How To Install a Crawl Space Vent Cover

If you have not already done so, now is a good time to install your crawlspace vent hole covers for winter. One of the surest causes of frozen water lines under your house is open crawlspace vent holes, also known as building vents. These are the rectangular holes spaced around the foundation of your home just below the siding. They allow outside air to enter and ventilate the crawlspace preventing the build-up of moisture under the house, which contributes to dry rot. Moisture, or condensate build-up, can also damage insulation.

In winter, if cold air enters the crawlspace, especially if the wind is blowing, it can lower the ambient air temperature to below freezing and your water lines will freeze and break.


Here are a number of ways to close up your crawlspace vent holes.

  1. If your crawlspace vent hole frames are plastic, insert Styrofoam vent blocks into the vents. They will fall out when the wind blows so secure them with duct tape or wedges.
  2. You can use bales of straw or hay to block the wind from entering the crawlspace. Then use the straw or hay as mulch on your garden or flowerbeds.
  3. You can also fill black plastic garbage bags with leaves and lawn clippings and block off the vents with them. Once again, you can use the contents of the bags as compost or mulch.
  4. If your vents are framed with wood, you can cut out rectangles of plywood measured to fit snugly and hold them in place over the vents with screws. Just anchor the screws in the wooden vent hole frames.
  5. In the absence of any of the above, you could also use black plastic and hold it in place over the vent holes with lathe strips nailed into the wooden frames.


The critical thing here is not so much what you use to close up those crawlspace vents as that you close them up tight. It is critical to block out all wind from your crawlspace to keep those water lines from freezing as much as possible. And don’t forget to insulate your water lines and use heat tape where possible and appropriate.

Following these tips and tricks will help insure that you spend a comfortable winter freed from worry about freeze-ups.

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