How to Replace Foundation Vent Screens

Foundation vent screens provide summer ventilation under the house and protect against rodents and other animals. Inspect for damage annually and replace foundation vent screens as soon as possible to avoid intrusion by wild and feral animals. The method used for replacing a vent varies depending on the foundation and type of replacement vent.

Check the foundation vent screens in crawl spaces for damage at least annually. A mouse can squeeze through a 1/4-inch hole, while a rat only needs a hole the size of a quarter. Damaged or missing vents allow access for rodents, wildlife and feral cats.

Overgrown foundation plantings can conceal foundation vents and other openings. Trim shrubs and other plants to allow at least 12 inches between the foundation and foliage. This increases air circulation and improves access to the vents and foundation.

The basic foundation vent screen consists of a metal or ABS plastic frame with louvers and/or a screen to prevent rodents and other pests from accessing the crawl space. Some foundation vents feature movable louvers to close the vent in winter, while other models include a removable cover.

Some foundation vents include a built-in fan that pulls the air out of hard-to-vent crawl spaces. These types of vents must be plugged into a GFCI outlet to prevent accidental electrocution if the unit gets wet.

There are also foundation vents intended for fire prevention, which is an asset in the fire-prone Western states. These vents incorporate a honeycomb structure that closes when exposed to temperatures of 572 degrees Fahrenheit and above. This prevents flames and embers from entering the crawl space.

Measure the damaged screen and frame to ensure that the new vent will fit the space. While the standard size of a foundation vent hole is 8 x 16 inches, double-check the size and depth before purchasing replacement vents.

Put on safety goggles, a dust mask, and gloves before you begin removing the old vent. Removal varies according to the type of foundation and replacement vent. Some retrofit foundation vents are intended to fit inside the old frame. Cut out the damaged screen and then fit the new vent into the old frame and screw it into place.

When replacing the entire foundation vent, unscrew the old vent and replace it with the new vent. Tabs and screws will hold it securely in the hole. If mortared into the hole, use a heavy-duty flat chisel and hammer to chip out the mortar. Clean around the edges of the hole before mixing and applying a quick-setting mortar. Insert the new foundation vent and press it into place.

In cold climates, close the louvers or cover the foundation vents to keep freezing air out of the crawl space and to protect water pipes. While foil-faced insulation board cut to size and duct-taped over the vent may suffice, it's not very attractive. If the vents didn't come with a removable cover, consider painting rigid foam insulation board to match the foundation and gluing magnet strips around the inside edges of the board. Press the magnets against the metal frame to hold the cover in place.