With Little Attention paid to Design - Crawlspaces Fail Over and Over Again

 

    How often does the average homeowner enter into their crawlspace?  If you answered never, you would be right more than 85 percent of the time.

     Crawlspaces are like the unnamed relative that no one talks about at the family reunion.  Crawlspaces just don’t get any respect. Crawlspaces are probably the most misunderstood and least visited area of a home.  At least the basement has a visitor and a casual inspection every once in a while.

     Nine out of ten of my clients state that they have never ventured into the crawlspace:  Out of sight, out of mind. But one of the most common building defects, and potentially the most destructive, is a vented crawlspace with uncontrolled moisture problems.

     The failure of the foundation walls to adequately keep out surface water is very common.  Brick and concrete block, or CMU, are not impermeable.  Additionally, homes that are located on a slope are also prone to hydrostatically-driven ground water intruding into the crawlspace.  Improper drainage of rain gutters and roof drains surrounding the building can greatly contribute to water moving through the foundation walls.

     Mechanically induced and passive pressure differentials can be the driving forces for transport of malodors, moisture, and mold-laden air from the crawlspace into the occupied spaces.  Tracer gas studies have well documented that crawlspaces do communicate with occupied spaces above.

 

State of Denial

     Everyone wants to ‘have a conversation” about this or that lately.  And the reason most of these conversations never take place is because one or more of the parties doesn’t want to face the facts.  The same holds true with the crawlspace design issue.  New homeowners don’t want to be told that their value engineering of the crawlspace design could potentially cost them much more in the future:  “We won’t be living down there so just do the minimal”.  General Contractors don’t want to be told that their brick and block foundations are open freeways for moisture to invade the building envelope.  The fact is that unsealed crawlspaces in conditioned homes have all of the necessary design ingredients for trouble.   An unsealed crawlspace is a prime science experiment on how buildings fail.

     In the not so distant past, when confronted with crawlspace moisture problems, most home builders would throw up their hands and recommend installing ventilation fans. They couldn’t be more wrong.

 

The Culprits

     One of the main driving forces behind moisture problems within vented crawlspaces is the lovely comfort provider we call the air conditioning system.  This mechanical system alone accounts for more than half of the thermal, pressure, and water vapor differentials that can wreak havoc in a vented crawlspace.  Before we had air-conditioning all of the crawlspaces were open and above grade, unless they had a basement.   With the widespread use of conditioned air we changed the construction to include walled and below grade crawlspaces, further compounding the problem. With the installation of the air conditioning system we can turn the wooden floor system into a condensation plane in the crawlspace.  Wood + Moisture + Time = Mold.  Mold is nature’s way of returning all of the suitable building materials back to the earth.  It’s the best recycler on the planet.

     If you’re air conditioning system happens to be located in the crawlspace, any breach in the vapor barrier of the duct wrap insulation can result in condensation on the duct work when the outdoor humidity levels are high.  This condensation is then wicked into the surrounding duct insulation until the R-value drops to zero and the ducts all sweat like a glass of ice tea on a hot Georgia afternoon.  This perpetual condensation machine ensures that you will have continuous moisture problems until that dynamic is changed.  These conditions increase your cooling costs and shorten the life expectancy of the equipment and duct work.

     Many air conditioning systems installed in unsealed, damp crawlspaces should be given combat pay for having to work in a hostile environment.

 

The Science

     Dr. Joseph Lstiburek of Building Science Corp. led the charge almost twenty years ago by challenging the conventional construction practice of building vented crawlspaces. His revolutionary thinking, supported by endless data, contends that crawlspaces should not be vented.  His data is defensible and his logic sound.

     We are short-sighted in our typical view of the building envelope.  Everyone would agree that the envelope consist of four walls and a roof.  I would argue that it has six sides.  The floor plane separating the crawlspace from the occupied space is the sixth side of the building envelop.  Does it not make sense to construct or protect this large surface area the same as we do the other five envelope planes?   Instead this plane is constructed of raw wood and frequently subjected to a rain forest environment.  Do the math; a 1,600 sq. ft. crawlspace actually has over 3,000 sq. ft. of raw wood (think high-grade mold food) exposed for the taking.

     Few building codes take into account the fact that a ventilated crawlspace creates a sixth plane of the building envelope.  Four walls, one roof, and now a floor plane that is not treated as the other five in regards to protection against liquid water, water vapor transmission, R-values, or permanency.

     Is it just me or do building codes seem to lag behind building science (and common sense) by at least 10 years?  The codes vary by state but generally require the vented crawlspace must have at least 1.0 sq. ft. of opening per 150 sq. ft. of floor space.  If you lay down a ground vapor barrier the requirement is for 1.0 sq. ft. opening per 1,500 sq. ft. of floor space.  The requirements do not address what to do with moisture that collects under the ground vapor barrier.  These requirements ignore the fact that lateral moisture intrusion through the foundation walls and entrainment of humid air condensing on cool surfaces are major sources of moisture in crawlspaces.

     Half of the crawlspace problems we encounter happen on paper before the first shovelful of dirt is moved at the construction site. Many, if not all, of these design faults are preventable if we apply common sense.  But it appears that common sense is not common.  Why do we keep building houses with crawlspaces that do not have effective moisture controls?

 

Dealing with Mold

     Mold in a crawlspace does not just magically appear.  It is a symptom of a failed system that is out of balance.  When I say system, let’s think back to how the house is designed and constructed.  A number of different systems (roof, wall, window system, etc.) all come together to form a secure barrier against the outdoor elements.  We like to control our environment, temperature, relative humidity (RH), indoor air quality, what we breathe, and ambient conditions to make the lives of humans, and our pets of course, safer and more comfortable. That’s the basic premise of living in a conditioned house.

     Microbial growth (mold) can occur on surfaces with a sustained level RH level of >70 percent in the air.  Many of the crawlspaces we analyze have continuous RH levels in excess of 90 percent.  With these high RH levels, the moisture content within the wooden floor joists and sub-flooring increases and the mold is off to the races.  Can we agree that we should not have mold growth on the inside of the building envelope? Then why do we accept designs and construction that do allow for mold growth inside the building envelope?

     Crawlspace encapsulation has really gained momentum in the last 10 years.  There are a number of novel and innovative practitioners throughout the U.S. and Canada who are developing new ways of dealing with crawlspaces.  Larry Janesky of Basement Systems, Inc. has done a very credible job of advancing the discussion and researching best practices in the retro-fit arena.  Sealing the crawlspace and concreting the floor is gaining in popularity as well.  The problem is that one size does not fit all in solving crawlspace problems.  There are many commonalties with problem crawlspaces, but a thorough evaluation must be made in order to permanently resolve the specific causative conditions on a site by site basis.

     Most compromised crawlspaces have moisture, mechanical, and mold problems.  Many contractors address only one or the other.  If the contractor is not technically capable of dealing with all three of these issues they should partner with other professionals to ensure the final product not only deals with the contaminants but permanently changes the causative factors.

     Permanent encapsulation of an existing crawlspace is a labor intensive process when performed properly.  The ultimate goals are to change the space from dynamic to static semi-conditioned environment where you can control moisture in liquid or vapor phase.

     Many of the band aids that we are seeing installed will not last 6 months much less 30 years.  Many of these practitioners have no understanding of the building dynamics that are occurring or the science behind proper crawlspace modification.  Changing the dynamics of the crawlspace and providing for a sure fix for the life of the house is the ultimate goal.  There are no silver bullets or magic wands to correct crawlspace deficiencies, just common sense solutions that provide permanent remedy to the design flaws addressing the driving forces behind crawlspace failures.

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Discussion Link

1. With our current understanding of the importance of moisture free crawlspaces doesn’t it make sense to properly control the foundation on which all of the other components of your house are built?

2. How do we engage those officials developing Building Codes to take a second look at the current code language?    

3. Should licensing be required for crawlspace modifications?

4. At what point do the mortgage lenders include crawlspace conditions in their loan approval process?

 

     Concerned with the conditions in your crawlspace?  The first data collection step is easy.  Purchase a small digital hygrometer (relative humidity meter) with a remote sensor.  Place the sensor in your crawlspace with the digital monitor on kitchen counter.  Monitor the Relative Humidity levels for 7-14 days, preferably in the warmer months.  If the levels hit 70% or greater you will want to investigate the issue further.

 

     While in the crawlspace did you see any evidence of moisture intrusion?  Did you see or smell any evidence of mold growth?  If so, you might want to join this conversation...

 

Symptoms inside the home may include:

• Scalloped or buckling floors

• Musty or malodors emanating from an undisclosed source

• Ill-fitting wooden doors and windows that stick

• Sagging floors

• Visible mold growth on the baseboards and flooring.

• Cracks inside the foundation

• Cracks on the interior/exterior walls

• Energy losses due to compromised insulation values

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