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Should I Seal Off Crawl Space Vents or Keep Them Open?

There is an ongoing debate between homeowners and home builders on whether to seal crawl space vents. People who recommend you seal these vents state that it keeps moisture out. Others say that it keeps the moisture in. There are benefits to both, but what is the right answer?

In this article, we will answer your questions about sealing your crawl space vents. We will also let you know how you can seal your crawl space vents and encapsulate the space yourself.

The Issues with Crawl Space Vents

Crawl spaces are the unoccupied and unfinished areas underneath your home between the ground and the first floor. The purpose of a vent in this space is to allow outside air to circulate under the floor, which is vital in the summertime when the air is more humid. Underneath your home, moisture can build up and encourage mildew and rot. In the winter, the air is drier, and any pipes underneath your home may freeze.

Hot, humid air enters the crawl space in the summertime and creates condensation on cold surfaces such as pipes and ducts. This moisture can encourage the growth of mold. In the winter, the cold air may cause cold air under your feet, creating high energy bills. Air will then rise from underneath into your home, bringing with it mold spores and musty odors.

Venting does not solve the issue of mold because it does not get rid of the humidity. However, sealing the vents only seals the condensation and mold inside the crawl space.

Should You Seal Off Crawl Space Vents or Keep Them Open?

Neither venting nor sealing solves the problem if there is moisture in the crawl space. However, there is a solution: Eliminate all groundwater seepage, then seal off the vents.

We recommend sealing your vents after eliminating moisture for a few reasons:

  • It is much easier to deal with a closed environment than an open one. Venting means there are many more variables to deal with than if it was closed. Rain, snow, groundwater, or humidity could cause moisture issues in your crawl space. If you have these issues in a non-vented crawl space, there are fewer variables to consider.
  • You can manage humidity without using a vent. You can install an industrial-strength dehumidifier that will reduce the area’s humidity, thus preventing mold and mildew from growing. Household dehumidifiers will not suffice; they are too small and can only wring out a small amount of water. A powerful, energy-efficient dehumidifier will take care of any moisture that may happen after sealing your vents.

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How to Deal with Moisture Issues in Crawl Space Vents

Prevent Groundwater Seepage

Before you seal off your vents, you will want to remove moisture in your crawl space. Moisture often comes from groundwater seepage.

Groundwater seepage happens when there is an excessive amount of water in the ground near your basement floor, crawl space, or foundation wall. The pressure of this groundwater causes it to seep through small cracks in the foundation or floor. If this happens, it causes moisture buildup, leading to mold and mildew in the future.

Take the following measures to prevent seepage:

  • Ensure that your yard is sloped away from foundation walls
  • Ensure downspouts and sump pump discharge directs away from the residence
  • Install drain tile and a sump pump inside or outside of your foundation wall to relieve groundwater pressure
  • If you have a sump pump and drain tile to relieve groundwater foundation, check it regularly to ensure it is in working order

An efficient drainage system and the sump pump will work wonders to eliminate and prevent groundwater seepage. Once you have fixed water leakage and waterproofed the area, you can seal the vents. Make sure there are no leaks around the rim joist, sill plate, or cable penetrations.

Encapsulate the Crawl Space

Once you have removed the moisture from your crawl space, you can seal and encapsulate it. Encapsulating your crawl space means you are adding a lining to your crawl space to avoid leaks. Typically, you use a polyethylene barrier to cover floors, foundation walls, and ceiling.

You can encapsulate your crawl space yourself, but we recommend calling a professional to help. If you decide to encapsulate it yourself to prevent moisture issues, here are the steps you should take:

  1. Clean the area and measure foundation walls, floor, and other areas you will cover.
  2. Cut the barrier material into pieces to cover each wall. Cut them slightly bigger than you will need so you can overlap pieces.
  3. Add double-sided seal tape under the floor joists.
  4. Attach the barrier along the foundation walls, making sure there are no gaps.
  5. Attach the barrier along the floor, and make sure to overlap seams by several inches.
  6. Add additional tape if needed for an airtight seal.

Once finished encapsulating the space, install a high-efficiency dehumidifier to manage any moisture that may occur.


Professional contractors have training and equipment to remove moisture from crawl spaces and encapsulate them to prevent further damage.

You can seal your crawl space yourself. However, if you solicit professional help, you will know there is no trace of moisture left in the area.

Call an expert to seal your crawl space–call All Dry USA today! We’ll take a look at your space and take care of clearing seepage and encapsulating the crawl space for you.

Ben Suiskind
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