Mold in the Home – What to do?

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mold in the home

Mold in the Home – What to do?

What to do about mold in the home, how to avoid it, how to clean it up, is mold testing a good idea? etc. This blog focuses on residential mold tips. Many of these best practices are drawn from the following government-sponsored resources on healthy homes:

I’m not always a fan of the simplified points structure and uni-directional language of healthy building rating systems, however, often these systems effectively whittle down complex concepts and scenarios into just a few sentences… this is from the NHHS:

Moisture Prevention & Control (6.1)

Requirements: Building material that is discolored or deteriorated by mold or mildew or causes a moldy or earthy odor shall be cleaned, dried, and repaired. Structurally unsound material shall be removed and replaced.

mold in the home

More Mold than You Want to Deal With

Removal and repair of moldy material shall be conducted in accordance with New York City Guidelines on Assessment and Remediation of Fungi in Indoor Environments. (Outside of NYC we recommend following the industry-accepted guidelines of the IICRC S520 -Standard and Reference Guide for Professional Mold Remediation)

The underlying cause of excessive dampness or moisture, or moldy or earthy odor shall be corrected.

Rationale: Indoor dampness and mold are associated with a variety of adverse health effects including asthma-related health outcomes and respiratory illness. Damp indoor environments can increase the presence of biological agents such as mold, dust mites, and bacteria.

Building Materials & Systems for Mold Prevention

Ventilation and Moisture Control (5.3)

Requirement: Natural or mechanical ventilation, or a combination of the two, shall deliver fresh air to every habitable room and bathroom and be capable of removing moisture-laden air and other contaminants generated during cooking, bathing, and showering. The air exhausted from a bathroom, toilet room, or kitchen shall not be vented into habitable space or an attic.

Rationale: Proper circulation of outdoor ventilation air throughout a habitable space, naturally through openings in the building envelope and/or mechanically with fans and HVAC systems, is important to dilute and remove airborne indoor chemical agents, and reduce airborne transmission of biological agents, humidity, and mold…

mold in the home

Air Sealing for Better Indoor Air Quality

Air Sealing for Air Quality (5.4)

Requirement: Openings into dwellings and dwelling units shall be sealed to limit air movement…

Rationale: Controlling air leakage into homes can save the occupant money by making the home energy efficient and can prevent health problems associated with moisture. Airborne moisture can lead to mold in the home which causes respiratory distress in children and adults, including those with asthma, allergies, or other respiratory diseases.

Plumbing System and Mold (2.3)

Requirement: Every plumbing fixture, stack, vent, and water, waste, and sewer pipe shall be properly installed, maintained in a safe and functional order, and be kept free from obstructions, leaks, and defects.

Rationale: Plumbing leaks may cause mold growth on building materials. People who are exposed to molds may experience nasal and eye irritation, respiratory and allergic diseases, and asthma exacerbation.

mold in the home

Plumbing Leaks and Mold Prevention

Bathroom Fixtures and Moisture Control (2.5)

Requirement: Every dwelling shall have a bathroom equipped with the following:

  • A toilet… in good working condition, sealed to the floor, and properly connected to the dwelling’s water supply and to a waste pipe leading to an approved sewage system
  • A sink in good working condition, with a stable connection to the wall or securely attached to the floor. The sink shall be properly connected to the heated and unheated water supply and a waste pipe.
  • A bathtub or shower …  properly connected to the heated and unheated water supply and a waste pipe.
  • Bathroom and toilet room floor surfaces shall be cleanable and made of nonabsorbent waterproof materials. Bathroom wall materials that cover the wall extending 48 inches above a bathtub and 72 inches above the floor of a shower stall shall be cleanable and made of nonabsorbent waterproof materials.

Rationale: Poorly maintained bathrooms can cause water damage, mold growth, and associated health issues. Exposure to bathroom-related biological agents can cause respiratory and gastrointestinal symptoms. Exposure to mold can cause symptoms such as nasal stuffiness, eye irritation, wheezing, skin irritation, allergic reactions, and asthma exacerbation.

Mold & Moisture Action Steps

These actions steps are from the “Help Yourself to a Healthy Home” guide from HUD.

  • Use downspouts to direct rainwater away from the house. Make sure your gutters are working.
  • Slope the dirt away from your house’s foundation. Make sure the dirt is lower six feet away from the house than it is next to it.
  • Repair leaking roofs, walls, doors, or windows.
  • Keep surfaces clean and dry—wipe up spills and overflows right away.
  • Store clothes and towels clean and dry—do not let them stay wet in the laundry basket or washing machine.
  • Don’t leave water in drip pans, basements, and air conditioners.
  • Check the relative humidity in your home. You can buy a kit to do this at a home electronics or hardware store. Stop using your humidifier if the relative humidity is more than 50%.
  • If the humidity is high, don’t keep a lot of houseplants.
  • Wipe down shower walls with a squeegee or towel after bathing or showering.
  • Cut down on steam in the bathroom while bathing or showering. Run a fan that is vented to the outside or open a window.
  • Run a fan vented to the outside when cooking.
  • If you have a dryer, make sure it is vented to the outside.
  • Use a dehumidifier or air conditioner to dry out damp areas.
  • If you use a humidifier, rinse it out with water every day. Every few days, follow the manufacturer’s directions for cleaning it or rinse it out with a mix of 1/2 cup chlorine bleach (Sometimes called sodium hypochlorite. “Clorox” is one brand.) and one gallon of water.
  • When you use your air conditioner, use the “auto fan” setting.
  • Throw away wet carpeting, cardboard boxes, insulation, or other things that have been very wet for more than two days.
  • Increase airflow in problem areas—open closet doors and move furniture away from outside walls where mold is growing. Move your furniture around once in a while.
  • Prevent moisture from collecting on windows by using storm windows. If you live in an apartment, talk to your landlord about putting on storm windows.
  • Keep people with asthma or allergies away from damp areas of your home.
  • Cover window wells if they leak.
  • After cleaning up mold, using a high efficiency (HEPA) vacuum or air cleaner may help to get rid of mold spores in the air. You may be able to borrow a HEPA vacuum. Call your local or state health department to ask.
  • If you find an area of mold greater than 15 square feet, it’s best to hire a professional to get rid of it. (You can find mold remediators trained and certified by the IICRC.)
  • Clean up the mold with a mix of laundry detergent or dishwashing soap and water OR chlorine bleach with soap and water. Do not mix chlorine bleach with any product that contains ammonia.
  • If you think mold may be causing you or your family health problems, see a doctor. [HBS has a list of doctors (MDs and NDs) who specialize in environmental illnesses.]

How to Clean Up Mold?

This blog got too long… so please see the next one on how to clean mold for the DIYers. If you have questions or are worried about mold in your house or office, we can help by providing a mold and moisture inspection, mold testing, writing a mold remediation protocol, and offering quality control by clearance testing after remediation.


Healthy Building Science is an environmental consulting firm which provides mold testing services 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.