How to Ventilate a Crawlspace

If you have a crawlspace under your home, it is a good idea to ventilate it. Though some controversy exists as to whether crawlspace ventilation is necessary, a crawlspace that is not ventilated and gets too moist or damp will cause mold and mildew to grow in the crawlspace. It's best to ventilate the crawlspace with outside air to protect against too much moisture.

Difficulty: Moderate

Instructions

Things You'll Need:

• Mechanical crawlspace ventilation system (ventilators and intake vents)

1. Make sure there are enough vents for the size of your crawlspace. Standard Building Code calls for 1 square foot of vented opening per 50 square feet of crawlspace area.

2. Draw outside air in with a power intake vent at one end of the crawlspace. Some powered intake vents have sensors which allow the unit to come on only when the air outside is less humid than the air inside the crawlspace.

3. Place a mechanical ventilator on the wall opposite the intake vents. Usually 1 ventilator for use with 2 intake vents is sufficient, though some suggest 3 to 4 intake vents are better (see Resources below).

4. Cover the ground of the crawlspace with polyethylene sheets to trap moisture and reduce humidity levels. This will decrease the need for constant ventilation of the crawlspace.

5. Take care to vent your crawlspace in carport wells and behind porches beneath which there is only earth, as these areas tend to be poorly ventilated. Air can get stagnant in these areas and cause wood rot.

Tips & Warnings

• In many cases, a ventilation system cannot keep up with moisture levels in a damp crawlspace if there is no polyethylene covering.
• Check crawlspace vents regularly to make sure they are opening and closing properly and replace those that are not.

Resources

• Order a crawlspace foundation ventilator here.
• Find out about crawlspace ventilation kits here.

[abasements]

on 11/5/2009 I would strongly suggest NOT ventilating you crawlspace. There are many reasons why, but one would be for the cold air entering the crawlspace in the winter. See http://basementsolutions.blogspot.com/2009/11/cold-floors-above-my-crawl-space.html for more details