Where Does Mold Grow in a House?

David J. Allen

I spent the better part of 2 ½ years learning about mold and indoor air quality because my child's life depended on it. Now I help others avoid ever having to experience the same thing. The mold industry suffers from conflicting opinions and I do my best to distill loads of data into something practical and useful. I love hearing from and helping readers. • "A house desecrated by mildew, mold, or fungus would be a defiled place to live in, so drastic measures had to be taken." — Leviticus 14:45

As a general rule, the parts of the home that are most susceptible to mold growth will be the areas that are damp, warm, and dark.

That said, there are certain mold hot spots around the house that many homeowners don’t consider, yet they frequently become infested with mold.

If you want to prevent any major mold problems from developing, it’s important that you monitor the high-risk rooms and areas of your home or apartment.

You’ll catch and can handle any problems early, saving you time, huge sums of money (and, for many people, misery due to health conditions that can develop due to mold growth.)

Ideal Conditions for Mold Growth

First and foremost, mold requires the presence of moisture to develop. If the air in a room has a high moisture content or water is regularly lingering on the surfaces, that part of the house is going to be at risk for mold growth.

Mold also thrives in warm environments; specifically, the fungus is in heaven when the temperature is in the range of 70 to 85 degrees Fahrenheit.

One thing mold doesn’t like, though, is sunlight. The ultraviolet (UV) rays from the sun can actually kill off mold spores. So, for reasons of self-preservation, mold typically sticks to parts of the home that aren’t exposed to much sunlight.

Ultimately, any part of the home that’s wet, warm, and away from any sources of sunlight is going to be the perfect environment for mold to rear its ugly head.

However, all three of these conditions being met is not necessary for the invasive fungus to develop. As long as moisture is present, there’s always the possibility of mold growth.

So, which parts of your home should you be regularly checking for the presence of mold?


Let’s get the obvious one out of the way first. As you’ve probably guessed by now, bathrooms are a major culprit for mold infestations, and they should always be on your checklist for mold searches.

Bathrooms feature multiple sources of water, they’re often very warm, and they’re rarely exposed to direct sunlight—in fact, they’re relatively dark in many homes.

While running the bathroom exhaust fan during showers can certainly reduce the risk of mold, there’s still a very strong chance that the fungus will develop over time. What you can do, though, is stay diligent about catching any new mold colonies in the early stages of growth.

Then, you can use a mold-killing agent and scrub the fungus away before it gets the chance to expand. 

Within your household bathrooms, there are a handful of spots that you should periodically check for mold:

  • On the shower walls
  • On the floor mat
  • In the toothbrush holders
  • Around the toilet
  • Around the bathtub


While kitchens are often brightly lit rooms and sometimes feature windows, they also tend to be very warm and humid. Plus, with all of the food that’s prepared and served in the kitchen, there are usually many different surfaces around that mold can appear on.

Obviously, the goal should always to keep mold away from the area where your family’s food gets made, so it’s important to regularly check for the toxic fungus.

Some of the places in the kitchen where mold may show up include the dishwasher, underneath the sink, the refrigerator, hidden corners of the counter, the dirty dishes, and any produce or bread that has been sitting out for a prolonged period.

If you make an effort to keep your kitchen clean and tidy, it will certainly decrease the chances of mold growth, and that includes tasks like cleaning out the fridge and washing dishes right away after using them.


Another part of the home that can frequently harbor mold growth is the basement. Basements are often dusty and very poorly ventilated, which can create a dirty environment with stagnant air.

Beyond having poor ventilation, basements are also prone to mold for an another reason entirely:

The concrete floor and walls of a basement aren’t just porous, they’re also hydrophilic—they attract and suck up liquid water from the surrounding ground, and water vapor (or moisture) from the air. No, it won’t flood your basement over time, but it will be enough to cause mold on its own, particularly in a basement.

And that’s why basements are one of the few areas of a home where a dehumidifier is a must.

Then, if any element of moisture is introduced, such as a plumbing leak or a water backup due to a drainage clog, it can become an ideal situation for mold to flourish.

And, because it’s so easy to go days or weeks without spending any time down in the basement, those mold colonies often have plenty of time to grow and spread.

Your basement doesn’t have to turn into a mold hot spot, though. As long as you inspect the area periodically, keep the room ventilated, and get any water leaks repaired promptly, you should be able to keep the fungus at bay.


Much like basements, household attics are often poorly ventilated and dusty, and since warm air always rises, they tend to be pretty warm as well.

As long as your attic stays dry, you shouldn’t encounter a mold issue, but if your roof isn’t in good shape, you could have a problem on your hands. If your roofing is damaged or deteriorating, there’s a high likelihood that water will find its way through the roof and into the attic.

And if that’s the case, it may take nothing more than one significant rainstorm for mold to start growing at the top of your home. So, to give yourself the best chance of avoiding such a situation, keep your attic clean and have your roofing occasionally inspected.

Laundry Rooms

If your home (or leased apartment) has a laundry room, that room is also prone to mold growth. At least more so than the rooms and spaces without running water. Mold can grow both inside of the washers, as well as on the floor if wet clothes are left out, or if a fair amount of water drips off clothing being moved between the washer and dryers. It’s helpful to step into the laundry room occasionally and listen for any sounds of dripping or lightly running water. A moisture meter can you detect hidden water or dampness, such as inside walls.

To clean mold out of your washer, pour in a cup of bleach or hydrogen peroxide in—one or the other, never both—and then run an empty load at the machine’s hottest possible setting. Since washing machines are non-porous, they’re one of the few appliances where you can actually use bleach to deal with mold.

Air Conditioner Closets

Air conditioning units don’t run on water, but they do generate a certain amount of it as a byproduct of cooling the air in a home. Condensation (and, less often, ice) builds up in parts of the unit. This condensation and run off is typically taken care of with drip lines.

Modern air conditioners are also one of the reasons you usually do not need a separate dehumidifier in most rooms of your home or apartment. Can you use them in some places, like a garage or basement? Yes, and if the humidity is high enough, you should.

But a properly sized and working air conditioner removes both the moisture and the heat from the air in a room. Collected and removed from the air, the water vapor turns to liquid form within the a/c, where it’s collected in drip pans and removed with condensate drains.

If those drains are clogged or overflowing, mold will eventually grow in an a/c closet.

Any Room With Plumbing, and Rooms or Hallways Adjacent to Rooms With Plumbing

Beyond the above specific rooms, mold is more likely to grow in any room of the house with plumbing in it. Plumbing is usually confined to the kitchen, and any bathrooms, but in order for water to get to those rooms or spaces, it, of course, has to travel under or through other rooms. If a leak develops in the pipe lines that feed the sink, dishwasher,

As you can see, there’s a bit of a pattern when it comes to where mold is most likely to grow in your home. But if you keep your home clean and dry, take proactive action to repair leaks, and consistently monitor the damp, warm parts of your household, you can greatly reduce the odds of a serious mold problem developing.