Marine	n/a	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value
5 and Marine 4	n/a	Only for R13 and only if in the higher range of innate R-value.	n/a	n/a
6	n/a	n/a	n/a	n/a
7 and 8	n/a	n/a	n/a	n/a

Like loose fill fiberglass, mineral wool is a cheaper insulation option. However, also like loose-fill fiberglass, loose-fill mineral wool is not always the best option for walls.

Mineral Wool Batt

Climate Zone	Mineral Wool Batt for Wood Frame Wall	Mineral Wool Batt for Mass Wall R-Value	Mineral Wool Batt for Basement Wall R-Value	Mineral Wool Batt fro Crawl Space Wall R-Value
0	R13 at higher range of innate R-value. Appropriate for 0 and 10ci.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
1	R13 at higher range of innate R-value. Appropriate for 0 and 10ci.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
2	R13 at higher range of innate R-value. Appropriate for 0 and 10ci.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
3	Only for 0 and 15ci and only at higher range of innate R-value.	Appropriate for R8. Will over-insulate. R13 at higher range of innate R-value.	Appropriate for 5ci. Will over-insulate. R13 only if in the higher range of innate R-value.	Appropriate for 5ci. Will over-insulate. R13 only if in the higher range of innate R-value.
4 except Marine	n/a*	Appropriate for R8. Will over-insulate.  R13 at higher range of innate R-value.	Appropriate for 10ci. R13 only if in the higher range of innate R-value.	Appropriate for 10ci. R13 only if in the higher range of innate R-value.
5 and Marine 4	n/a	Only for R13 and only if it is in the higher range of innate R-value.	Appropriate for 15ci and only if in the higher range of innate R-value.	Appropriate for 15ci and only if in the higher range of innate R-value.
6	n/a	Only for R15 and only if it is in the higher range of innate R-value.	Appropriate for 15ci and only if in the higher range of innate R-value.	Appropriate for 15ci and only if in the higher range of innate R-value.
7 and 8	n/a	n/a	Appropriate for 15ci and only if in the higher range of innate R-value.	Appropriate for 15ci and only if in the higher range of innate R-value.

Mineral wool batt is great at preventing unwanted sound and moisture from entering the home.

However, because of the irritating nature of mineral wool, protective equipment should be worn. This can increase the cost of installation and make things more complicated. 

Loose-Fill Cellulose

Climate Zone	Loose-Fill Cellulose for Wood Frame Wall R-Value	Loose-Fill Cellulose for Mass Wall R-Value	Loose-Fill Cellulose for Basement Wall R-Value	Loose-Fill Cellulose for Crawl Space Wall R-Value
0	R13 but only if it is in the higher range of R-value. Appropriate for 0 and 10ci.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
1	R13 but only if it is in the higher range of R-value. Appropriate for 0 and 10ci.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
2	R13 but only if it is in the higher range of R-value. Appropriate for 0 and 10ci.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
3	n/a*	Appropriate for R8. R13 only if it is in the higher range of innate R-value.	Appropriate for R5ci. R13 only if it is in the higher range of innate R-value.	Appropriate for R5ci. R13 only if it is in the higher range of innate R-value.
4 except Marine	n/a	Appropriate for R8. R13 only if it is in the higher range of innate R-value.	Appropriate for R10ci. R13 only if it is in the higher range of innate R-value.	Appropriate for R10ci. R13 only if it is in the higher range of innate R-value.
5 and Marine 4	n/a	Only R13 and only if it is in the higher range of innate R-value.	n/a	n/a
6	n/a	n/a	n/a	n/a
7 and 8	n/a	n/a	n/a	n/a

Cellulose insulation is cost-effective and also is made up mostly of recycled materials, making loose-fill cellulose both cheap and environmentally friendly. But it can slip and compress in walls.

Plastic Fiber Batt

Climate Zone	Plastic fiber for Wood Frame Wall R-Value	Plastic fiber for Mass Wall R-Value	Plastic fiber for Basement Wall R-Value	Plastic fiber for Crawl Space Wall R-Value
0	Appropriate for use.  Can over-insulate.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
1	Appropriate for use.  Can over-insulate.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
2	Appropriate for use.  Can over-insulate.	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
3	Only if it is in the higher range of innate R-value.	Appropriate for use.	Appropriate for use. Will over-insulate.	Appropriate for use. Will over-insulate.
4 except Marine	Only if it is in the higher range of innate R-value.	Appropriate for use.	Appropriate for use.  Can over-insulate.	Appropriate for use.  Can over-insulate.
5 and Marine 4	Only if it is in the higher range of innate R-value.	Appropriate for R13. R17 only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.
6	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.
7 and 8	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.

With a much higher maximum R-Value of 7.2, it is easier for plastic fiber batt to meet R-Value recommendations. This allows it to be installed more readily in homes within the climate zones of zero through three.

Plastic fiber insulation is, however, more expensive than most types of insulation materials. 

Polyurethane Spray Foam

Climate Zone	Polyurethane for Wood Frame Wall R-Value	Polyurethane for Mass Wall R-Value	Polyurethane for Basement Wall R-Value	Polyurethane for Crawl Space Wall R-Value
0	R13 only if it is in the higher range of innate R-value. Appropriate for 0 and 10ci.	Appropriate for use. Will over-insulate.	No insulation  required.	No insulation  required.
1	R13 only if it is in the higher range of innate R-value. Appropriate for 0 and 10ci.	Appropriate for use. Will over-insulate.	No insulation  required.	No insulation  required.
2	R13 only if it is in the higher range of innate R-value. Appropriate for 0 and 10ci.	Appropriate for use. Will over-insulate.	No insulation  required.	No insulation  required.
3	Only if it is in the higher range of innate R-value.	Appropriate for R8. R13 only if it it in the higher range of innate R-value.	Appropriate for R5ci.  Will over-insulate. R13 only if it it in the higher range of innate R-value.	Appropriate for R5ci.  Will over-insulate. R13 only if it it in the higher range of innate R-value.
4 except Marine	Only 13 and 10ci and 0 and 20ci and only if it is in the higher range of innate R-value.	Appropriate for R8. R13 only if it it in the higher range of innate R-value.	Appropriate for R10ci. Will over-insulate. R13 only if it it in the higher range of innate R-value.	Appropriate for R10ci. Will over-insulate. R13 only if it it in the higher range of innate R-value.
5 and Marine 4	Only 13 and 10ci and 0 and 20ci and only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.
6	Only 13 and 10ci and 0 and 20ci and only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.
7 and 8	Only 13 and 10ci and 0 and 20ci and only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.	Only if it is in the higher range of innate R-value.

Spray foam insulation is more likely to be appropriate for use in more extreme cold climates.

Of the two types of spray foam insulation, the open-cell form is more flexible, making it easier to install. However, the density of closed-cell form means that it is more likely to reach the higher range of R-values, making it a stronger insulator.

Foam Boards

Climate Zone	Foam Board for Wood Frame Wall R-Value	Foam Board for Mass Wall R-Value	Foam Board for Basement Wall R-Value	Foam Board for Crawl Space Wall R-Value
0	R13 only if it is in the range of higher innate R-value. Appropriate for 0 and 10ci	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
1	R13 only if it is in the range of higher innate R-value. Appropriate for 0 and 10ci	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
2	R13 only if it is in the range of higher innate R-value. Appropriate for 0 and 10ci	Appropriate for use. Will over-insulate.	No insulation required.	No insulation required.
3	Only if it is in the range of higher innate R-value.	Appropriate for R8 R13 only if it is in the range of higher innate R-value.	Appropriate for R5ci. R13 only if it is in the range of higher innate R-value.	Appropriate for R5ci. R13 only if it is in the range of higher innate R-value.
4 except Marine	Only for 20 and 5ci, 13 and 10ci, and 0 and 20ci and only if it is in the higher range of innate R-value.	Appropriate for R8 R13 only if it is in the range of higher innate R-value.	Appropriate for R10ci. R13 only if it is in the range of higher innate R-value.	Appropriate for R10ci. R13 only if it is in the range of higher innate R-value.
5 and Marine 4	Only for 20 and 5ci, 13 and 10ci, and 0 and 20ci and only if it is in the higher range of innate R-value.	Only if it is in the range of higher innate R-value.	Only if it is in the range of higher innate R-value.	Only if it is in the range of higher innate R-value.
6	Only for 20 and 5ci, 13 and 10ci, and 0 and 20ci and only if it is in the higher range of innate R-value.	Only if it is in the range of higher innate R-value.	Only if it is in the range of higher innate R-value.	Only if it is in the range of higher innate R-value.
7 and 8	Only for 20 and 5ci, 13 and 10ci, and 0 and 20ci and only if it is in the higher range of innate R-value.	Only if it is in the range of higher innate R-value.	Only if it is in the range of higher innate R-value.	Only if it is in the range of higher innate R-value.

Foam boards suited to extreme cold climates and they are also the only insulation style that can prevent the movement of heat through the structural elements of the walls. 

The rigid nature of this material makes it harder to install. 

Sources

https://www.energystar.gov/campaign/seal_insulate/identify_problems_you_want_fix/diy_checks_inspections/insulation_r_values#:~:text=R%2DValue%20is%20a%20measure,and%20locations%20in%20the%20home.

https://codes.iccsafe.org/content/IRC2021P2/chapter-11-re-energy-efficiency#IRC2021P2_Pt04_Ch11_SecN1102.1.3

https://www.thespruce.com/size-insulation-for-2×4-and-2×6-walls-1821598#:~:text=Insulation%20for%202×4%20Walls&text=Since%20modern%20two%2Dby%2Dfours,%2Dby%2Dfour%20stud%20walls.

https://www.familyhandyman.com/list/pros-and-cons-of-the-residential-insulation/

https://tigerfoam.com/sprayfoaminsulation/open-cell-vs-closed-cell-foam-which-should-i-choose/#:~:text=Open%20cell%20foam%20is%20full,the%20name%20suggests%2C%20completely%20closed.