Crawl Space Ventilation

Use of Crawl Space Vents, Vapor Barriers and Heat Will Eliminate Crawl Space Moisture Problems

By Mark J. Donovan

Crawl spaces are frequently dark, dank half cellars that are nothing more than breading grounds for mold, mildew and decay. I bought a small camp years ago that had a dirt floor crawl space. Crawling through it was a frightening experience on multiple levels. Between the critter remains that littered the floor of the crawl space, and the dripping insulation hanging from the floor joists, I could barely stomach 5 minutes crawling through it. Shortly after owing the camp, I wound up tearing it down and building a new one, partially due to the effects of a home that had lacked an adequate crawl space ventilation system.

Much of the subfloor was rotted out, and the home had a musty smell that I could not eliminate, all due to poor crawl space ventilation and moisture issues.

If you own a home with a crawl space, it is imperative that adequate crawl space ventilation be installed in it to prevent the situation that I ran into. Most crawl spaces have small crawl space vents installed in them, however they are usually inadequate. I have been in numerous crawl spaces that had crawl space vents installed that dripped of moisture.

Crawl space ventilation not only includes the installation of crawl space vents, but managing them properly. Crawl space vents should be left open during warm, moist periods of the year to allow high moisture levels in the crawl space to vent out. During cold, dry periods of the year the crawl space vents should be closed to prevent cold air from permeating the crawl space. This said, opening and closing crawl space ventilation systems even twice a year, is too much of a pain for many homeowners. A solution to this problem is the installation of powered crawl space vents.

Powered crawl space vents have small fans that can automatically turn on via a temperature/humidistat control sensor.

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Though powered crawl space vent systems offer an improved solution for crawl space ventilation, they do not eliminate the moisture issues in a crawl space altogether. The installation of a vapor retarder, a.k.a. vapor barrier, on the floor of the crawl space can dramatically reduce moisture levels in the crawl space.

When used in conjunction with a powered crawl space vent system you can produce a quality crawl space ventilation system that will protect your home from mold, mildew and rot.

An alternative to a crawl space ventilation system is to create an unventilated crawl space. The advantage of an unventilated crawl space is that the space can be used for storing items that are susceptible to cold or hot temperatures.

To create an unventilated crawl space, you need to install a vapor barrier on the floor, as well as insulation on the walls of the crawl space. Finally, you need to introduce some level of heat into the crawl space.

Crawl space venting

By introducing these three components into the crawl space, crawl space ventilation becomes unneeded. An unventilated crawl space is effectively employing the same functions/features that are implemented in a standard basement, and thus like a basement, ventilation becomes unnecessary. A basement has a vapor barrier installed under the basement slab, insulation in the floor joist bays that are adjacent to the outside walls, and a heating system. Combined these components make for a low moisture basement or crawl space without the need for venting.

For more help on Basement Additions, see’s Basement Remodeling Bid sheet. The Basement Remodeling Bid Sheet will help ensure that your hire the right contractor so that your basement remodeling project is done correctly and you get the project finished on time and budget.

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