What Is Mold Resistant Drywall
Mold resistant drywall, often called "green board" or "purple board" depending on the manufacturer, replaces the paper facing on standard drywall with fiberglass or other synthetic materials that don't support mold growth. The gypsum core remains the same, but the fiberglass facing is inherently inhospitable to the moisture and organic material that mold spores need to colonize.
Performance Specifications
Mold resistant drywall meets ASTM C1658 standards, which test moisture resistance and mold growth inhibition. In testing, standard paper-faced drywall shows visible mold growth within 24 to 48 hours when exposed to high moisture and mold spores. Mold resistant drywall typically shows no growth or minimal surface growth under the same conditions. However, this does not mean the drywall is waterproof. Standing water or sustained humidity above 85% for extended periods can still compromise the gypsum core underneath.
Where to Install It
Building codes and the EPA recommend mold resistant drywall in high-moisture areas including bathrooms, basements, kitchens, laundry rooms, and crawl spaces. The International Building Code (IBC) Section 2506.2 requires moisture-resistant drywall in wet areas of commercial buildings. For residential properties, it's especially critical in bathrooms where humidity regularly exceeds 60%. If you've had prior mold growth or water damage in a specific location, mold resistant drywall should be part of the remediation protocol when replacing affected areas.
Important Limitations
Mold resistant drywall is a deterrent, not a guarantee. It works only when moisture control is functioning. If a wall cavity has a persistent leak, condensation, or poor ventilation, mold will colonize the wood framing, insulation, and the gypsum core itself, regardless of the drywall facing. During mold inspections, we find active mold behind mold resistant drywall regularly because the underlying conditions (humidity, water infiltration) were never addressed. The fiberglass facing buys time, typically 1 to 3 years longer than standard drywall in high-moisture conditions, but it is not a substitute for vapor barriers, proper grading, functional exhaust fans, or drainage systems.
Installation and Cost
Mold resistant drywall costs 10 to 20% more than standard drywall. Installation is identical to standard drywall, but taping, mudding, and painting must account for the fiberglass facing, which requires proper primer and paint. Vapor barriers should still be installed behind the drywall in below-grade basements. In remediation work, if mold has affected an area, all contaminated drywall must be removed and replaced, regardless of type. Mold resistant drywall becomes cost-effective only as a preventive measure in new construction or renovation.
Common Questions
- Can mold resistant drywall prevent a basement mold problem? No, not alone. A basement with water seepage, poor drainage, or high humidity will develop mold behind any drywall type. Mold resistant drywall must be paired with sump pumps, perimeter drainage, dehumidifiers, and vapor barriers to be effective.
- How do I know if my drywall is mold resistant? Check the drywall edge or a cut corner. Mold resistant drywall has a colored fiberglass facing (typically green, purple, or pink) instead of white paper. Your contractor or home records may also document this during inspections or renovations.
- Should I replace all my drywall with mold resistant drywall? Only in moisture-prone areas. Bedrooms, living rooms, and other dry spaces don't need it. Focus on bathrooms, basements, and areas with prior water damage or humidity issues.