Notice the floor joists. When I first examined the house there was so much air moving through the foundation, I thought the HVAC ducts were disconnected.
What happens if the interior grade is higher than the exterior grade?
It is almost impossible to install insulation in contact with the subfloor.
Indoor air quality is becoming a major issue in homes, schools, etc
What do you think the interior coils look like?
My monitor is located next to my coffee maker. Notice how clean the joists are.
Wet bulb is the temperature of evaporation. Dewpoint is the temperature of condensation. Saturation point is where dry bulb temperature = wet bulb temperature
Closed Conditioned Crawlspace Construction
Closed Crawlspace Construction
Services PowerPoint by Todd Witt
@ Synergy Airflow and Ventilation
For years, the building code incorrectly
required foundation vents. It assumed
that foundation vents bring in the
“good dry air” and let out the “bad
Crawlspace vents work fine in moderate,
dry climates. However, in the southeast,
warm, humid outside air enters through
vents, hits a cool interior surface, and
Thermostatically controlled foundation vents
open in warm weather when they should be
closed. Foundation vents should always be
closed, or better yet, eliminated.
Issues we witness in traditional vented
• High humidity resulting in condensation that leads to
moisture, mold, structural, and indoor air quality issues.
• Musty odors.
• Condensation or “sweating” on air conditioning ductwork and
equipment, insulation, water pipes, gas pipes, electrical wires,
• Buckled and cupping hardwood floors.
• Insect, termite, rodent, and animal problems.
• Spray foam installed in the underbelly.
• Improperly installed fiberglass batt insulation.
• Cold floors.
• Motorized foundation vents installed in an attempt to dry out
Condensation on wood framing promotes
“unidentifiable biological agent” growth due to
high moisture levels in the crawlspace. Wood
rot is caused by fungi that break down the
cellular structure of wood. Keep in mind that
wood decay known as dry rot will not occur
Could rusted gas lines be an issue? This
house was less than 6 months old, on a flat
lot that was properly graded and drained.
Notice the deteriorating wood flooring
Notice how water is “raining” from
this duct system in a vented
crawlspace. Notice the incomplete
If there are problems outside of
the ducts, what is going on inside
“Buckled” and “cupped” hardwood floors are
prevalent in vented crawlspaces. We witness
large amounts of money wasted in misguided
attempts to fix the symptoms instead of the
There is a lot of misinformation concerning why
hardwoods experience “buckling” and
“cupping”. Many companies sell and install
motorized foundation vents that greatly
increase moisture levels by pulling in hot, humid
air and wasting electricity.
Other “crawlspace experts” sell
products such as the Wave, EZ
Breathe, and Humidex that pull air
from your home into your
crawlspace and create multiple
issues and should be avoided. See
Improper bulk water management
is the leading cause of building
failure in the U.S. and it must be
Bulk moisture issues in
crawlspaces result from…
• Proper exterior grading is not provided.
• The interior grade of the crawlspace being much lower than
the exterior grade and as a result it “pools” water.
• There are no gutters installed.
• Proper interior and exterior drainage is not provided.
• HVAC condensate is not properly drained away from the
• Landscaping material such as mulch is built up around the
exterior of the foundation.
• Sprinkler systems direct water against the foundation.
• Exterior “damp-proofing” is not provided.
Note that this crawlspace has a
lower interior grade than the
A lower interior grade than the
exterior grade “pools” moisture.
When building your crawlspace..
• Always build up the interior grade several inches above the
• Drain the foundation to its lowest point.
• Consider “french drains” and sump pumps for added safetly.
• Add an additional row or two of concrete blocks.
• Install multiple crawlspace accesses.
• Install a “sacrificial layer of poly” during construction.
• Control bulk water entry during construction.
• Do not build up flower gardens around the foundation that
can hold moisture and slope them properly away from the
• Keep sprinklers from wetting the foundation.
• Use gutters and extend them from the foundation.
• Drain HVAC condensate away from the foundation. •19
Notice that the lack of gutters
directs water straight into the
This sidewalk was trapping water
from lack of gutters and directing it
into the foundation.
This homeowner paid us $30k to correct
the moisture issues caused by improper
grading and drainage. Get us involved
early in your construction project!
Money spent during construction on
gutters, proper grading, and french
drains can save thousands of dollars
later. It costs much more to fix later!
Interior footings and trenches
need to be backfilled so that they
do not collect water.
We routinely see traditional fiberglass
insulation installed in vented,
improperly built crawlspaces. It
becomes wet and serves as a medium
for “unidentified biological agents”.
Notice I didn’t say the “M” word.
Keep in mind that floor insulation doesn’t work
unless it is in complete contact with the sub-
flooring. Homeowners have spent millions of
dollars for a product that is not working. The
2009 IRC requires insulation to be in complete
contact with the floor system.
Installed improperly Moisture and gravity
Notice where the moisture had been
trapped by kraft-faced/paper backing on
the traditional fiberglass insulation. We
remove existing fiberglass insulation and
dispose of it.
Oftentimes we must clean the joist
with an anti-microbial agent and
wipe it down.
Spray foam insulation stays in complete
and constant contact with the subfloor but
it has the potential to trap moisture if
there is a water leak.
• I witnessed major vented crawlspace issues
growing up in the termite pretreatment and
• In 2003, I built one of the first, if not the first,
closed crawlspace construction homes in
• I knew almost immediately that this was the
way to build crawlspaces.
• You would be comfortable taking a sleeping
bag and spending the night in one of our
• Can you say that about your crawlspace? •30
A few of the lessons I learned…the
foam I installed in the block
deteriorated and I did not properly
air-seal and insulate my band joist.
Building scientists and building
codes now confirm that unvented,
sealed, conditioned crawlspaces
are the way to go!
• Contact us and we will confirm your specific
building department’s code requirements.
• A 2” to 3” termite viewing strip is required.
• Contact your termite company before
installing a closed crawlspace system.
• Note that several of the termite companies
that refuse to guarantee these systems
actually sell foundation vents in an attempt to
dry out the crawlspace.
We now leave the 3”-5”termite
viewing strip where the concrete
block meets the wood.
We use can foam or caulk to seal the small
gap between the concrete block and wood.
This meets building code requirements
and is accepted by termite control
companies. We will be happy to confirm
the details with your termite control
We recommend using a termite
bait system such as “Sentricon”
instead of a liquid applied termite
We use 10 mil black or white poly
as the vapor barrier. Keep in mind,
it is not a moisture barrier.
• Installing a 20 mil poly pool liner inside of your crawlspace
• It is overkill. Save the pool liners for pools.
• It is incredibly expensive.
• It does not pass code in new construction.
• It fails to air seal the rim joist/band joist where much of the
air leakage occurs.
• 10 mil poly works as well as a pool liner.
• We install 1 ½ - 2” of closed cell foam on your interior
foundation walls and rim joists/band joists for less money.
• That leaves you added money to spend on a home energy
audit that helps ensure your home is “Synergized”.
• There is rebate money available well as low interest rate
loans for existing construction.
Why we don’t recommend 20 mil pool
We are HVAC sizing and design
experts and we can show you…
• Creating a true air barrier and thermal barrier in the
underbelly of your subflooring is almost impossible.
• Moving your HVAC unit and ducts into the thermal
barrier such as a closed, conditioned crawlspace
greatly reduces your heating and cooling load.
• Moving your ducts inside the thermal envelope
eliminates the code required need to duct test and
reduces R8 duct insulation requirements.
• The advantages of all-electric heat pumps and why
atmospherically vented/B-vented gas appliances
cannot be located in your crawlspace. •39
• 50% of your home’s air originates in your crawlspace.
• This air is pulled in due to the “stack effect” –
conditioned air leaks out through ceiling
penetrations and is replaced by unconditioned air in
• The lack of fresh air ventilation multiplies the
• The lack of returns or jumper ducts in bedrooms
multiples the problem.
• Leaking ducts outside of the conditioned space
multiplies the problems.
• Encapsulating the attic with spray foam helps
eliminate the “stack effect”.
In new construction, we are required to
install supply ducts. The air helps
condition the crawlspace and keep it dry.
It also warms the floor in the wintertime
making it more comfortable.
We recommend a commercial grade
dehumidifier to help remove moisture that may
get into the crawlspace. These units require
Appliance grade dehumidifiers do
not work in crawlspaces.
Notice the height above of the ducts.
We see many homes with the supply
and especially the return ducts sitting
in standing water.
Well above grade! Sitting in water and mud!
Notice the multiple leaks around the ducts
from the package unit and how the
fiberglass is dirty from filtering the air
leakage. What do you think the interior
HVAC coil looks like?
Notice how the ductwork and
penetrations are completely sealed.
Unsealed penetrations are a common
entrance area for insects, spiders,
small animals, and snakes.
We routinely find leaking ducts.
Leaking supply and return ducts are
not as big of an issue when they occur
in an encapsulated, conditioned
crawlspace instead of outside the
We install hygrothermometers with remote
sensors that monitor the humidity and the
temperature in the crawlspace as well as the
home. Keep in mind that relative humidity tells
us how close the conditions are to saturation at
a specific temperature.
Hygrothermometers help us confirm..
• Whether HVAC systems are properly sized or
• When additional dehumidification needs to be
added or if there are issues with the
• High interior humidity issues that cause dust
mites and poor indoor air quality.
• If there are moisture issues such as water
leaks in the crawlspace.
• A “Synergy Home” with low humidity
and low moisture content controls dust
problems due to dust mites as well as
hardwood floor and carpet issues.
• Carpet and carpet pads are a main
contributor to dust mites and indoor air
• We recommend installing a central
Closed crawlspace construction and
proper HVAC design helps control
Radon. Notice the improperly
installed venting above, instead of
below, the ground cover.
We inspect numerous homes with
clothes dryers and exhaust fans
vented into the crawlspace.
We make sure construction debris
such as HVAC register cut-outs are
removed from the crawlspace and
not covered up in order to prevent
Properly installed sump pumps
with sump basins and french drains
are often necessary.
We have found that wrapping the
piers completely is unnecessary.
This is proper detailing of a pier.
As added safety, we recommend…
• Do not store combustion engines or toxic
substances in your crawlspace.
• Bi-yearly crawlspace inspections. Immediately
inspect anytime flooding occurs.
• Inform other trades not to disturb the ground
cover or spray foam.
• Strongly against using inexperienced
contractors that lack proper understanding of
building science principles for your closed
When it comes to crawlspaces….
“out of sight, is out of mind” for
most homeowners but these
problems don’t magically go away.
Most often, they get worse…much
What is going on inside of your
Contact Synergy Airflow and
Ventilation LLC for a free crawlspace
inspection and consultation.
Todd Witt (256) 616-2264
Office (256) 350-1779