How to Choose and Use Insulation

With various types of insulation available, selecting the right one for your project can be challenging. In this article, we’ll explore different insulation options, their characteristics, and how to use them effectively. This Old House general contractor Tom Silva showcases the wide world of insulation, showcasing various materials and their applications.

Understanding Insulation R-Value

R-value is the primary metric used to measure insulation effectiveness. It indicates how well a material resists heat transfer. The higher the R-value, the better the insulation performance.

What Is R-Value?

R-value represents a material’s thermal resistance per inch of thickness. It measures how effectively insulation slows or stops heat transfer. In winter, insulation keeps heat inside the house, while in summer, it prevents heat from entering.

Importance of R-Value in Insulation Selection

When choosing insulation, take note of the required R-value for your climate and the space you’re insulating. Different areas of your home may need varying levels of insulation. For example, attics typically require higher R-values than walls.

To find out how much insulation you already have, climb into your attic and use a tape measure to measure from the top of the insulation down to where it touches the top of the plaster or wallboard. Fiberglass batts have an R-value of about 3.5 per inch, so if you measure 3.5 inches of fiberglass, you have roughly R-13. Once you know what you have, you can determine how much more insulation you need to meet the recommended R-value for your climate region.

Types of Insulation

There are several types of insulation available, each with unique properties and applications. Let’s explore the most common options.

Cellulose Insulation

Cellulose insulation is made from shredded newspaper treated with boron, which acts as a fire retardant and insecticide. It has an R-value of about 3. 6 per inch.

It features the following key benefits: 

• Blown into wall cavities
• Environmentally friendly
• Effective sound barrier
• Suitable for retrofitting existing walls

Fiberglass Insulation

Fiberglass is one of the most common insulation materials used across the country. It comes in batts or loose-fill form and has an R-value of about 3.2 to 3.6 per inch.

Here are some installation tips:

• Avoid compressing the material, as it reduces the effectiveness
• Fit batts loosely into stud bays
• Use proper protective gear when handling

Spray Foam Insulation

Spray foam insulation comes in two types: open-cell and closed-cell. Both are applied as a liquid and expand to fill gaps and cracks.

• Closed-cell spray foam: Closed-cell foam offers a higher R-value of 6. 0 per inch. It forms a rigid surface and provides excellent air and moisture barrier properties.
• Open-cell spray foam: Open-cell foam has an R-value of 3. 6 to 3. 8 per inch. It expands significantly after application, making it ideal for filling hard-to-reach areas.

Recycled Denim Insulation

Made from ground-up blue jeans, this eco-friendly option comes in batts and installs similarly to fiberglass insulation. It has an R-value of about 3. 2 to 3. 6 per inch.

Foam Board Insulation

Foam board insulation, such as expanded polystyrene (EPS), extruded polystyrene (XPS), and polyisocyanurate, offers varying R-values ranging from 3. 6 to 6. 5 per inch. These rigid panels are perfect for insulating foundations, walls, and roofs.

Before switching to spray foam insulation, This Old House general contractor Tom Silva used to build a 2×4 wall, insulate between the studs with batting (paper face removed), then cover the whole thing with foil-faced polyisocyanurate panels sealed with foil tape before putting up wallboard. In hot, humid climates, rigid panels can go on the exterior of a house, over the studs—typically a weak spot in an insulation system—but under the siding, where the boards become an effective vapor barrier. In colder climates, the boards can go inside the walls, where you want the moisture barrier to keep warm air from escaping.

Mineral Wool Insulation

Mineral wool insulation is made from molten rock or industrial waste products spun into fibers. It has an R-value of about 3. 7 to 4. 2 per inch and is available in batts or loose-fill forms. 

Benefits include:

• Excellent soundproofing
• Fire-resistant
• Moisture and mold-resistant

Insulation Installation Methods

The installation method depends on the type of insulation and the area being insulated. Here are some common techniques:

• Batt installation: Batt insulation, typically fiberglass or denim, is cut to fit between wall studs or floor joists. It’s important to avoid compressing the material during installation.
• Blown-in insulation: This method is used for cellulose and loose-fill fiberglass insulation. The material is blown into wall cavities or attic spaces using specialized equipment.
• Foam board installation: Foam board insulation is easy to install and is often used as continuous insulation on exterior walls, under floors, and on roofs. Boards are cut to size and adhered in place, with seams taped or sealed to create an airtight installation.
• Loose-fill installation: Mineral wool and cellulose insulation are often installed as loose-fill in attics and wall cavities. This method involves blowing the insulation material into the space, achieving an even and comprehensive coverage.
• Spray foam application: Spray foam insulation requires professional installation. It’s sprayed as a liquid and expands to fill gaps and cracks, creating an effective air and moisture barrier.

When adding batt insulation to an attic that already has a layer in place, always use unfaced batts to prevent moisture from becoming trapped between layers. Place the new layer perpendicular to the old one to cover any gaps, and butt adjoining batts snugly together without compressing them. Never lay heavier batts, such as cotton, over lighter ones like fiberglass—the weight will compress the lower layer and reduce its effectiveness. Always cut batts to fit around obstructions rather than stuffing them around ducts or piping, which compresses the air-trapping pockets in the material and reduces its insulating properties.

Pro Tip: As far as This Old House general contractor Tom Silva is concerned, low-density polyurethane spray foam is the insulation technology to beat. It forms a lock-tight bond with studs and sheathing that blocks all air movement, flexes enough to accommodate seasonal wood movement, and retards moisture passage. While spray foam is expensive, its installation costs are offset in the long run by lower heating and cooling costs.

Insulation Vapor Barriers and Retarders

Managing moisture is foundational when insulating your home. Vapor barriers and retarders play a significant role in controlling moisture movement through walls and ceilings.

Vapor Barriers

A vapor barrier, such as polyethylene sheeting, completely blocks moisture transfer. It’s typically installed on the warm side of the wall in extreme climates.

Vapor Retarders

Vapor retarders slow moisture transfer while allowing some breathability. They’re often preferred in mixed climates where both heating and cooling are necessary.

Types of vapor retarders include:

• Foam board insulation
• Kraft paper facing on batt insulation
• Special paint primers

Air Barriers

While vapor barriers and retarders control moisture flow, air barriers prevent air leakage by sealing cracks and gaps in your home’s envelope. Proper air sealing increases insulation’s effectiveness and overall energy efficiency.

Common air barrier materials include:

• Caulking and weatherstripping
• House wraps
• Spray foam

Choosing the Right Insulation for Your Project

Selecting the appropriate insulation depends on various factors, including your climate, budget, and the area you’re insulating.

• Budget constraints: While closed-cell spray foam offers excellent performance, it can be up to four times more expensive than fiberglass or cellulose. Factor in long-term energy savings when making your decision.
• Climate considerations: Your local climate plays a central role in determining the type and amount of insulation needed. Consult local building codes and energy efficiency recommendations for guidance.
• Health and environmental impact: Think through the environmental impact and health safety of insulation materials. Opt for eco-friendly options like recycled denim or cellulose if sustainability is a priority.
• Retrofit vs. new construction: Some insulation types, like blown-in cellulose or fiberglass, are ideal for retrofitting existing walls. Others, such as spray foam or batt insulation, are better suited for new construction or major renovations.

Insulation Best Practices

To maximize the effectiveness of your insulation, follow these best practices:

• Check for proper air sealing before installing insulation
• Use appropriate protective gear when handling insulation materials
• Avoid compressing insulation, as it reduces its effectiveness
• Install insulation to the full depth of the cavity
• Pay special attention to areas prone to air leakage, such as around windows and doors

Pro Tip: When insulating an attic, don’t let batts or loose fill cover the soffit vents along the eaves. The airflow from the soffits to the ridge vent keeps the roof cool and prevents ice dams. Staple plastic or foam baffles to the roof sheathing near the eaves to keep insulation away from the vents and maintain proper ventilation.

Professional vs. DIY Insulation Installation

While some insulation projects can be tackled by experienced do-it-yourself (DIY) homeowners, others require professional expertise.

When to DIY

Batt insulation in accessible areas, such as unfinished attics or open wall cavities, can often be installed by homeowners with proper preparation and safety precautions.

When to Hire a Professional

Complex projects, such as spray foam installation or insulating existing walls, are best left to professionals. They have the necessary equipment and expertise for proper installation and peak performance.

Cost Implications of Professional Installation

Professional installation incurs labor costs in addition to material expenses. To evaluate your options, compare quotes from multiple reputable contractors to make sure you receive quality service at a fair price. Professional installation can be wise if you aim for comprehensive coverage and long-term energy savings.

Insulating Different Areas of Your Home

Different parts of your home have specific insulation requirements. Understanding these needs leads to better performance and comfort.

• Attics: Use loose-fill or batt insulation between and over joists, and seal all gaps and cracks to minimize air leakage.
• Basements and crawl spaces: Basements and crawl spaces are prone to moisture issues. Use moisture-resistant materials like closed-cell spray foam or foam board insulation to protect these areas from dampness and mold.
• Floors: Insulating floors above unheated spaces prevents heat loss and improves overall comfort. Batt insulation or rigid foam boards can be installed between floor joists to achieve this.
• Walls: When insulating walls, consider factors such as existing drywall, electrical wiring, and plumbing. Blown-in insulation or dense-packed cellulose can effectively fill wall cavities without extensive renovation.

Our Conclusion

Choosing the right insulation helps you maintain a comfortable and energy-efficient home. Think through factors such as R-value, climate, budget, and installation method when making your decision. While some insulation projects can be DIY, don’t hesitate to consult professionals for complex installations or expert advice. Proper insulation improves your home’s energy efficiency, reduces utility bills, and improves indoor comfort.

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