Spray Foam vs Fiberglass Insulation in the Upstate (Climate Zone 3A)

We’re South Carolina Spray Foam Insulation, and we’ve spent more than 15 years insulating homes and commercial buildings across Greenville and the Upstate.

Greenville, Spartanburg, Anderson, Greer, Easley, Simpsonville, Taylors, Mauldin, Clemson, Seneca, and Rock Hill all sit in the Piedmont, inside IECC Climate Zone 3A.

That means humid subtropical weather, long cooling seasons, damp crawl spaces, and red clay soil that can hold moisture around a house longer than people expect.

Fiberglass can work in the right assembly, but in our climate it often gets asked to do jobs it was never designed to do.

Why Fiberglass Struggles In Zone 3A

Fiberglass is mostly a thermal insulation.

It slows heat transfer when it stays dry, stays fluffy, and is protected from moving air.

Warm, damp air moves through gaps around the band joist, plumbing penetrations, rim areas, and open framing cavities.

Once fiberglass gets washed by that air, it stops performing like the label says.

When it absorbs moisture, it can compress, sag, pull away from the floor, or fall out completely.

That is common under older homes across the I-85 corridor, especially where red clay and poor drainage keep crawl spaces damp.

When fiberglass sags, the R-value on paper does not matter much because the insulation is no longer in full contact with the surface it is supposed to protect.

Spray Foam Changes The Assembly

Spray foam works differently because it insulates and air-seals at the same time.

Open-cell spray foam expands into cracks, joints, and irregular framing pockets.

Closed-cell spray foam does the same while adding higher R-value per inch and stronger resistance to moisture movement.

Fiberglass does not air-seal.

If humid air can move through or around the insulation, the building can still feel sticky, drafty, or uneven even when the cavity is full.

Spray foam helps stop that air movement at the surface where it is installed.

In Zone 3A, that matters because moisture rides on air.

R-Value That Holds Up Over Time

Closed-cell spray foam delivers about R-6 to R-7 per inch.

Open-cell spray foam delivers about R-3.5 to R-4 per inch.

Those numbers are useful, but the better question is how much performance stays in place after years of humid weather.

Fiberglass can lose real-world performance when it gets damp, dirty, compressed, or displaced.

Spray foam is installed as an adhered insulation layer, so it is much less likely to sag out of a crawl space floor or leave open gaps around framing.

That is why we look at air movement, moisture exposure, and access conditions before we recommend a product.

Where Each Product Makes Sense

We are honest about the tradeoff: fiberglass is cheaper upfront.

For a dry, well-sealed, easy-to-access area, that lower first cost may be the reason someone chooses it.

But in many Upstate crawl spaces, the cheap option can become expensive if it absorbs moisture, loses contact, or has to be removed and replaced.

Spray foam costs more upfront because the material and installation process are different.

It is helping control air movement, improve comfort, and keep insulation performance more stable over time.

Open-Cell Or Closed-Cell

We install both open-cell spray foam and closed-cell spray foam.

Open-cell is often used where expansion and air sealing are the priority and the assembly can dry appropriately.

Closed-cell is often considered where higher R-value per inch and stronger moisture control are important.

In crawl spaces, moisture behavior usually drives the conversation.

We also offer air sealing, vapor/moisture barrier work, crawl space insulation, new-construction insulation, and insulation testing/evaluation.

Pricing And Incentives

Spray foam pricing is by board foot only.

A board foot is one square foot of coverage at one inch thick.

If the foam is installed thicker, the cost increases proportionally.

Open-cell spray foam runs $1.00 to $1.60 per board foot installed.

Closed-cell spray foam runs $1.60 to $2.60 per board foot installed.

Duke Energy serves the Upstate, and rebate amounts vary by measure and change annually, so current amounts should be confirmed before planning around them.

The federal 25C energy-efficiency tax credit expired December 31, 2025, so no federal insulation tax credit currently applies.

FAQ

Is Spray Foam Always Better Than Fiberglass?

No. Fiberglass is cheaper upfront and can be reasonable in dry, protected assemblies.

In humid Zone 3A crawl spaces, spray foam usually gives a stronger long-term result because it air-seals and stays adhered.

Why Does Fiberglass Fall Out Of Crawl Spaces?

Moisture, gravity, air movement, and poor support all work against it.

Once it gets heavy, compressed, or pulled away from the floor, it no longer performs the way it should.

Does Spray Foam Stop Humidity?

Spray foam helps by reducing air movement, and that matters because humid air carries moisture into building assemblies.

Moisture control still depends on the whole crawl space, including drainage, vapor/moisture barrier details, and the condition of the structure.

Should We Use Open-Cell Or Closed-Cell?

It depends on the assembly, access, drying potential, and moisture risk.

We evaluate the building first, then recommend the foam type that fits the job.