Reward Insulated Concrete Forms as a Vapor Retarder
September 1st, 2009 | Lets Get Technical! | ICF Construction, Moisture research, Technical Data, Vapor, Vapor Barrier, Vapor Retarder
Reward iForm wall acts as a vapor retarder.
• Vapor retarders are used to prevent condensation within walls.
• Reward iForm with an inside finish of gypsum wallboard painted with latex paint is adequate to prevent condensation within walls for buildings in the continental U.S.
• Avoid the use of
> Low-permeance wall paper such as vinyl on the inside surface
> Low-permeance and unvented exterior finish materials on the outside surface
Vapor retarders (also called vapor barriers) are used to prevent, or more correctly greatly reduce, water vapor (moisture) from moving through building materials and condensing on cold surfaces within the wall. The rate of moisture flow through walls by vapor diffusion is called permeance and is measured in perms.
Water vapor permeance of building materials. The water vapor permeance of the Reward iForm wall system with 1/2-in. gypsum wallboard varies from 0.2 to 0.3 perms depending on the wall thickness. A material or system with a permeance of less than 1 perm is generally considered “nonbreathable” and a vapor retarder.
Materials such as cast-in-place concrete, polyethylene, and aluminum foil qualify as vapor retarders since they are low permeance materials when joints are properly sealed; whereas fiberglass insulation and unpainted gypsum wallboard do not. Building materials have water vapor permeances from very low to very high. Actual values for a given material vary depending on the moisture content of the material.
Two commonly used test methods are the water method (wet cup) and desiccant
method (dry cup) methods in ASTM E962. Specimens are sealed over the tops of
cups containing either water or desiccant, placed in a controlled atmosphere usually
at 50% relative humidity, and weight changes measured. The change in weight
represents the rate of moisture passing through the specimen.
Water Water Vapor Permeance for Selected Building Materials
Vapor retarder placement. The location of a vapor retarder within the wall is just as important as its permeance. A vapor retarder should prevent moist air from entering the wall but also allow moisture that gets into a wall to escape. Two vapor retarders within a wall, or a “double vapor retarder” should be avoided since this would not allow the moisture between the vapor retarders to dry.
Reward iForm with an inside finish of gypsum wallboard painted with latex paint is adequate to prevent condensation within walls for buildings in the continental U.S. The concrete acts as a vapor retarder and does not allow moisture to pass through the wall. In winter, the painted gypsum wallboard and concrete prevent moist indoor air from condensing within the wall. In summer, the concrete prevents humid outdoor air from passing through the wall to the cool air-conditioned side. The concrete is allowed to dry either to the inside or outside. The concrete and expanded polystyrene (EPS) insulation in the Reward iForm are not compromised by being moist, and the iForm has no cavities for moisture to collect.
Since the Reward iForm acts as a vapor retarder, low-permeance finishes that do not allow the wall to dry to the inside or outside surfaces should be avoided. For this reason, low-permeance materials on the inside surface such as vinyl wallpaper should be avoided. Low-permeance and unvented exterior finish materials should also be avoided. Masonry or brick veneer should be vented and/or have weep holes. Vinyl siding or other exterior finish materials should have a permeance greater than 1.0 perms.
Continuity. A vapor retarder must be continuous to be effective. The Reward iForm Wall System provides this continuity. Sheet materials such as polyethylene can act as a vapor retarder in a frame wall system, but all joints between sheets of material must be tightly sealed. The concrete in the Reward iForm is continuous around the
building and does not have these types of joints.
Buildings with high humidity. The above recommendations are for temperatures and relative humidity’s found in typical buildings: indoor relative humidities may be as high as 35% in winter and 80% in summer.6 Special recommendations provided by a building scientist or other design professional are recommended for other
conditions or where an indoor pool, hot tub, industrial processes, or other high humidity applications are present.
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Due to manufacturing processes, EPS thickness, EPS type and the uniqueness of the Reward iForm, this analysis, information and report is only to be used with Reward iForm and is not to be used with any other ICF system
Green Building
Reward ICFs with painted gypsum wallboard acts as a vapor retarder to prevent moisture from condensing on cool surfaces of a wall.
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important as its permeance. A vapor retarder should prevent moist air from entering
the wall but also allow moisture that gets into a wall to escape. Two vapor retarders
within a wall, or a “double vapor retarder” should be avoided since this would not
allow the moisture between the vapor retarders to dry.
Reward iForm with an inside finish of gypsum wallboard painted with latex paint is
adequate to prevent condensation within walls for buildings in the continental U.S.
The concrete acts as a vapor retarder and does not allow moisture to pass through
the wall. In winter, the painted gypsum wallboard and concrete prevent moist indoorVapor retarder placement. The location of a vapor retarder within the wall is just as important as its permeance. A vapor retarder should prevent moist air from entering
the wall but also allow moisture that gets into a wall to escape. Two vapor retarders within a wall, or a “double vapor retarder” should be avoided since this would not
allow the moisture between the vapor retarders to dry.
Reward iForm with an inside finish of gypsum wallboard painted with latex paint is adequate to prevent condensation within walls for buildings in the continental U.S.
The concrete acts as a vapor retarder and does not allow moisture to pass through the wall. In winter, the painted gypsum wallboard and concrete prevent moist indoor
