A Quick Guide to Understanding Sealed Crawl Spaces

Sealed crawl space with moisturebarrier and insulation

Topics in This Article

Why would you seal a crawl space?

We’re entering spooky season; so let’s talk crawl spaces! An unhealthy crawl space can be a breeding ground for issues like moisture, humidity, mold, and high energy bills. If that list isn’t enough to scare you, crawl spaces can also be home to unwanted creepy crawlers and critters (we love opossums, but not enough for them to be living in our homes rent-free).

Today’s post will focus on benefits of conditioned crawls and strategies to achieve a healthy crawl space. If you’re looking for more info on vented crawls, stay tuned! Part 2 will be coming soon.

Should a crawl space be sealed?

Sealed crawl spaces create a much friendlier environment for you & your home. There are many benefits to having a sealed crawl space, especially in our humid North Carolina climate. These are are the top 3 benefits of a sealed crawl space:

  • Reduced energy consumption + costs
  • Healthier indoor air quality
  • Moisture Management

Reduced Energy Consumption + Costs

From an energy standpoint, since all your ducts are in a nice conditioned environment, rather than an unconditioned crawl space or attic, you’re getting a lot of benefit. If you have your ducts in an unconditioned space, they’re fighting the outdoor air temperature while trying to condition the air that’s going into a house, which causes your equipment to work harder.

Healthier Indoor Air Quality

Believe it or not, air entering the house can come up through the crawl space, so by managing the air quality in that space, you’re contributing to the indoor air quality inside the home.

Moisture Management

Moisture management is one of the number one issues we face in North Carolina. (More on moisture management in the humid southeast.) Sealing a crawl space offers the ideal strategy for starting at the ground up in managing humidity and the moisture coming through the ground to the building structure. Less moisture means less risk to the structure, which creates a much friendlier environment for your building structure.

Should I use a dehumidifier in my crawl space?
So long as you’ve thoroughly air sealed the crawl, are supplying adequate supply air and monitoring moisture levels an active dehumidification system shouldn’t be necessary. Should you see levels spike or have challenges with maintaining healthy humidity levels a dehumidification system might be something you’d want to explore.

All the right components work together to create a properly sealed crawl space

Here are the components to creating a properly sealed crawl space:

  • Moisture Barrier
  • Thermal Barrier
  • Drainage Strategy
  • Supply Conditioned Air

Moisture Barrier

By using a plastic sheathing that completely covers the ground and laps up the walls a bit, we can prevent moisture from coming up through the earth itself and making its way into your crawl and conditioned spaces.

Thermal Barrier

Adding insulation to the crawl space walls thermally isolates the conditioned crawl from the ambient environment

Drainage Strategy

By grading to the lowest point and adding a drain (like a French Drain), we can provide a drainage path for any water that gets in the crawlspace. This is a critical failsafe should a leak occur

Supply Conditioned Air

Adding conditioned air to the space regulates the temperature but more importantly, it creates positive pressure, which keeps vapor from coming in. Air and moisture want to move from high to low pressure so think of the space like an inflated balloon.

How will a sealed crawl space help with building programs and incentives?

Sealed crawl spaces are not a requirement in building programs like HERS, ecoSelect, and ENERGY STAR. However, the reduction in energy consumption from a sealed crawl space will positively affect building performance scores.

A HERS score will drop about 3 HERS points when changing a vented to a closed crawl in the average 2,000 sq ft home (assuming ductwork moves to a conditioned space).

Questions about your crawl space strategy?

As with most things in life, the devil is in the details — especially when it comes to crawl space encapsulation. Having a third-party energy rater inspect the installation and performance test the home helps ensure all the components are working as intended. 

If you’ve got a spooky crawl space or questions about your building strategy, don’t hesitate to reach out! Schedule a meeting with one of our building science specialists or fill out the form to get started.

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