Hi Nobes,
You asked how often a mold inspection is needed. I'd think the answer would depend a bit on your climate. If I lived in the desert, I'd have little concern. If I lived in Florida, more concern- or at least awareness.
Also contributing is how dry the room is & how well ventilated. For example, we have to use exhaust fans in bathrooms during summer to get rid of post-shower humidity or mold starts. In winter, they're not needed.
And, there's always the basement/crawl space factor. Both tend to stay more humid and darker than the habitable rooms. Mold enjoys humidity and darkness.
A big mold hiding place in the home is under the rim of toilets & in the area hidden above the rim wash holes. Pour white vinegar in the overflow tube until you see it trickle out under the rim of the bowl. Wait 10 or so minutes and watch the bowl as you flush. Yikes!
Another is the p-trap on your air conditioner's evaporator. Mold grows in those and spores on the water's surface are picked up by negative pressure when the air conditioner operates. They get sent into the rooms. It's best to flush those with clean water every week or two. (You can buy them with a flip-up cap for this purpose.)
Keep in mind that surface mold is nearly always visible to your eye. Surface molds are common on tile grouts, concrete, caulks and wood. Unfortunately, they are not visible if behind a damp wall.
I think Fawana's mention of self-test kits is a fantastic idea for suspect areas. Air tests & surface tests are available. Sometimes an unscrupulous mold inspection company will call out mold when none is present just to make a remediation sale.
Ventilation and de-humidification are wonderful allies for mold control. Sunlight is also helps to keep mold in check.
UV light at 254 nm will kill most species in seconds, but is dangerous to use improperly. We have a UV light in our air handler (fan on low 24/7) to kill airborne molds, but note that our air handler is not a typical furnace. It briefly holds the air in the UV chamber. I don't know how well these work in regular furnaces.
HEPA air cleaners will trap mold quite well as long as the filter is clean so that air does not go around it.
What ever you do Do Not treat any mold with chlorine containing products. Mold goes into "defense mode" and throws spores quite a distance. I took university & government sponsored sanitation & health safety courses as part of my job, which is where I learned that startling fact. We saw demonstrations. Boy do those spores fly far!
Quaternary ammonium is a product that will not cause mold to throw spores. It also has what is called "residual". As long as it remains on the surface, mold will never grow again. You can buy un-scented at restaurant supply houses. That's what is used in low temperature dishwashing machines and to wipe tables and cutting boards.
Household 5% white vinegar also kills mold in about 10 minutes of wet time. It will clean the mold off better than quats, but does not have residual.
Hydrogen peroxide at 3% also kills in about 10 minutes.
Super oxygenated water is advertised to kill mold, but it has to be made within minutes of being used or it won't work at all. (Not much of a DIY product!)
Personally, I kill the stuff with vinegar, rinse and then apply the quat at about 200 - 300 parts per million.
I hope some of this proves helpful. If you see no mold, have no damp walls or wall-floor junctions and generally feel good, I think this isn't by any means a panic situation. But the fact that you're thinking about is great!
Paul
