Appeal 4996

N1104.9.1 Vapor barriers

This appeal is to waive the requirement for a vapor barrier/retarder. The building code requirement is as follows:

Vapor barriers shall be installed on the warm side (in winter) of all insulation as specified in this subsection.

1. Exterior walls. The exterior walls of new buildings shall have a vapor barrier installed when thermal insulation is installed. The warm side vapor barrier shall have a 1-perm dry cup rating or less.

In addition, and relevant to the appeal, the 2003 and 2006 IECC have very limited language addressing vapor retarders. Both read the same.

It is Section 402.5 in the 2006 edition, which states "The building design shall not create conditions of accelerated deterioration from moisture condensation. Above-grade walls, floors and ceilings not ventilated to allow moisture to escape shall be provided with an approved vapor retarder. The vapor retarder shall be installed on the warm-in-winter side of the thermal insulation. Exceptions: 1. In construction where moisture or its freezing will not damage the materials. 2. Frame walls, floors and ceilings in jurisdictions in Zones 1 through 4. (Crawl space floor vapor retarders are not exempted.) and 3. Where other approved means to avoid condensation are provided.

This section was rewritten in the 2007 IECC Supplement, which will be incorporated into the 2009 IECC Code when published.

The IECC also has Section 103.1 which states "This code is not intended to prevent the use of any material, method of construction, design or insulating system not specifically prescribed herein, provided that such construction, design or insulating system has been approved by the code official as meeting the intent of this code and literature from the material manufacturer on the proper installation and use of their specific product can be persuasive in supporting such alternate method.

This is a bedroom addition to an existing home (see page 7 of the plans). The construction is being provided by Arciform (phone: 971-230-0045). The appeal concerns the vapor barrier requirement for the exterior walls of a new bedroom on the second floor. The exterior wall cavities have been completely filled with GreenFiber Cocoon spray-applied cellulose insulation. Cellulose is an excellent insulator, providing a high R-Value, completely filling the wall cavity, preventing air transfer, and having preferred environmental qualities. The exterior wall is otherwise typical, and the drywall will be painted with a VOC-free paint (PVA paint is not desired due to the effect on the cellulose insulation noted below, as well as the PVA paint’s toxicity).

The recommendation of GreenFiber and all other cellulose manufacturers is that cellulose insulation be installed without a vapor barrier/retarder. This recommendation has been made for at least 20 years. The overwhelming body of evidence reveals that vapor retarders may often be unnecessary with any insulation, and are certainly inappropriate for spray-applied cellulose insulation. (Please see attachments for manufacturer comments and studies).

From the manufacturer: “Because of its mass density (high airflow resistance) and hygroscopic properties (moisture holding), GreenFiber Cocoon Insulation has the capacity to store up to 30% of its weight in moisture vapor while retarding its passage by air movement. In other words, it retards the flow of moisture vapor, and performs best when moisture vapor is allowed to enter or exit from either side. The chance of any significant amount of moisture vapor actually passing completely through from one side of the insulation to the other is highly unlikely given the dynamics of our daily environment. Even if enough moisture vapor were present to freeze on the exterior sheathing, GreenFiber Insulation would absorb it again as it melted. Make no mistake, GreenFiber Insulation is not classified as a vapor retarder, since it cannot be tested by ASTM E96; the only recognized test method for classifying vapor retarders. On the other hand, GreenFiber Insulation does meet the criteria on an exception since it creates an alternative construction where moisture or its freezing will not damage the materials.“

The recommendations of this and other cellulose manufacturers is to not install a vapor retarder with cellulose insulation. In addition, historical and recent materials science prove that a vapor retarder is not needed with cellulose insulation.

From the manufacturer: “When applied within exterior walls, we do not recommend the use of a vapor retarder on the warm-in-winter side, primarily due to GreenFiber's mass density and hygroscopic properties. This application without a vapor retarder is considered an alternate method under the provisions of Section 106 of the 1999 National Building Code (NBC), relating specifically to Chapter 13 and Section 723.3.1 and additionally to Sections 101.2 and 103.1 of the International Energy Conservation Code.”
“According to the ASHRAE Handbook, page 23.8, the use of a vapor retarder at both exterior and interior locations is undesirable because it can restrict not only the entry of moisture into the insulation but the escape of any moisture as well. Section 1406.3.6 of the NVC requires a water-resistive barrier of 15-pound asphalt felt, which is classified as a vapor retarder (ASHRAE Handbook, page 24.17), to be attached to the sheathing behind the exterior wall veneer. This creates a technical problem between the requirements of building code and energy code. A vapor retarder on both sides of the exterior wall was determined to be one of the aggravating causes for EIFS system failures in North Carolina, Washington and Vancouver, B.C.”
“Additionally, since the intent of the energy code regarding the use of vapor retarders is to avoid creating "conditions of accelerated deterioration from moisture condensation", it would not be prudent to risk the possibility that moisture or water could become trapped within the wall by vapor retarders on both sides.”

The City of Portland Bureau of Development Services, in its publication The Plans Examiner, March 2007 (see attached or http://www.portlandonline.com/shared/cfm/image.cfm?id=149882 ), recognized the problem, stated that airflow is the primary concern, and stated that cellulose is an effective alternative:

“In recent years, further research and a more complete understanding of moisture and air dynamics in residential buildings has lead to additional effective moisture control strategies. Research has shown that water vapor diffusion driven by vapor pressure is not a major transport mechanism in Portland’s mild marine climate. That is because indoor vapor pressures are not very high for most of the year. Rather, air leakage is the primary way that water vapor is transported from indoor spaces into the structure.”
”This discovery means that stopping air leaks into the structure is more important than vapor retarders in preventing moisture damage.”
“Air tightness can be achieved in several ways. One is to seal leakage sites in the exterior envelope using caulks and sealants. For example, low-expansion foam is often used between the rough opening and window and door frames. Another effective method is to completely fill cavities with insulation so that air cannot travel into the cavity. This blocks moisture transport as well as convective loops that degrade insulation effectiveness. Spray-in foam, wet-spray cellulose, dense-pack cellulose and spray-in fiberglass are examples of insulation techniques that completely fill structural cavities.”

In addition to the above recommendations, the attached documents contain the results of many studies showing that countless numbers of homes with cellulose insulation and no vapor retarder have been found to contain no moisture problems.