Moisture brings durability and air quality problems with it, and myriad green products are designed to manage it and keep it out. Given the variety of products available, we look for those that meet key performance standards and that make sense in a whole building assembly—such as vapor-permeable weather-resistive barriers that not only prevent moisture from entering the building envelope but also allow drying when the envelope gets wet.
Delta-Dry is a stiff, egg-carton-textured, 5/16"-thick, vapor-impermeable housewrap made with 22-mil, virgin HDPE. When properly installed, the weather-resistive barrier creates a ventilated rainscreen, while blocking moisture migration through the wall assembly. Similarly, Delta-MS for subsurface use is an air-gap membrane constructed from 6 mm-thick HDPE, with a pattern of dimples molded into the surface. When installed, the membrane is held off the wall to allow any moisture in the concrete to migrate to the outer surface, condense on the inside surface of the membrane, and flow into the foundation drain. Because HDPE is impervious, soil moisture is unable to penetrate but will also flow to the foundation drain.
Foundation and slab drainage that improves drainage around foundations and slabs increases the durability of buildings by enabling water to drain from around the structure.
Installing foundation and slab drainage is relatively inexpensive to do during construction and impossible or at least expensive to do as a retrofit. It’s also usually required by codes. Proper drainage design is site-specific, taking into account the location of the water table, soil type, grades around the building, and other factors, and requires careful attention. One feature that is often not included, but that GreenSpec recommends, is an at-grade cleanout.
While many conventional drainage products can get the job done, GreenSpec lists drainage products offering reduced environmental impact, recycled content, or other unique performance properties.
Sheet waterproofing is usually made from rubberized asphalt, isobutylene-isoprene rubber, or EPDM. Products listed here are manufactured using alternative materials, such as the more environmentally benign HDPE.
Weather barriers are materials intended to resist air and moisture that has penetrated
the cladding system. Standards and building codes refer to materials that resist liquid water as either water- or weather-resistive barriers (WRB). When combined with flashings, WRBs are part of a system of bulk water resistance often called the concealed drainage plane.
Any rigid sheathing, sheathing membrane, or flexible sheet good that resists bulk water can be combined with flashings to create the concealed drainage plane, or weather WRB). WRBs are typically flexible sheet goods (often house wraps and building paper that come in wide rolls) whose sole or primary purpose is resisting bulk water. WRBs can also be fluid-applied designed for roller or spray gun application.
WRBs may also perform as a primary component of air barrier systems. The vapor permeability of WRBs varies considerably; many are formulated with relatively high vapor permeability to promote evaporative or diffusive drying to the exterior of the building assembly.
Flexible sheet products qualifying for GreenSpec comply with ASTM E2556-10, “Standard Specification for Vapor Permeable Flexible Sheet Water-Resistive Barriers Intended for Mechanical Attachment” Type II Minimum Performance Requirements and are neither gross cross woven nor perforated. Liquid applied products comply with AC 212, "Acceptance Criteria for Water-Resistive Coatings used as Water-Resistive Barriers over Exterior Sheathing."
Weather barrier products listed here contribute to durability and/or reduce the potential for indoor air quality problems associated with moisture and mold.
Note that the vapor permeability of materials designated as the weather barrier can vary widely and the desirability of low or high or no vapor permeability is always in the context of the primary direction of wetting, the primary direction of drying, and the vapor permeability of all the other components in the assembly.
Also note that terminology for materials meant to manage moisture in exterior building enclosures varies widely, even among specifiers and code officials. Master Format language is unclear for this section, using terms such as vapor, air infiltration, and thermal variation in language that can only be described as cryptic. GreenSpec uses the term weather barrier to mean the system of materials achieving a continuous manage of liquid moisture, the dedicated drainage plane interior to the building cladding, often referred to as the WRB.
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