Wall insulation retrofit: methods, costs, and what to expect

If your home was built before the mid-1970s, there is a good chance your walls have little or no insulation. Even homes built in the 1980s and 1990s may have insulation that falls short of current energy codes. Retrofitting wall insulation improves comfort, reduces energy bills, and eliminates the cold, drafty feeling that plagues many older homes.

The good news is that modern retrofit techniques let you add wall insulation without tearing down drywall or gutting rooms. This guide covers the methods available, what each costs, and what to expect during the process.

When walls need insulation

Not every home needs a wall insulation retrofit. Here is how to determine if yours does.

Homes built before energy codes

Most homes built before the mid-1970s have little or no wall insulation. National energy codes did not require wall insulation until the late 1970s, and enforcement was inconsistent for years after that. If your home was built before 1980, there is a high probability that your walls are under-insulated or uninsulated.

Signs of inadequate wall insulation

Watch for these indicators:

• Cold exterior walls. Press your hand against an exterior wall on a cold day. If it feels noticeably cold compared to interior walls, insulation is missing or insufficient.
• Drafts at outlets and switches. Air leaking through electrical boxes on exterior walls is a strong sign that the wall cavity is empty or poorly insulated.
• High energy bills. Uninsulated walls can account for 25% to 35% of a home’s total heat loss.
• Uneven temperatures. Rooms on the windward side of the house feel colder in winter, even with the heating system running.

Confirming the problem

An infrared thermal imaging scan is the most accurate way to identify missing wall insulation. Many energy auditors and insulation contractors offer this service, often for free as part of a quote. The scan shows heat loss patterns through the walls, clearly highlighting areas with no insulation.

You can also check yourself by removing an electrical outlet cover on an exterior wall, turning off the breaker first, and looking into the wall cavity with a flashlight. If you see empty space or very thin insulation, a retrofit is worth considering.

Wall insulation retrofit methods

Three main methods are used to insulate existing walls without a full tear-out.

Drill-and-fill (dense-pack blown-in)

Drill-and-fill is the most common and cost-effective wall retrofit method. The contractor drills a series of small holes (1 to 2 inches in diameter) into each wall cavity, inserts a fill hose, and blows cellulose or fiberglass to the proper density. The holes are then patched and sealed.

How it works, step by step:

1. The contractor identifies each wall cavity (typically every 16 inches between studs).
2. A hole is drilled at the top of each cavity, either from the exterior (through siding and sheathing) or from the interior (through drywall).
3. A fill hose is inserted and dense-pack insulation is blown in until the cavity is full.
4. The process is repeated for each cavity, including above and below any fire stops or blocking.
5. Holes are patched, and siding or drywall is repaired.

Materials used: Dense-pack cellulose (R-3.2 to R-3.8 per inch) is the most popular choice for drill-and-fill. It fills cavities completely and resists air movement better than loose-fill fiberglass. Dense-pack fiberglass (R-2.2 to R-2.7 per inch) is an alternative that handles moisture better but provides less air resistance.

Cost: $1.50 to $3.00 per square foot of wall area.

Injection foam

Injection foam uses a slow-expanding foam that is injected into wall cavities through drilled holes, similar to the drill-and-fill process. The foam expands to fill the cavity completely, including around wiring and pipes, and then cures in place.

Advantages over blown-in: Injection foam provides a more complete fill with no settling, better air sealing, and higher R-value per inch. It flows around obstacles that blown-in material may bridge over, such as wiring bundles and plumbing runs.

Disadvantages: Injection foam costs 30% to 50% more than dense-pack cellulose. If the foam is not formulated correctly or over-injected, it can expand with enough force to crack drywall or bow siding. Hiring a contractor experienced with injection foam is important.

Cost: $2.00 to $4.50 per square foot of wall area.

Interior removal and re-insulation

When walls are already being opened for a remodel, renovation, or repair, it makes sense to insulate at the same time. This method involves removing interior drywall, installing insulation (batts, spray foam, or blown-in with netting), and hanging new drywall.

When this makes sense:

• During a kitchen or bathroom remodel where walls are already open
• When walls have severe moisture damage, mold, or pest infestation that requires remediation
• When you want to add a vapor barrier or upgrade wiring and plumbing at the same time

Cost: The insulation portion costs $0.50 to $3.50 per square foot depending on material, but the total cost is much higher because it includes demolition, drywall, taping, and painting. This method is only practical when combined with other renovation work.

Cost breakdown

Here is what to expect for a wall insulation retrofit on a typical single-story, 2,000-square-foot home with approximately 1,200 to 1,500 square feet of exterior wall area.

Factors that affect cost

• Siding type. Vinyl and wood clapboard siding are easy to remove and replace, keeping costs lower. Brick, stucco, and stone veneer require drilling from the interior, which adds drywall patching costs.
• Number of stories. Multi-story homes require scaffolding or ladder work for upper floors, adding to labor costs.
• Obstructions. Older homes with balloon framing, fire stops, or cross-bracing may need additional holes drilled to reach all sections of the wall cavity.
• Existing insulation. If walls have partial insulation that needs to be removed (due to damage or incompatibility), removal adds to the cost.
• Wall depth. Standard 2x4 walls hold about 3.5 inches of insulation, reaching roughly R-13 with fiberglass or R-14 with cellulose. Deeper 2x6 walls hold 5.5 inches and reach higher R-values.

Choosing the right material for walls

The best material for your wall retrofit depends on your goals, budget, and the specific conditions of your home.

Dense-pack cellulose

Best for most retrofit projects. It fills cavities thoroughly, resists air movement, and is the most cost-effective option. Cellulose is treated with fire retardants and is made from recycled paper products. Its main drawback is that it absorbs moisture, so it is not ideal for walls with known moisture problems.

Injection foam

Best for homes where air sealing is the top priority and budget allows the premium. Injection foam fills around all obstacles and provides a more complete air barrier than blown-in material. It also will not settle over time.

Fiberglass blown-in

A solid option that handles moisture better than cellulose. It works well in humid climates or walls that have occasional moisture exposure. However, it provides less air resistance than dense-pack cellulose, so it may not reduce drafts as effectively.

For a deeper comparison of insulation materials, see our spray foam vs. fiberglass guide.

What to expect during installation

Knowing what happens on installation day helps you prepare and set realistic expectations.

Before the crew arrives

Clear furniture and belongings away from exterior walls if the contractor is drilling from inside. If they are working from the exterior, ensure clear access around the perimeter of the house. Move vehicles away from the work area and make sure pets are secured.

During installation

A typical drill-and-fill crew consists of two to three workers. One operates the blowing machine (usually set up in the driveway or on a truck), while the others drill holes and fill cavities. The process is noisy but not disruptive to the rest of the home.

Expect some dust, especially if drilling from the interior. Contractors should lay down drop cloths and clean up debris as they go.

Patching and finishing

After filling all cavities, the crew patches the drill holes. Exterior holes are sealed and siding is replaced. Interior holes are patched with drywall compound. The patches may need sanding and paint touch-up, which the contractor may or may not include in their scope. Clarify this before signing the contract.

Timeline

Most single-story homes are completed in one day. Two-story homes or homes with complex siding (brick, stucco) may take two days. You can stay in the home during the work, though it may be noisy.

Hire a qualified wall insulation contractor

Wall insulation retrofits require experience and precision. An improperly filled wall can leave voids that defeat the purpose, or an over-filled cavity can damage drywall and siding. Look for contractors with specific retrofit experience, not just general insulation installers.

Get free quotes from insulation contractors who specialize in retrofit work:

• Utah | Salt Lake City
• Idaho | Boise
• Colorado | Denver
• Oregon | Portland
• North Carolina | Charlotte | Raleigh
• Tennessee | Nashville
• Florida | Tampa
• Arizona | Phoenix
• Ohio | Columbus

Frequently asked questions

For more on choosing the right insulation professional, read our guide to choosing an insulation contractor. For attic-specific advice, see our attic insulation guide. For broader insulation information, visit our insulation contractor hub.