Ventilation is important in portable sheds because it controls temperature, prevents moisture damage, and improves air quality. Consumers often don’t give much thought to the need for ventilation in their portable shed, especially if they’re planning to use it just for storing items like garden tools and outdoor equipment. They assume these items won’t be affected by heat, cold, or inadequate airflow. But that’s a mistake because lack of ventilation can result in high humidity and moisture, which can lead to mold, mildew, and rust. Moisture buildup occurs when humidity in the air cools and condenses, forming water droplets form on interior walls, floors, and both the exterior and interior of objects in the shed. Over time, this can cause the shed to rot and expensive damage to its contents.
Types of Ventilation
There are two general classifications of ventilation for portable sheds: passive (unpowered) and active (powered).
Passive Ventilation
Passive ventilation for typical standard portable sheds (without optional upgrades to ridge and soffit vents) includes wall vents, gable vents, and eave vents. This type of ventilation relies on the natural airflow through the shed. Vents should be placed both low and high on the walls to increase the effectiveness of the ventilation. As warm air rises and exits through vents at the top of the walls, it draws cold air into the vents near the bottom. This is known as convective air flow. The greater the vertical distance between the vents at top and bottom, the greater temperature variation will be, and the stronger the air flow. This is why taller chimneys are more effective than shorter ones. Vents should also be placed on opposite ends of the shed for cross-ventilation, so air is circulated the entire length of the shed.
Active Ventilation
Active ventilation for portable sheds includes solar or electric fans to move air into, through, and out of the shed. Another option is a turbine or “whirlybird” roof vent turned by the wind to exhaust air. Fans should be placed high in the shed, near the vents to help exhaust warm air. To prevent insects, rodents, birds, and bats from entering the shed, vents should be covered with screens.
Ventilation does more than control moisture. It also helps maintain air quality. Erez Halfon, general manager of Mobeno Solar Solutions, which sells Zula solar-powered ventilation units, said, “Particulates and allergens that accumulate in standing air in a closed room or building can lead to difficulties in breathing and illness like asthma. Active ventilation is especially helpful because it forces air movement to expel those particulates and allergens, as well as gas and paint fumes and other harmful substances in the air from items that are commonly kept in a storage shed.”
Temperature Control
Temperature regulation is an important part of moisture control and ventilation. Both temperature extremes can cause problems. Warm air holds more moisture than cold air, and when the temperature cools below the dew point, it condenses into water droplets. Maintaining a stable temperature that’s neither too hot nor cold helps prevent damaging humidity and condensation and, therefore, reduces the amount of ventilation needed.
Temperatures can also be controlled by sealing gaps and cracks in walls and joints to reduce air movement that interferes with cross ventilation and air circulation. Convective air flow requires movement from lower cold areas where it enters the shed to high warm areas where it exits. Filling holes and gaps prevents irregular air currents that break up the desired air flow through the shed.
Another way to help maintain a stable temperature is by using insulation, radiant insulation, or a radiant barrier. The most common insulation types for portable storage sheds are fiberglass batt and rigid foam board. Fiberglass batts are the least expensive but need vapor barriers or vapor retarders to protect them from moisture buildup in a heated storage shed.
Reflective insulation (bubble wrap/foil insulation) has only a small insulation value to retain heat. It’s best for warmer climates to reflect solar radiation to keep heat out. A single-layered radiant barrier (reflective foil) has no insulation R-value. Like reflective insulation, a radiant barrier is designed for warmer climates to reflect solar energy to keep the shed interior cool. Because reflective foil is just a single layer, it’s less expensive than reflective insulation. Both are easy to install but need an air gap between the material and wall to work effectively.
In some cases, reflective insulation and fiberglass batt can’t be used together. In those cases, the best choice for the intended purpose should be chosen.
Occupied Sheds
Ventilation is even more important when portable sheds are intended for use as hobby shops, offices, etc. (Note: This is different from having a code-compliant shed designated for use as a permanent, habitable domicile, which has more stringent, legally enforceable requirements.)
Carefully controlling humidity and temperature is crucial for health reasons in situations where people will be inside for extended periods. In these situations, owners may want to upgrade to more expensive, but more effective, spray foam or even mineral wool insulation. Spray foam should be applied by a professional, but it provides increased air sealing and moisture resistance compared to less expensive options for portable storage sheds. Mineral wool is especially known for sound insulation and fire resistance, which could make it a good option for an office or music studio that has expensive equipment and would benefit from sound reduction.
An occupied portable shed would most likely have electricity available and could have at least minimal continuous heat to keep it above the dew point. This will prevent condensation and reduce the amount of ventilation needed. Also, a consumer could use a humidifier that turns on automatically (using a humidistat) to keep humidity at a set level.
While portable storage sheds typically aren’t built with a ridge vent, they are often available as an upgrade. A shed purposely designed for occupation should have a ridge vent working in tandem with an eave or soffit vent to improve ventilation.
Unheated, unoccupied portable storage sheds typically lack floor insulation. A heated, occupied portable shed should have an insulated floor to help prevent heat loss and maintain a stable temperature, to reduce the opportunity for condensation to form, to decrease the amount of ventilation needed, and to improve comfort.
In addition, a heated, occupied portable shed would benefit from having a house wrap like Tyvek installed on the exterior between sheathing and siding to block wind and water from penetrating the walls but allow moisture to escape. Finally, an insulated, occupied portable shed may also benefit from having a vapor barrier installed over the interior studs to prevent interior moisture from building up in moisture-susceptible insulation such as fiberglass batts, open-cell spray foam, and cellulose. If closed-cell spray foam or thick rigid foam insulation is used, a vapor barrier won’t be needed, as these materials already control moisture.
Conclusion
Portable shed ventilation is affected by humidity, temperature, and air flow. Using insulation to prevent large temperature fluctuations can help lower the amount of ventilation needed. Strategically placing vents will promote convective air flow and reduce the risk of excess humidity and condensation and resulting mold, mildew, and rust. Proper planning for the intended use of the shed and taking steps to ensure adequate insulation and temperature control will help ensure that a portable shed provides years of reliable service and satisfaction. GSCB
