Types of Household Mold
We're HVAC and air-quality specialists, not a medical or environmental lab — this is general reference information, not a diagnosis. On-site testing is the only way to know what's actually in your home.
One of the most common indoor/outdoor molds. Often found on HVAC coils, ductwork, and damp surfaces. Generally less associated with severe biotoxin concerns but can trigger allergy and asthma symptoms.
A large genus with many species; commonly found in dust, HVAC systems, and water-damaged materials. Some species are of particular concern in CIRS-related testing panels.
Common on water-damaged wallpaper, carpet, and insulation. Frequently identified in ERMI and HERTSMI-2 panels as a water-damage indicator species.
The species most associated in public awareness with severe health concerns. Requires sustained moisture to grow — typically a sign of a significant, ongoing water intrusion problem, not routine humidity.
Another water-damage indicator species, often found alongside Stachybotrys in chronically wet building materials like drywall and subfloor.
Want to know what's actually present in your home? We run on-site qPCR testing (ERMI/HERTSMI-2 style) with same-visit results — see our mold testing methods guide or the full Mold & CIRS Support page.
Why species identification changes the response
Not all mold findings mean the same thing, which is exactly why species-level testing beats eyeballing a stain. Common outdoor-origin species at low indoor counts tell a very different story than water-damage indicator species like Stachybotrys or certain Aspergillus and Chaetomium findings — the latter point to a moisture history that needs locating, not just surface cleaning. For CIRS-recovery households, the distinction is central: protocols key on indicator species and their loads, which is why our on-site qPCR testing reports species and quantities rather than a vague 'mold present.' The species list is the map; it tells you whether you're looking at normal environmental background, a past event that was never fully addressed, or an active moisture problem still feeding growth somewhere you haven't found.
Where each type tends to hide in Southern California homes
Our region's patterns are specific: condensate-line and drain-pan growth thrives wherever AC runs hard against humid coastal air; duct-board and lined ductwork absorb moisture events invisibly and hold them permanently; post-war crawlspaces collect decades of ground moisture under original flooring; attic spaces near marine air grow problems on the underside of roof sheathing; and slab-era homes hide wicking at the wall base behind baseboards. Knowing where each species profile tends to live is what turns a lab result into a found source — and finding the source, not spraying the symptom, is the entire game.