Most joists are six to seven inches tall, and if they are completely filled with material, they are insulated at R-21. However, the DOE recommends that attics in Southern homes be insulated with 13 to 14 inches, or R-38, of insulation at minimum.
R21 insulation achieves a higher R-value despite being thinner than R19 because it's denser and has an optimized structure that reduces heat transfer more effectively. While air is still the primary insulator, how well the fiberglass traps that air (and limits its movement) makes all the difference.
The recommended R-value for attic insulation can vary depending on the climate zone in which you live. The U.S. Department of Energy recommends attic insulation levels of R-49 to R-60 for most homes in colder climates, and R-30 to R-49 for homes in warmer climates.
Excellent Thermal Performance Owens Corning™ R-21 EcoTouch® insulation is specifically engineered to solve the efficiency problems of exterior 2x6 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.
When comparing R13 to R21 insulation, the variance represents a substantial difference in thermal resistance. Moving from an R13 to an R21 insulation means gaining a higher resistance to heat loss, contributing to a more energy-efficient and comfortable living space.
ABOUT INSULATION
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.
Depending on where you live and the part of your home you're insulating (walls, crawlspace, attic, etc.), you'll need a different R-Value. 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.
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.
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.
While loft insulation is an effective way to improve energy efficiency and reduce heating costs, over-insulating can lead to several potential issues. Firstly, over-insulation can lead to poor ventilation in the attic, which can cause moisture buildup and increase the risk of mould growth.
If you're concerned about having a positive impact on the environment, fiberglass batt is probably the best insulation option for your attic.
The higher the R-Value, the better the thermal performance of the insulation. The recommended level for most attics is to insulate to R-38 or about 10 to 14 inches, depending on insulation type.
As mentioned above, you can always increase your R-Value simply apply an extra layer of insulation over your initial layer.
R13 insulation is generally more affordable, which makes it an attractive option for budget-conscious projects. However, R19 insulation offers better long-term advantages because of its higher R-value. Why? Because the R-Value translates to a greater energy savings over time.
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).
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.
You can use faced or unfaced batting when installing between the roof rafters of finished attic spaces. When using paper or plastic batting insulation, that moisture barrier should face outward toward the attic space. Even if the attic space is unheated, it's typically warmer than the outside air in winter.
For 2×6 walls, you need an R-value of 19, and the recommended wall insulation R-value for all zones falls between 19 to 21. If you decide to insulate the ceilings, they should have a minimum ceiling insulation R-value of 30.
The absolute minimum for attic insulation R-values across the country is R-30, with upper recommended ranges between R-49 and R-60 for zones 1 through 3.
So R in R-Value is for Resistance. The number is a scale where higher is better. R-13 is a typical value for 2x4 stud walls. R-21 is a typical value for a 2x6 wall that has been blown with a dense packed Fiberglass.
For standard 2x4 walls, which are common in older homes, an R-value of R-15 is considered good, while R-21 is excellent. This can be achieved with high-performance fiberglass batts, dense-packed cellulose, or a combination of cavity insulation and continuous insulation.
Too much insulation will leave humidity and moisture to accumulate in your attic space. This can lead to mold growth on your walls and insulation. There might also be water damage to the support beams in your home's roof.
Also, when laying down additional insulation, work from the perimeter toward the attic opening. Never lay insulation over recessed light fixtures or soffit vents. Keep all insulation at least 3 inches away from recessed "can" lights, unless they are rated IC (Insulated Ceiling).
You can choose from different materials like cellulose (made from recycled paper), fiberglass, or mineral wool. Cellulose is an eco-friendly and cost-effective insulation for attics. Fiberglass and mineral wool are also popular choices because they are good at keeping heat in or out and resist moisture and pests.