Insulation Cost: Average Prices & Cost Factors

Insulation slows the movement of heat through a home's attic, walls, and floors. It keeps heat inside in winter and outside in summer, so the heating and cooling system works less. Its effectiveness is rated by R-value, and a higher R-value means more resistance to heat flow.

The cost of an insulation job depends on which material you choose, where it goes, and how hard that space is to reach. An open attic is the easiest and cheapest place to add insulation. Finished walls are the hardest, because the installer has to fill closed cavities without tearing the walls open.

Each material has a different price, R-value per inch, and best use. Fixr lists these installed ranges:

• Fiberglass is the most familiar option, sold as batts and rolls or as loose fill. It is inexpensive and works well in open wall framing and attic floors.
• Cellulose is made largely from recycled paper treated with fire retardant. It is usually blown in, which makes it a common choice for attics and for filling existing walls.
• Mineral wool, also called rock wool, resists fire and moisture and dampens sound. It costs more than fiberglass.
• Polystyrene rigid foam boards are used on foundation walls, under slabs, and as continuous insulation on exterior walls.
• Polyurethane spray foam expands to fill gaps and seals air leaks at the same time. It is the most expensive material in the table.

The cheapest material per square foot is not always the cheapest per unit of R-value. Some materials need more thickness to reach the same rating, so compare quotes at the R-value you want, not just by the square foot.

Where the insulation goes can matter as much as what it is made of.

Attic

Attics usually give the best return because heat rises and many attics are under-insulated. Blowing loose-fill fiberglass or cellulose over the existing layer is fast. Air sealing gaps around light fixtures, plumbing, and wiring holes before adding insulation helps the new layer perform as rated.

Existing walls

Insulating finished walls is a retrofit job. Installers drill small holes, blow in cellulose or fiberglass or inject foam, and then patch the holes. The work is slower and more involved than open framing, which is why the range is wide.

Garage

Garage insulation matters most when the garage is attached or has living space above it. Insulating the shared wall and the ceiling below a bedroom usually comes first. Garage doors can be insulated separately.

Total cost scales with the area being insulated. Fixr gives these whole-home ranges:

Few projects cover every surface at once. Most homeowners start with the attic, then move to walls, crawl spaces, or the basement as budget allows. An energy audit can show where a house loses the most heat, which helps you spend on the areas that matter first.

Spray foam is priced differently from batts and loose fill because the installer mixes and sprays the material on site with special equipment. This Old House breaks out the labor share.

Replacement adds a removal step. Old insulation may need to come out if it is wet, moldy, compressed, contaminated by pests, or in the way of air sealing. Removal costs $1 – $3/sq ft according to Fixr, and that is charged before any new material goes in. Old vermiculite insulation can contain asbestos; if you see gray-brown, pebble-like fill in an attic, leave it in place and have it tested by a qualified professional.

The per-foot figures below come from two sources that measured different things.

Fixr covers a mix of materials and areas, while This Old House focuses on spray foam, which may explain its higher range. Other differences may come from the R-value targeted, the thickness installed, whether air sealing and removal are included, and how easy the space is to reach. Crawl spaces and tight attics take longer to work in.

Rolling out fiberglass batts in an open attic or unfinished basement is a manageable DIY job with gloves, long sleeves, eye protection, and a respirator. Some home centers lend a blowing machine when you buy enough bags of loose-fill insulation.

Spray foam, wall retrofits, and removal of old insulation are better left to contractors. Spray foam requires protective equipment and correct mixing, and the house may need to be vacated while it cures. Contractors can also check for ventilation problems, wiring, and moisture issues that affect how well insulation works.

For recommended R-values by climate zone, the U.S. Department of Energy publishes guidance by region. Some utilities also offer rebates or free energy audits, so check with yours before you hire.