The Problems Caused By Dirt Crawl Spaces
Often moisture problems inside a building are caused by dirt crawl spaces. Buildings are
comprised of organic materials such as wood and filled with object made of wood and
cellulose. The moisture problem cause by a dirt crawl space results in moisture coming
from the exposed earth and the resulting moisture in the air. Therefore, mold which lives
in outdoor organic materials and requires moist cellulose and decaying organic materials
to live and reproduce becomes a HUGE problem. Ground Based Moisture
The exposed earth found in a dirt crawl space causes water vapor to form in the air. How
does this happen? The moist earth starts to dry and the water vapor moves upward into
the air. The air flow draws this moisture into different areas of the building. In most
regions of the country, you can never dry the earth because there is a wet season or rain
that permeates into the soil. Therefore, this results in a never ending stream of water
vapor invading your building.
Groundwater can also enter directly into a building. This can occur by flooding or
seeping in during a heavy rain. It can enter under the footing and between the footing and
walls. It can also enter directly through concrete block walls and through cracks in
poured concrete. After the water seeks in, it sits there and slowly turns into water vapor
which diffuses into the building areas.
Concrete block walls are very porous and do not have perfect mortar joints. They suck
water into them which creates a wet surface on the inside of crawl space walls. In
addition, damp air passes through concrete block walls. All of this just creates more
moisture going into the air and dissipating into the building at large.
Crawl spaces often have poor or no exterior footing drains and many times do not even
have waterproof exterior wall coatings. Sometimes, drains can be found inside crawl
spaces. These drains do not drain anything.
The water hardly ever touches any of the building parts. It is the water vapor that destroys
a building. This is called relative humidity and with high relative humidity a building can
be destroyed.
Air brings moisture with it wherever it goes. It can certainly get into the smallest of
spaces. When air is heated or cooled, the relative humidity level changes. Warm air holds
more moisture than cold air. The relative humidity of air goes down by 2/2% for every
degree we heat it and up by 2/2% for every degree we cool it.
Why do crawl spaces tend to be cool? Crawl spaces tend to be cool because the ground is
55 degrees year round as opposed to ground surface temperatures which change based on
the season and the location. When warm air is brought into a crawl space the air is cooled
and the relative humidity rises. As you know, a high relative humidity level brings with it
mold, decay, and attracts vermin.
The Problems of Venting Crawl Spaces
Venting crawl spaces does not solve the problem. Keep in mind that relative humidity
refers to the amount of moisture the air can hold at a given temperature. Let us take the
example of a hot summer day and this air entering the crawl space. If 84 degree air with
75% relative humidity enters the vents and the crawl space is 66 degrees with a wall
temperature of 62 degrees, then there will be a 48.4% increase in relative humidity. If at
84 degrees the air started out with 75% relative humidity and we now have to add 48.4 %
increase to the relative humidity, it is now at 123.4%. At over 100%, the air cannot hold
onto moisture anymore. What occurs is rain or condensation. 100% relative humidity is
the dew point-the point at which the air gives up its moisture and dew/rain/condensation
form.
If crawl space air was colder than crawl space surfaces, it would rain in the crawl space.
This is never the case. The surfaces of the crawl space are always colder because the
exterior water and dampness are always entering through these while warmer air is
coming in through the vents. Therefore, the crawl space air is always warmer.
When condensation occurs the dirt floor, ducts, and pipes get wet and drippy because
these are the colder surfaces. Insulation, joists, girders, wooden wall board and other
materials will get wet. The porous materials will soak up the moisture and mold will start
growing. This is the start of building destruction.
Why Do People Build Homes With Dirt Crawl Spaces?
The basic reason that homes are built with dirt crawl spaces is simply to save money. It
sure costs money to pour or slab a basement. Right out of the gate, a home built with a
dirt crawl space is completely dysfunctional and the deterioration and associated costs
start immediately. So if you want to buy a home that is going to start aggressively rotting
and deteriorating, this is the home for you. If one would never consider buying a home
with a dirt basement floor then one should never contemplate buying one with a dirt
crawlspace. Dirt is dirt and comes with a whole host of immediate problems. You would
never vent a basement so why would you vent a crawl space. However, in building with
dirt crawlspaces, they are often build with vents and seem to accept this as normal. It is
very far from normal.
Why Care If I Never Go Into My Crawlspace?
If the homeowner thinks it is nasty and awful down there and wants to avoid the dirt
crawlspace but doesn’t think anything really needs to be done about it, he or she is
wrong. If the homeowner cares about the heating bill, about rotting their home, mold and
its health problems, allergies, or huge costs to rebuild then something needs to be done to
fix the dirt crawl space. Paint does not last long, windows and doors stick, hardwood
floors buckle, and carpets get moldy in homes with this problem. If you do not want to
lose a LOT on your resale value, then you definitely care about fixing the crawl space
problem. It is absolutely unavoidable.
A home operates as one entity. This occurs due to air flow in a structure. The air in a
home permeates everywhere. The air moves through the home via the stack effect or
through the HVAC system. It is a fact that 1/3 to ½ of the air one breathes on the first
floor of living space came through the crawl space. This is also true of basements. Think
of it this way, if someone painted in the crawl space or basement, you would smell it
pretty soon wouldn’t you?
Take the example of radon gas. It has been known for years that the levels of radon gas
on the first floor of living space will be about 1/3 of the amount that was measured in the
basement or crawl space. Radon only comes from the ground therefore this demonstrates
how air moves in a house from bottom to top.
What is the stack effect? The stack effect is when warm air moves upwards in a house. In
the summer and winter, warm air rises because it is lighter that cold air. Eventually it
escapes from the upper levels of our home. It is not possible to create a total vacuum in
our homes, so when air escapes the upper levels of our homes, new air enters the house at
the lower levels, the crawl space and basement. Thus, the air your home takes in is
sucked from the ground or sub ground level. The false belief that air will flow in through
one vent and out the other vent is baloney. The air is sucked in through all the vents and
does not exit at all. It just flows upward into your home and eventually exits the upper
levels of the home. Venting never makes sense unless the outdoor air is 70 degree all year
long with a RH of 45%. Air can also come in through basement or crawl space holes,
joists in floor boards, duct chases and any tiny little openings.
Air Flow Through Ducts
Most crawl spaces have ducts. This is the main means of mixing all the air in the home.
Ducts can be made form sheet metal, or a combination of sheet metal, duct board, and
flex duct. Often air also escapes ducts at the joined sections.
Supply ducts blow the air that you pay to heat and cool the rooms in your home. As this
pressurized air passes the joint in the ducts, air leaks out. It is estimated that 2% of the air
leaks out at each joint. This causes the living spaces to be depressurized and the crawl
space to become more pressurized. This pushes the moldy air up faster than it would go
otherwise.
The return duct system takes air from the rooms being heated and cooled. These run
through the crawl space and when they leak they absorb bad basement or crawl space air
and blow it right back into the house.
One possible solution is to seal the ducts. This is done by applying duct mastic to every
joint in the duct system.
Mold
Mold is a large issue these days. People read about homes being torn down, lawsuits
being filed, and people getting sick. Mold eats dead organic matter and is one of the
natural systems that eliminate garbage and waste. Mold spores can remain dormant for
many years and when it gets wet; the mold becomes active and begins to devour the dead
material. Mold spores are everywhere and our clothes and home are all mold food. The
only factor that we can control is the humidity and moisture in our homes. Mold needs
70% relative humidity to grow. However, some types of mold can grow at much less
relative humidity.
One major allergen to many people is dust mites which live off shed skin flakes. These
critters live in you beds, carpet, and furniture. Dust mite droppings are tiny and float in
the air. These can cause allergies. They absorb water out of the air and require over 50%
relative humidity to live. By fixing the dirt crawl space/basement, the dust mites die off
and stop leaving droppings which cause allergies.
Termites, spiders, mice, and rats love damp crawl spaces and basements. These critters
bring diseases with them.
Fixing Groundwater Leakage
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Look for signs of leakage and pooling water
Look for waterlines, silt rings, or fine particles washed down to a low area.
Erosion points
How can this be dealt with? Install a sump pump. A hole must be put in then a sump liner
must be installed to keep the sump out of the mud, and to collect ground water form the
hole. The hole must be dug at the lowest level of the crawl space that is 22 inches deep
and as wide. The soil can be removed or spread around in the crawl space to fill other low
areas or crown the middle a bit. The crawl space floor should pitch down even slightly
towards the sump hole and not have the low levels where water can puddle before it gets
to the sump hole.
The sump liner next needs to be installed in the hole to keep the mud out and provide
proper housing to the pump. At times, a crawl space exists because there is a rock ledge
that could not be removed. Try to find the lowest spot where you can dig down far
enough.
A sump liner should be sturdy and have many holes to allow the water to enter and then
be pumped out. It also must have an airtight lid.
The sump pump itself should be a 1/3 HP cast iron pump with a mechanical float switch.
Pumps with pressure switches or ball on a wire switches should be avoided. A check
valve should be installed on the discharge line very close to the pump. The discharge pipe
should be 1 1 /2 pvc pipe and run to the exterior of the house.
The proper discharge line location should be where the water will continue to flow
downhill away from the property. You can always extend or move the sump discharge
location if the first location proves to be unsuitable.
The sump must have an alarm bell on it to tell you if the pump if not running for any
reason before the floor gets wet.
There also needs to be a floor drain with an airtight lid that lets water go down but
prevents damp air form coming up. If you do not need a sump in your crawl space, an
alarm should be installed on top of a plastic crawl space liner to alert you to a plumbing
leak.
In addition, the space between the sump liner and the hole must be filled with crushed
stone. This allows the water to flow from the dirt and through the sump holes to be
pumped out by the pump. A battery back up sump is also recommended. If the water rises
above the point where the primary pump should turn on for any reason including a power
outage, then the secondary system will automatically turn on the start pumping the water
out. With backup systems, there is an alarm that alerts you that the pump is running on
the backup system.
Another option is to dig a shallow trench at the perimeter to make the water flow to the
sump pump location. In more extreme cases, you can install a perforated pvc drainage
pipe and even add stone around it.
All downspouts should be extended well away from the foundation. Look for holes along
the foundation or a grade that pitches toward the foundation. These will need to be filled
in. Gutters should be kept clean also.
You can also run below grade pipes for the downspouts away from the house or direct the
water from each downspout to the surface but away from the foundation.
Isolating the House From the Earth
The solution must do the following:
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Stop water from flowing up form the soil.
Stop water vapor from flowing through or off the crawl space walls.
Allow water to drain from the walls to the sump location.
Allow water to drain from the floor to the sump location.
Not get ruined when someone crawls on it.
Be durable so it lasts as long as the house does.
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Be affordable
Concrete Floors
The concrete does not get ruined when someone stands on it. However, it must be
combined with ways to drain the walls and floors. Water vapor does go through concrete.
To stop water vapor form the floor, you have to lay down a vapor barrier of at least 6 mil
thick before pouring the concrete. Before putting down this vapor barrier a layer of clean
stone or gravel must be put down. Then the concrete can be laid.
The walls will need to be drained. Concrete block leaks readily. Plastic could be attached
to the walls but 6 mil plastic tears. A wire mesh can be attached to the wall over the
plastic and then a stucco coat of concrete can be added before the floor is poured.
Plastic Liners
The building codes typically allow the laying down of plastic liner to cut the venting
requirement by 90%. One great option for this is 20 mil polyester cord reinforced liner.
This product is called Clean Space. It is like a pool liner and can be fitted to your crawl
space to seal your home off from the earth. It is made of multiple layers of plastic with
different characteristics of flexibility and puncture and tear resistance. This combined
with 2 layers of polyester cord reinforcement means that this product is very durable and
the product is a white color. This creates a better visual environment.
Clean space is fastened to the upper part of the walls staying down 3 inches from the top
of the walls with fasteners along the top edge (permanently driven into holes in the
walls). The liner is then attached to the walls with fasteners along the top edge. It cannot
be pulled or town off.
The liner is sealed around obstructions and at seams by special tapes and sealants. The
top edge around the walls is sealed with urethane caulk. Rigid foal insulation board can
be installed on the crawl space walls under or over the liner if so desired.
Seal the Vents
They can be knocked out and mortared in or use exterior vent covers. Rigid pieces of
thick plastic will also work. Drill holes in the walls and screw or anchor into the
surrounding block around the vent using caulk and weather stripping to keep the outside
air out of the crawl space/basement.
A 2 inch thick foam block can be placed into the vent opening on the inside and caulked
in.
The crawl space will now start to dry out and should come to the same humidity level as
the upstairs.
Dehumidification
If you install a liner and do not seal the vents you will end up with condensation on top of
the liner or concrete in the summer. This is because the warmer air is touching the collar
liner surfaces. Air leaking in is the issue here. The vents need to be sealed. If the vents
have been sealed then you need to seal any other opening where air could be coming in.
This may be sill plates or opening around pipes etc. use whatever material will most
effectively do the job and last longest.
Concrete block cavities at the top of the walls which are not covered by the sill plate are
areas where outdoor air can enter. This space can be sealed using flash and caulking-you
can cover it with 1 x 4 treated wood and caulk it or fill it in with sprayed foam.
The stack effect causes air to be sucked into a home because the house sucks on the crawl
space. Now since you have sealed the ground, the crawl space can only get air from leaks
at the rim joists and sill plate region.
Air that gets sucked out of a crawl space is replaced by new air. To prevent this, you can
close up the paths that air can flow upstairs from the crawl space. The less air that gets
sucked upstairs, the less air that has to come into the house from outside. Be sure to seal
opening in the floor system above such as around ducts, wire and all other openings.
If you have sealed everything possible, and you are still getting condensation, then you
must use an effective dehumidifier.
Remember that dehumidifiers never work in vented or dirt crawl spaces since the
moisture is constantly. With a liner, you cam dry the crawlspace out. Mold is prevented,
growth is prevented, and as it is dry the mold and dust mites and eradicated. The air flow
rising from the lower levels is now dry air and helps to dry out the rest of the home.
If you wish to use a dehumidifier, it should be set up to drain automatically. Some of
these units can be ducted and do not have to be located in the space it is drying. It can be
installed in the crawl space or a room upstairs. The unit could be ducted so that it dries
the crawlspace and an upstairs room at the same time.
Dehumidifiers are very useful in transforming basements and crawl spaces. They can also
be added at any point in a project.
Furnaces and Water Heaters
If you have a furnace or water heater that requires air for combustion of oil or gas, air
may have to enter the crawl space for this purpose. This air, once it is used to burn the
fuel, goes up the chimney. If you create a vacuum in the crawl space because you sealed
it so tightly, then you will not have a draft to take exhaust gases up the chimney from the
furnace or water heater.
This section refers to appliances that are atmospherically vented-they take in air for
combustion. There is enough air in a basement even without vents that adequate
combustion air is not a problem. Normal air filtration in a building is considered adequate
by the building code for combustion air supply. However, a crawl space is smaller than a
basement and sealing it up tight is part of the plan to stop the moisture problem, then
there has to be a means for them to get air to have the proper draft all the time.
It is essential NOT to depressurize a space where combustion appliances are located.
One way of addressing this issue is to install 2 vents in the crawl space ceiling to the first
floor. The International Residential Code 2000 allows for installation of vents to
adjoining indoor spaces for combustion air.
A combustion air supply unit is one option. A fan unit is wired to the burner unit. When
the burner turns on, the fan blows in make up air and when the burner is off, a damper
closes to prevent outdoor air entry.
For new homes or when replacing your water heater or HVAC unit, you should use direct
vent appliances. Direct vent appliances are vented directly to the outside. Be sure to
always use a carbon monoxide alarm if you have combustion appliances or attached
garages.
Repair Costs
A solution involving concrete can cost about $9,000 on average and a solution involving
a liner about $5,300. However, the size of the space, how much drainage work needs to
be done, the sump pump installation, battery back up system, and dehumidification are
other items that can effect how a job is priced. Obviously, getting the problem fixed is
less costly than losing the value of your home to rot.
How Should I Condition the Crawl Space?
Why heat or cool a sealed crawl space since you do not live there? Because it is difficult
to 100% seal off every possible leak. If you want to semi-condition your crawl space your
former enemy duct leakage will now work for you. The average crawl space with ducts
has hundreds of cubic feet per minute of duct leakage. Heating and air conditioning will
keep the air dry. After you fix your crawl space, when your heat ducts leak, the air they
draw in is not full of moisture and mold spores. Duct leakage is another way to get
combustion air down into your crawl space. It is unlikely that your joints are sealed at all
points and therefore, this can provide some combustion air exchange.
It is essential that return duct leakage does not dominate. If a return duct has a large leak,
it is important to seal it so that it does not depressurize the space. This would cause the
crawls space to bring in bad outdoor air faster through tiny unsealed holes to the outside.
This could cause back drafting of any combustion appliances in the crawl space by
bringing make up air down the crawl space. No matter what the air in your crawl space is
flowing.
A fan also conditions the crawl space and brings upstairs air into the crawl space.
To get the air back upstairs, install several transfer grilles in the floor. However, if there
is any mold do not use this approach.
Another way is in line with the ASHRAE 62.2 ventilation standard, this is done by
installing a fan to exhaust the air to the outside and install 2+ transfer grills in the floor so
new conditioned air can enter the crawl space from upstairs.
The new ventilation standard states that fresh air must be added to the building envelope
at the rate of .01 cfm per square foot of the house and 7/5 cfm per occupant. The number
of occupants is defined as the number of bedrooms plus one. Therefore, a 2000 sq. ft.
home with three fans will need a 50 cfm fan.
Instead of adding an exhaust fan upstairs you can do it through the crawl space and get 2
things done at one-condition the crawl space and ventilate the house properly.
You can also dehumidify the crawl space. If there is significant mold, mold remediation
must be done.
Crawl Space Do Not Dos
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Do not put a vapor barrier or rigid insulation board on the ceiling of your crawl
space (unless home is on stilts).
Do not close vents without sealing the earth off.
Never use a fan to blow outside air into your crawl space.
Do not install a liner or concrete without removing organic material such as wood,
cardboard, insulation etc. from the dirt floor first.
Do not depressurize a space that has combustion appliances (over one Pascal).
Summary
In closing, it is essential to close off a dirt crawl space through concrete pouring or
sealing methods and to ensure that the air flow provides conditioned air to the crawl
space. By reading this article and addressing these points, a house can be saved from
rotting and the loss of investment capital associated with this.