This is What’s Happening in Your Crawlspace

Dirty Crawlspace

As it warms up outside and the air gets more humid, you might already be shoving the blankets and coats to the back of your closet. It’s springtime! You’re thinking about sunny days, Easter egg hunts with the kids, and trips to the pool.

The last thing you’re probably thinking about is your crawlspace. But you probably should be.

Why be concerned about your crawlspace? Because spring is when things start changing down there. And they’re not changing for the better.

They’re changing for the worse.

Here in metro Atlanta, the heat and humidity arrive in late March and early April. Then they stick around until October. If you’ve got a typical crawlspace – vents on the sides, dirt floor, air ducts and plumbing all over the place – it’s at least as humid down there as it is outdoors.

That’s a problem for 4 different reasons:

  1. Humid conditions can create moldy conditions. High relative humidity (RH) combined with stagnant air can quickly lead to mold growth on floor joists. And when mold starts growing in your crawlspace, it can be hard to get rid of – especially since it just grows back every year when it gets humid!
  2. Musty crawlspace air can migrate into your home. Due to duct leakage, your HVAC system might be pulling musty, mold-laden air from your crawlspace into your home. That dirty air also enters your living space through gaps and cracks in your flooring (think plumbing, electrical, and ductwork penetrations).
  3. Moisture makes fiberglass insulation sag and fall down. Ever wonder why the fiberglass batts under your floor always fall down? Yes, sometimes it’s due to gravity. Unless they’re well-secured between the floor joists (they often aren’t!), they’ll fall down. But humidity can make them fall, too. Moisture in the air saturates the batts, causing them to collapse under their own weight. So much for insulated floors!
  4. Insects love warm, moist environments. If you like roaches, spiders, and camel crickets, head down to your crawlspace this spring. You might see several of them. Oh, and the moist wood in crawlspaces is also hospitable to – you guessed it! – termites.

Crawlspaces cause so many problems, it’s a wonder so many homes were ever built with them. They’re basically uninsulated, dirt-floor basements with open windows.

And spring is when they really start getting nasty.

So, what can you do about it?

Great question. There are lots of products and methodologies for improving a humid crawlspace and mitigating the issues caused by excess moisture. Some are more effective than others.

For example, some people just put a vapor barrier on the crawlspace floor. Doing so prevents humidity from migrating into the crawlspace from the wet earth. It probably helps, but it doesn’t do anything about humid air coming in through the vents. How do you deal with that?

Other people lay a vapor barrier and seal the vents and put in a dehumidifier. That’s better, but it doesn’t do anything about air leakage from the joist bays. Or, for that matter, from the concrete walls. Those tend to soak up moisture from the surrounding earth all through the year.

This “solution” could also make the dehumidifier work overtime and run up your energy bills.

The best solution: crawlspace encapsulation

There’s just one almost foolproof way to fix all your crawlspace problems. Encapsulation! It’s a process that essentially transforms your crawlspace into a dry, insulated basement.

Here are the steps involved in a proper crawlspace encapsulation:

  1. Remove water from your crawlspace. And keep it out! Before making any big changes under your house, you’ll need to rid the area of standing water and mitigate any outstanding drainage issues.
  2. Remediate the mold. A good first step is to remove mold from floor joists and clean any air ducts that might have mold in them. Otherwise, you could end up sealing mold inside the crawlspace!
  3. Test for radon. While the vapor barrier you’re about to install helps prevent radon gas from entering your crawlspace, encapsulation can sometimes trap radon within the area when the gas is present. If you’ve got high levels of radon in your crawlspace, you’ll need to install a remediation system in conjunction with encapsulation.
  4. Install a vapor barrier. The best approach is to use a 12 or 20 mil plastic vapor barrier and install it all across the crawlspace floor, walls, and support piers. It should be sealed at the edges to prevent humidity from creeping over the sides.
  5. Seal the crawlspace vents. Yep! You’ve got to make it as if the vents were never there. That way, humid air can’t circulate so easily.
  6. Insulate the walls and joist bays. This is a good way to regulate temperature fluctuation in the crawlspace and save on energy bills. Since the walls are insulated, you can also remove those old fiberglass batts from the floor cavities.
  7. Seal all floor penetrations. With the fiberglass batts out of the way, it’s easy to find all the places where ductwork, wires, and pipes penetrate the floor. Then you can seal the gaps with canned foam.
  8. Dehumidify the space. How do you keep your crawlspace dry after doing all this work? A crawlspace dehumidifier. These energy efficient units can keep your crawlspace at 50-60% RH all year. That way, it’s practically impossible for mold to grow down there.

The result? No stinky, musty air. Better indoor air quality. Fewer allergy problems. More efficient HVAC. Lower energy bills. Fewer giant cockroaches.

What about my furnace? Doesn’t it need combustion air?

Yes. If you have a standard efficiency (80%) furnace, it needs to be in a vented space for proper combustion. What can you do if you want to encapsulate?

There are two options:

  1. Upgrade to a high efficiency furnace. These units have dedicated piping for combustion air, so they don’t require ventilation in order to operate.
  2. Install combustion dampers as part of the encapsulation. These can be configured to operate in conjunction with the combustion process. You get the ventilation you need to run the furnace in winter while minimizing air infiltration of the crawlspace.

Yes, your crawlspace really can be clean and dry.

Encapsulation works! It keeps crawlspace air out of your home and mitigates the negative effects of humidity beneath your home. Encapsulation can also extend the life of your HVAC system by improving efficiency and reducing microbial growth on the indoor coil.

Oh, and it might even increase your the value of your home. Many homebuyers love the idea of a clean, dry, problem-free crawlspace – especially if they had a yucky one in the past.

If you’re grossed out by what’s happening in your crawlspace right now or you’re wondering why your allergies seem so bad even though you’re indoors, well… crawlspace encapsulation might be the answer.

Rather not go down there and see? Don’t worry. That’s what we’re here for.

Image Credit: Shister