How to Check for Mold and Prevent Future Growth

Mold can be obvious or sneaky, and it’s not always easy to know how to check for mold if you’re not a pro. If you suspect mold spores anywhere in your home, we've put together a checklist to help you look for signs of mold. If this is one project you'd rather not do, you can hire a mold inspector near you to do a thorough investigation.

Think you can handle the job yourself? Here’s how to check for mold around your home:

1. Know What Mold Looks and Smells Like

Before you examine your home for mold, know the signs. Here are some common characteristics of mold:

• Smell: A musty, earthy odor that can smell like old socks

• Appearance: Often green, brown, gray, white, black, blue, or yellow. Can look like stains that are growing and make irregular spots on walls, furniture, floors, ceilings, ductwork, and grout

• Texture: Feels like leather, cotton, sandpaper, or velvet

• Location: May be near water damage, such as bubbling paint or water stains

2. Head to Your Basement

Your basement should be the first place you check for mold because it’s susceptible to moisture and humidity. Be sure to bring a flashlight to look in dark or narrow spaces. Here’s where mold is most likely to be found:

• The corners of your basement

• Near windows, vents, and window wells

• Behind and around appliances like your washer and dryer

• In or under the carpet

• In or on the drywall

• On or behind the baseboards

• Near your water heater and furnace

• On the coils of HVAC air handlers

• Around your sump pump

• Around pipes and ductwork

• In your closets

• Near the foundation where there might be leaks or water from the outdoors

• Between furniture and the exterior walls

You can prevent future mold growth by reducing moisture in your basement. For example, run a dehumidifier if you suspect any excess moisture. You may also want to check for water seepage and damp or smelly carpet and walls after heavy rain.

Have a particularly wet basement? It might be time to call in a professional. Basement waterproofing costs can go as high as $7,625, but it’s well worth the price if it keeps you from having to blow your emergency savings or take on debt to pay for high water damage repair costs.

3. Look in Your Above-Ground Rooms

Photo: photosbysabkapl / Adobe Stock

Mold and mildew can pop up wherever there’s moisture, so start by looking in rooms, such as your bathrooms, kitchen, and attic, or wherever you suspect a leak or water damage. 

Check for mold in these common areas:

Bathrooms

• Under and around the sink, especially near water pipes and valves

• Around the bathtub or shower, especially in the grout and around caulking

• Around the base of your toilet, behind it, and in the tank

• On your shower curtain or door

• Near the faucet and bathtub spout

• In your toothbrush and toothpaste caddy

• On the ceiling 

• On the bathroom rug and shower or tub mat

Kitchen

• Behind your refrigerator in the fridge drip trays and water dispensers 

• In, under, and around the sink, including near valves and water pipes

• In your refrigerator, including in food storage containers and drawers

• In your pantry, including any open or expired foods

• Around and in your microwave and stove

• In and around your trash can and recycle bin

Attic

• In your insulation

• Near your intake and exhaust vents

• On the roof, near possible leaks

• The underside of your roof deck

Garage

• Behind and under storage areas

• Around the windows and doors

• Near any areas with standing water 

All Rooms

• Under carpeting that got wet or feels damp

• On drywall that may have gotten wet or feels soft

• Behind peeling wallpaper

• In ventilation ducts near AC and heating vents

• Ceiling corners, as they trap water from roof leaks

• Around windows and window sills

• Furniture, including couches and mattresses

• Curtains and blinds

• Indoor plants, especially if they’re over-watered

• In your fireplace or chimney

• In crawl spaces

• In closets with limited ventilation

4. Test Your Walls for Mold

Mold can grow in and behind your walls, where it can be tough to see. But a distinct musty smell can give it away. Sniff the walls in areas that are prone to moisture, such as your basement and bathroom.

If you sense dampness or softness in your drywall, the mold might be eating away at the surface. You can test for mold by using a screwdriver to dig into the wall, but avoid areas near wiring and outlets. If you smell or see mold in your walls, contact a mold removal company near you.

5. Identify Indoor Leaks

If you spot mold near waste lines, water pipes, or plumbing fixtures, it might be because of a leak. Turn on the water and check the pipes and surrounding areas for dripping water. If you find the leak, it can help prevent further mold growth and water damage.

Hiring a local plumber can be helpful for tracking down leaky pipes, but it’s possible to do this yourself, as well. If you’re up for the task, here’s how to find a leak in your home.

6. Find Outdoor Leaks

If you see mold growing on your ceiling or an exterior wall, you may have a roof leak or other leak from outside, such as water seepage near your foundation. Make a note of where the mold is indoors by measuring the distance from the mold spot to the edge of the wall. Measure that same distance on the outside to identify where the leak might be happening.

Here are the key places to look for outside leaks:

• Roof flashing

• Vents

• Decks

• Window wells

• Near rotting wood

• The ground sloping near the house’s foundation

• Downspouts

7. Inspect Your Ductwork

If mold is growing on your ceiling under a register or duct and you don’t see signs of a roof leak, your ductwork might be the culprit. When warm and cold air travels through the ducts, moisture can build up in drain pans and on cooling coils. Remove your vents and look for condensation in and around your ductwork with a flashlight.

If you detect mold, your ductwork might be poorly insulated or be missing a vapor barrier. Contact a local HVAC professional to see if they can take care of the issue for you.

8. Use a Mold Test Kit

You can find mold test kids online or at home improvement stores. Look for a test that detects mold spores in the air, not just on surfaces. Mold testing usually takes a few days, and you’ll need to send the materials to a lab to determine the type of mold.

Follow the instructions on your mold testing kit. General steps include:

1. Close the doors and windows of the room you’ll be testing

2. Collect the air sample in a petri dish 

3. Limit traffic and airflow to the room while testing takes place (usually 48 hours)

4. Put the lid on the petri dish and tape it closed

5. Set the petri dish in a dark place

6. Check for mold growth

7. Test again if no mold is found

8. Send to the lab for mold analysis

If the kit does find traces of mold, it’s time to call in a professional. Mold can make you sick, especially if you have certain health conditions, so it’s important to act quickly.

9. Hire a Professional Mold Inspector

If you sense that you have mold in your house but don’t feel like you’ve found it all, it may be best to hire a professional mold inspector before remediation. They can catch spots you missed, identify the type of mold, and pinpoint the source of the problem. They can also help you remove mold and prevent mold outbreaks in the future—a professional mold inspection costs between $300 and $1,025.

10. Remove the Mold

If you discover a contained mold problem, such as a spot that’s smaller than 10 square feet, like mold on the bathroom ceiling, you can usually take care of it yourself. Use bleach, vinegar, and hydrogen peroxide to remove the mold, but tea tree oil is the most effective natural mold killer. It's a bit more expensive than other options (about $10 for a 2-ounce bottle), but a little goes a long way. Mix 1 teaspoon of tea tree oil with 1 cup of water and spray the mold. The solution kills the mold and prevents it from returning.

Professional mold remediation costs between $1,125 and $3,345 or $10 to $25 per square foot. It’s best to call in a pro if you suspect large-scale mold or black mold.

11. Prevent Mold Growth in the Future

To keep your home mold-free and your air and surfaces clean, you can take these actions to prevent future mold growth:

• Use a dehumidifier in your basement and other rooms with high humidity

• Ensure your attic is well-ventilated

• Check periodically for leaking faucets, pipes, and toilets

• Inspect your roof once a year or after a severe weather event

• Repair roof and plumbing leaks right away

• Keep attic vents clear of insulation and clutter

• Waterproof the exterior of your basement

• Clean and remove debris from your gutters and downspouts

• Ensure your home is properly insulated

• Run your bathroom fan during and after taking a shower or bath

• Leave your shower door open to let moisture escape

• Ensure your bathtub, shower, and tiles are well-caulked

• Clean surfaces regularly, especially counters, tubs, showers, floors, and tile

• Wash your bath rug monthly

• Dry moisture found near windows

• Clear out old food from your fridge once a week

• Clean the inside of your fridge a few times a year

• Put waterproof protectors on your mattresses

• Take out your trash at least once a week

If your home ever suffers from water damage, take action quickly to prevent mold growth. Use this water damage cleanup guide to prevent long-term damage, including mold and mildew buildup.

Jenna Jonaitis contributed to this piece.