The Problem is Moisture If you have excessive moisture in your crawl space, it’s coming from one of four sources: 1. Uncovered soil A properly installed vapor barrier is a critical factor in controlling moisture in a crawl space. Uncovered soil allows considerable moisture to evaporate, even if the soil appears to be dry on the surface. Open foundation vents and vapor barriers are intended to work in concert to allow your crawl to “breathe”. When the humidity drops outside the crawl at night, or in drier periods, moisture exits the crawl space through the open vents. If your soil is uncovered, it is constantly releasing moisture into the crawl, which negates the effect of the vents. Thus your crawl space stays humid, encouraging mold growth. 2. Rainwater intrusion Most homes we inspect have rainwater management issues. If water is not diverted away from the foundation of your home, it can sit against the foundation, and will eventually seep into the crawl space. In severe situations, standing water collects throughout the crawlspace. This is a serious condition that is renewed with every rainfall. We often see foundation walls like the photo to the right. At this home, rainwater collects in a large puddle against the outside of the foundation wall every time it rains. The water is passing through the blocks (foundation blocks are very porous), into the cavities, and falls to the bottom. The dark gray blocks in this photo are full of water. As the water seeps out of the lower blocks inside the crawl, it forms the standing water you see. If your foundation has below-grade vents, as pictured to the right, they must be installed properly, and maintained to prevent rainwater from spilling in. Inspect the grade around the vent wells (Those halfmoon shaped galvanized steel shields) to be sure that water runs away from the vent. Also, there should be at least 6 inches of small stones in the well below the bottom edge of the vent. This will provide a way for water to be absorbed into the soil during heavy rains, without spilling into the vent. The pictures shown here are of a foundation vent that was allowing more than 100 gallons of water to cascade in through the foundation vent with every rainstorm. 3. Plumbing leaks We routinely find minor leaks when inspecting a crawl space. These are sometimes in supply lines, but most often from drainage lines. The homeowner is usually unaware of these leaks because the ground absorbs the wetness which then slowly evaporates back into the crawl space air. Notice the water-soaked insulation in the photo at the right. There is so much moisture under this house that the insulation has become watersaturated. Eventually, this insulation will begin falling to the ground due to the weight of the water. 4. Humid air entering your foundation vents The original reason for venting crawl spaces was to provide air movement through the crawl space so that it could "breathe". Truth is that in many cases, the vents do little more than supply a constant source of additional moisture to your crawl space, particularly in the warmer months. Opening your windows after having your carpets cleaned is a good idea, but your crawl space is a very different place...it is cooler. In this area, a typical crawl space stays between 65° and 75°C in spring, summer, and fall. When hot moist air enters a cooler area, moisture condenses; here’s why: * * * RELATIVE HUMIDITY * * * The concept of "relative humidity" states that for every degree drop in temperature, relative humidity increases by about 2.5%. Let's do an example: If your crawlspace was at 70° and 80% humidity, and the outside air was at 90° and 90% humidity (typical for a mid-summer day in Greensboro or Winston Salem), then the outside air would cool 20 degrees upon entering a vent. This rapid cooling would increase the relative humidity by 50% (2.5 x 20). Add this to the 80% humidity already in the crawl, and we get 130%, which we know is not possible because water vapor condenses at 100%. When these very common conditions exist, moisture is condensing on surfaces in your crawl. This photo to the right is the A/C duct in close proximity to a crawl space vent on a hot summer day in Greensboro, North Carolina. This illustrates what we have just described, relative humidity, and what happens when the humidity goes to 100%. It was literally raining under this ductwork. Moisture is Harmful in Four Ways Excessive moisture in a crawl space can cause four problems: 1. Unhealthy air quality - mold spoors, pollen, bacteria Mold serves a critical role in our eco-system - it consumes dead organic materials and returns them into the cycle of life. Our problem is that mold is indiscriminant as to what organic material it consumes. All it requires is sufficient moisture, and it goes about its business with purpose. Mold and mildew thrive in moist dark environments...like your crawl space. Once a mold colony gets started, it will produce millions of spoors and release them into your crawl space air. * * * THE STACK EFFECT * * * The "stack effect" is a term used to describe the way air naturally rises through your home and out through vents in your roof. Much of this lost air is replaced by outside air coming in through your crawl space vents, then being drawn up into your home. In newer homes, the “stack effect” is minimal due to improved codes and building methods. In homes 30 or more years old, studies have shown that up to 50% of the air in the first floor has come from the crawl space. Like it or not, you are probably breathing air containing mold spoors, pollen, and who knows what else. Over time, breathing this air can be the cause of chronic allergies, respiratory problems, sinus and throat irritation, and more. 2. Energy loss - humid air is more costly to cool and heat A significant portion of the energy your home heating and cooling system consumes is spent removing moisture from the air. The reason is simple; dry air (45-55%) is more comfortable. The human body relies on evaporation to shed heat. In humid conditions, the body has to work harder to stay cool. That's the reason we prefer to avoid "hot and humid" and "cold and damp" environments. Crawl space vents provide a constantly renewing source of moisture and humidity that the stack effect draws up into our homes. This not only makes the HVAC system work harder, but can also cause cupping wood floors, peeling paint, musty odors, and more. 3. Insects and critters - and other things you'd rather not know about A dank dark dirt floor crawl space is the perfect environment to launch an unwanted mini ecosystem. First, moist wood is an insect magnet. Both ants and termites love it. Spiders like your crawl space because of all the other insects. Mice and rats also find the crawl to be a perfect home. Then of course, snakes and other critters often aren’t far behind. And they are all quite happy to live in your crawlspace. 4. Structure damage - replacing rotted structure is typically difficult and expensive Not all vented crawl spaces have mold. We have inspected homes 100+ years old that have vented dirt floor crawls, and found no trace of mold! There are so many variables in this situation that predicting the integrity and longevity of your crawl space can only be done through inspection by a trained and qualified technician. But, we do know for certain, that once mold starts to grow in your crawl space, it will continue to grow, and will eventually consume enough of your home's structure to cause serious damage. Structural repairs in your crawl space can easily run into the thousands of dollars. Both the problem and the solution are simple: THE PROBLEM: Moisture + Organic Material = Mold and Bacteria Growth THE SOLUTION: Permanently remove the moisture from your crawl space There are three steps to drying out your crawl space: 1. Stop moisture intrusion - through the foundation and through the vents. Correcting rainwater management issues is typically easy and inexpensive. Often times this is simply a matter of creating a "reverse grade" that slopes away from your foundation, and re-directing downspouts. Of course, your gutter system has to be clear and in good working order. And about those vents...seal them tight, once and for all. We install 2” foam board panels in each foundation vent, and seal them in place with spray foam insulation. We also seal the rim band around the entire interior of your foundation. This provides a permanent barrier for moist air and insects. 2. Install a permanent vapor barrier on the floor, the walls, and the columns. There are a number of excellent crawl space vapor barriers available today. They have been engineered and manufactured to provide a permanent moisture barrier that isolates your home from the earth and the environment. We use a true 18mil polyethylene liner on the floor, walls, and columns. The liner is sealed against the foundation, and all seams are taped with 4” waterproof tape. Our liner is warranted for 25 years. 3. Dry the air and the structure - mold can't survive below 60% humidity. There are two ways this can be accomplished, and each has its own merits. Option 1: Condition the Air Conditioning your crawl space means treating it as if it were a basement. This is accomplished simply by adding one or more supply and return vents in your crawl, so that your system includes the crawl space air with the air in the rest of your home. Most HVAC systems can easily handle the additional square footage of your crawl because the encapsulation process significantly lightens the system load by reducing moisture in both the crawl, and your home. Option 2: Install a Dehumidifier We use Oscar Air Dri-Crawl Space™ dehumidifiers in all our encapsulation projects requiring a dedicated dehumidifier. They have been specifically designed to withstand the rigors a crawl space environment demands, and are simply the best quality units on the market. The advantage with installing a proper dehumidifier is that 5-15 days after the encapsulation is completed, your crawl space will be below 60% humidity, and it is R.I.P. Mold...case closed. FAQs & Myths "I have a plastic liner on the floor now. Isn't this good enough"? In a typical 1200 square foot crawl space, anywhere from 10 - 24 gallons of water can be evaporating from the soil every day. Having a plastic vapor barrier on top of the dirt floor caps off most of this moisture, and is required by code. The problem with just having a vapor barrier is you still have moisture entering through your foundation vents, your foundation walls, and any seams in your plastic sheeting, which often results in humidity levels well above 65%. “How important is the thickness of the liner”? To serve permanent duty in a crawl space, the liner should be at least 14 mils thick, and have string reinforcement to prevent tearing. The encapsulation industry is only 8-9 years old, so it is anyone’s guess how long a liner will actually last. Most liners have a 25 year warranty, and it is likely they will last far longer than that. One thing to be aware of when selecting liner thickness, is how it is measured. One of the biggest players in the industry claims a liner thickness of 20 mils, but that is measured on top of the strings. The actual thickness of their material (the plastic in between the strings) is only 14-16 mils. If you are paying extra for thicker material, find out how it’s measured. "Should I remove my floor joist insulation"? If your floor joist insulation is damaged by moisture, it should be removed as it has likely lost most of its insulating value. If it is still in good condition, it can and should stay in place. "Should I insulate my foundation walls"? If you are encapsulating your crawl, insulating your foundation walls is a good option, but only in one of two situations: 1. Your floor joist insulation has been damaged by moisture or mold, and needs removal. 2. You have no insulation in your crawl space. We use 2" rigid foam-board insulation on foundation walls. This type of insulation is relatively impervious to water and insects. After the liner is installed over this, your crawl space temperature is primarily maintained by the earth, which is a relatively constant 68°F, year round. Cold floors are history. "Which is better - conditioning the air or dehumidification"? Because both methods will get the job done, each crawl space must be evaluated individually, along with the owner's preferences. The most important considerations are: 1. Will there be floor joist insulation in the "ceiling" of your crawl space? If you have floor joist insulation, and you condition the crawl with your home's HVAC, you can inadvertently create a "refrigerator" under your home. If the temperature in your crawl is 10°F cooler that the living area, relative humidity can increase by 25%, which might be enough to stimulate mold growth. Conditioning the crawl generally requires the removal of the floor joist insulation, and the installation of foam board insulation on the walls. 2. Conditioned air requires no maintenance in the crawl. A dehumidifier does, although not much. 3. A dehumidifier will absolutely dry your crawl space to safe levels. Conditioning will sometimes fall short, especially when the HVAC system is either under-sized, or inefficient. 4. Installing supply and return ducts typically costs $400-500. A good quality crawl space dehumidifier will cost $1,200 or more. "Do I need a drainage system and sump"? Some of my competitors will try to sell you this component, whether you need it or not. In reality, unless your home is on wet-lands, on the down-side of a sloping terrain, or on a lake front, you probably just need to properly manage your rainwater, even if you now have standing water in your crawl. Again, each situation is unique, so get the advice of a professional before deciding. "Can I just close the vents and install a dehumidifier"? Yes. This will definitely lower the humidity level in your crawl space, but...because moisture will continue to enter your crawl through the "closed" vents, as well as through your porous foundation walls, your dehumidifier may run continuously, and likely burn out in the first year. Whether or not the dehumidifier you installed will pull the moisture down below the 60% threshold is questionable at best. Sorry, but you are rolling the dice on this one. "Should I use a fan blowing out one of the vents to help pull the moisture out of my crawl space"? No! If the humidity is very low outside, this might reduce the moisture in your crawl. But, if the humidity and/or outside temperature is higher than your crawl space, you could actually be adding to the moisture already there.