The Problem is Moisture - HousePro Home Improvement

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
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
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
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 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:
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 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
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
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:
Moisture + Organic Material = Mold and Bacteria Growth
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
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. 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
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
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.