Practical Advice for Home Building or Renovating to Prevent Mold and Optimize Indoor Air Quality

When you keep moisture out, ventilate properly, and use sound building materials your home can be a very healthy and mold-safe place to live.

Building a custom home is an exciting and, at times, overwhelming adventure. My husband and I collaborated on 2 such adventures when we were first married. Each home was designed and built to our specifications. All materials that were used were chosen by us. My husband was working in the building industry at the time and was able to be onsite for the majority of both builds and served as the general contractor. There was definitely a large amount of security in knowing that our homes were thoughtfully and soundly built. And, even though we were not consciously choosing “healthy” or always the most “mold-safe” building materials (we obviously had not been affected by mold yet at this time), we built beautiful homes where we enjoyed the happy early years of marriage and babies.

Then, the housing/building market crashed, and my husband was forced out of building and to look to other industries for work. We were also forced to move frequently for his work. It was then that we were relocated to homes that were found by his company and were often sight-unseen to us prior to move-in day. It was also during this time that we moved into the home with the toxic mold problem throughout the HVAC unit that made us all so sick. With the mold situation came great upheaval and new building challenges, because we were forced, under tremendous health and financial strain, to take our home almost down to the studs to have it properly remediated. (Note: We were advised that proper remediation required us to gut the interior of the home of anything the mold had touched or penetrated, so that our family could safely return, live there, and continue to recover our health. This may sound extreme; however, when someone has mold sickness and increased sensitivity, all mold, down to microscopic spores and hyphae, must be addressed. This is precisely why there are so many failed remediations.)

Even though we had built our own aesthetically-fit homes in the past, we realized how much we didn’t know about building an intrinsically healthy home. It was crazy how all of the things that seemed to matter to us before when we were building our homes, like the size of the master bedroom closet, or whether to tray or coffer ceilings, just didn’t matter to us anymore. The things that mattered to us with this re-build and that we poured our resources into were all health- and indoor-air quality-centered, like HVAC design for optimum air flow and dehumidification (dehumidification not being a request most homeowners have), using all metal ductwork to prevent dust and mold, re-grading our yard to route water away from our foundation, and on and on.

The new list was endless, pricey and rather unsatisfying, because nothing on it was something that most people would even notice when they came to our home. For example, my remediated attic with beautiful new systems, ductwork, and clean, bagged insulation is not necessarily what I care to show off to my friends when they come over for dinner, even though the vast majority of our renovation budget went into it. The funny thing is that I really value all of these healthy improvements to my home much more than I ever did the wow-factor things in our previous homes, because these things are what make our home safe, healthy and mold-free for us today. Of course, no matter how healthy you make your home and how well you plan, there are ALWAYS things that can happen (leaks, storm damage, flooding due to human error or faulty appliances, etc.). The difference is that now we have redone things to mitigate many of the main indoor air quality issues that homes can have (improper air flow, poor ventilation, excess moisture, outside water intrusion, etc.). Thus, we can live with a degree of security that, if and when those things do happen, we stand a better chance of being able to fix them before mold sets in and our home makes us sick. We also have a checklist of things to look for while living in the home that will help us to catch and fix an issue BEFORE it leads to disaster.

So, where am I going with all of this?

Today, at the request of a reader who is embarking upon building her own custom home, I am going to put all of that hard-earned “building a healthy, mold-free home” knowledge to use. I will share with you some of the key components that you need to be aware of and try to implement if your intent is to optimize your home for indoor air quality (IAQ) and wellness, especially when it comes to mold.

Since I am not a professional builder, all of my recommendations and advice are going to be in very general and simplified terms. I am going to do my best to give you the big picture of what a IAQ- and mold-safe home looks like to me. Everyone is definitely different and has different priorities and pain points, so my list will need your own personal adjustments and additions. I always advise you to do your own research and due diligence on any building or construction strategy you are going to implement for your own home. I also advise you to consult with certified professionals in the Building Biology and IAQ fields to make sure you are doing what is healthy and correct for your unique situation and budget. This is one of those situations when spending a couple hundred dollars on the front end for professional consultations, inspections, and input will actually SAVE you money in the end.

I have taken the liberty of dividing my list into sections: General Construction, HVAC/Ventilation/Dehumidification/Air Filtration and Purification, Outdoors–Landscaping/Grading/Water-Intrusion Prevention, Interior Design, and Bells and Whistles. That way, if you are only interested in one or two pieces of the puzzle, you can skip around to the parts that interest you most.

So, without further ado, here are, in my opinion, the main considerations and action steps for building or renovating a home for optimal indoor air quality and mold safety:

(Note: Please forgive me if I jump around a bit. This is A LOT of information. I could not cover everything, but I did try to, at least, touch on all areas that I could think of to get you the most information that you need to get started or to guide you in the right direction.)

#1:

Before you embark on this journey, you need to be mentally and financially prepared to spend more on everything. It is just the way the world works now. All of the building materials that you are used to seeing and that most builders have become used to using are designed to be inexpensive and easily sourced, aka “builder grade.” For the most part, those materials are not going to work for you. You may even have to really scale your square footage or scope of project to account for the additional material expense. This is not because the things you need to use are so difficult to find (all materials I will advocate are natural materials that have been used for decades to build homes), it is just because they are not as frequently used anymore and have become harder to source.

General Construction:

• When designing your home, open floor plans with high ceilings and open spaces allow for better ventilation and air flow.
• Consider steel framing instead of wood. It costs more, but will cannot rot.
• Before you buy, inspect the building materials, hold them, smell them. Look for dampness as sometimes builders will leave materials out in the rain. If they smell bad, are damp, or just feel uncomfortable, try something else. If it bothers you to hold it for a few moments, it may become intolerable to live in over time. Most “builder grade” materials–plywood, drywall, particle board, contain formaldehyde, a known carcinogen. Thus, your body will help you identify things that are dangerous to your system. (Note: The Environmental Working Group is a great resource for non-toxic building supplies.)
• Avoid treated ANYTHING—wood, grout, etc. If a material has been treated, it is likely treated with chemicals. In addition, if mold starts growing on a treated material, chances are, that particular mold is one bad customer. For example, most drywall absorbs and maintains water. Mycotoxin-producing molds such as aspergillus, stachybotrys and penicillium are commonly found in water damaged homes.
• Avoid particle board at all costs for kitchen cabinets, counters, bathroom enclosures, and furniture. Particle board is made with harmful chemicals
• Specify exterior grade plywood EVERYWHERE in and on the home. Exterior grade is usually raw or contains less formaldehyde than interior grade plywood.
• Lead-free solder should be used for all electrical work. You want to avoid lead ANYWHERE in your home.
• Insulation is difficult, but you should stay away from foam and fiberglass. Try blown-in cellulose, or Airkrete (a non-toxic, mineral-based insulation that is 100% fireproof without the addition of flame retardants), or natural, bagged insulation.
• Plaster interior walls will be more serviceable, durable, sound-proof, and dust free (the less dust, the less mold and allergens) than drywall (the perfect food for mold once wet), but they do cost more.
• Roofing design should be such that there are drip edges and proper flashing at all points where water could enter the home via the roof. Do not skimp here. Think like a raindrop and trace your path as you hit the rooftop. Anywhere surfaces intersect on a roof is a prime spot for water seepage. These areas include the edges of skylights and chimneys, soil stacks, vent fans and roof valleys, as well as the intersection of the roof deck and dormer walls. The best material to use for flashing is galvanized metal. Avoid low-slope roof or flat roof designs and opt for pitched. A pitched roof has the benefit of gravity pulling water off of the house and allows for less accumulation in peaks and valleys.
• The roof needs to be vented along its peak through a roof ridge vent and around its edges at the soffits to allow the attic to breathe. You should feel a slight breeze blowing through a well-vented attic when the wind blows.
• Avoid building with a crawlspace, if possible. Slab construction tends to be best for IAQ integrity and mold issues. Basements must be built with concrete and partially or completely finished. Never put carpet in a basement. If this tells you anything over 80% of homes with indoor air quality issues are built on a crawlspace or basement. Of those with a basement, 95% of them had wall-to-wall carpet in the basement. Those are facts that you cannot ignore.
• When your home is plumbed, ask for easy access to the water main, so that you can shut the water off to your home when you leave town. Then, if there is a leak or a pipe bursts, your home is stable and not filling with water and mold while you are away.
• For air quality, a detached garage is best. If you want to have an attached garage, make sure it is properly sealed from the home, so that carbon monoxide is not pulled inside to the air you are breathing.
• After construction is complete and everything is caulked and painted, allow the house to air out for at least 3-4 weeks with all windows open and fans running. Most building materials off gas VOCs and other chemicals. Airing everything out will allow much of these pollutants to disperse before you move in. In addition, any pollutants will be less likely to adsorb into and onto the interior surfaces and furnishings, only to off gas later.

HVAC/Dehumidification/Air Filtration and Purification:

• Work with an experienced mechanical engineer to design the proper HVAC system and ductwork for your home. It is helpful if the HVAC expert is knowledgable about indoor air quality.  I ask if they understand the impact mold has on human health.  These professionals are hard to find, but those that emphasize IAQ will understand. I also ask if anyone in their family is allergic or sensitive to mold. You want to make sure they know your system is to include whole-house air filtration/purification that does not employ ozone, whole-house dehumidification units for all HVAC systems, optimal air flow and ventilation throughout the living space, no interior communication through air flow systems with a crawlspace, unconditioned attic, or unfinished basement, and ease of access to unit(s) for service, checking and filter changes.
• Do not employ in-slab ductwork or ventilation. (Read my post on this topic HERE.)
• Use smooth, metal ductwork throughout your home. Do not use fiberglass or flex duct with insulation. Metal is less likely to trap moisture and to grow mold. There should be no air flow obstruction where ductwork is bending or going around corners. You want your ductwork designed so that air has a clear path to the inside or to the outside.
• Ventilate any rooms with excess moisture to the outside, such as bathrooms and the kitchen. Do not vent ANY exhaust fans into the attic or garage. Make sure bathrooms fans are adequate for the size of the rooms. They have to be able to move the air efficiently to dry out the bathroom. Consider installing a timer switch on your bathroom exhaust fan to run for 30 minutes after your showers.
• Work with a local, experienced, vetted, licensed and insured HVAC company for system installation and maintenance. Here, again, this person or company should be IAQ knowledgeable.  Companies that deal with major brands (Trane, Lennox, etc.) will understand. You need a reliable company installing and servicing your system regularly, so that they can catch and fix problems early.
• Have emergency cut-off switches/alarms placed in the pans of HVAC units, water heaters, and dehumidification units. These will trip the shut-off switch if the pans start to fill with water. This will prevent a major leak and major water damage.
• Make sure that the furnace flue vents to the side of the home, away from wind, if possible.
• Prior to installation, have an HVAC contractor remove and replace the fiberglass panels that line the plenum of your HVAC (Heating, Ventilation and Air Conditioner) unit. These panels contain spun fiberglass, the fibers of which are carried in the air stream that passes through this chamber in the furnace. Have these replaced with non-fiber insulation, preferably placed on the outside of the unit, if insulation is still needed. (Note: Microscopic fiberglass chards penetrate the lungs and sinuses and create divots in the mucosal wall that can cause infection or mold accumulation.)
• Use only pleated, MERV 8 or higher, air filters in your furnace and change them frequently, ideally every one to two months. These filters capture airborne mold and particulates and lower the amount of dust in your home. If you allow them to get too full, though, they cannot do a proper job of filtering your air.
• Do not place HVAC units in an attached garage. This pulls air from the garage directly into your home. I probably don’t need to tell you why this is bad for your health, but gas and carbon monoxide from car exhaust should not enter the home.
• Make sure air ducts that run to a basement or crawlspace (if you have one) are tightly sealed. This avoids moist indoor air from leaking out in winter, which would allow moisture to condense on basement or crawl space walls, causing mold. If you do have a crawlspace, it needs to have a proper moisture/vapor barrier, and be cleaned and treated, so that it does not harbor mold. Basements and crawlspaces also need to be properly dehumidified.  Dusty dirt floors in crawlspace are critical to avoid.
• Do a good job of insulating any air ducts that run in your attic to avoid condensation and mold inside the ducts during hot summer days. Fiberglass should NOT be used.
• Seal all air openings to the attic from the conditioned living space below. This includes installing weather stripping around the attic hatch or stairs, and sealing around the chimney and pipes. (This prevents mold from forming in the attic and outer walls of your home, because if warm air enters a cold attic, it can cause snow to melt on the roof. Water will run down the roof and refreeze at the lower edges where the roof gets cold again over the overhangs and soffits. More melting snow then pools behind the ice, and the water gets under roofing shingles, dripping onto insulation in the attic and causing mold to grow. You see this as discoloration on your room ceilings and along the tops of your outer walls.)

The Outdoors–Landscaping/Grading/Water-Intrusion Prevention:

• Design adequate runoff schemes for rooftop rainwater. Doing so takes care of 90% of mold problems in a basement. This involves keeping gutters clear of debris and making sure downspouts are large enough and are in good working order. Make sure downspouts extend several feet away from the foundation, so that rainwater does not pool near the foundation. Check them regularly if you have many trees or leaves.
• Grade the earth that is around the house so that there is at least a 5-10-degree slope for rainwater to drain away, not towards, the foundation.
• If the ground around your house generally slopes toward your foundation on any side, install drain tile under the soil to carry excess rainwater away. Landscapers can install French drains that will collect water and divert it to wherever drainage is collected. It is neighborly to avoid drainage to the neighbors yards or home.  It just transfers or creates problems for them.
• Don’t let a sprinkler spray directly against the side of the house.
• Plant your flowerbeds and shrubs away from the house, so that regular watering does not cause water to pool against the house.
• Use ground cover rather than maintenance lawn to absorb water and runoff. Well placed and selected bushes and trees absorb water under the ground.

Interior Design:

• Introduce lots of natural light inside your home with plenty of windows. All windows should open to take advantage of natural ventilation. Even high, out-of-reach windows can be fitted with electric openers. Use energy-efficient, low maintenance windows, low-e casements are the best. Windows must be properly installed with mechanical flashing, low expansion and a weather resistant barrier.
• Avoid carpet altogether. Also, formaldehyde, used as a color fixative, and glues used in carpet backing can outgas for years, not just a few weeks after installation. In addition, carpet collects and traps pesticides, dirt, mold and bacteria, and is a breeding ground for mold, especially when the indoor humidity rises above 65%.
• Whenever possible, choose solid surface flooring and cover floors with area rugs that can be periodically shaken and aired out. Some solid flooring options are hardwood floors with a beeswax finish, ceramic and quarry tile, cork (cannot grow mold), stone and marble are also good. Avoid laminate and vinyl flooring, if possible.
• Avoid vinyl wall coverings and wallpaper. Both tend to harbor moisture and mold, not to mention that they require adhesives that can be very toxic.
• Use solid wood and water-based, acrylic finishes where needed.
• Use non-VOC paints. I recommend AFM Safecoat paints which are formulated specifically for chemically sensitive people. Miller Paints, Sherwin Williams Harmony, Benjamin Moore Natura, and YOLO Colorhouse, are also good.
• Whenever possible, only use natural fibers for upholstery, fabrics and rugs. Natural fibers generate beneficial negative ions, keeping you more alert and energized. Also, few natural fibers outgas. Nylon, plastics and synthetic materials emit harmful positive ions, which cause fatigue and chemical sensitvity.
• Avoid horizontal surfaces (shelves and cabinet tops), they collect dust. Use cabinets instead of shelves all the way to the ceiling—especially in the kitchen and bathrooms. (No particle board!)
• Employ built-in furniture as much as possible. Have everything finished before it is brought to the site to cut down on sawdust. Remember, any sawdust inside your home can get into ducts. Once in your ductwork, it will encounter moisture, which can lead to mold. Built-ins will also cut down on your furniture budget.
• Take this opportunity to scale back on knick-knacks and non-necessary items. Any clutter leads to dust accumulation. Dust accumulation can then lead to more allergens and mold.

Bells and Whistles (and other randomness):

• Purchase a top-loading, rather than a front-loading washing machine. Front loaders are notorious for mold and mildew. Your laundry room should also be properly ventilated, preferably with a supply and a return vent to help condition the space and speed the drying process for any wet or hung clothing. Dryers should always we vented to the outside to expel moist, hot air outside of your home.
• Install a whole-house water filtration system to filter out chlorine and chemicals from municipal water supplies. Whole-house filtration is superior, because our skin absorbs as much chlorine when we shower as if we drank an eight-ounce glass of tap water.
• Create an outbuilding or storage shed, totally separate from your home to store unused solvents (all of which contain volatile compounds) and or chemicals. (Note: Paints need to be stored in air conditioned space or it goes bad. But, this shouldn’t be a problem, because you are using zero-VOC paint.) Also, store any yard/lawn equipment there, or any other gas-containing equipment there. Only purchase as much as you need and safely discard the remainder rather than leaving it around.

Whew! Did you get all of that?

That is all I have for you—or all I can think of anyway. I am sure there is something I forgot, or a point I only just touched on that you would like to hear more about. If that is the case, please write to me at catherine@moldfreeliving.com. I love hearing from you.