Continuous Perimeter Foundation Vents

The next innovation in crawl-space ventilation
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Sponsored by Joto-Vent System USA, Inc.
By Kathy Price-Robinson

Learning Objectives:

  1. Discuss moisture buildup in crawl spaces, the consequences of excess moisture, and how crawl-space ventilation protects the building and occupant health.
  2. Compare conventional foundation vent systems, their effectiveness, long-term performance, and health impact.
  3. Identify a new option/alternative for venting a foundation built over a crawl space.
  4. Define continuous foundation ventilation systems and their sustainable benefits.
  5. Describe several case studies of projects where continuous perimeter foundation vents were specified.

Credits:

1 AIA LU/HSW
1 AIBD P-CE
0.1 IACET CEU*
AAA 1 Structured Learning Hour
AANB 1 Hour of Core Learning
AAPEI 1 Structured Learning Hour
SAA 1 Hour of Core Learning
MAA 1 Structured Learning Hour
NSAA 1 Hour of Core Learning
OAA 1 Learning Hour
NLAA 1 Hour of Core Learning
NWTAA 1 Structured Learning Hour
 
This course can be self-reported to the AIBC, as per their CE Guidelines.
This course is approved as a Structured Course
Approved for structured learning
This course is approved as a core course
Approved for Core Learning
Course eligible for OAA Learning Hours
This course is approved as a Core Course
Course may qualify for Learning Hours with NWTAA
This course can be self-reported for Learning Units to the Architectural Institute of British Columbia

Every so often, a new way of building homes emerges that is so simple, so elegant, and yet so revolutionary that the mind can hardly grasp it.

Take the case of a continuous perimeter foundation vent system. This low-profile, honeycomb crawl-space venting system is placed between the concrete foundation wall and the wooden sill plate to provide passive airflow around and through the entire perimeter of the home’s crawl space. This eliminates the need for conventional vent boxes either in the concrete foundation or cut into the rim joist.

All images courtesy of Joto-Vent System USA, Inc.

The latest innovation in crawl-space ventilation provides continuous airflow with no dead air pockets in the crawl space, eliminating the need for unsightly and troublesome openings in the foundation wall or rim joist.

“I’ll never go back to cutting vent holes into rim joists and foundations,” says Takeshi Kaneo of TK Home Design and Build in Bellevue, Washington, who has used the perimeter venting system in two of his projects. “I wish I had known it was available in the United States sooner.”

Not only does this venting system provide continuous and foolproof venting into and out of the crawl space, but the thin 3/sup>⁄4-inch (20-millimeter) composite venting strips provide a capillary break between the concrete foundation wall and the wooden sill plate, eliminating the need for a pressure-treated wooden sill plate and preventing sill rot and sill breakdown from wicking moisture from the concrete foundation. Additionally, as a treated sill plate is not needed, neither is galvanized hardware.

The system has been used for more than four decades in Japan and is the most common crawl-space ventilation system used there.

Innovative Design and the Kobe Earthquake of 1995

Prior to the Kobe Earthquake in 1995—which measured 6.9 on the Richter scale, killed more than 6,000 people, and destroyed more than 400,000 buildings—many crawl spaces were vented in the conventional method using openings in the foundation wall, while others used the perimeter venting system. After the earthquake, some observers noted a difference in how each type of building fared.

“After inspecting the devastation, we found that homes using perimeter venting systems survived for two main reasons,” says Takashige Maebayashi, a Japanese-licensed architect and director of engineering and development for Joto USA. “The first reason is that the use of the continuous venting system doesn’t require cutting the foundation for crawl-space ventilation. Houses that used the conventional style methods naturally have weakened foundations and are more susceptible to damage. The second reason is that with the perimeter venting system the sill plate is separated from the foundation and so it won’t decompose, which aided in supporting a long-term structurally sound foundation.”

With every catastrophic disaster, building codes and practices tend to change. After the Kobe Earthquake in 1995 destroyed more than 400,000 buildings, the use of perimeter venting systems increased.

This house has a continuous perimeter vent system for crawl-space ventilation. The absence of vent holes in the foundation is a preferred aesthetic by some architects.

In the two decades following the Kobe Earthquake, adoption of the perimeter venting system has skyrocketed. One company alone has provided perimeter venting systems to more than 4.5 million new Japanese homes.

A Sleek Aesthetic

A final consideration is the sleek elegance of this venting system, allowing complete passive crawl-space ventilation with just a thin and nearly unnoticeable presence, and without the common—and some would say unsightly—large openings currently cut into foundations or rim joists every 8 feet or so to allow for airflow.

For architects, engineers, and builders in North America, however, while those holes cut into the foundation or rim joist ventilation may be ugly and even detrimental to the integrity of the foundation, the practice continues because “it’s the way things have always been done.”

Erik de Buhr, an owner and builder in Eugene, Oregon, and founder and co-executive director of a nonprofit that helps solve homelessness, sought out the new venting system as a solution to a design problem.

“While designing our house, I realized that our stem wall was going to be too short to use the standard plastic crawl-space vents,” he says, adding that he “wasn’t looking forward to using them anyway because, in my opinion, the vent boxes detract from the clean exterior look of the house and don’t do a very good job.”

So the questions arise: Is the conventional box venting method the only way to go? Is it the best way? Is there a better way? This course examines this innovative manner of passively venting a crawl space evenly and unobtrusively around the entire perimeter, and compares it with the traditional method of box vent openings to which most have become accustomed. Let the designer or builder be the judge.

We begin with why crawl space ventilation is so critically important.

How and Why Moisture Builds Up in Crawl Spaces

Providing ventilation under a raised foundation house is as old as the North American building trade itself. While some homes are built over basements, or more recently on grade-level concrete slabs, there are plenty of locations and soils and climates where separating the foundation of the home from the ground is the best design.

Consider raised homes built for centuries in the Northwest or Southeast of North America. Pilings set deep in the ground provide anchors for the raised foundation. While the temperature at the surface of the ground varies widely depending on season and climate, the temperature becomes less changeable and more moderate below the surface. This relatively warm below-surface ground temperature produces moisture, and this is the reason for the building practice of a raised foundation built up on a crawl space. While the soil below alternately gets wet, dries out, freezes, or unfreezes, the foundation raised above it remains unaffected. And with air flowing freely underneath the house, natural breezes carry away ground moisture. The raised design also allows easy access to plumbing, electrical, and mechanicals under the floor.

As building practices changed, the pilings on which the foundation sat became a reinforced and poured concrete foundation wall on which the foundation sat. To create the necessary airflow to keep moisture from accumulating, the code required holes in the foundation wall to allow air to freely move in and out of the crawl space. Screens or louvers were also required to prevent rodent intrusions.

Moisture in crawl spaces is a persistent problem. Moisture in the form of water can even enter a crawl space after construction through the vent holes.

 

[ Page 1 of 5 ]       
Originally published in Architectural Record

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