Can you add foam insulation to existing walls?

Quick Answer

Yes, it is possible to add foam insulation to existing walls. The most common way is to use spray foam insulation. With this method, the foam is sprayed into wall cavities through small holes drilled into the drywall or siding. The foam expands and hardens, sealing cracks and gaps while providing insulation. Other options include injecting loose-fill insulation through holes or removing siding to add rigid foam boards. Adding insulation to existing walls can significantly improve a home’s energy efficiency.

What is foam insulation?

Foam insulation refers to various plastic-based materials used to insulate buildings. The main types used for retrofit foam insulation projects include:

• Spray polyurethane foam (SPF): A reactive foaming agent is sprayed into wall cavities where it expands 30-60 times its liquid volume. SPF has an R-value of 6-8 per inch.
• Injectable foam insulation: Low expanding foams are injected through holes drilled into the drywall. Expanding foams have an R-value of 3.5-4 per inch.
• Rigid foam boards: Rigid panels of expanded polystyrene (EPS), extruded polystyrene (XPS) or polyisocyanurate are installed over wall framing or exterior sheathing. Rigid foams have an R-value of 5-6 per inch.

Foam insulations work by forming millions of tiny air pockets that resist conductive and convective heat transfer. Compared to traditional fiberglass batts, foams provide better insulation, air sealing, strength and water resistance. They can insulate irregularly shaped spaces and deal with moisture better.

Why add insulation to existing walls?

There are several reasons homeowners choose to add insulation to existing walls:

• Improve energy efficiency – Adding insulation reduces heat loss through walls, lowering heating and cooling costs.
• Increase comfort – Better insulated walls keep indoor temperatures more stable.
• Prevent moisture issues – Insulation reduces cold surface condensation that can cause mold and rot.
• Reduce noise – Foam insulation helps block exterior noise from entering the home.
• Qualify for incentives – Some utility rebates and tax credits require attic insulation and air sealing first.
• Improve durability – Insulation increases a wall’s structural strength and rigidity.
• Make renovations easier – Insulated walls provide a good base for finishing a basement or addition.

Upgrading insulation also increases a home’s value. The US Department of Energy recommends all exterior walls have an insulation R-value of at least R-13 to R-23. Adding insulation is one of the most cost-effective ways to improve energy efficiency in existing homes.

Can you install spray foam insulation in existing walls?

Spray polyurethane foam (SPF) is the most effective way to add insulation inside existing framed exterior walls. The benefits of spray foam include:

• Fills gaps and crevices to form a complete air seal.
• Adheres tightly to surfaces and framing.
• Expands to fill the entire cavity thickness.
• Does not shrink or settle over time.
• Higher R-value per inch compared to other insulations.
• Adds structural strength to walls.
• Moisture and mold resistant.

The open-cell SPF used for retrofit foam insulation projects has an R-value of around R-3.7 per inch. It can be applied up to 5.5 inches thick per pass, so two passes yield R-20+ in a 2×4 wall cavity.

Here are the steps to install spray foam insulation in existing walls:

1. Prepare the walls – Remove electrical cover plates, vents, insulation and drywall as needed to access stud cavities.
2. Air seal penetrations – Seal all electrical, plumbing and wiring penetrations with foam.
3. Install backer rods – Place foam backer rods around windows, doors and other gaps to control foam spread.
4. Apply primer – Prime surfaces with SPF primer for better adhesion.
5. Spray foam – An experienced installer applies SPF using special spray rig equipment.
6. Trim foam – Trim excess foam with a serrated knife once cured.
7. Replace drywall – Patch or replace drywall, vents and outlets removed during the process.

While do-it-yourself spray kits are available, hiring a professional SPF contractor is highly recommended. They have the proper equipment and expertise to apply foam correctly for maximum efficiency and safety.

What are the best practices for installing new wall insulation?

Here are some best practices when adding insulation to existing walls:

• Choose an insulation R-value appropriate for your climate zone. The US Department of Energy provides recommendations.
• Prepare walls by removing existing siding, wallpaper, etc. Patch cracks and holes.
• Test for asbestos if your home was built pre-1980. Take proper precautions if found.
• Consider using spray foam insulation for best air sealing and energy performance.
• Ensure electrical boxes won’t be covered or crowded by new insulation.
• Use experienced contractors qualified to perform insulation retrofits.
• Keep insulation at least 3 inches from chimneys, vents and flues.
• Make sure insulation fills the cavity without gaps, compression or sagging.
• Install foam backer rods between framing and windows/doors to limit air leakage.
• Seal all penetrations through top and bottom plates with caulk or foam.
• Replace any vapor barriers damaged during installation.

Following best practices for preparing surfaces, selecting materials, injecting/installing insulation, air sealing, and finishing ensures quality results and maximum energy savings from adding insulation.

How much does it cost to add insulation to existing walls?

The cost to add insulation to existing walls ranges from $1,200 to $4,500 depending on the method and type of insulation used.

Here are typical price ranges:

• Blown cellulose loose-fill insulation – $1.20 to $1.50 per sq.ft.
• Fiberglass batts – $1.50 to $2.25 per sq.ft.
• Spray foam insulation – $3.00 to $7.00 per sq.ft.
• Rigid foam insulation panels – $2.50 to $4.50 per sq.ft.

Expect to pay about $1,200 to insulate a 500 sq.ft. home with cellulose and up to $4,500 for spray foam. The insulation cost for a 2,000 sq.ft. home ranges from $3,000 (fiberglass batts) to $12,000 or more (spray foam).

Additional costs may include:

• Wall prep and drywall repair – $2.00/sq.ft.
• New siding – $3.50+ per sq.ft. for vinyl, more for other sidings
• Electrical revisions and outlet extensions – $150+ each
• Dumpster rental fees for debris removal

To determine the total project investment, get multiple quotes from experienced insulation contractors. Focus on insulation R-value and proper installation more than just price. Added insulation will pay for itself over time through energy savings.

What are the different types of insulation you can add to existing walls?

There are several types of insulation suitable for retrofitting walls in existing homes:

Loose-Fill Insulations

• Cellulose – Made from recycled paper products and treated with fire retardant. Very common for wall retrofits. R-value 3.2 to 3.8 per inch.
• Fiberglass – Insulation made from spun glass fibers. Treated for fire safety. Cost-effective option with an R-value around 2.7 per inch.
• Mineral Wool – Made from natural rocks and recycled slag. Higher density than fiberglass. R-value per inch 2.7 to 3.0.

These loose-fill insulations are blown into wall cavities through holes drilled into the drywall or exterior siding. Materials are packed tightly to achieve the desired R-value.

Foam Board Insulation

• Expanded polystyrene (EPS) foam – Rigid foam board used to insulate exterior walls. R-value of 3.6 to 4.4 per inch.
• Extruded polystyrene (XPS) – Foam board with higher density and R-value (5+ per inch). Strong moisture resistance.
• Polyisocyanurate – Foil-faced foam with the highest R-value (6.5+ per inch). Used for exterior insulation.

Foam boards are cut to fit between wall studs or applied over sheathing. Provides additional insulation and weatherproofing.

Spray Foam Insulation

• Open-cell spray foam – Soft foam with R-3.7 per inch. Allows some vapor penetration.
• Closed-cell spray foam – Very dense rigid foam with R-value of 6-6.5 per inch. Best air seal.

Spray foam completely fills gaps and cavities, providing a superior air barrier. Provides structure and insulation in one application.

Any of these wall insulation materials can significantly improve energy efficiency when properly installed. Choose a type suitable for your climate and goals.

Is it worthwhile to add insulation to existing walls?

Adding insulation to existing walls is almost always a worthwhile investment for homeowners. The benefits make it one of the most cost-effective home upgrades you can make.

Here are 5 key reasons why adding wall insulation is worthwhile:

1. Energy Savings – Insulated walls prevent heat loss in winter and heat gain in summer. This can reduce heating and cooling costs by 10-20% or more.
2. Improved Comfort – More comfortable air temperatures year-round, fewer drafts and cold spots, less exterior noise.
3. Increased Property Value – Insulation adds value and makes homes more attractive to buyers.
4. Rebate Eligibility – Many utility companies provide rebates and incentives for wall insulation projects.
5. Environmental Benefits – Less energy usage reduces a home’s carbon footprint from power generation.

The added costs of insulation are generally recouped in less than 5 years through energy savings. Insulation also provides benefits that are harder to measure, like noise reduction and increased comfort. As energy costs continue to rise, the value of wall insulation will only become more worthwhile in the future.

Conclusion

Adding insulation to existing exterior walls is an excellent way to improve the energy efficiency and comfort of your home. Foam insulation provides the highest insulation R-value per inch along with superior air sealing. Fiberglass and cellulose are cost-effective options for loose-fill wall cavity insulation. The project cost ranges from $1,200 to $4,500 depending on the home’s square footage and insulation type used. While not a small investment, the long-term savings from reduced energy costs make the project very worthwhile – insulation typically pays for itself in less than 5 years. Furthermore, insulation adds to the resale value of your home. Following best practices for wall preparation, installation and air sealing ensures you gain the full benefits of adding insulation to existing walls.