Interior Heating & Cooling Insulation

8 Things to Know About Blown-In Insulation

Learn about the materials, methods, and costs of this insulation solution so you can keep your home comfortable and your utility bills low.
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5 Things to Know About Blown-in Insulation

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Today’s building codes require a minimum amount of insulation in walls and attics, but older homes were often under-insulated, so the answer for some homeowners may be blown-in insulation. Blown-in insulation consists of tiny pieces of material (think confetti) that are literally blown into walls and attics via a long hose. Keep reading to find out if blown-in insulation might be your solution to comfier conditions and lower energy bills.

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1. Blown-in insulation fills between existing wall studs and ceiling joists quickly and easily.

During new construction, batt insulation—thick strips of spun fiberglass or a paper-based product—is cut to fit between wall studs and ceiling joists before wallboard is put up to increase insulation values. Installing batts in most existing homes, however, is rarely feasible, as drywall would have to be torn down, a messy, expensive, time-consuming proposition. Blown-in insulation can be added to attics and walls without the hassle. What’s more, this type of insulation can also seal small gaps and spaces as it settles, filling these sneaky spots where cold air would otherwise come in. And in addition to creating an insulating blanket, blown insulation helps reduce sound transfer between the outdoors and the indoors, so unwanted street noise will also be softened.

2. Blown-in wall insulation has a few disadvantages in terms of coverage and aesthetics.

To install blown-in insulation in existing walls, holes are drilled at the top of each stud space (usually on the exterior), and material is blown in via a long, flexible hose. The hole is then sealed with a plug that matches the siding. While the plugs are closely matched to the color of the siding, if the siding is brick or stucco, the plugs are often noticeable.

Another disadvantage of blown-in insulation for walls is that an obstruction in the wall space—such as a drainpipe, an outlet box, or any other type of unseen barrier (for example, a cross-board between studs the builder might have added for stability)—can keep the insulation from filling the entire stud space, leaving a void with no insulation.

After a few years, blown-in insulation tends to settle downward by a few inches, which slightly reduces its overall thermal resistance (known as R-value), because it leaves a small section at the top of the stud space uninsulated. Blowing in additional insulation is an option, but most homeowners forego this step because it’s such a small area.

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3 Types of Blown-in Insulation and Where to Use Them

3. There are three main types of blown-in insulation.

What is blown-in insulation made of, anyway? The three most common types of blown-in insulation are loose-fill fiberglass, cellulose, and rock wool—each with its own pros and cons. Minimum suggested insulation values vary by geographic zones, and you can find the recommended values for your region on this Energy Star map. The higher the R-value of blown-insulation, the greater the insulating effect. Not all types of blown-in insulation offer the same thermal value, but in most cases, even adding a little insulation is better than not adding any at all.

  • Loose-fill fiberglass: This light-as-air insulation is manufactured from glass that is heated to a liquid and then spun into thin fibers. When blown into attics and wall spaces, loose-fill fiberglass offers an average R-2.5 thermal value per inch (the higher the number, the greater the insulating effect). You’d need a thickness of about 7.5 inches of fiber glass blown-in insulation to match the insulating value of a batt of R-19 insulation (R-19 is a common batt value). One bag of loose-fill fiberglass will provide a thermal value of R-19 over a 106.6-square-foot area.
  • Cellulose: For eco-minded homeowners, cellulose is often the insulation of choice, because it’s made from finely shredded recycled cardboard or newspaper. This is the most common type of blown-in insulation on the market, and it’s chemically treated to resist mold and fire. A downside to cellulose is that if it gets wet (from a leaky roof or pipe), it can lose its fluffiness and become soggy and compacted, which reduces its R-value. Cellulose insulation has an average thermal value of R-3.7, so you’d need just over five inches to equal an R-19 batt. A bag of cellulose will cover 36.7 square feet at a thermal value of R-19.
  • Rock wool: Also called “mineral wool,” this type of blown-in insulation is made from blast furnace slag (a byproduct of firing iron and iron ore). The slag is heated, combined with other minerals, and then spun into an airy product that resembles the texture of raw sheep’s wool. Rock wool insulation has a thermal value of R-3.3 per inch, but a single bag will only cover 60 square feet at a thermal value equal to R-19. Due to its excellent fire resistance, rock wool is often called for in areas subject to fire codes, such as a connecting wall between a house and an attached garage, or in the floor between a garage and a FROG room (finished room over garage).

For all of the above types of insulation, hiring a professional installer will add approximately $15 per square foot in labor fees. (See below to learn about taking this on as a DIY project.) Federal tax incentives for insulating a home expired in 2011, but some homeowners can still take advantage of state tax credits, which can help offset blown-in insulation costs. Check the Department of Energy’s DSIRE website to see if you can benefit from tax credits.

4. Blown-in insulation can be purchased from lumberyards and home improvement centers.

Bags of both cellulose and loose-fill fiberglass insulation are readily available at most lumberyards and home improvement stores. Rock wool insulation, however, may need to be ordered (from the same stores), because it’s more of a specialty item. In addition to the insulation, you’ll need a blower if you intend to install it yourself. Some stores will loan you a blower free of charge if you purchase 10 or more bags of insulation.

RELATED: How Much Does Insulation Cost to Install?

Blown-in insulation being installed between attic trusses

5. DIY blown-in insulation can be installed in the attic, but leave the walls to a pro.

As with all home projects, it’s only natural to wonder, “Can I do blown-in insulation myself?” Blowing insulation into walls is best left to the pros because it involves drilling into stud spaces that may contain electrical wiring and pipes. However, blowing insulation into an attic can be a DIY task. It doesn’t require any special skills but will require you to crouch under low, sloping attic rafters in order to distribute the insulation evenly. Follow the instructions printed on each bag of insulation and on the blower, as well as the below tips to help you safely and successfully complete an attic-insulating project.

  • Recruit a helper. Someone needs to load the bags of insulation into the blower, which will remain on the floor below, while the other person distributes the insulation via a long hose.
  • Don protective gear. Blowing in insulation is a messy prospect and you’ll need to wear a dust mask, protective eyewear, gloves, and old clothing that you can toss out when you’re done.
  • Never stand on joists. If you stand on joists in the attic and lose your balance, your foot will go right through the drywall ceiling below. Don’t risk injury and damage to your home. Instead, position two pieces of about two-by-three-foot plywood across the joists to give you a stable standing area. As you work you can stand on one piece of plywood as you reposition the other piece of plywood.
  • Box-off electrical boxes and recessed can lights. Insulation should be kept away from recessed can lights because the insulation does not allow the heat generated by the lights to dissipate. When heat builds up in a recessed can light, it can cause the light bulb to burn out prematurely. It also presents a slight fire risk because some older can lights can become very hot and ignite cellulose insulation (it’s fire-resistant, not fireproof); there’s less of a risk with fiberglass insulation, which will only melt if it gets too hot. Use scrap plywood or wallboard to build a box around each recessed light, leaving a minimum space of three inches between the light and the box. You’ll also want to box-out around any electrical junction boxes that might be in the attic, just to ensure that an electrician won’t have to go digging around in the insulation to find them in the future.
  • Use battery-operated lights to see into dark corners. Today’s LED headlamps are great for directing bright light into the dark corners of an attic, but if you don’t have one, use a portable battery-operated work light to see what you’re doing.

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6. Properly installed blown-in insulation can last a long time, but it varies by material.

Cellulose insulation being held in a person's hands

Though it is a long-term solution for most homes, will blown-in insulation need to be replaced at some point down the road? Broadly speaking, blown-in insulation lasts anywhere from 20 years to a house’s lifetime. Under ideal conditions (e.g., professional installation, little or no water damage, minimal settling), this insulation material will maintain most of its thermal resistance for decades.

Fiberglass insulation commonly lasts for around 80 to 100 years, but it should be checked for signs of damage around 15 years after installation. Rock wool, meanwhile, is particularly moisture-resistant and the least likely among blown-in insulation materials to require replacement across a home’s lifespan, lasting up to 100 years. Although it’s the most eco-friendly blown-insulation option of the three, cellulose insulation only lasts for 20 to 30 years on average because of its recycled makeup and low moisture resistance. Like fiberglass insulation, homeowners should begin checking cellulose insulation in the attic for noticeable degradation around 15 years after having it installed.

7. You or a pro can remove blown-in insulation from the attic by vacuuming it out.

Just as DIY blown-in insulation installation is possible, it’s also feasible to remove blown-in insulation from your attic on your own—with the right tools and protective equipment. Contractors typically use large industrial vacuums for blown-in insulation removal, but it is possible to suck out all the insulation from an attic with a high-capacity wet/dry shop vacuum or HEPA vacuum. You’ll just have to bag the vacuum’s contents more frequently until the attic trusses are clear of the insulation. Otherwise, you can rent an industrial vacuum to make the job easier or hire a professional to do the work for you (the latter will be necessary either way when removing blown-in insulation from walls).

Before you vacuum insulation out of the attic, first protect yourself: Wear long sleeves, pants, gloves, and a respirator to avoid skin or lung damage, and use a headlamp or work light so you can see what you’re doing. As is the case when you’re installing it, it’s also recommended to work with a partner when removing blown-in insulation. After all of the insulation has been extracted from the attic, contact your local waste management authority for recommendations and instructions on how to properly dispose of your specific type of insulation.

8. Blown-in insulation costs more for attics than it does for walls.

How much does blown-in insulation cost? It depends on how it’s installed. Labor’s an important factor; contractors generally charge between $40 and $70 per hour. Labor costs are essentially unavoidable when installing blown-in insulation in walls, but that hourly fee can be ignored by DIYers who insulate their attics themselves. The DIY approach comes with its own costs, though, as blowing machine rentals typically run around $100 to $200 per day.

The main blown-in insulation cost to consider is the insulation itself. Including labor, fiberglass is the most affordable of the three options at around $0.50 to $1.10 per square foot, followed by rock wool at $1.40 to $2.10 and cellulose at $2.00 to $2.30. Materials aren’t the only driver of price, since local building codes’ required R-values for insulation differ between attics and walls. Attics (R-30 to R-60) often need greater thermal resistance than walls (R-13 to R-23). Coupled with the large surface area of most attics, this makes blowing insulation into the attic more expensive than blown-in wall insulation.

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