Insulation is an important component of energy efficiency in buildings. It prevents heat loss in winter and heat gain in summer, allowing HVAC systems to operate more efficiently. Styrofoam, also known as extruded polystyrene (XPS) foam, is a popular insulation material due to its low cost and high R-value (resistance to heat flow). However, styrofoam insulation also has some drawbacks that are important to consider.
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Low moisture resistance
One of the main disadvantages of styrofoam insulation is that it absorbs moisture relatively easily. The cells in the foam can take on water vapor, which reduces the insulation’s R-value over time. This means it performs worse as an insulator in damp environments compared to other materials like foil-faced polyiso boards or closed-cell spray foam. Moisture absorption also causes styrofoam to swell, putting pressure on surrounding structural materials which can lead to cracks or damage. Water retention also provides an environment for mold growth. For these reasons, additional steps like adding a vapor barrier are required when installing styrofoam in moist areas like below-grade foundations.
Vulnerability to compression
While rigid, styrofoam insulation is softer and more vulnerable to compression compared to other rigid insulation types. The R-value of styrofoam can become permanently reduced if exposed to compression forces over time. For example, if used on an exterior basement wall and backfilled with compacted soil, the soil pressure could compress the styrofoam and lower its insulating performance. Using a stronger covering material is required to prevent long-term compression issues. Styrofoam’s vulnerability to compression also makes it a poor choice for high-load structural applications.
Off-gassing of blowing agents
Styrofoam insulation off-gases blowing agents – the chemicals used to puff up the polystyrene foam during manufacturing. Older styrofoam products used CFCs and HCFCs as blowing agents which contribute to ozone depletion. While modern styrofoam is made with more eco-friendly blowing agents like pentane or CO2, some off-gassing still occurs. Studies show low levels of styrene and other volatile organic compounds (VOCs) are released from polystyrene over time, which can accumulate in indoor air and may have health effects. Proper ventilation is required to dilute any accumulating VOCs in buildings insulated with styrofoam.
Flammability
Like many foam plastic insulations, styrofoam is combustible and emits toxic fumes when burned. This makes it a poor choice as insulation in fire-prone environments. Building codes require additional fireproofing measures like fire-rated drywall when using styrofoam insulation on building interiors. Special fire-rated products like Dow Thermax sheathing can be used in exterior wall assemblies to provide fire resistance. Still, extreme caution should be exercised when using styrofoam insulation near potential ignition sources.
Durability issues
While styrofoam can last for decades if properly protected, some durability issues can occur:
- Degradation from UV exposure if left unprotected outdoors
- Insect damage in areas with termite activity
- Rodent damage if left exposed in accessible areas
These durability issues require taking precautions like adding protective coverings, performing pest control, and limiting use to well-protected interior applications.
Difficulty with complex geometries
Rigid styrofoam insulation boards are manufactured in simple shapes like sheets and cylinders. Achieving complete insulation coverage on complex geometries like pipes or irregular wall cavities can be difficult compared to spray foam or loose-fill insulation. Small foam scraps must be cut and pieced together to fill gaps around complex surfaces. Special adhesive is required to bond styrofoam properly to other materials which adds time and cost to the installation process.
Global warming potential
While modern styrofoam does not use ozone-depleting substances, the blowing agents still have high global warming potential (GWP). For example, the 100-year GWP of pentane is around 20 times that of carbon dioxide. This means released blowing agents from styrofoam significantly contribute to global climate change. The overall environmental impacts from resource extraction, manufacturing, and end-of-life must also be considered with styrofoam insulation.
Landfill waste
Polystyrene foam is difficult to recycle and is not biodegradable. Styrofoam insulation panels removed during building renovations or demolition often end up in landfills. There they will persist for hundreds of years since Styrofoam breaks down very slowly. The space occupied by discarded styrofoam is unavailable for other uses. Some municipalities have even banned styrofoam products from landfills due to limited capacity issues.
Conclusion
While inexpensive and widely available, styrofoam insulation comes with trade-offs. Its low moisture resistance, compressibility, flammability, off-gassing potential, lack of durability, and disposability issues make it a less than ideal insulation product from an environmental standpoint. Safer, greener insulation materials are available, such as mineral wool, cork, sheep wool, cellulose, and low-GWP polyurethane or polyisocyanurate foam. The use of styrofoam insulation may be appropriate in some applications where additional protective steps are taken, but understand the disadvantages before using this product.
| Disadvantage | Description |
|---|---|
| Low moisture resistance | Absorbs water vapor which reduces R-value and allows mold growth |
| Vulnerability to compression | Can become permanently compressed, lowering R-value |
| Off-gassing of blowing agents | Releases VOCs into indoor air |
| Flammability | Burns easily and emits toxic fumes |
| Durability issues | Can degrade from UV, insects, rodents, etc. |
| Difficulty with complex geometries | Hard to achieve complete coverage around irregular shapes |
| Global warming potential | Blowing agents have high 100-year GWP values |
| Landfill waste | Not biodegradable or easily recycled |
Alternatives to Styrofoam Insulation
If the disadvantages of styrofoam insulation seem too significant for your project, there are safer, more sustainable alternatives to consider:
Mineral Wool
Mineral wool like rock wool and fiberglass provide excellent fire resistance and sound dampening with moderate R-values. Less oil is used in production compared to plastic foams.
Cellulose
Made from recycled paper products, cellulose contains borates for fire and insect resistance. It fills cavities well and settles over time.
Cork
Sustainable cork is naturally moisture and pest resistant with a low thermal conductivity. Available as rigid boards and loose fill.
Sheep Wool
Renewable and biodegradable wool insulation comes with low embodied energy. It buffers humidity well.
Green Foam
Foams using water or CO2 as blowing agents have a lower environmental impact than traditional plastic foams.
Consider both the advantages and disadvantages of each insulation type for your specific project requirements. An insulation material that is safest for the planet should be prioritized whenever feasible.