The garage is designed to accommodate parking the cars and store tools for gardening, car cleaning and servicing. As cars may be wet and covered in dirt tracked in from the wet roads during winter, it is essential to design the floor, wall and roof finishes to cope with the additional moisture or fire threat.
Code R302.6 requires the house be separated from the garage by a wall having ½-inch drywall on structural walls and 5/8-inch drywall on the garage ceiling with habitable rooms above. Fire-rated type X drywall treated with mold inhibitor is advised to eliminate the added risk posed by mold growth.
Vehicles parked in the garage after traveling in wet or icy conditions will result in an additional moisture load in the garage. Given the often dark and damp conditions in the garage, the surfaces of the walls and ceiling will be prone to mold growth. Let’s look at some ways to select the correct type of drywall to mitigate this risk.
Why Should You Use Mold-Resistant Drywall In The Garage?
The garage typically contains some of the most combustible materials in a home. The fuel, plastic and rubber components of the vehicles parked in the garage are highly combustible and burn at a high temperature. Other fuel-powered machines such as lawnmowers and gasoline-powered tools are another source of combustible fuels.
The garage is also home to electrical installations such as power distribution boxes and car charging stations. The high voltage equipment installed in garages makes the risk of an electrical fire starting in the garage most likely.
Cars and trucks are often still wet from outside weather conditions when parked inside the garage after a trip. The combination of warm engine components and dampness dripping from the vehicle will result in high humidity levels in the garage. Given the absence of light in a closed and damp garage, the conditions are ideal for mold growth.
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Very few garages are included in the house’s HVAC plan, resulting in extreme conditions of cold, heat, and humidity potentially existing in garages. These factors make it essential to consider drywall that will provide fire-retardant, mold resistant and insulating properties.
DID YOU KNOW? Homeowners insurance do cover black mold but only when a peril covered by the policy causes it. Here’s an article I wrote about the exceptions to black mold coverage and why it’s still best to eliminate the risk of damage posed by mold growth in your home.
What Are Moisture and Mold Resistant Drywall Made Of?
Moisture and Mold Resistant Drywall has a gypsum center with paper walls, just like regular drywall, but is made moisture resistant by applying green wax infused paper.
The mold resistance is obtained through the addition of fiberglass mesh as a backing instead of paper. As fiberglass is non-organic, the mold has no source of food on which to settle and grow.
Fire retardant drywall contains chopped fiberglass in its core for extra fire resistance. The drywall comes in a 5/8-inch thickness, allowing the wall to have double the thirty minutes of fire retardation of ½-inch drywall.
The two types of fire-resistant drywall are Type X and Type C, which both have a higher density of gypsum and contain glass fiber to maintain structural integrity.
The Type X drywall is designed to withstand one hour of exposure to direct flames. Type C drywall must surpass the one-hour flame exposure and compensate for shrinkage that may occur during exposure to fire.
The 5/8-inch Type X or Type C fire retardant drywall has mold resistance due to the glass fiber structure and sandwich surfaces making it the ideal choice for use in garages.
The 9 Different Types Of Drywall In The US
The big-box stores in the US all typically stock nine different types of drywall ranging in thickness from ¼-inch, 3/8-inch, ½-inch and 5/8-inch and 4 x 8 ft. sheets. The cost of the different thicknesses and types can vary significantly, and it is best to plan well what type to buy for various applications and building code requirements.
1. Regular Drywall
The most commonly used type of drywall comes in ¼, 3/8, and ½ thicknesses and consists of a gypsum core sandwiched between paper outer walls.
Regular type drywall is used inside single-level houses to cover walls and ceilings that require no specialty type drywall.
2. Moisture/Mold Resistant Drywall
The gypsum center is thicker in the moisture and mold-resistant type drywall and the paper walls are replaced with wax-infused glass fiber walls.
The wax infusion will impart moisture resistance, and the non-organic glass fiber will not provide an organic food source for mold to grow on.
3. Fire-Rated Drywall
Fire-rated drywall is made from a thicker glass fiber reinforced gypsum center sandwiched between glass fiber-based mesh layers.
The glass fiber and gypsum are fire retardant and capable of withstanding a direct flame for double the amount of time that regular drywall.
The gypsum is infused with glass fiber to maintain its structural integrity for longer during exposure to fire.
4. Blue Board of Plasterboard
The surface of the plasterboard is rough and absorbent to provide an excellent surface to plaster or apply thick finish coats. The plasterboard is a good sound barrier and is resistant to deformation and breaking.
Tape and plaster are used to cover the joints between plasterboard before covering the entire surface with a 1/8-inch thick coat of plaster.
5. Abuse Resistant Drywall
In areas where drywall can be easily damaged, like garages, workshops, foyers and high traffic areas, abuse-resistant drywall is practical.
The compressed gypsum core used in abuse-resistant drywall is encapsulated with a high fiber reinforced mesh to resist cracking and distortion.
6. Flexible Drywall
To cater to curved walls, arches and ceilings, flexible drywall is designed to accommodate the curvature required without cracking or breaking.
A heavier gauge paper liner and thinner gypsum core will allow the flexible drywall to bend without cracking.
TIP: You can also make regular drywall flexible by cutting grooves into the backside of the board, allowing it to curve in both directions.
7. Lightweight Ceiling Drywall
Preventing sagging on large ceilings, gypsum reinforced lightweight drywall was developed. This drywall is also excellent for installers handling a lot of drywall panels every day.
The boards are rigid enough to suit 24-inch on-center framing instead of the standard 16-inch on-center framing designs, providing material and weight savings.
8. Foil-Backed Drywall
Specialized foil-backed drywall was designed for use over wood or metal framing to create a vapor barrier and increase the R-values of the drywall.
The recommended application for this type of drywall is for interior or exterior walls and ceilings where the intrusion of moisture is discouraged.
9. Volatile Organic Compounds (VOC) Absorbing Drywall
Volatile Organic Compounds (or VOC) are emitted from plastics and rubber compounds. The pungent smell often associated with a car that has been parked in the sun for a few hours is caused by VOC emitted from the plastic components and fabrics of the interior.
In buildings, the VOC is emitted from paints, wood glue in the plywood and particleboard and insulating materials. Homeowners will also introduce sources of VOC via the use of cleaning materials, furniture polish, carpets, synthetic fabrics and aerosol products.
The AirRenew drywall draws the VOC and traps them chemically in the specially formulated gypsum core.
Conclusion
The building code requires that the drywall to clad garage walls and ceiling be fire and mold-resistant.
Fire-rated drywall is ideal for this purpose as the fiberglass mesh is inorganic and will not support mold growth. If there are habitable rooms above a garage, 5/8-inch thick fire-rated drywall must be used.
Mold resistant drywall is more expensive than regular drywall. But it is also more durable and takes less upkeep, so the longer you live in your home, the more it pays for itself.