Whether you live in Florida or Alaska, proper insulation is important to stay comfortable and save money in your home. Some state codes only require attic/roof insulation, but insulating walls is also important to maintaining the home’s “climate”.
Knowing the amount of space inside a 2×6 wall is essential when working towards installing insulation to meet the recommended R-value for your home based on your climate zone. Insulation that is too thick or too thin can reduce the insulation’s effectiveness and impact the R-value negatively.
2×6 walls have a 5.5” space for insulation. For climate zones 0-2, loose-fill fiberglass will be the best and potentially the only option. Slightly over-insulating can increase the options. All insulations can be used for climate zones 3-8 but continuous insulation may be needed in some cases.
Choosing Insulation Depends On
Where You Live
Depending on where you live, the local weather and climate will vary.
For insulation to properly combat outside conditions, such as temperature changes, you must know your location’s climate zone.
Climate zones range from one to eight with the average temperature decreasing as the zone number increases.
Increasing zone numbers also correlate with a higher recommended R-value.
In short, an R-value is a measurement of how successful insulation is at slowing or stopping the movement of heat through it.
Higher R-values indicate insulation that is more successful at stopping heat flow.
Areas that experience lower temperatures, such as climate zones five through eight, are going to need insulation with higher R-values.
Inherent R-Value of the Insulation
Whatever the recommended R-value is for your climate zone, this R-value can be achieved with many kinds of insulation.
Each type of insulation will have an inherent R-value per inch. For example, if an insulation type has an R-value of 3.0 per inch, three inches of the material will provide an R-value of nine.
It may seem that the recommended R-value can be easily reached by just increasing the thickness of the insulation, but it is, unfortunately, not that easy.
There is a limited amount of space available for insulation between walls.
In order to buy and install insulation in a cost-effective way, it would be wise to buy insulation that has a high enough R-value so that the recommended R-value can be reached within the limited space between the walls.
The Space Available in 2×6 Walls
Just like 2×4 walls do not have a perfect four inches of space between walls, but rather 3.5 inches, 2×6 walls often have 5.5 inches of space between walls.
For wall insulation, it is best to have a thickness near to 5.5 inches.
Like any other Goldilocks situation, too big or too small is not ideal.
If the insulation material must be thicker than 5.5 inches to achieve the ideal R-value, and it is pressed into the wall space anyways, the thermal resistance of the insulation will be decreased due to compression.
Insulation that is crammed into an area will have fewer air pockets and because air pockets are so important in retaining heat, the insulation will not perform as well.
Additionally, insulation that reaches the ideal R-value at a thickness of much less than 5.5 inches means that there are air gaps in the wall and space for the insulation to slip or sink, which also compromises the effectiveness of insulation.
Selecting Insulation for 2×6 Walls
What R-Value You Need
The table below is adapted from Section 1102.1.3 of the International Residential Code (IRC). These are the internationally recognized building code requirements for insulation.
However, each state and territory of the USA has the option to adopt all or only part of the IRC, so the exact requirements can differ.
| 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&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 |
The insulation required for mass walls, basement walls, and crawl space walls, is not relevant to this discussion. A 2×6 wall is a wood-framed wall.
What Are the Inherent R-Values of Insulation?
One form of insulation that will be explored is the loose-fill kind, consisting of loose fibers. The most common types are fiberglass, mineral wool, and cellulose.
Loose-fill insulation is not the commonly used form for walls because it cannot be secured easily as sheet insulation. When it is used, the walls are constructed and loose-fill insulation is subsequently blown into the enclosed space.
R-values of loose-fill insulation:
- Fiberglass ranges from 2.2 to 3.4 per inch.
- Mineral wool ranges from 2.8 to 4.0 per inch.
- Cellulose ranges from 3.2 to 3.8 per inch.
Batt or roll insulation (sheet insulation) is the form of insulation that is more typically used in walls. They are not rigid, but they do hold their form. The most common types are fiberglass, mineral wool, and plastic fiber.
R-values for sheet insulation:
- Fiberglass is often around 4.3 per inch (different to the loose-fill version)
- Mineral wool is often between 3.0 to 4.3 per inch.
- Plastic fiber ranges from 4 to 7.4 per inch. The large range is due to the different kinds of plastic that can be used.
There are two more forms of plastic insulation: spray foam (polyurethane) and rigid foam board.
- Open-cell spray foam polyurethane has an R-value between 3.5 and 4.0 per inch.
- Closed-cell spray foam polyurethane R-values are between 5.5 and 7.0 per inch.
- Foam board insulation’s R-Values range from 3.6 to 8.0 per inch. Again, the wide range is because there are different types of plastic that can be used.
Which Insulation Types Will Fit in the Wall?
For this chart, a thickness of within half an inch will pass (5 inches) but any over 5.5 inches will not pass due to issues with fit and compression.
| Insulation Type | R-Value Ranges | Climate Zone 0-2 Approved? | Climate Zone 3 Approved? | Climate Zone 4-8 Approved? |
| Loose-fill fiberglass | 2.2-3.4 | R13 possible with inherent values of R2.4-R2.6. | 0 and 15ci possible with inherent values of R2.8-3. | Insulation would be too thick. |
| Loose-fill mineral wool | 2.8-4.0 | The insulation would probably be too thin. | R20 possible with inherent values of R3.7-R4.0. 0 and 15ci possible with inherent values of R2.8-3. | 0 and 20ci possible with inherent values of R3.7-4.0. |
| Loose-fill cellulose | 3.2-3.8 | The insulation would probably be too thin. | R20 possible with inherent values of R3.7-3.8. | 0 and 20ci is possible with inherent values of R3.7-3.8. |
| Fiberglass batt | 4.3 | The insulation would probably be too thin. | 13 and 10ci possible. | 13 and 10ci possible. |
| Mineral wool batt | 3.0-4.3 | The insulation would probably be too thin. | R20 possible with inherent values of R3.7-4.0. 13 and 10ci possible with inherent values of R4.2-4.3. 0 and 15ci possible with inherent value of R3.0. | 13 and 10ci possible with inherent value of R4.2-4.3. |
| Plastic fiber batt | 4.0-7.4 | The insulation would probably or definitely be too thin. | R20 possible with inherent value of R4.0. 13 and 10ci possible with inherent values of R4.2-4.6. | R30 possible with inherent values of R5.5-6.0. 20 and 5ci possible with inherent values of R4.6-5.0. 13 and 10ci possible with inherent values of R4.2-4.6. 0 and 20ci possible with inherent values of R3.7-4.0. |
| Open cell polyurethane spray foam | 3.5-4.0 | The insulation would probably be too thin. | R20 possible with inherent values of R3.7-4.0. | 0 and 20ci possible with inherent values of R3.7-4.0. |
| Closed cell polyurethane spray foam | 5.5-7.0 | The insulation would be too thin. | The insulation would be too thin. | R30 possible with inherent values of R5.5-6.0. |
| Foam boards | 3.6-8.0 | The insulation would probably or definitely be too thin. | R20 possible with inherent values of R3.7-4.0. 13 and 10ci possible with inherent values of R4.2-4.6. | R30 possible with inherent values of R5.5-6.0. 20 and 5ci possible with inherent values of R4.6-5.0. 13 and 10ci possible with inherent values of R4.2-4.6. 0 and 20ci possible with inherent values of R3.7-4.0. |
Insulation Forms: Advantages & Disadvantages
Loose-Fill Insulation
Loose-fill insulation, regardless of type, is not ideal for use in walls. As mentioned earlier, you have to almost completely close up the wall before you can install the insulation because it needs the barrier of the wall to hold it in place.
Over time, you are more likely to experience settling and the development of gaps in the insulation with loose-fill options.
The actual process of blowing in insulation can be messy, resulting in the release of potentially harmful particles into the air.
It is also not a one-person job, and you need specialized equipment.
On the other hand, loose-fill insulation is so much easier to install around obstacles, like wiring, piping, and electrical fittings, which will definitely be present behind most walls.
Sheet Insulation
Batt or roll insulation (sheet insulation) is more commonly used in walls.
The flexible, yet shape-holding nature of this insulation makes installation so much easier on the whole.
There will be less airborne dust as a result of handling the insulation, which means a lower health risk via inhalation exposure.
Sheets can come with a vapor-retarder facing, which can eliminate the need for a vapor barrier.
Using staples, glue, or simply friction, these sheets of insulation will stay upright in the walls, so you can leave the drywalling to the end.
A disadvantage with sheet insulation is that you have to cut it to size in some cases. You also have to try to fit it around pipes, wires, etc., without compromising the function of these things and without over-compressing the insulation itself.
Spray Foam Insulation
Spray foam insulation is self-adhering, so you don’t have to worry about staples.
The closed-cell version can get you a high R-value with little product, but the open-cell version can allow you to fill spaces and eliminate air gaps in the walls.
There are three main problems with spray foam insulation:
- It is toxic during application and curing.
- It has to be covered because it carries a higher fire risk.
- It sticks to every point of the surface to which it is applied, making it difficult to move or remove. This is particularly important when it comes to accessing pipes, wires, electrical fittings, etc., behind the wall.
Foam Board Insulation
Foam board insulation is also easy to install in terms of securing it in place.
It’s not going to cause itching or the release of fibers into the air in any significant way.
These plastic boards also have really high inherent R-values, which means less material will need to be purchased and installed.
However, it requires a thermal barrier because of the fire risk associated with it.
Additionally, it cannot conform to the shape of spaces or bend in order to fit through smaller openings.
The higher inherent R-value can also be a disadvantage for wall insulation if the R-value requirements are lower.