Double insulation, in the simplest terms, is the use of two insulation layers instead of one. This can be achieved by using two different types of insulation materials or doubling up on the same material.
As a general guideline, it's advisable to install double layers of thermal insulation throughout your house. Nevertheless, this may not be feasible in all areas due to space limitations. Typically, it's not practical to add two layers of insulation within the walls of your home.
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.
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.
In many cases you can add new insulation on top of old insulation, unless the old insulation is wet, mouldy, or vermiculite. If the old insulation is dry but appears to have previously been wet, you should look for the cause and repair the problem.
Removing old insulation is generally recommended if it's damaged, contaminated with mold, or infested with pests. However, if the insulation is in decent shape and just needs a boost, adding a new layer on top can be a cost-effective option.
Stacked insulation can impede this airflow, further reducing its efficiency. If your home already has insulation, you might think adding new batts on top of the old ones is a cost-effective solution.
Because its structure is more complex than single-layer insulation, the cost is relatively high. Additionally, in some cases, double-insulated cables may fail due to spalling between the inner and outer insulation layers.
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.
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.
Leaving Too Many Gaps
One of the biggest problems DIY homeowners face is leaving too many gaps in their insulation. Gaps or insulation that isn't secured correctly can leave the building structure open to air and moisture leaks. Spray foam insulation is best for reaching into small cracks and any areas left open.
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.
Unless your home was specially constructed for energy efficiency, you can probably reduce your energy bills by adding more insulation. Many older homes have less insulation than homes built today, but even adding insulation to a newer home can pay for itself within a few years.
By creating an extra barrier against heat transfer, double insulation reduces the amount of heat that escapes from a building during winter and prevents heat from penetrating a building during summer. This results in less energy required for heating and cooling, thereby enhancing energy efficiency.
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.
Vacuum insulated panels have the highest R-value, approximately R-45 (in U.S. units) per inch; aerogel has the next highest R-value (about R-10 to R-30 per inch), followed by polyurethane (PUR) and phenolic foam insulations with R-7 per inch.
Attics are one of the most common areas for R30 insulation. Since heat rises, an uninsulated attic can become a major source of heat loss in winter and heat gain in summer. Installing R30 insulation helps create an effective thermal barrier, maintaining a stable indoor temperature.
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.
Many of the newer small electrical appliances and tools do not have a the third grounding prong on the plug. Typical examples are blenders, coffee makers, blow dryers, drills, and other power tools. Appliances and tools of this type are called "double insulated".
For most long-term applications, double bubble foil insulation is going to be the better option to use. Because of the double layer of polyethylene bubbles, double bubble insulation provides the most effective thermal break, making it harder for radiant heat to transfer through than with single bubble insulation.
The answer is yes, you can put new insulation over old.
The R-value of double bubble insulation is typically R-3.5 to R-4, depending on the thickness of the insulation. The ICC International Building Code allows you to add additional R-values with trapped air space between the reflective surface of the bubble and the outer wall.