Insulation retains a home’s heat in the winter and keeps out hot air in the summer. Insulation can be made from a variety of materials, including fiberglass, mineral rock or wool, cellulose, foam, polystyrene, and more. Insulation professionals can determine what type of insulation is best for a home and how to prep the space. The cost of having insulation professionally installed is only about 10 percent more than paying for materials, equipment rentals and personal time to do it yourself, says Russ Lewis of Green Attics in Fort Worth, Texas. Professionals receive contractor rates on materials, are experts at the job and have the industrial equipment to complete the project in a lot less time it would take the average homeowner. Several factors affect the overall cost of insulation installation.
The Department of Energy explains that "an insulating material’s resistance to conductive heat flow is measured or rated in terms of its thermal resistance or ‘R-value’—the higher the R-value, the greater the insulating effectiveness." Basically, higher R-values are better at keeping heat in or out. Different regions have different building code R-values that new homes must meet. Lewis of Green Attics says in his region, the minimum R-value is 30, while the Department of Energy says the ideal R-value for homes in his region is 49.
Different types of insulation all have different R-values. According to Lewis of Green Attics, "Cellulose has an R-value of 3.2 per inch of depth, while fiberglass ranges from an R-value of 2 to 2.5 per inch of depth." The number of inches of insulation is not as important as the combined R-value of those inches. Generally, if insulation is in a good condition, professionals apply new insulation on top of existing insulation to bring a home up to the desired R-value level.
Size of space
Insulation professionals need to know the type of insulation material (and its R-value) currently in the home and the average depth of that material in order to calculate what is needed to bring insulation up to (or beyond) local code. Lewis of Green Attics can generate a pretty accurate quote if customers tell him the square footage of their attic and the depth and type of existing insulation. For example, Green Attics charges 50 cents per square foot of batting and $1 per square foot for blown insulation. For one job, Lewis added 8 inches of insulation to a 2,700-square-foot space to bring it up to an R-value of 30 for $1,800.
Be wary of contractors who quote prices only in inches, says Lewis of Green Attics. Inches matter less than R-value. The same quantity of inches in fiberglass and cellulose do not have the same R-value.
Removing old insulation
It may be necessary to remove old insulation before installing new insulation. According to Lewis of Green Attics, these are the three most common reasons why:
Heavy pest activity, such as rat droppings or animal nests
Old, lower-grade cellulose insulation has become a dust source and leaks a fine dust throughout the house
- The culprit here is brown cellulose insulation (as opposed to preferred white), which, when manufactured, was mixed with shredded cardboard. The cardboard creates the dust particles as it breaks down. The dust is so fine that it leaks through minute holes and keeps homes permanently dusty.
Here are some pricing examples from Green Attics for removing unwanted insulation:
Removal by machine: ~ $1 per square foot
- Complete removal of insulation in a 3,100-square-foot attic @ $1.10 per square foot = $3,410. This job took 12 hours.
Hand removal: $1.35 per square foot
- Hand removal can be necessary when debris—such as wood chunks from a wood shake roof—is present. Debris can make sucking out the insulation by machine impossible.
To seal the top plates of the wall stud cavities before applying a new layer of insulation Green Attics charges $300–$450. This polyseal stops air gaps at the ceiling level, making new insulation more effective. The cost to seal top plates in 2,500 square foot home: $350.
Foam injection and spray
Foam is another form of insulation that can be sprayed onto walls during new construction or can be retrofitted into an existing house by injecting it into the sheetrock. Lewis of Green Attics charges $3–$5 per square foot to inject foam into an existing home. Foam insulation costs more to install because of the extra tools, labor and materials required. Lewis says that to retrofit foam, contractors must drill two to three holes per 16-inch stud cavity into the sheetrock to use for injecting the material. In addition to the cost of labor for this project, there’s also the added cost of repairing the hundreds of holes in the drywall after the job is complete. Green Attics charged $5,500, including one day of labor, to apply spray foam to the interior of a pitched roof in an attic that required no drilling.