Cutting Edge Insights
with Dr. Lee

How your home can appear to ‘leak’ water

Last week, I discussed how your home (or building, or wall assembly of any structure) could actually leak water yet still be 100% airtight.  It comes down to the size of a water molecule in a vapor state versus the size of other elements suspended in space – what we call “air”.

And we know that water in a vapor state, a single molecule of H20, is infinitely smaller than liquid water – which consists of trillions of molecules of H20 connected together by virtue of the polarity of the molecule itself (The H2 end has a positive charge and is attracted to the negative charge of the O end of the molecule).

In building science, it is said that, “If you can’t build a structure that is resistant to bulk water, forget about trying to make it airtight.”  The premise is that no one ever received an emergency call at 2 A.M. about a house “leaking air”, although roof leaks would be considered a relatively common home emergency.

From that point forward, it follows that, “If you can’t build an airtight home, forget about trying to control vapor flow.”  In other words, airtightness helps control vapor.

And if you are successful in controlling bulk water, air, and vapor, you will find that controlling heat – “thermal drive”, if you will – really isn’t that difficult.

Back to water – there are other ways your wall assembly can “appear” to leak water without actually having a leak.

The biggest and most common way is condensation.  That is water undergoing a phase change from a vapor state to a liquid state.  It’s actually pretty common outdoors – that’s where “dew” comes from.

In your house, there are many activities that involve the production of water vapor – including but not limited to breathing, cooking, and bathing.  If there is a condensing surface – such as glass, or any surface at a lower temperature, the warm, moist air is chilled upon contact with that surface and loses its ability to hold water (warm air can hold more water than cooler air).   Water vapor in air then “condenses” to liquid state on the condensing surface.

Other important terms: 

  1. Relative humidity is a measure of the proportion of water vapor in air compared to the maximum amount that air at that temperature can hold.
  2. Dew point is the temperature at which the air would be 100% saturated with water vapor.  It usually represents a cooler temperature than the current ambient temperature, because rarely does the relative humidity remain 100%.  The dew point is dependent on atmospheric pressure as well.For the consummate “don’t you have something better to think about” discussion, look up “psychrometric chart”.{Yes, that’s the correct spelling. No, it doesn’t have anything to do with mental health.}
    Q:  How can I control water in my home, office, etc. so that I don’t get condensation?

    1.  Make sure you have good ventilation.  A very airtight home needs to have fresh air brought in from outside via a mechanical system known as an ERV (energy recovery ventilator) or HRV (heat recovery ventilator).  Of course, you could simply place a make-up air duct on your HVAC return, but there’s an energy penalty with doing so.Ventilation means more than bringing in fresh, outside air.  It also means discharge of interior air that is likely to be at a higher humidity level due to breathing, bathing, laundry, cooking, etc.

    2.  Make sure that your air conditioning doesn’t short cycle.  In other words, it needs to run long enough to remove humidity from the air (this is called latent cooling).  If it only runs a couple minutes until the thermostat set point is satisfied, you are not removing much humidity from the air.

  3. Make sure you don’t have hidden sources of humidity.  A hidden source can be a damp basement, where water has infiltrated over the years but it may not be visible in liquid form because it evaporates into the air.  Another common, hidden source is a crawl space.  A crawl space can have a dirt floor…Mother Earth is a terrible (or great, depending on how you look at it) source of moisture because the ground is usually wet.  A dirt floor needs to have a 100% sealed vapor barrier on top of it.  Also, crawl spaces in older homes are known to have vents to the outside.  These vents probably should be sealed off to prevent moist air from infiltrating.I say probably because I don’t know 1) how likely you are to have radon in the ground where you live and 2) whether you have an existing radon collection/exhaust system.  It’s more prevalent in some areas than others, and when you are building new, it’s very easy and inexpensive to make sure you exhaust any soil gases to the outside.  Remember, I give ideas, not advice, due to the many inherent unknowns.
    Q:  What does all this have to do with real estate investing?
    A: Regardless of whether you invest in existing real estate or in new construction, real estate is where we all live.  We all deserve to live in healthy homes with good indoor air quality.  Further, it’s helpful if we understand various factors that determine our indoor air quality.  If we invest in real estate, in essence we are building (or maintaining) real estate that others live in.  While it is possible that “others” in this sense may not be as sophisticated as we are and may not have the same high expectations with respect to indoor air quality and moisture control, it’s a fact that if we build in a robust manner, we can build (and/or maintain) structures that will stand the test of time and provide for the health of their occupants.

For a deeper dive on this topic, feel free to peruse my collection of videos on indoor air quality that were recorded at the beginning of the COVID-19 pandemic here:

For information on how building concepts such as humidity control and indoor air quality translate into a better return on real estate investment, download our eBook immediately below.

Until next time,

Dr. Lee Newton


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