With heavy rainfall comes a tremendous amount of moisture. Leaks and condensation increase, temperatures and warm drying daylight decrease.
These are optimal conditions for mold growth, both interior and exterior. As exterior mold spores explode in number some of them are bound to settle in our indoor environments. Here’s an overview from the EPA on Mold growth in the home.
So what can you do to reduce to likelihood mold will take hold?
I have some tips to minimize the conditions conducive to mold growth and maximize you and your family’s health.
Mold needs 3 conditions for optimal growth:
- The Right temperature. Some mold species can grow at low (below 50 degrees F) and other species at high (above 90 degrees F), but most common mold species that grow indoors grow ideally at 55-85 degrees F. Unfortunately this is the optimal temperature for human comfort. So it is unlikely you can keep your home at a temperature that is inhospitable for mold growth. So we will not concentrate on that.
- An organic food source. Different species of mold like to eat different things, but they all need something organic to munch on. Many mold species love cellulose, i.e. wood and paper. These are the natural composters and when it rains these species start to eat up all the fallen branches and leaves in the forest, as well as our yards emitting millions of spores that make their way into our homes. Inside our homes molds like to eat wood. This is what “dry rot” is, fungi usually consisting of 2 species, Ascospores and Basidiospores. Other species like to eat paper, such as cardboard boxes, books, and paper backed wallboard, such as sheetrock. Pennicillium/Aspergillus and Stachybotrys (colloquially known as toxic black mold) are often found on wet or moist paper. Cladosporium, the species most often found growing on windowsills and in bathrooms, can eat a variety of Biofilms (household dust consisting of epithelial cells (dead skin cells) insect parts, pet dander, natural fibers such as cotton and linen, etc.). Some mold food sources we cannot easily remove from our home such as framing lumber and wallboard, but others we can, such as cardboard boxes.
- This is the big one and the one I will be giving tips on below. Mold needs moisture. There is a common saying in our business: “Mold is the symptom, moisture is the problem”. Mold growth either needs liquid water or high humidity. Liquid water can come from condensation on windowsills and in bathrooms, or from leaks, either internal or external. Without liquid water mold will not become active unless the humidity is high, usually 60-80% RH depending on the species. When the humidity is high enough, mold can become active and grow by absorbing moisture directly from the air.
Here are some tips to reduce both food sources and moisture in your home and thus reduce the likelihood and amount of mold that may grow inside your home:
Let’s start outside. When it rains water can easily enter what we call the “Building Envelope”. It is very important to make sure your site drainage system is clear from debris and working properly to move rain water away from your home, foundation, and crawlspace.
- Clean the roof of any leave or other debris.
- Clear gutters
- Make sure downspouts are in good repair, not clogged, and properly attached any extensions or the site drainage system.
- Make sure all property drains are clear of debris and flowing freely.
Check the “Building Envelope” for possible sites of water intrusion, i.e. leaks.
- Window and doorframes are spots where water can intrude. Check all door and window frame caulking for cracks and gaps and repair where necessary.
- Inspect the sealant around roof penetrations. Repair where necessary.
- Check building siding for cracks, peeling paint, holes, etc. Anywhere water may be able to get in.
After a heavy rain walk around the entire house and look for standing water, and clogged drains. Look inside the crawlspace and make sure there is no hidden flooding. Carefully check the inside of the house, take a close look at the ceilings, around windows and doors, and walls for small leaks. Because all big leaks start out as small leaks! Check under sinks and around tubs and toilets to make sure there are no plumbing leaks adding moisture to the interior of your home.
Assuming there are no leaks and your drainage system is working well, what other sources of moisture can address?
Inside a home the occupants can produce a tremendous amount of moisture. On average each human occupant expires (breathes) and perspires (sweats) about 2 POUNDS of water into the air a day. Pets can also add to this moisture source. During the winter we often close out windows, as it is cold out, and most residential heating systems have no way of bringing in fresh air or ventilating out moist, stale interior air. Thus interior humidity can often increase to levels above 60%, which is ideal for mold growth.
So what can we do about Mold Growth?
- Monitor interior humidity. Small, portable humidity monitors are available for around $10-15 and can be placed around the home. If RH (relative humidity) is consistently above 65%, action should be taken. Ideally, interior RH should be between 45-55% RH. Below 40% RH mucous membranes start to dry out and can cause occupant discomfort.
- Open windows when practicable to help flush out moisture and other interior contaminants. Even 1 hour a day can make a big difference, although 3-4 hours is recommended.
- Run ventilation fans in bathrooms and kitchens to help exhaust excess humidity from cooking and bathing. Run fans in bathrooms for at least 20 minutes after bathing. Timer switches can be installed on most bathroom exhaust fans and are highly recommended.
- Wipe excess condensation from windowsills. Inspect windowsills often. Do not keep curtains closed as this can trap moist, cool air and promote excessive condensation.
The above tips can help reduce moisture sources, what can do we do about reducing mold food sources?
- Do not keep books, papers, or cardboard boxes in moist areas such as attics, garages, basements or crawlspaces. Attic and crawlspaces should not be used as storage areas, but if you must store items in a garage or basement, we recommend sealed plastic bins.
- Keep areas mold likes to grow clean and dry. This means cleaning dust (biofilms) from windowsills, baseboards, and doorframes. Vacuum carpet regularly with a HEPA vacuum. The recommendation is to vacuum and sweep one day per week PER OCCUPANT, including pets!
- Check behind drapes and furniture for hidden condensation and biofilms. Allow airflow to reach these areas by opening drapes often and moving furniture a few inches from walls, especially exterior walls that can become colder and promote condensation.
Also, trust your nose, that musty smell is a sure indication of active mold growth. That musty smell is caused by microbial VOC’s, airborne chemicals that are a metabolic by-product of mold digestion.
If you think you have a hidden source of mold, call a professional Certified Microbial Investigator for a full mold inspection. Excessive interior mold can cause structural damage to your home and its contents, as well as allergic and respiratory reactions in some occupants. Take heed and be diligent, and you can survive this hopefully wet winter relatively mold-free.