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Ask the Carpenter: Dealing with the dangers, cost of mold removal

Ask the Expert Home Improvement
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Q. I returned to my home to find that the pressure release valve on the hot water heater had failed in the on position. My unfinished basement was a hot, steaming mess. There was water on the floor and condensation on the ceiling. There was black mold on the plaster around the stairwell and yellowish mold in the ceiling. My insurance company arranged for water removal, and there are two industrial dehumidifiers working now. The adjuster is waiting for one more quote. Both companies expressed concerns about mold spores traveling upstairs. One mentioned getting the air tested by an industrial hygienist. My husband has a serious health condition, so we have to do it right. I have a $10,000 limit on my policy, so we’ll pick up the rest, but in your experience, how high could the costs go? We have a 1,600-square-foot Cape built in 2000.

B.F.S.

A. A single flooding event can create a significant mold problem unless the affected area is dried within 48 hours. I’m assuming the company that your insurance agency contracted with to do the initial damage cleanup specializes in this work. They should have cleaned and sanitized the water-damaged materials as soon as possible.

I hope they disposed of anything that could not be cleaned and dried. Porous surfaces such as gypsum wallboard, carpeting, and insulation cannot be cleaned and must be disposed of. Once that is done, the key is to reduce the moisture that leads to mold growth by thoroughly treating your basement and using a dehumidifier.

There are thousands of types of fungi and molds capable of causing allergic symptoms in sensitized persons. According to the Environmental Protection Agency: “Allergic reactions to mold are common. They can be immediate or delayed. Molds also can cause asthma attacks in people with asthma who are allergic to mold. In addition, mold exposure can irritate the eyes, skin, nose, throat, and lungs of both mold-allergic and non-allergic people.’’ Your goals should be to remediate the mold, repair the damage, and lower the humidity in your basement.

Testing for airborne mold spores is not usually necessary in order to identify a mold problem. Conduct a visual inspection; if you can see mold, then you have a problem and should consult a professional mold inspector.

If you have less than 10 square feet of mold, you can remediate the area yourself, following EPA guidelines (www.epa.gov/mold/mold-cleanup-your-home#Tips-andTechniques). If you have more than that, which is what you are facing, the EPA recommends its guide titled “Mold Remediation in Schools and Commercial Buildings’’ (www.epa.gov/mold/mold-remediation-schools-and-commercial-buildings-guide).

If you choose to hire someone to address the problem, make sure the person has experience cleaning up mold. Check the provider’s references and certification and ask the contractor to follow the guidelines of the EPA or the American Conference of Governmental Industrial Hygienists.

The field of indoor air quality investigation and remediation is relatively new. As a result, many scammers have emerged to profit from a homeowner’s lack of knowledge and desire for a healthy home. If you decide to have an industrial hygienist test your home, make sure it’s a reputable company and ask for references.

According to houselogic.com, “remediation costs vary depending on how much and where mold exists,’’ and it could cost $10,000 to more than $30,000 to repair widespread structural damage.

Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to homerepair@globe.com or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at pages.email.bostonglobe.com/AddressSignUp.