Mold Basics & Health
How mold grows indoors: spores, hyphae and shifting ecology
In plain English
Molds are microscopic fungi that feed on dead organic material. They spread as spores too small to see. When a spore lands somewhere with enough moisture and a suitable temperature, it takes up water, swells, and sends out thread-like hyphae. These knit into a mat called a mycelium, which is the part you can eventually see. Many spores are dry and light, so once airborne they can travel through a building and settle far from where they started.
R520 describes a building as an ecosystem made of small microenvironments: wall cavities, ceiling spaces, crawlspaces, ductwork, carpets, upholstery and bathrooms. These collect dust and spores routinely. When water arrives and is not dealt with quickly, common molds such as Aspergillus, Penicillium and Cladosporium grow first. If wetness continues, the community shifts toward species that need more water, including Stachybotrys and Chaetomium.
The stated goal of remediation is to get back to a normal fungal ecology. R520 defines that as the kinds and proportions of mold found in buildings of the same region that have not been water-damaged and are well maintained. It is not a sterile building, and no remediation can produce one.
“types and predominance of molds typically found in non-water-damaged, environmentally-well-maintained structures”
Key points
- Mold needs moisture, a food source and a suitable temperature to grow from spores.
- Hidden spaces and soft furnishings act as reservoirs for dust and spores.
- Longer wetting shifts growth toward water-loving species like Stachybotrys.
- Damp buildings often carry bacteria alongside the mold.
- The target is normal background for the region, not zero mold.
Official text
This topic is covered in our own words because the standard behind it is copyrighted; we cite it below rather than reproduce it.
Citations
- IICRC S520 Reference Guide, IICRC S520 Standard and Reference Guide for Professional Mold Remediation — Reference Guide — Ch. 2, pp. 13–15. Best practice