Is the DELTA®-VENT SA Air Barrier or ZIP System® Sheathing Better for Energy-Efficient, Green Construction?
Many of today’s building codes have been updated to better promote airtight construction because that conserves energy and reduces carbon emissions. Architects and builders can choose from a variety of sheathing and air barrier options that meet or surpass these more demanding 21st-century codes.
ZIP System® wall sheathing and DELTA®-VENT SA high-performing water-resistive air barrier are two future-proof systems available to designers and contractors. ZIP System® features a wood-based sheathing combined with an air- and water-resistive overlay. ZIP sheathing features resin-impregnated kraft paper bonded to an oriented strand board (OSB) structural panel.
DELTA®-VENT SA is a flexible three-ply membrane, rather than a rigid structural panel. It is a vapor permeable, water-resistive air barrier that’s popular in green building.
ZIP System® Sheathing problems
Compared to DELTA®-VENT SA, ZIP System® sheathing problems extend to a number of areas, which we’ll cover in more detail:
- Fastener issues
- Taping challenges
- Joint spacing requirements
- Air infiltration resistance
- Water resistance
DELTA®-VENT SA features a super-durable triple layer design. The top and bottom layers consist of tough, spun-bonded polypropylene that is exceptionally tear-resistant. It also resists the deleterious effects of ultraviolet sunlight, even when it remains exposed for lengthy periods during construction. By contrast, ZIP sheathing is a wood-based product that is more vulnerable to damage before and during installation.
Every time a worker wields a hammer to install a Zip System® panel, there’s potential for damage that may compromise air and water resistance. Some hammer blows miss their target. It is also possible for nails to be over-driven or mis-driven. Without appropriate remediation, damage to the kraft paper overlay potentially compromises the air/moisture barrier. In the field, many of these problematic mis-hits may not be addressed. Even when they are, every nail hole potentially compromises airtightness.
DELTA®-VENT-SA is a self-adhesive water-resistive barrier that eliminates the need for fasteners altogether, solving these unintended fastener issues. When fasteners are later used to secure cladding over the envelope, the adhesive serves the additional purpose of sealing around the fastener. The high tensile strength of the membrane and the reliable long-term adhesion passes and exceeds the most stringent testing and standards.
It is vital that surfaces are dry before taping or tape adhesion may become a problem quickly, compromising the system’s integrity. With ZIP System® sheathing, every seam must be successfully taped and carefully rolled. Out in the field, this may not always occur. Any lack of adhesion, especially along horizontal runs, may lead to fishmouthing, or cupping, that can collect water. This water may infiltrate the wall system, increasing the potential for deterioration and decreased insulation R-values.
DELTA®-VENT SA removes these taping issues not only by virtue of its application, but also with the added front side adhesive strips that seal the laps where the upper and lower layers meet.
Joint spacing requirements
There is a need to maintain 1/8 inch spacing at every seam to allow for the expansion and contraction of the Zip Systems® panels. Given repeated expansion-contraction cycles, tape adhesion may decline over time, particularly in climates with greater temperature extremes. These gaps also compromise the insulating capacity of the panel.
Restrictive spacing requirements and changes in the panel size are not a concern with DELTA®-VENT SA. The 3-ply membrane maintains its structure over time. Furthermore, the pliable nature of DELTA®-VENT SA gives an elongation that allows for the building’s natural expansion and contraction during seasonal changes without compromising the membrane.
Air infiltration resistance
DELTA®-VENT SA is exceptionally airtight because it is aggressively self-adhering. Seams are not compromised by the potential problems associated with ZIP taping. In fact, the front side adhesive ensures an air and watertight glue-to-glue seal when overlapping layers. Thanks to its 50-perm vapor permeance rating, DELTA®-VENT SA facilitates the proper drying of an exterior wall system should incidental moisture does intrude. The vapor permeance of ZIP System® sheathing is 12-16 perms, considerably less than the 50-perm rating of DELTA®-VENT SA.
Since ZIP System® is a wood-based product, excessive moisture intrusion can have a deleterious effect on the entire wall system. ZIP System® wall sheathing is watertight only when properly taped at every joint and corner, and only when all punctures, cuts and other surface anomalies are properly repaired at installation. Also, the edges of the product are somewhat vulnerable to taking on moisture before installation. This can potentially lead to a wall system that is not as air or water-tight as intended.
DELTA®-VENT SA is a vapor permeable, water-resistive membrane. While wood-based sheathing naturally has a propensity for moisture damage, DELTA®-VENT SA does not. This protects the integrity of the entire wall system. The durable and fully-adhered barrier has built-in watertight seams to envelope the wall entirely providing continuous protection from even harsh wind-driven rain.
The superior qualities of Dörken’s DELTA®-VENT SA create a drier exterior wall system which significantly reduces mold potential, minimizes component deterioration, and preserves R-values. It also provides the kind of energy-saving air barrier that proponents of green building construction value.