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How Deep Should Blown-In Insulation Be in Your Attic?

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When it comes to insulation, most people think about the R-value and how much they need for their home. But what about depth? How deep should blown-in insulation be in your attic? In this article, Stellr Attic Insulation in Austin, Texas, will discuss the recommended depth for blown-in insulation and what factors might affect that recommendation. Keep reading to learn more!

Before we answer the question, let’s first understand what a blown-in insulation system is.

What Is A Blown-In Insulation?

A blown-in insulation system (BIIS) uses high-pressure equipment to force small fragments of insulation material into cavities or spaces in your home. The benefit of this system is that it can fill small and hard-to-reach spaces that other insulation methods cannot. Thus your home’s energy efficiency will be greatly increased.

Fiberglass is the most common type of blown-in insulation system, but there are other options like cellulose and mineral wool. Each of these materials has its benefits and drawbacks, so be sure to consult with a professional before making a decision.

Now that we know what a BIIS is, let’s get back to the question at hand:

How Deep Should Insulation Be In Your Attic?

On average most attics will need about 10 to 14 inches of insulation. A quick way of determining if your attic has adequate insulation is by observing the level of your insulation in relation to your floor joists. If the level of insulation is below the floor joists, you likely need more insulation.

You can’t discuss insulation without mentioning the R-value. R-values measure the heat flow resistance of materials. Insulation is better when the R-value is higher. For instance, 10 to 14 inches of insulation equals an R-value of 38.

There are other factors to consider regarding insulation depth, like the climate you live in and your home type.

Let’s now look in detail at the different types of insulation to help you make a decision.

Type of insulation

As mentioned earlier, there are three main types of insulation: fiberglass, cellulose, and mineral wool.


Fiberglass is the most popular type of insulation. It’s made from tiny glass fibers and is available in two forms: batts and loose-fill. Loose-fill is the option for blown-in insulation. It can fill small spaces and odd-shaped areas that would be difficult to insulate with batts.


Recycled paper products used to manufacture cellulose insulation and fire retardants are often added to the process. It’s environmentally friendly and provides good coverage for hard-to-reach areas. However, it does settle over time and can absorb moisture, so be sure to have it professionally installed.

Mineral wool

Mineral wool is made from spinning molten rock or steel into fibers. It’s non-combustible and doesn’t absorb moisture, making it an ideal choice for wet or humid climates. It’s also resistant to pests and rodents, so this is a good option if you have a problem with creatures in your attic.

Is it possible to over-insulate an attic?

The role of insulation in your home is to keep heat in during the winter and out during the summer. Insulation can, however, have negative effects when too much is applied. An attic that’s too well insulated may retain unwanted moisture, leading to mold and mildew growth. So, when installing insulation, you should factor in your attic space’s ventilation and air circulation. This will influence the general air quality of your home.

Attic insulation: Should Old Insulation Be Removed First?

Before overlaying old insulation with a new one, you should inspect the current state of your insulation. If it’s in good condition, you can leave it in place. However, wet, moldy, or insulation that has excrement from rodents should be removed. Otherwise, installing new insulation over such insulation will decrease its R-value and effectiveness.

How Frequently Should Attic Insulation Be Replaced?

Attic insulation can last for decades, sometimes up to 80 years. However, its R-value will decrease over time as it settles. And usually, the 15-year mark is when most homeowners see a significant drop in R-value. Here are some telltale signs that you need to replace your attic insulation:

– A moldy smell in your attic

-An increase in pests like rodents or insects

-An increase in your energy bills

On average most attics will need about 10 to 14 inches of insulation for an R-value of 38. However, the depth of insulation you need in your attic depends on various factors, including the climate you live in. There are several types of insulation, including fiberglass, cellulose, and mineral wool, each with its advantage. In addition, insulation usually settles over time and loses its R-value, so you may need to replace it every 15 years. And finally, If you notice any telltale signs of your attic insulation needing replacement, don’t hesitate to call a professional.

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