Is it Mold or Dirt?
The first thing you should do is locate every spot that is moist or damp around your house. Mold can grow in almost everywhere if it’s wet enough. If you’re not sure that is mold or dirt, you should buy a mold test and test the area.
Look for Outside Leaks!
If mold is growing on an exterior wall or ceiling, first look for a leak in the wall or roof as a test for mold. Measure from the moldy area to a reference point like a door, then find the spot on the other side of the wall or ceiling. Closely inspect nearby vents, roof flashing, decks, window wells and anywhere wood is rotting.
Open the area with a Screwdriver.
There are many types of molds, and some of them causes rot. If you want to know how to find mold in your house, probe the suspect area with a screwdriver or other sharp tool as a test, and if the wood is soft or crumbles, the fungi have taken hold and rot has begun.
It’s also very important to check for Plumbing leaks.
Let the water run while you check the pipes and surrounding area for damp spots to see if there’s mold from water leaking. Once the leak is found, fix it.
Inspect the Ductwork!
If mold forms on the ceiling under a duct or register and there’s no sign of a roof leak, badly insulated ductwork may be the cause.
Warm, moist air condenses and forms water on ducts carrying cold air through the attic or crawl space.
In cold weather, moisture forms anywhere warm air escapes—for instance, at unsealed joints between duct sections.
Inspect your ductwork as a test for mold.