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. Generally, batt insulation is the least expensive wall insulation material but requires careful installation for effective performance (see page 4).
The general recommendation is a minimum R13 in a 2x4 wall. If you're going to go with batts I would recommend looking into mineral wool instead of fiberglass. It provides a lot of benefits including a higher R-value per inch.
Excellent Thermal Performance Owens Corning™ R-15 EcoTouch® insulation is specifically engineered to solve the efficiency problems of exterior 2x4 walls. “High density” means more fibers per square inch. It delivers a higher R-value per square inch in less space than standard insulation products.
There are two ways to get to R20 if you have a 2x4 wall. One is to make the wall thicker and use batt or blown insulation. If you add 2 inches to the thickness of the wall you can use batts made for a 2x6 wall. A regular 2x6 fiberglass batt is only R19, but high density fiberglass or rock wool will get you over 20.
no, R19 will not provide better sound attenuation than R-13. In fact, just like thermal properties, it will actually provide less. What you're trying to block are airborne noises. An R11 sound batt will provide the best attenuation in a 2x4 wall compared to any of the fiberglass insulation products.
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.
Insulation to Use
For 2x4 walls, use R-13 or R-15 insulation. For 2x6 walls, use R-19 or R-21 insulation. With either type of wall, use kraft-faced fiberglass or mineral wool insulation.
For exterior walls, the Department of Energy recommends a minimum of R-13 to R-23, but given Chicago's climate zone (Zone 5), aiming for the higher end of this range is advisable. For standard 2x4 walls, which are common in older homes, an R-value of R-15 is considered good, while R-21 is excellent.
2×6 construction creates more room for wall insulation, which can help enhance home efficiency and reduce cooling and heating bills throughout the warmest and coldest months of the year. Keep in mind, though, this is dependent on the climate you are building in.
You can use both in similar places and climates. R15 insulation offers slightly more thermal resistance than R13 insulation, but it also costs more. Ultimately, it's difficult to justify paying a significantly higher price for R15 when R13's insulative properties are only slightly lower than R15.
According to the U.S. Department of Energy, R-values for exterior walls in colder climates should be at least R-13 to R-23. In milder climates, a lower R-value may be sufficient. For example, in a moderate climate, an R-value of R-13 to R-15 is typically recommended.
R19 Insulation offers superior thermal insulation compared to R13. With a typical thickness of 6.25 inches, R19 fiberglass is designed for use in 2x6 wall cavities, making them suitable for colder climates where higher thermal resistance is necessary.
Usually, these studs are around 75mm to 100mm thick, which means that you could potentially introduce 100mm thick wall insulation to help to prevent heat from escaping through your walls.
Modern conventional home building normally makes use of 2x4 lumber (top line above, second from left) in constructing exterior walls.
However, the advantages of using 2 x 6 framing are: Structural strength of building is increased significantly. There is a big difference in compressive strength, resistance to buckling, and lateral deflection between a 9' 2x4 wall and a 9' 2x6 wall.
So, for 2x4 at 12” oc the maximum span is about 7'-6”, which is about the distance you need.
A double 2x4 of #2 hemlock, commonly called hemfir, carrying a span of 4′ with an unknown tributary area fails at about 360 pounds per linear foot. These two boards can carry so much weight because they are so short.
Faced insulation is better at preventing moisture damage; however, it can't be layered like unfaced insulation. For this reason, unfaced insulation is better for keeping your house warm in the winter. It also offers better sound protection.
The R-value for wood ranges between 1.41 per inch (2.54 cm) for most softwoods and 0.71 for most hardwoods. Ignoring the benefits of the thermal mass, a 6-inch (15.24 cm) thick log wall would have a clear-wall (a wall without windows or doors) R-value of just over 8.
A 2x4 wall cavity can be insulated from R-13 to roughly R-25. A 2x6 wall can be insulated from R-19 to R-39. Material selection, density, and cavity depth all play a role in the “cavity” R-value of a wall.
Adding two R-13, 3.5” batts to a 2”x6” (5.5”) wood stud cavity will not provide an R-26. The total of 7” of insulation is reduced in thickness to 5.5” thereby losing the R-value associated with its full thickness.
In nonbearing exterior walls, 2x6 studs spaced at 24 in. on center can be up to 20 feet in height (Table 3). Framers and builders may be reluctant to switch to 24 in.