While an increase in assumed framing factor from 15% to 25% can reduce the calculated overall R-value of a wood-frame wall by more than 10%, the effect on steel is even more dramatic (see Figure 1).
The R-value depends on the type of insulation, its thickness, and its density.
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.
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.
You can blow fiberglass or cellulose, dry material into the cavity behind a cheesecloth type barrier before the drywall is hung. You can also do a wet spray of cellulose, very popular or a specific fiberglass came out a year ago. All of these could provide a larger R-Value in a 2x4 wall,
While an increase in assumed framing factor from 15% to 25% can reduce the calculated overall R-value of a wood-frame wall by more than 10%, the effect on steel is even more dramatic (see Figure 1).
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.
Typical recommendations for exterior walls are R-13 to R-23, while R-30, R-38 and R-49 are common for ceilings and attic spaces. Use the JM insulation calculator to determine the recommended R-value for your project, as well as how much insulation you'll need.
Use R-13 or R-15 kraft-faced fiberglass or mineral wool insulation rolls for 2x4 stud 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.
Generally, walls are made up of several layers of different materials. The R-value of a composite wall is calculated by adding the effective R-values of each of the layers of the wall.
Johns Manville R20 Fibreglass Insulation Batts - Sound Barrier - 63.3-sq. ft. - 5.5-in Thick for 2 x 4 Walls.
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.
Therefore, insulation whose thickness changes for any reason over the years of use will see a decrease in its R-value, thus reducing its insulation effectiveness, and in exceptional cases, dropping to zero.
Apparent R-value
In particular, for a loose or porous material, the R-value per inch generally depends on the thickness, almost always so that it decreases with increasing thickness (polyisocyanurate (colloquially, polyiso) being an exception; its R-value/inch increases with thickness).
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.
Fibreglass batt insulation is one of the cheapest insulation methods due to its affordability, ease of installation, and solid thermal performance. Fibreglass batt insulation is a cheap internal wall option, costing about £10 per m² due to low material costs.
Aerogel insulation offers the highest R-value of any insulating material at less weight and thickness—ideal for construction, refineries, pipelines, and thin-gap thermal barriers.
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.
Exterior Garage Walls
Typically these will be constructed from standard 2-by-4 studs which will define the amount of insulation that you can have installed. You should be targeting an R-Value of R-13 or R-15 in these areas to properly maximize your insulation in this application.
R15 insulation offers slightly better thermal insulative properties than R13. Some of its formats are a fraction of an inch thicker than R13, making it more effective at helping with energy efficiency. However, the difference is minimal.
Key Differences: Thermal Resistance: R-21 polyiso boards offer higher thermal resistance compared to R-19, which makes them more effective at reducing heat transfer in colder climates.
There are many options for creating better insulated walls, such as staggered stud framing, double walls, or I-joist walls. These all allow for thicker, better insulated walls with a higher R-Value.
In general, 2 x 4 wall framing is structurally sufficient for many small garages and sheds. When bearing wall heights do not exceed 10 ft. 2 x 4 framing is generally code compliant.