Everything You Need to Know About Spray Foam Insulation

There are many popular insulation options for sheds, including fiberglass batts, rigid foam boards, and spray foam. Different options offer advantages for different needs, but the one we consistently recommend here at South Country Sheds is spray foam insulation. 

For Florida sheds, spray foam addresses the two biggest comfort killers: relentless heat and persistent humidity, as it provides superior airtight sealing. This guide covers everything you need to know about spray foam insulation, so you can make the right choice for your shed and better understand why this is our go-to.

What is Spray Foam Insulation?

Spray foam insulation is a high-performance polyurethane material that expands on contact to fill gaps and creating an airtight, moisture-resistant barrier. Two liquid chemical components mix during application, react quickly, and expand to seal cavities, cracks, and seams in walls, ceilings, and floors.

Unlike fiberglass batts or cellulose that come in pre-cut pieces, spray foam conforms precisely to the surface where it’s applied. The foam fills irregular spaces, works around wiring and pipes, and creates a continuous thermal envelope without gaps. For Florida sheds, this seamless coverage matters, especially with constant heat and humidity.

Types of Spray Foam Insulation

Spray foam comes in three main density categories. Each type serves different applications and budgets, so understanding the differences helps you pick the right fit for your project.

High-Density Spray foam

High-density spray foam is the most rigid option, typically used for roofing applications and exterior walls where maximum structural support matters. This type offers the highest R-value per inch (a measure of thermal resistance) and exceptional moisture resistance. The tradeoff? It comes at a premium price point and is usually overkill for standard shed insulation.

Medium-Density Spray Foam (closed-cell)

Closed-cell foam is dense and rigid, acting as both insulation and a vapor barrier. It’s the go-to choice for areas exposed to moisture or requiring added structural strength—think crawl spaces, exterior walls, and hurricane-prone regions where wind resistance matters.

Closed-cell foam typically delivers R-values between R-6 and R-7 per inch. In practical terms, that means a 2-inch layer provides roughly the same thermal resistance as 4 inches of fiberglass.

Low-Density Spray Foam (open-cell)

Open-cell foam is lighter and more flexible, with a spongy texture that makes it excellent for soundproofing. It expands more than closed-cell (up to 100 times its original size), filling large cavities efficiently at a lower cost per square foot.

Open-cell foam provides R-values around R-3.5 to R-3.7 per inch. While that’s lower than closed-cell, the cost savings can be significant for interior applications where moisture isn’t a primary concern.

Understanding Spray Foam R-values

R-value measures thermal resistance—the higher the number, the better the insulation slows heat transfer. Spray foam delivers more R-value per inch than any other common insulation material, which matters when wall cavity depth is limited.

Here’s how spray foam compares to other insulation types:

• Closed-cell spray foam: R-6 to R-7 per inch
• Open-cell spray foam: R-3.5 to R-3.7 per inch
• Fiberglass batts: R-2.9 to R-3.8 per inch
• Cellulose: R-3.2 to R-3.8 per inch

In practical terms, 2 inches of closed-cell foam provides roughly the same thermal resistance as 4 inches of fiberglass. For most sheds in Florida, even a thin layer of closed-cell foam makes a noticeable difference in interior comfort during summer months.

Open Cell vs. Closed Cell Spray Foam

Choosing between open-cell and closed-cell foam depends on your specific situation—climate, budget, and what you’re insulating all play a role.

For Florida sheds, closed-cell foam is typically the better choice. The humidity, heat, and hurricane exposure all favor a denser product that blocks moisture and adds structural integrity.

Which Type of Spray Foam Insulation is Best?

The “best” foam depends entirely on your priorities and application. Neither type is universally superior—each excels in different situations.

Closed-cell works well when:

• Moisture exposure is likely (coastal areas, flood zones)
• You want added structural rigidity
• Wall cavity depth is limited
• Maximum R-value per inch matters
• Hurricane resistance is a priority

Open-cell works well when:

• Budget is the primary concern
• Soundproofing matters more than moisture resistance
• You’re insulating interior walls
• Large cavities need filling economically

For our Florida sheds, we typically recommend closed-cell spray foam. The combination of moisture resistance, structural strength, and superior thermal performance aligns with the realities of Florida weather, including humidity that hovers around 70-80% for much of the year.

Benefits of Spray Foam Insulation

1. Air & Moisture Barrier

Spray foam creates a seamless seal that blocks air infiltration and moisture penetration. In Florida’s humid climate, traditional insulation can trap moisture against wood framing, leading to rot and mold over time. Spray foam eliminates the gaps where that moisture would otherwise collect.

2. Superior Energy Efficiency

Because spray foam eliminates gaps and thermal bridging (where heat transfers through framing members), it dramatically reduces heat transfer. A well-insulated shed or workshop stays cooler in summer and requires less energy to climate-control if you’re running AC or dehumidifiers.

3. Increased Structural Strength

Closed-cell spray foam bonds to wall studs and roof decking, adding measurable rigidity to the structure. For hurricane-rated buildings, this extra strength helps the entire assembly resist wind uplift and racking forces during severe weather.

4. Pest & Rodent Resistance

Unlike fiberglass batts that rodents love to nest in, cured spray foam creates a solid barrier that pests can’t easily penetrate or inhabit. For storage sheds and workshops where you’re keeping equipment or supplies, this protection adds real value.

5. Long Lifespan With Minimal Maintenance

Spray foam doesn’t settle, sag, or degrade like traditional insulation. Once properly installed, it maintains its R-value and air-sealing properties for the life of the structure, often 50 years or more without replacement.

Disadvantages of Spray Foam Insulation

1. Higher Upfront Cost

Spray foam costs more than fiberglass or rigid foam boards, sometimes 2-3x as much per square foot. However, the energy savings and longevity often offset this initial investment over time, particularly in climate-controlled spaces.

2. Professional Installation Required

Unlike rolling out fiberglass batts, spray foam application requires specialized equipment, proper mixing ratios, and experience to achieve consistent coverage. Improper installation can lead to off-gassing, incomplete curing, or poor adhesion.

3. Ventilation Concerns

During application, spray foam releases fumes that require proper ventilation and protective equipment. The cured product is chemically inert and safe, but the installation process demands professional handling.

4. Difficult to Remove

Once spray foam cures, it bonds permanently to surfaces. Future modifications, such as installing new wiring, adding plumbing, or making structural changes, become more challenging because the foam must be cut away to access the framing.

Get the Spray Foam Insulation You Need for Your Florida Shed

Adding spray foam insulation transforms a basic storage shed into a comfortable, climate-controlled workspace or hobby room. The difference is immediate—cooler summers, drier interiors, and a structure that’s better equipped to handle whatever Florida weather brings.

At South Country Sheds, spray foam insulation is available as an upgrade on any of our sheds. All you need to do is contact us to discuss building and insulating your shed.

FAQs About Spray Foam Insulation