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Employees
Mold in Sub-Floor Crawlspaces
There has been a lot of media attention recently to mold in homes, and with some degree
of justification. While it is true that mold is present practically everywhere, the type of
mold, the amount of mold, and the location of the mold is at issue. Mold is an important
part of our earth's ecosystem and plays an active role in the decomposition of materials.
This is a good thing in nature, but not such a good thing in the closed environment of a
home. New home construction is "tighter" than older construction and this is a two edged
sword. Tight construction results in energy savings, but also reduces the number of "air
exchanges" with the exterior, thus allowing a buildup of radon gas, toxic gasses from
construction material out-gassing, moisture, humidity, and you guessed it - mold.
If your house was built in the last 15 years or so, and if you are in a highly expansive soil area, you may have a structural floor systems in the basement, suspended over a
crawlspace. This construction method has been adopted to prevent the upheaval and
damage of concrete floors in basements. There is a definite structural benefit from this
type of construction, but along with that benefit comes an unintended liability - these
crawlspaces are perfect environments for mold growth. Why? Because for mold to grow
three elements must be present - moisture, food, and warmth. A sub-floor crawlspace
generally has all three - in abundance. Of these three elements, moisture is KING. The
"food" for mold growth is, unfortunately, your home! The warmth is there because of the
depth of the crawlspace below grade, and is generally around 60 degrees, which is plenty
warm for mold to grow. Since you cannot eliminate the "food" source, it becomes
obvious that controlling moisture is the key to preventing, or minimizing mold growth.
But wait a minute - the builder installed a ventilation system in your crawlspace, right?
And a perimeter drain system, right? This was supposed to keep down the humidity level
in the crawlspace, right? So you shouldn't have a problem with mold, right? Well, maybe
not - but don't be so sure. When was the last time you looked into your crawlspace
anyway? I thought so! Out of sight; out of mind!
I can't tell you how many times we have opened crawlspace access panels to be greeted
with a virtual swimming pool beneath the basement. This may sound extreme, but it is all
too common. Hopefully, this is not the case at your home, but you should check to make
sure. Obviously this extreme condition doesn't occur just because of deficient ventilation.
Many factors can create this condition, including: lack of a functional sump pump;
defective perimeter drain system; poor exterior drainage; groundwater; excavation into
bedrock; plumbing leaks; etc. In this scenario, mold is just one of your concerns. You
could also have, or could develop, structural damage as a result of these conditions.
More common is the case where the drain and/or sump pump ARE functioning properly,
the exterior drainage IS decent, there is NO groundwater or plumbing leakage, but there
is HIGH HUMIDITY in the crawlspace! Here is the case where the ventilation system is
not doing its job. Unfortunately, there are no strict design guideline for sub-floor
ventilation systems. Most builders install a single inlet vent and a single outlet
fan-powered vent, and expect this to be adequate. In fact, it may be adequate if the
crawlspace is small enough, if there is minimal ground moisture, and if the system is
installed in a manner that creates cross ventilation of the space. Very often however,
these conditions do not exist, and the ventilation system installed is just plain inadequate. If relative humidity exceeds 60%, you can bet there will be mold growth. A more
conservative threshold of acceptability is 50% - any more than that and the potential is
there for problems.
So what is the solution? Since moisture is King, eliminating the moisture sources is
crucial. Without moisture mold cannot grow, or survive. INCREASED VENTILATION
is the most important component for reducing humidity to prevent mold growth. For
basement sub-floor crawlspaces that exceed 800 square feet, we recommend TWO inlet
vents and TWO outlet fan powered vents. The vents should be placed as close as possible
to the basement corners and the inlets should be on opposite sides from the outlets, to
create cross ventilation. The fan vents should be on a de-humidistat set no higher than
40%.
If you have a sub-floor crawlspace, grab a high powered flashlight, open the access
panel(s) and look for the following (I also recommend wearing a dust mask, even if just
peeking in from the opening):
(A) If standing water is present, anywhere in the crawlspace, you need an engineering
inspection to determine the causes and effects of the water, along with plans for
remediation. Mold will certainly be an issue in this case.
(B) If the soil is damp to wet, but with no standing water, or if you see condensation on
the floor joists and/or foundation walls, you need increased ventilation and probable
attention to exterior drainage and/or landscape irrigation. Your perimeter drain system is
also suspect in this scenario. This condition should also be evaluated by an engineer, and
mold will also be an issue.
(C) If the air in the crawlspace feels or smells dank, there may be high enough humidity
to allow mold to grow and the ventilation system should be evaluated.
(D) If the ground is bone dry and the air feels dry and fresh, consider yourself lucky...
for the time being! Close the access panel and make a note in your daily planner to check
again in 3 months.
And what if mold is present? What should you do? As previously stated - that depends on
the type and quantity of mold, and where it is located. The dreaded "black mold" is of
greatest concern, but not all black mold is toxic. Short of testing, there is no way to tell if your black mold is toxic black mold. Fortunately, toxic black mold does not appear to be
all that common. But any mold can cause health concerns, even the non-toxic varieties,
so don't take its presence lightly. Mold can be killed, but if the moisture condition
that
gave rise to the mold is not corrected, it will be back. So, again, moisture is KING.
Tackle that problem first and then have the mold killed (as a minimum), or removed,
depending on the quantity and the location. If the mold is on wood, it can usually be
killed and removed without having to replace the wood, as long as the wood is still
structurally sound. Mold on drywall, carpeting, pads, or other porous surfaces, however,
usually requires replacement of those materials. It is strongly recommended to hire a professional restoration company for the job.
Remember, prevention is always easier (and less expensive) than remediation, and early
detection of a problem is always better than discovery after damage has occurred. So get
down there and check your crawlspace today, and every 3 months thereafter. If you have
any questions, please feel free to call me for a free phone consultation.
Michael D. Coyle, P.E.
(303)745-5209
www.coyle-inspect.com
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