When insulating exterior walls, what type of insulation and insulation thickness should you use? Adding too little insulation means wasted energy. Adding too much insulation—stuffing in more than is needed—can also waste energy.
The right type of insulation to use for your home's exterior walls comes down to the thickness of the walls.
Walls built with 2x4s: Use R-13 or R-15 kraft-faced fiberglass insulation or mineral wool insulation when the house's exterior walls are built with 2x4s.
Walls built with 2x6s: Use R-19 or R-21 kraft-faced fiberglass insulation or mineral wool insulation when the house's exterior walls are built with 2x6s.
How to Know the Thickness of Your Home's Walls
Measuring the size of exterior wall studs by looking at the edge of a window or door can be difficult. But it's easy to check if you have a drill, a stud finder, and something thin to probe with, like a kitchen skewer.
Turn off circuit breakers to wiring running through the wall.
Find two wall studs with a stud finder.
Drill a 1/8-inch into the drywall.
Stop after you have drilled about 1/2-inch.
Insert the probe until it stops.
Mark the probe where it touches the wall. Remove it.
Measure the distance. If it's 4 inches, you have 2x4 walls. If it's 6 inches, you have 2x6 walls.
If the measurement is other than 4 inches or 6 inches, the probe may have hit a pipe, a fire block, or another obstruction. Drill in another area and try again.
Insulation For 2x4 Walls
Wall assemblies, especially those in older homes, are built with two-by-four (2x4) studs. The wall thickness will be 3-1/2 inches, not 4 inches. The width of modern 2x4s is 3-1/2 inches.
Use R-13 or R-15 kraft-faced fiberglass insulation or mineral wool insulation rolls for 2x4 stud walls. While rated differently, these two types of insulation are close enough in thickness that they can both fit in these wall systems.
Older homes, especially those predating the 1950s, may employ two-by-fours with a true measurement of 2 inches by 4 inches. In this case, use R-13 or R-15 fiberglass or mineral wool insulation. There is no 4-inch thick-faced fiberglass insulation in batts or rolls on the common market.
R-Value
R-value is a standard unit of measurement for determining, among many things, how effective your insulation will be. The R refers to absolute thermal resistance. Higher R-value numbers mean that theinsulating material resists the cold or heat from the outside better. Thickness, density, and type of materials are some factors that contribute to R-value.
Insulation For 2x6 Walls
In homes that have exterior walls built with 2x6 studs, use R-19 or R-21 kraft-faced fiberglass insulation or mineral wool insulation.
This combination ensures that the insulation is neither too loose nor too tightly packed within the walls.
Best Insulation for 2x4 and 2x6 Wall Studs
Insulation Type
Thickness of Insulation
Appropriate for This Wall Type
R-13
3 1/2 Inches (+/-)
Two-by-four (2x4) stud walls
R-15
3 1/2 Inches (+/-)
Two-by-four (2x4)stud walls
R-15
3 1/2 Inches (+/-)
Two-by-four (2x4) stud walls with true 4-inch depth.
R-19
6 1/4 Inches (+/-)
Two-by-six (2x6)stud walls
R-21
5 1/2 Inches (+/-)
Two-by-six (2x6)stud walls
How Insulation Works
Fiberglass and mineral wool insulation works partly by trapping air pockets within the insulation. If you cram too much insulation into a wall that is too thin, you reduce the insulation's air pockets and thus reduce its ability to provide thermal resistance.
A thick down-filled jacket or sleeping bag works the same way. When the feathers fluff up and create air pockets, thermal resistance is at its greatest. Bags or jackets that are wet or have been rolled up for a long time do not retain body warmth because there are fewer and smaller air pockets.
Tip
Spray foam insulation is another option. Spray foam insulation seals all areas of the cavity: walls, floors, and ceiling, along with the structural members, holes, cracks, and seams. Spray foam cannot lose its shape, except under extreme pressure. It will not sag or settle over time.
Tiny air pockets created within the insulation are what help keep a home toasty and warm, not the actual strands of fiberglass, mineral wool, or paper facing.
Striking a perfect balance between too little insulation and too much insulation will keep you and your family warm throughout the winter or cool in the summer.
Other Insulation Types
Insulating the exterior walls is just a start. Use these other materials and methods to keep your home weathertight:
Install thick insulation battsin the attic.Batts are long strips of unrolled and unfaced fiberglass insulation. Installing attic insulation is one of the most valuable ways to save energy and keep your home warmer.
Add blown-in cellulose wall insulation. Cellulose insulation does not fit the wall cavities as adequately as fiberglass or mineral wool insulation, but it's a good option if the walls cannot be opened up.
Seal up door and window cracks with caulk. Cold air seeping into your home has a detrimental effect on your home's heat envelope.
Install exterior wall sheathing beneath new siding. Sheathing can help boost your walls by as much as an extra R-6 level.
Add storm windows at the beginning of each cold weather season to the front of your existing windows.
Replace your windows.Your current windows may have already lost the insulating gas between their panes. Replacement of the entire window is the best way to fix this problem.
In homes that have exterior walls built with 2x6 studs, use R-19 or R-21 kraft-faced fiberglass insulation
fiberglass insulation
Glass wool is an insulating material made from glass fiber arranged using a binder into a texture similar to wool. The process traps many small pockets of air between the glass, and these small air pockets result in high thermal insulation properties.
or mineral wool insulation. This combination ensures that the insulation is neither too loose nor too tightly packed within the walls. Two-by-four (2x4) stud walls with true 4-inch depth.
In most wall applications, you will use R-13 or R-15 kraft-faced fiberglass insulation rolls for these two-by-four stud walls. While rated differently, these two types of insulation are close enough in thickness that they can both fit into modern two-by-four wall systems.
The DOE Insulation Fact Sheet (DOE/CE-0180) can be ordered from the Energy Efficiency and Renewable Energy Clearinghouse or accessed from the Internet at www.ornl.gov/ roofs+walls. Fiberglass and rock wool batts—2x4 walls can hold R-13 or R-15 batts; 2x6 walls can have R-19 or R-21 products.
So r30 walls are a great idea in any climate. There is no way he put R30 into a 2x4 wall. Many new homes that are 2x4 framed require by code 1” of exterior insulation to bring the effective r value to 20+. R 60 is recommended in my area for ceilings.
If you need more than the r-value of 27.5 the board insulation gives you in the 2x6 space here are two ways to do it. Either fur out the bottom of the rafters/joists to give you the needed additional 1/2 inch thickness or put 1/2 inch board insulation across the bottom of the rafters/joists.
While rated differently, these two types of insulation are close enough in thickness that they can both fit in these wall systems. Older homes, especially those predating the 1950s, may employ two-by-fours with a true measurement of 2 inches by 4 inches.
R-value is a metric that tells us how well insulation performs at reducing heat loss. When comparing R13 to R15, insulation designated as R15 performs better at reducing heat loss than R13. R-values are generally cumulative, meaning that you can stack two layers of R6 insulation boards to achieve R12.
The thermal barrier of a home should consist of a continuous layer of insulation on all sides—including the lowest floor, the exterior walls, and the ceiling or roof. Doubling the thickness of insulation will double the insulation's R-value, cutting heat loss in half.
R-value is used to judge thermal insulation performance and the higher the number, the better the product's insulating ability. So R19 has better insulating ability than R13. Now R-Value ranges widely across products and home applications. Indeed you will see R60 in some places and R13 in others.
To increase the energy efficiency of your home, you can boost the R-value of walls by adding more batt insulation between wall studs or installing foam-board insulation.
In fact, adding too much insulation to your walls can lead to problems such as poor ventilation, mould growth, and condensation. This is because thicker insulation can block airflow and trap moisture, leading to indoor air quality issues and even structural damage.
Can you over insulate your attic? The answer is yes! Past a certain point, insulation in a vented attic will do more harm than good. In most of the United States, achieving an R-Value of 38 is more than sufficient.
It is possible to over-insulate your house so much that it can't breathe. The whole point of home insulation is to tightly seal your home's interior. But if it becomes too tightly sealed with too many layers of insulation, moisture can get trapped inside those layers. That's when mold starts to grow.
When blown or sprayed cellulose insulation is used, the R-value is typically R-20 for 2x6 walls. Exterior insulating sheathing is typically added as expanded polystyrene (EPS) at R-4/inch, extruded polystyrene (XPS) at R-5/inch or foil-faced polyisocyanurate at R-6.5/inch.
Faced fiberglass costs between $0.50–$2.00 per square foot, while unfaced fiberglass costs $0.50–$1.75 per square foot. Faced insulation is best for locations prone to moisture, while unfaced insulation is best for dry, interior locations. Unfaced insulation is more sound-proof and cost-friendly.
This yields R-4.37 for a 2x4 wall and R-6.88 for a 2x6 wall. In summary, the opaque area makes up 14% to 22% of the wall assembly, yielding an R-value of 4.4 to 6.9 depending on framing thickness.
There is a direct relationship between the amount of insulation and the amount of heat transfer. The bigger the R value, the better the insulation is at slowing down the heat transfer. So R19 is better insulation than R13, and R30 is better than R19. The larger the R value, the better the insulation value.
At the end of the day its a no brainer. The higher the R-value, the better the thermal performance of the insulation. To increase your R-Value simply apply an extra layer of insulation over your initial layer.
R-value is used to judge thermal insulation performance and the higher the number, the better the product's insulating ability. So R19 has better insulating ability than R13. Now R-Value ranges widely across products and home applications. Indeed you will see R60 in some places and R13 in others.
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