Do You Need A Solution to Your Wet, Damp, Vented Crawlspace?

Share This Post:
Do You Need A Solution to Your Wet, Damp, Vented Crawlspace?

Are you tired of living above the mold & mildew farm under your home?

Is it making you sick and tired?

Atlanta’s vented crawlspaces are wreaking havoc with homeowners struggling to control high levels of humidity inside their homes.

Today, in fact – I supervised the installation of closed cell foam insulation on the foundation walls of a 4500 ft2 crawlspace that has been “closed-up”, (encapsulated)  by two separate companies, simply because “it wasn’t done right in the first place”.


Here’s the kind of calls I receive almost on a daily basis…

 > Bob, we can smell the crawlspace. An “earthy” smell. (“Earthy smell” can mean wood rot, organism activity, or more. It’s associated with dampness, an enemy to your home).

> We hear noises in our air ducts, and/or see small tufts or balls of fiberglass insulation being blown into our vent covers. (Rodents have chewed into the flex ducts or duct board, and are contaminating your air ducts).

> There’s standing water in my crawlspace.

> “I see splotches of a white powdery substance on my joists. I see black mold in places under the house.

> Bob, there’s mildew growing in my closet. And my shoes have mildew inside of them…

> Etc, Etc, Etc.

Everything I’ve mentioned above relates to poor Indoor Air Quality, (IAQ). Assuming that your home has central HVAC systems to control the indoor comfort, I will offer my suggestions for how to combat these issues.

  1. First of all, you need a “Whole House” approach. Hire a $500 Home Performance consultant before you start shelling out money (lots of money) on expensive upgrades and equipment.

  2. In the crawlspace, as I see it, you have two basic options to effectively lower the moisture being drawn upward into your living spaces:

    a. Seal and insulate the subfloor with closed cell foam insulation. This is quick, and lot’s more affordable than option b. Although, it doesn’t bring any improvement to your HVAC system in the crawlspace. Closed Cell foam insulation has three properties that you benefit from:

    1. It’s a THERMAL barrier!

    2. It’s an AIR barrier!

    3. It’s a MOISTURE barrier!

Therefore, you benefit because now your floors are NO LONGER NEGATIVELY INFLUENCED by the humid, damp, unhealthy (cold in winter) uncontrolled conditions in your vented crawlspace; but instead are positively influenced by the dryer, controlled conditions in your living space.

When choosing option a, I offer my clients the opportunity to have their unprotected air duct system sealed and insulated with closed-cell foam insulation.

And, it goes without saying, you want to remove the old fiberglass floor insulation before applying the foam insulation.

            b. Your second option for the crawlspace is to encapsulate it, and apply closed-cell foam insulation to the foundation walls if your HVAC system is under the house. Be sure to address any bulk-water intrusion (with french drains, etc) first! If you have a gas furnace and/or water heater under your house, there are special considerations that must be made. If you aren’t understanding these health & safety issues, it’s more reason to hire a Home Performance Consultant as your guide!

I’ve written extensively about the steps involved with a crawlspace encapsulation, so I won’t repeat it here.

Dealing with your crawlspace will go a very long way toward resolving high levels of indoor RH.

But, you can still have issues! If your AC system is not dialed-in just right, I’ve found some homes to continue to have stubbornly high RH during Atlanta’s mild-temperature early-fall and spring days. Those days where our AC doesn’t run enough, because it’s so mild outdoors.

This is more prevalent for homes with foam insulation in the subfloor, than the encapsulated crawlspace clients. Because, the encapsulated crawlspace home has a dedicated, stand-alone dehumidifier protecting the crawlspace from elevated levels of RH, which positively influences the living space. I know… I live in a house with exactly this system!

Not Quite Finished Yet… the AMAZING Whole House Dehumidifier

     3. If we’ve performed option A or B in the crawlspace, and the house continues to have stubborn levels of higher RH, we recommend a whole-house dehumidifier, (WHD). These are wonderful machines! Attached to your main HVAC system, they maintain and control the humidity for the entire area of your house that is served by your air duct system.

The machine we recommend, by Aprilaire, samples the air 5 minutes every hour. When it detects RH in the air ducts higher than your setpoint, it signals the fan in your furnace to come on, and begins drying the living-space air moving through your ducts. When it detects dryer air that matches your setpoint, it shuts off the fan blower, and resumes the sampling schedule. Because it utilizes the fan in your furnace, and is attached to your airducts, it’s removing moisture from the entire area served by your hvac system!

There is one thing you need to know about the WHD… the dryer air it produces is distributed through your duct system. This air is a few degrees warmer than the ambient air. Therefore, in summer months when the AC is not operating, but your WHD is operating, you may feel a very small amount of warm airflow from your vents. Once explained, I’ve never had a client complain.

The Awkward Relationship Between Temperature & Humidity 

In a recent class, I was taught that 83% of Atlanta’s summer temperatures are below 85%. Our lack of comfort inside our homes stems more from uncomfortably high RH inside our living spaces, rather than from high temperatures. So I ask… why are the HVAC guys always recommending larger systems? Is the lack of comfort our homeowners currently experience connected more to the high RH inside the home?

I have found that keeping my indoor RH between 45-50% means that I don’t need my temperature so cool. Air that is dryer than 45% leads to static electricity, dry lips, etc. Higher than 50% and I’m needing my AC to run more and more to feel the cool airflow across my skin.

Supersize it?

One last word about sizing your AC. If your system is sized too large for your home, it may not run enough to remove the moisture from the air. In other words, it comes on, blasts the house with cold air, and shuts off. If your home is reasonably insulated and air tight, it may be awhile before your thermostat calls for more AC.

But as the humidity keeps increasing, you’re getting mildew in your closets, behind furniture, and elsewhere… and complain that you’re not cool enough in your home.

Not being a licensed HVAC contractor, I’m careful with my words. But I have read and been taught that your AC system needs to run at least 20 minutes before it effectively begins removing moisture from your home. So part of the answer lies in proper equipment sizing for our homes.

Like I always say, your home is a system, and all of these systems are connected and influence the effectiveness of each piece, like a modern car.

If you’re living on top of a vented crawlspace, this is a great place to get started toward a home with safer, healthier Indoor Air Quality!

You might also enjoy...

Get Started Here

Get an Instant Quote!

Use our EZ esimate calculators to generate your estimate in an instant. Simply fill out your information, answer a few questions, and an email with an estimate will arrive in your inbox! Choose below between an attic insulation, or bonus room insulation estimate and get started.