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Is Crawlspace Ventilation Required?

Those Screened Vents May Not Be Necessary

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Unvented Crawlspace

Unvented Crawlspace

Public Domain; U.S. Dep't of Energy
Even if you don't know what crawlspace ventilation is, you've probably seen those rectangular, screened vents along the side of foundation walls and wondered what they were about.

The International Residential Code (IRC), which "brings together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences," according to EnergyStar, has made changes regarding crawlspace ventilation.

In the past, crawlspaces were treated like spaces that did not belong to the house envelope. They were a not-interior, not-exterior space.

Some homeowners and builders like unvented crawlspaces because these exterior ventilation windows make it that much harder to heat and cool the house.

Unvented Crawlspace Requirements

But with IRC changes, crawlspace can be unvented; that is, in the traditional way of venting from the exterior. Now, you have the option of "unventing" a crawlspace by these two major points:
  1. Mechanically circulating air between the upper conditioned area and crawlspace; and
  2. Completely sealing up the crawlspace floor with vapor retarding material. This means lapping the edges of the vapor retarder up against the inner foundation walls and sealing up any seams between retarder sections.
Also, crawlspace walls must be insulated to appropriate R-values.

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