Can Homeowners & Pros Prevent Mold?
Homeowners often wonder if mold can be entirely eliminated from their home. Sadly, the answer is no. Don’t panic, mold naturally occurs in every environment. Humans have evolved to coexist with small amounts of this tiny microbe. Many foods humans love, including cheese and soy sauce, contain mold. Antibiotics like penicillin, which transformed modern medicine, are derived from mold.

With good design, mold isn’t a problem in the home. However, when mold spores find favorable conditions for growing explosively, huge trouble develops. Although black and green colonies are the most prevalent colors, mold stains also come in grey/white, orange/yellow or even brown tints. No matter the color, high concentrations of mold cause allergic reactions and respiratory problems. Extreme exposure may lead to neurological issues and even death. Large colonies also degrade the building’s structure and finishes. Of course mold stains look bad too.

Why Does Mold Grow Explosively?
Like any living organism, mold needs the right conditions to grow including; food, moisture, favorable temperature and oxygen. Deny mold any one of these necessities and voila, no colony. Sounds easy right? Unfortunately humans also need oxygen and favorable temperatures (mold likes the same temps as us and more). So these items can’t easily be modified for mold reduction.

Which leaves food and moisture. A mold colony forms when organic building materials, including wood or wall paper (food), have consistently achieved a high water content (moisture). Luckily through careful design, either food or moisture can be reduced, providing great tools for fighting mold. Water can be minimized, coming from a variety of preventable sources as we’ll discuss below. Designers can also employ the right (as in low food content) material for the moisture conditions, which we’ll also discuss.

Detecting Mold
The EPA has no guidelines for healthy mold concentrations unlike radon, lead paint or asbestos. Perhaps because mold is a naturally occurring substance. Everyone has their own tolerance for mold. Swipe testing surfaces for spores isn’t common. Instead, if you can see mold stains in your home – you have a problem. Not sure the stain is mold? Then test a sample to verify your suspicions.

Sometimes colonies are hidden behind wall paper, paneling, carpet, cabinets or buried inside the wall/ceiling/floor behind drywall or tiles. Mold can also reside in ducts and vents. If you suspect mold because of smell, water damage or health issues. It’s time for exploration. Just be careful, don’t damage finishes that can’t easily be repaired. And don’t accidentally release massive quantities of spores into the air.

Removing Mold
With reasonable precautions homeowners can remove mold themselves. Although EPA remediation guidelines suggest large areas over 9 square feet may be too large for do-it-yourselfers.

On hard surfaces, thorough scrubbing will likely remove the mold. However, porous materials must be removed and discarded. Unfortunately, this includes grout, caulk, drywall, ceiling tiles, carpet and wallpaper. Once drywall or other porous materials are removed, be sure to scrub the underlying framing or surface to kill any remaining mold before placing new finishes. Some contractors also insist on sealing framing or sheathing with Kilz primer or other stain and smell reducing product before replacing finishes. Stained wood surfaces to be repainted should also be presealed.

Several cleaning solutions kill mold. The most popular are:
• Bleach – 1 cup per gallon of water
• Borax – 1 cup per gallon of water
• Ammonia – 50% per 50% water

Always wear safety equipment when removing mold:
• N-95 respirator
• Rubber gloves
• Safety goggles
• Your favorite long sleeve super hero costume

For large and dense areas of mold, consider plastic barricades to reduce air bourne mold spread and to reduce construction dust. Vacuums with HEPA (high-efficiency particulate arrestance) filters effectively clean mold from surfaces. They can be rented from Home Depot and other stores. But remember, mold won’t grow on every landing surface. Mold needs the right conditions. These steps are for reducing human contact and there’s no specific protocol as with asbestos. So don’t give into scare tactics when hiring the work out.

Mold Resistant Home Design
Removing mold means you’ve already lost – your home isn’t mold resistant. After remediation explore why your home encourages mold growth. Then fix the underlying problem, even if this means a lifestyle change or remodeling project. If you’re designing new, live and build wisely following a mold resistant philosophy. Then you’ll never need a respirator.

Buildwise’s Philosophy of Mold Resistant Design: The Crouton Theory
The best defense is adopting a holistic anti-mold philosophy when designing and living in your home . The basic mindset is simple. And it leads to a more healthy home, generally. We call it the Crouton Theory of mold resistance.

Treat your house like a dried crouton instead of a moist bread slice. Focus on keeping organic building materials dry. Ensure all assemblies and moisture laden rooms dry easily and quickly. Where moisture occurs naturally, use water/mold resistant materials. Sadly this simple philosophy is rarely translated effectively in the field. Following are key actions everyone should consider.

Below Ground
Perhaps the most prevalent places for mold growth are basements and crawl spaces. Which makes sense, they’re below ground and dirt holds moisture. When building new or remediating leaky basements:

• Install foundation drains around the perimeter and sometimes even on the inside (double drain system).
• Ensure your foundation walls are continuously damp-proofed all the way up to finish grade.
• A drain screen or layer of gravel backfill keeps moisture from entering the foundation wall by directing liquid to drains below.
• When using caissons, seal the void space with polyethylene sheets to keep water on exterior and draining into pipes.
• With spread footings slope the exterior footing for drainage with a grout topping before damp-proofing,
• In high water table areas consider no basement. If you must have a basement use a drain system that criss-crosses below the basement floor and drains to a sump pit. As a last resort ask a pro about waterproof details, which are very expensive and hard to achieve.
• Minimize moisture further by installing a vapor barrier under basement slabs. Crawl spaces should be treated like mini basements. Ensure there’s a vapor barrier above grade, with seams taped and edges mechanically fastened to foundation walls. Don’t vent directly to the exterior, which causes cold spots and condensation. Instead introduce warm house air as if it was living space. Insulate all basement and crawl space walls and rims. But don’t insulate the ceilings where heated living space is above.

Surface Drainage
Older homes rarely have moisture resistant construction below ground, so surface drainage becomes critical. But drainage is also important for new builds. Good surface drainage details include:

• Most soils engineers recommend a minimum slope of 12 inches of slope for the first 10 feet away from the foundation. Then a minimum 2 percent slope to an engineered drainage system, like a street curb.
• Back fill next to the house should be well compacted and water-resistant (but not fully water proof).
• Don’t plant anything within the first 5 feet. Don’t allow automatic sprinklers or supply lines within 5 feet or directed towards the house.
• Make sure the house has gutters. Downspouts should have 5 foot leaders draining onto splash blocks away from the house.
• Always extend foundation walls at least 6″ above grade and consider a stone or brick wainscot to protect walls from snow or splashing rain.

Avoid Flood Zones
Never buy or build in flood zones if it can be avoided. If you must, take precautions by building on stilts (piers) or above an open car port. If you already live in flood territory, buy flood insurance. After the big one hits, consider rebuilding somewhere else. Above all, don’t rebuild the way it was. At minimum make flood resistant changes.  Even if you’re only near a flood zone (especially on the coast), be prepared. Extreme weather events are getting more common, so expect flooding. Download the free Coastal Construction Manual from FEMA

Prepare For Hurricanes and Tornadoes
If you live in hurricane territory, make sure your home is ready for high winds and driving rain:

• Secure loose gutters and other exterior features.
• Reinforce your roof with tie down clips.
• Install reinforced windows/doors and shutters.
• Consider building a safe room or storm shelter. See the FEMA safe room site for more information.

Eliminate Leaks: Roof & Walls
Roofs and walls, also called the “exterior envelope” should be designed to keep water out. Unfortunately, too often designers don’t use the right details for the climate. Consider the following:

• Only install tried and true exterior finishes on roofs and walls. New fangled materials may look good, but they often perform poorly for keeping out water.
• Remember the substrate is important. This is your second line of defense against leaks. Always use lapped building paper on walls and approved underlayment below roofing.
• In high precipitation areas, install rain screens and other recommended details which create an air space behind siding, creating a drainage path for wind-driven rain.

• Generous overhangs (24″ or greater) with gutters really do protect the walls and minimize water leaks. Entry doors should be protected by a larger roof covering.
• Avoid flat roofs in wet climates. Even in dry climates, make sure flat roofs aren’t completely flat (ensure 1/4″ per 1 ft min. slope). In all climates, be wary of those McMansion style complicated roofs that slope into each other. Always install “cricket” roofs behind chimneys and flash copiously.
• Flashing is critical. Always flash at roof to wall connections, above openings, where decks meet walls and all horizontal material changes. Also good to flash behind ornamental features and above columns, trellises, etc. It’s hard to over flash, but easy to fall short.
• Trim above windows and door openings need to be flashed on top. But these openings also should be pre-wrapped or flashed with window tape and sill “pan” flashing before units are installed.
• Vertical joints between materials and at openings aren’t flashed, they’re caulked. Periodically check these joints since caulk degrades over time. Recaulk when the joint opens. Never rely on caulk for horizontal joints – these need to be flashed.
• Don’t have any flat horizontal surfaces on the exterior. Always slope parapets, wainscot caps, etc.
• Ensure all penetrations, for plumbing stacks, flues, etc. have the correct flashing cap termination.

• In cold climates install ice dam protection. These are self sealing sheets usually installed on the first three feet of your roof, starting at the fascia. The lowest part of your roof is most susceptible to ice damming, these sheets minimize leaking into attic through roofing nail holes. Well ventilated attics prevent against ice forming in the first place.

Monitor Home Air Pressure
Indoor air pressure is an issue most homeowners and pros ignore. But negative pressure effects moisture inside the home, by literally sucking water through tiny openings in the wall or roof. Deadly gasses can also be trapped, so it’s  good to avoid negative pressure with the following practices:

• Ensure all combustion appliances including furnace, boiler and water heater have makeup air or are hi-efficiency, sealed units. Ideally these units should be in heated rooms but sealed from living space.
• Keep fireplace dampers closed when not in use. When open a chimney stack effect can suck considerable air from the home. That air needs to be replaced somehow. When dampers are open consider opening a window.
• Operating kitchen hoods, clothes dryers and exhaust fans creates negative pressure. When in use consider opening a window.
• New highly sealed homes are at greater risk for negative air pressure than old leaky homes. With new homes, consider a central venting system – usually attached to your air conditioning ducts.
• Poorly designed HVAC systems can cause negative air pressure. Have your system inspected, ideally a neutral air pressure system is desired. Although some engineers like a slightly positive system.

Eliminate Leaks: Inside
Leaky plumbing and drainage of appliance condensation should always be monitored. If allowed unchecked, they provide a continuous source of warm moisture that mold loves. Regularly maintain the following:

• Check all supply valves, especially hidden inside vanities and other cabinets. Also check all traps and drains. Have all leaks repaired.
• Don’t forget to check the main water valve or exterior water shut-offs hidden behind access panels in the wall or ceiling.
• When building new, install “disaster pans” and drains below water heaters, boilers, dishwashers, washing machines and other water hungry appliances that can fail.
• Address backed up drains and sewer main quickly. If a drain or sewer presents a continuous problem, consider replacing.
• Toilets can leak at the supply valve, but also at the floor connection. The toilet connects to a drain pipe via a wax ring. If the toilet floor bolts loosen, a slight rocking can release water onto the floor and into the framing below. Eliminate movement by tightening bolts or replacing the wax ring. Some installations require two wax rings to achieve a good seal.

• Much smart home technology seems based on a solution looking for a problem. However, consider employing smart home technology for monitoring potential leaks by installing a wireless water sensor. Plug-in these little sensors near problem areas and receive warnings on your mobile phone when leaks are detected. These sensors provide a great first line of defense, especially for places not visible during daily activity. They’re also simple and painless to install. The D-Link sensor uses a home’s existing wifi network. Apple announced leak sensors will be added to its Home Kit accessories and smart home app.
• If you’re completely neurotic get a moisture meter and test surfaces for moisture. Then you’ll know for sure if leaks are present. And they’re easy to use. Amazon sells a few models for $20.00 or less.

Control Humidity
Surprisingly, mold only needs an inside air humidity above 50% to grow. Monitor humidity levels and take action if needed:

• Install exhaust fans in all bathrooms and other rooms generating high humidity.
• In naturally humid areas consider running air conditioning or dehumidifiers.
• Don’t install water features inside the home. Keep fountains outside and away from exterior walls.
• Don’t install hot tubs and pools inside the home without proper venting.
• Large aquariums should also be handled with care. Make sure they don’t leak and don’t increase humidity.

• Avoid condensation by eliminating “thermal bridges”. Single pane windows, slab floors with no exterior insulation at edges and metal frames that extend from outside to inside all create a bridge for the cold. These cold surfaces readily condense moisture in warm inside air during winter.
• Uninsulated ducts in attics cause a thermal bridge and condensation. If you have attic ducts, make sure they’re insulated. When building new avoid ducts in unheated space if possible. If not, insulate them well.
• Install a good vapor barrier. Most homes today have wood framed walls with insulation between studs. These walls are relatively inexpensive and energy-efficient. But they need a vapor barrier on the correct side to minimize condensation and excessive wetting during temperature extremes (think winter in cold climates and summer in warm areas). The trick is to place a vapor barrier on the warm humid side. Almost as critical is ensuring the wall easily dries. The current fad, using OSB and foam insulation for the exterior sheathing and a plastic vapor barrier on the inside, creates a sealed space ripe for mold. Tests show two coats of latex paint on drywall, with gaskets at switches, etc., create a great vapor barrier that also allows the wall to dry towards the interior.

Use Materials Wisely
We’re often surprised with how designers regularly violate basic mold resistant design rules by installing inappropriate materials for the given moisture conditions. Practical material use guidelines include:

• Don’t install layered finishes including paneling or wall paper in basements. This prevents walls from drying to the interior when moist. Older homes are especially prone to moist basement walls.
• Don’t use inside or delicate materials for outside applications. They won’t resist the weather and will leak or fall apart eventually.
• Use water-resistant finishes, including ceramic and stone tile in bathrooms where repeated wetting is likely. Buy a shower squeegee and use it. Beadboard wall paneling looks great in baths, but expect trapped water and mold behind.
• Make sure tile finishes have the appropriate substrate, like cement board. Ensure showers have a vinyl pan below floor tile. Remove opened or mold stained grout and caulk, then replace it. If mold appears to be rising from behind, investigate further. Your substrate may be incorrect and molding.
• Design floors near exterior doors for wet foot traffic. Carpet or wood in an entry, bathroom or mudroom soaks up water and can mold. Sorry, the recent fad of installing wood floors in kitchens, baths or laundry rooms is also a problem. Not only does wood rot and mold in these locations. Wood floors also warp when drying after a soaking.
• Keep  wood and composite siding away from dirt, leaves and plants. Don’t build up planter boxes next to the home. Don’t have planting strips between sidewalks and walls either. They trap moisture against the wall. Consider raising siding from the ground with a brick or stone wainscot, especially in areas with deep snow or splashing rain. If your foundation is too low and wood framing is near grade, install flashing behind the wainscot or siding. And consider Hardie Board or other cement based product.

During Construction
If your construction project gets soaked before “dry in” (a layer of underlayment on roof sheathing), make sure all framing and sheathing thoroughly dries before proceeding. Don’t underestimate the moisture added during water dependent construction, including floor slabs, toppings and sprayed water based insulation. Trapping unnecessary moisture behind finishes creates serious future problems. This moisture encourages mold, but also delaminates sheathing and wreaks havoc with finishes.

When in doubt, pull out the moisture meter to ensure products meet industry standard moisture contents before drywall is applied. For framing lumber 15%-19% moisture is usually considered acceptable. Plywood should be around 5% moisture content when delivered, but will rise a little after delivery and installation. Softwood for trim and cabinets should not exceed 7%-9% moisture. Hardwood for finishes should not exceed 6%-8% moisture.

Some hardwood flooring suppliers suggest maximum subfloor moisture should be 12%-13%. Their product should be within 2%-4% of the subfloor moisture for floating installations to prevent visible movement. Thankfully these moisture contents also minimize mold growth.

Images:
Moldy Window adapted from Duboix on Morgue File
Mold on Ceiling after Hurricane Katrina by Infrogmation
Crouton Salad adapted from Verygreen
House on Stilts by FEMA
Ice Dam by State Farm Insurance
Water Around Building by Andreas Lischka
Unused Entry by Liz West
Condensaiton by Lars Plougman
Bad Entry Floor by Donaleen
Spray Foam by Dunk Tank Technician