5 Things to Know About Blown-in Insulation

Learn about the materials, methods, and costs of this insulation solution to keep your home comfortable and your utility bills low.

By Glenda Taylor and Bob Vila | Updated Oct 5, 2020 5:09 PM

5 Things to Know About Blown-in Insulation

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Layering on sweaters is one way to stay warm in a poorly insulated house, but while you’re bundling up, your furnace is still working overtime to ward off the chill and your home’s water pipes could be at risk of freezing and breaking. Today’s building codes require a minimum amount of insulation in walls and attics, but older homes were often under-insulated, so for many owners of such homes, the answer is blown-in insulation: tiny pieces of material (think confetti) that is literally blown into your walls and above your ceiling via a long hose. Keep reading to find out if blown-in insulation might be your solution to comfier conditions and lower energy bills.

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-in insulation helps reduce sound transfer between the outdoors and the indoors, so unwanted street noise will also be softened.

RELATED: 7 Places That Could Use More Insulation—and Why

2. This means of insulation has its disadvantages.

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 to blowing insulation into wall spaces is that an obstruction in the wall—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.

Consult with a professional insulation contractor
Some jobs are better left to the pros. Find trusted local insulation experts and compare multiple quotes for your project.
3 Types of Blown-in Insulation and Where to Use Them

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

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 thermal resistance (R-value), 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 insulation to match the insulating value of a batt of R-19 insulation (R-19 is a common batt value). A bag of loose-fill fiberglass costs about $35 dollars, and one bag 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 runs about $11.50 and 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 features a thermal value of R-3.3 per inch, but it is much more expensive than either loose-fill fiberglass or cellulose—a single bag runs approximately $140, and will only cover 60 square feet at a thermal value equal to R-19. Despite its high price point, 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 the cost of insulating. Check the Department of Energy’s DSIRE web site to see if you can benefit from tax credits.

4. Blown-in insulation can be purchased from lumberyards, 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; if not, you can rent a blower from a construction rental store for about $65 to $80 per day.

Tips for Using Blown-in Insulation

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5. Handy homeowners can install blown-in insulation in the attic.

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 tips below 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.
Consult with a professional insulation contractor
Some jobs are better left to the pros. Find trusted local insulation experts and compare multiple quotes for your project.