An example of this is in an attic. If the existing attic insulation is an R-19, you may choose to add another layer of R-19. Two layers of R-19 at 6¼ ” thick will achieve a total R-value of 38. So adding an R-19 batt to an existing R-19 batt will give you a total insulation value of R-38.
In calculating the R-value of a multi-layered installation, the R-values of the individual layers are added: R-value(outside air film) + R-value(brick) + R-value(sheathing) + R-value(insulation) + R-value(plasterboard) + R-value(inside air film) = R-value(total).
When calculating the R-value of a multilayered installation, add the R-values of the individual layers. Installing more insulation in your home increases the R-value and the resistance to heat flow. In general, increased insulation thickness will proportionally increase the R-value.
By doubling the insulation layers in your loft, you increase its R-value, which in turn reduces its U-value (lower U-value is better). This results in better insulation and improved energy efficiency for your living space.
In theory, you can stack foam pads indefinitely for your desired r-value, with most foam pads having an r-value of 2-2.2, but they get bulky really fast and impractical. A combination of foam pad + inflatable pad is common for making your R-value 4 inflatable pad suitable for winter.
There are times when more than one layer of insulation will be used. An example of this is in an attic. If the existing attic insulation is an R-19, you may choose to add another layer of R-19. Two layers of R-19 at 6¼ ” thick will achieve a total R-value of 38.
Sleeping pad R-values range from less than 2 (minimally insulated) to 5.5 or more (very well insulated).
Thicker is better
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.
Thermablok® Aerogel is a revolutionary advancement in thermal technology offering the thinnest insulation available to prevent thermal and cold bridging. Classed as a Super Insulation, Aerogel has the highest insulation value of any known material with the lowest thermal conductivity value of any solid (0.015W/mK).
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.
Insulation ratings can be improved by adding more layers of insulation. You can mix the type and material of insulation too. For example, if your attic already has fiberglass insulation blankets installed, you can improve its R-value by installing blown-in cellulose insulation on top of the blankets.
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.
Spray foam insulation offers better longevity because it can be used with traditional construction methods such as bricks and blocks, which are more durable than SIPs. Spray foam is an alternative that allows you to have the best of both worlds.
For example, our polyiso rigid foam boards have R-values between 6.5 and 6.8 per inch. If two layers are installed, it doubles the R-value and cuts heat/conditioned air loss in half. For reference, plywood has an R-value of 1.25.
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.
The optimal R-value for most homes is 30, but you can go as high as 38 if you live in a tropical climate. Anything higher than 38 indicates an over-insulated space. While you might think that too much insulation can't be bad, there are some significant consequences to consider.
High R-value: Because foam board insulation has a greater R-value than standard fiberglass/batt insulation, it is more effective at insulating and decreasing heat loss.
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.
It's a reasonable question—after all, if one layer of insulation is good, wouldn't two be better? Unfortunately, the answer is no. Stacking insulation doesn't improve R-value in the way you might think, and it can actually create more problems than it solves.
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.
The Short Answer
If your house has too much insulation, it becomes too tightly sealed, and moisture becomes trapped inside. If there isn't proper ventilation, especially in the attic where the warm air travels when it rises, mold will grow, and your home's air quality can decline.
Closed-cell spray foam has a far better R-value per inch than other, less effective insulations like cellulose, fiberglass, or even open-cell foam. All these have R-values ranging from R-3.2 to R-3.8 per inch. The R-value of closed-cell foam is R-6.5-7 per inch.
For winter camping, you generally want an R-value of at least 5, while three-season campers only need an R-value of 2 or more for most conditions. R-values are additive, so stacking two pads on top of each other provides an R-value that is more or less the sum of their individual R-values.
R-values for sleeping pads usually range from around 1 to 7, while thicker memory foam mattresses can creep into the double digits. When purchasing a new sleeping pad or camping mattress you have a wide R-value range of options between air inflated, closed cell foam or self inflated.