Top 10 Tips to Look for Water Damage and Mold in Buildings

/ / Environmental Testing, Healthy Building Inspections & Testing

Top 10 Tips to Look for Water Damage and Mold in Buildings

Every year the rains return, soil dampens, leaks pop up, and mold in buildings becomes much more prevalent than during dry times. This winter’s forecast “El Niño” may bring more rain and possible flooding than California has seen in a decade. Many of our buildings are going to leak in places we were not aware of when the skies were clear.

From the State of California—Health and Human Services Agency California Department of Public Health

Statement on Building Dampness, Mold, and Health – September 2011

“CDPH has concluded that the presence of water damage, dampness, visible mold, or mold odor in schools, workplaces, residences, and other indoor environments is unhealthy………….we strongly recommend addressing water damage, dampness, visible mold, and mold odor………… protect the health and well-being of building occupants, especially children.”

Mold is ubiquitous; mold spores are floating around in the air everywhere, all the time.

The total number of spores and specific species can vary wildly. While a small amount of mold is growing in all of our homes, especially in kitchens and bathrooms, this growth rarely triggers symptoms for normal occupants. Significant mold growth due to water damage is of the greatest concern. Hidden water damage can promote significant mold growth that can seriously affect occupant health.

A direct request from a client:  ….how to find a new place that has a lower chance of having a mold issue” (they already have a confirmed mold issue in their current environment).

The best way, by far, would be to have any new home you are considering moving into inspected and tested by a Certified Microbial Investigator.  A standard residential Mold/IAQ Inspection with air and/or surface sampling will typically identify if any significant mold growth is active in a home.

However, the cost of an inspection can be impractical if you are looking at multiple places to move to. Below are 10 tips you can use to identify water damage and mold in buildings prior to purchase or signing a long-term lease. Use these tips to narrow your search and then invest in a professional inspection when you have found the “one”.

Mold in Buildings

No Downspout

10) Drainage: At minimum this usually means gutters and downspouts.

  • Do the downspouts tie into a site drainage system?
  • Are the gutters clogged with leaves and other debris?
  • Walk around the property, is it on a hill?
  • Will water flow toward the building when it rains?
  • Are there drainage culverts, channels, and storm drains?
  • Are these drains clear or clogged with debris?
  • Is there evidence of water splashing onto the building siding?

Proper drainage is key to preventing excess moisture entering a building, a basement, or crawlspace and leading to dry rot or mold growth.

9) Building Envelope – Roof, windows, doors, siding, foundation – Leaks from Exterior

Mold in Buildings

Peeling Paint on Siding

Look at the roof, is it in good condition?

Are the roof penetrations well sealed or is the sealer old and cracking?

Check the ceiling inside for signs of roof leaks, water staining, bubbling, etc.

Look carefully around siding, window and door frames?

  • Is the caulk cracked or smooth and in good condition?
  • Are the frames cracking?
  • Is the paint peeling?
  • Are there cracks or other gaps (where a chimney meets the wall may be one) that may allow water to enter the building envelope?

All are signs that water may be able to enter the building envelope.

8) Leaks – Interior – Plumbing – Freshwater and Drain Plumbing

Water and moisture don’t only come from the outside. The internal plumbing system can leak and provide moisture for mold growth.

  • Check under all sinks, kitchen, bathrooms, laundry room for visible leaks and musty smells.
  • Look around tubs and showers for signs of leaks, mold growth, and bubbling. Tiles that are coming loose are often a sign of moisture in the wall behind.
  • Look at drains for signs of leaks.

7) Condition

Mold in Buildings

Clogged Drain

What is the overall condition of the space? Run down or pristine? Likely somewhere in between, but the general condition can give you a clue how good long term maintenance has been. Shoddy maintenance can allow water damage to fester and mold growth to set in.

6) Condensation

Single pane windows are notorious for excessive condensation.

  • Are window sills cracked and stained?
  • Are window sills dirty or showing visible mold growth?
  • Check the back of blinds and drapes for signs of condensation and mold growth.

Older homes, prior to the 1970’s, are usually not insulated. Large pieces of furniture placed against cold, outside walls can facilitate condensation and mold growth.

  • Check behind large dressers, bookshelves, or headboards for condensation and mold.
  • Closets that share an outside wall can be problematic. The excess condensation, limited airflow in a closed closet, as well as plenty of organic material for mold to eat (cotton and wool clothes, cardboard boxes, etc) can lead to a significant mold infestation.


5) Ventilation

Bathrooms without sufficient ventilation can be very problematic for condensation. If there is water staining and mold growth or mold stains on the ceiling or walls (some growth in the shower and bath is normal, but not outside of those areas) it is likely condensation is a problem.

  • Does the bathroom have a good exhaust fan?
  • Is the fan register clean or clogged with dust and debris?
  • Does the bath fan have a timer?

Many older buildings only have windows for bathroom ventilation. Adding a fan to the window or the bathroom may be necessary to counteract excessive condensation. Kitchens should have exhaust fans for the stove top to exhaust excess moisture from cooking to the exterior. Some older buildings only have recirculating fans or no fans at all.


4) HVAC System

The HVAC (Heating, Ventilation and Air Conditioning) system is very important to maintaining both occupant comfort and good air quality. Often the HVAC system is the only way to filter the air we breathe inside our homes, although not all HVAC systems have filters. Dust, moisture and pests (insects and rodents) can hide out in ducts and other areas of the HVAC system.

  • If the system has a filter, check it! Is it dirty or clean?
  • Change the filter regularly and use the best quality filter the system can handle.
  • Check the ducts and registers with a flashlight. Are they dirty or clean? Any signs of insect or rodent infestation. Take a sniff, there should be no foul or musty odors.
  • Lift floor registers and look inside for dust and debris.
  • Some systems don’t have ducts, such as radiant floor heat or wall or space heaters.
  • Check wall heaters for buildup of dust and debris. The insides should be clean.
  • A portable air HEPA filter may be advised if the building has radiant heating.


3) Housekeeping

Mold in Buildings

Visible Mold Growth on Baseboard and Wall

Does the building seem “clean”? Remember to check the hard to reach places.

  • Check the tops of door and window frames for dust buildup.
  • Check under the refrigerator. This area can build up quite a bit of debris and mold can grow on the condenser coils.
  • Check behind large items such as cabinets and couches.
  • Mold can easily grow on “biofilms”. Household dust is considered a biofilm, as it is composed of organic material (skin cells, insect parts, cotton and cellulose fibers, pet dander) that mold can use as a food source.
  • Does the building have carpet? Does the carpet appear clean? Is the carpet stained? Carpet can hold moisture from cleaning and spills as well as pet urination. In addition to other contaminants carpet tends to accumulate settled mold spores that come in the air from the exterior.   Carpet can hold mold spores which can become active under conditions of high humidity.

2) Musty Smell

Probably the second biggest “red flag” for a building you may occupy. A musty smell = ACTIVE MOLD GROWTH. Trust your nose and if there is a moderate to strong musty smell, RUN AWAY.


Mold in buildings should not be visible, with the exception of small amounts around sinks, baths, and showers. Sometimes a minor amount around window sills is acceptable. But if you see visible mold growth on walls, ceilings, baseboards, under sinks, etc. this is a sign of a significant mold infestation.

As stated by the California Department of Public Health:
visible mold or mold odor in schools, workplaces, residences, and other indoor environments is unhealthy”.

I hope you can use the above top 10 tips to help find a healthy and happy place to call home!


Healthy Building Science is an environmental consulting firm providing mold testing and mold inspection services for commercial, residential, multi-family, buildings, offices, industrial and manufacturing workplaces, hospitals and medical facilities, and single-family homes in the greater San Francisco Bay Area and all of Northern California including the cities of San Francisco, San Jose, Oakland, and Sacramento.