Domicile cup fungus is a sign of water damage within a structure. While this fungus is not known to be toxic, its presence is a clear warning that an area of the home is experiencing chronic moisture intrusion and high humidity levels. The fungus itself is a decomposer that thrives on a variety of materials found in homes, including wet wood, plaster, and the paper backing on drywall. Eliminating this fungus permanently requires a two-step approach: removing the visible growth and, more importantly, finding and correcting the underlying environmental cause.
How to Identify Cup Fungus in Your Home
The physical appearance of Peziza domiciliana is distinct. The fungus begins as a small, rubbery, cup-shaped structure, often yellowish-tan to pale brown in color. These fungal bodies can grow to a diameter of 2 to 10 centimeters, sometimes flattening out to resemble a wrinkled saucer as they mature. You will often find them growing in clusters, or gregariously, on surfaces.
The fungus is frequently discovered in areas with persistent dampness, such as unfinished basements, crawlspaces, or under carpets and floorboards affected by a leak. It has been documented growing on a wide range of substrates, including sand, cement, plaster, and wet drywall. Its presence is a definitive indicator of a serious, underlying moisture problem that must be addressed.
Safe and Immediate Physical Removal
Before disturbing the visible fungus, you should take basic safety precautions to limit the spread of spores. Wear gloves and a dust mask rated for fungal remediation, and ensure the area is well-ventilated. The fungal bodies can forcibly release a cloud of microscopic spores when touched or disturbed.
The most effective immediate step is to gently scrape or lift the fungal bodies from the surface without crushing them, then dispose of them immediately in a sealed plastic bag. Simply removing the cup will not eliminate the problem, as the main body of the fungus is embedded within the damp material. After physical removal, treat the surface with a cleaning agent like a mild detergent or a 6% acetic acid cleaning vinegar.
A vinegar solution can be sprayed directly onto the affected area and allowed to dwell for an hour to dissolve fungal residues. Hydrogen peroxide at a 3% concentration is another effective, non-toxic option for sanitizing the surface. This surface cleaning is only a temporary measure to remove the visible growth and spores, and it does not penetrate deep enough to kill the root of the organism.
Eliminating the Environmental Root Cause
The permanent elimination of cup fungus hinges entirely on removing the constant source of water that sustains it. This fungus is a saprobe, often feeding on cellulose from wood or the paper backing on gypsum board. Peziza will rapidly die off once the substrate is no longer damp.
The first action is to methodically locate the source of water ingress, which may be hidden within the structure. Common origins include plumbing leaks from pipes or fixtures, foundation cracks that allow groundwater to seep in, or poor exterior drainage that directs rainwater toward the home’s perimeter. Water that pools against the foundation due to improper grading or clogged gutters is a frequent cause of the severe dampness this fungus prefers.
For minor surface leaks, a simple repair may be sufficient to dry out the area, but extensive water damage requires a more aggressive approach. Any visibly saturated building material, such as wet drywall, insulation, or rotten wood, must be removed and properly discarded, as these materials act as a continuous reservoir for moisture and a food source. If the moisture source is a major structural issue, such as a foundation breach or complex plumbing leak, consulting a foundation specialist or a licensed plumber is necessary.
The overall goal is to achieve and maintain a dry environment, as the presence of Peziza is a warning of conditions that can lead to more severe issues like wood-destroying rot. Fixing the leak must be followed by allowing the affected structural components to dry completely. This process can be accelerated by using high-volume fans and dehumidifiers.
Long-Term Strategies to Prevent Recurrence
Once the moisture source has been repaired and damaged materials removed, ongoing environmental controls are necessary to prevent the fungus from returning. The general rule for preventing all indoor fungal growth, including Peziza, is to keep the relative humidity (RH) below 60%. Ideally, the indoor humidity level should be maintained between 30% and 50% year-round.
To achieve this range, consider using a dehumidifier in basements or crawlspaces, which naturally run cooler and are more prone to elevated humidity levels. Proper ventilation in moisture-prone areas like bathrooms, kitchens, and laundry rooms is also necessary; ensure that exhaust fans vent air outside, not into the attic. In winter, controlling condensation by maintaining a slightly lower humidity, between 30% and 40%, can prevent surfaces from becoming damp.
Regularly inspect areas that were previously affected to ensure they remain dry and that no new leaks have developed. Exterior maintenance, such as ensuring gutters are clean and downspouts direct water away from the foundation, will help preserve the dry environment. Controlling the moisture eliminates the necessary condition for Peziza domiciliana to grow, ensuring it does not return.