Spray foam is the preferred choice for crawl spaces in high-humidity regions, where temperature control and moisture resistance are critical. It provides superior air sealing and moisture control compared to fiberglass. In dry, mild climates with minimal insulation needs, fiberglass may suffice if budget is the primary concern.
Spray foam outperforms fiberglass in sealing gaps and preventing mold and air leaks. This article outlines key factors to evaluate, supported by installation data, material properties, and climate-specific performance. Flatland Roofing & Insulation has direct experience installing both systems in varied residential and commercial projects across Texas.
Key Differences Between Spray Foam and Fiberglass for Crawl Spaces
| Feature | Spray Foam Insulation | Fiberglass Insulation |
|---|---|---|
| Material Type | Polyurethane (Open/Closed Cell) | Glass Fibers |
| Air Sealing | Excellent (Seals all gaps) | Poor (Requires vapor barriers) |
| Moisture Resistance | High (Especially Closed Cell) | Low |
| Mold Prevention | Effective | Vulnerable |
| Thermal Resistance (R-Value) | R-6 to R-7 per inch (Closed Cell) | R-2.2 to R-3.8 per inch |
| Installation Surface Contact | Expands to fill voids | May sag or gap over time |
| Lifespan | 30+ years | 10–25 years (degrades in moisture) |
| Cost | Higher upfront | Lower upfront |
| Code Compliance | Meets energy codes easily | Often needs added components |
| Pest Deterrence | Non-fibrous; less pest-friendly | Can harbor nesting materials |
Technical Specifications Comparison
| Property | Open Cell Foam | Closed Cell Foam | Fiberglass Batt |
|---|---|---|---|
| R-Value per Inch | 3.6–4.3 | 6.0–7.0 | 2.2–3.8 |
| Vapor Permeability (perm) | 10+ | <1 | Variable |
| Density (lb/ft^3) | 0.5 | 1.75–2.2 | 0.5–1.0 |
| Expansion Ratio | 100:1 | 30–50:1 | N/A |
| Installation Time | Fast with spray rigs | Fast with spray rigs | Moderate (cut/fit) |
| Air Barrier Rating | Yes | Yes | No |
Climate-Specific Performance
Hot-Humid Zones (e.g., Texas Gulf Coast, South-Central Plains)
Closed cell spray foam is effective against condensation and heat infiltration. Fiberglass often fails due to trapped humidity and mold growth.
Arid Regions (e.g., West Texas)
Spray foam still benefits performance, but fiberglass may be acceptable if crawl space has proper ventilation and minimal air infiltration risks.
Cold Climates (Northern Plains)
Spray foam reduces ice dam risks and keeps ductwork from freezing. Fiberglass requires perfect installation with vapor barriers to perform comparably.
Mixed-Humid Zones (e.g., Central Texas)
Moisture swings make fiberglass less reliable. Spray foam maintains stable performance year-round.
Things to Consider Before Making a Decision
- Crawlspace Condition: Unvented crawl spaces benefit more from foam; vented ones may work with fiberglass if well ventilated.
- Existing Moisture Issues: Foam provides a moisture barrier. Fiberglass can worsen mold problems.
- Project Budget: Fiberglass is cheaper initially but may require replacement or repairs sooner.
- Energy Efficiency Goals: Foam offers air sealing that lowers HVAC demand significantly.
- Pest Control Needs: Fiberglass is easier for pests to burrow into.
Bonus Tip: In older homes with inconsistent framing or irregular gaps, spray foam adapts better to unpredictable voids.
Common Questions People Ask Before Deciding
Is spray foam too expensive for small crawl spaces?
For tight crawl spaces, closed cell foam can be installed efficiently with minimal waste, making cost differences smaller than expected.
Will fiberglass work if I already have a vapor barrier?
Only if the vapor barrier is fully sealed and the fiberglass is installed without gaps or compression.
Can I mix both materials?
In some cases, foam can be used on rim joists while fiberglass is used on floor joists. This hybrid approach works if properly detailed.
Do energy codes require spray foam?
No, but foam often makes compliance easier by meeting both insulation and air barrier standards.
Services Flatland Roofing & Insulation Provides for Crawl Spaces
- Closed Cell Spray Foam Installation: High-performance insulation ideal for moisture-prone crawl spaces.
- Open Cell Foam for Air Control: Applied where air sealing is needed without a vapor barrier.
- Insulation Removal and Replacement: Removes degraded fiberglass and installs efficient alternatives.
- Dense Pack Cellulose Retrofit: Where spray foam isn’t suitable, cellulose can provide improved performance over fiberglass.
Get Expert Insulation Guidance
For expert input on choosing the right insulation system for your crawlspace, contact Flatland Roofing & Insulation.
- Phone: (806) 606-6794
- Email: info@flatlandroofcoatings.com
Flatland Roofing & Insulation brings hands-on experience across a wide range of insulation types and project requirements. Get in touch for straightforward, technically grounded advice tailored to your structure and climate.
FAQ About Spray Foam and Fiberglass in Crawl Spaces
How long does spray foam last in crawl spaces?
Closed cell spray foam typically lasts over 30 years without losing performance if not exposed to UV.
Can spray foam be applied over existing fiberglass?
No. The fiberglass must be removed to ensure proper adhesion and effectiveness of foam.
Does spray foam attract termites or rodents?
No. It offers no food value and is too dense for tunneling.
How do I know if my crawl space has moisture problems?
Look for musty smells, sagging insulation, or water staining on joists and subfloor.
Is DIY fiberglass installation effective?
Only if perfectly installed with no compression, gaps, or missing vapor barrier which is rare without professional oversight.