Barricade® Building Wrap achieves the five basic requirements for an effective air barrier system: continuity, impermeability, durability, strength, and stiffness.
Air barrier systems control the airflow, and the moisture associated with it, between a conditioned space and an unconditioned space. Controlling airflow is essential to a safe, healthy, durable, comfortable, and energy-efficient building and home. Importantly, a properly installed and high-quality air barrier is critical to avoid the following problems caused by uncontrolled airflow.
Any product with air permeance less than 0.02 L/(s • m2) @ 75 Pa pressure differential (0.004 cfm/sf @ 0.3 in. w.c. or 1.56 psf pressure differential), when tested by the ASTM E2178, Standard Test Method for Air Permeance of Building Materials, qualifies as an air barrier. However, effective air barrier systems have five basic requirements:
A continuous air barrier system is critical to controlling the transfer of heat, moisture, and air. The continuous air barrier system provides an airtight building envelope that separates the unheated and heated spaces and is continuous between all the building enclosure elements. The building enclosure includes the above-grade and the below-grade parts of the building that physically separates the exterior from the interior environments. The building enclosure includes three interactive elements: the exterior environment, the enclosure system, and the interior environment. A building enclosure usually consists of the following components:
A successful air barrier system is a combination of the air barrier assembly and building enclosure elements, connected by air barrier accessories so to prevent air leakage at the joints between minerals, elements, assemblies, and systems and penetrations through them, such as pipes and conduits.
Elements of an air barrier system must be impermeable to air flow. Air infiltration causes tremendous heating and cooling energy loss and allows moisture and condensation to collect in the walls. Condensation creates mold and mildew, which is unhealthy and causes structural damage.
ASTM E2178 is the standard test method for air permeance of building materials the International Energy Conservation Code (IECC) codes and ASHRAE 90.1 consider 0.02 L/s.m² 75 Pa (0.004 cfm/ft² 1.57 psf) as the maximum allowable air leakage for an air barrier system material for the opaque enclosure.
A quality air barrier material is durable and, if required, accessible for maintenance. A quality air barrier remains durable during and after exposure to ultraviolet (UV) rays, cold, and moisture.
The stiffness of a quality air barrier ensures the successful performance of an air barrier system.
The air barrier systems stiffness and rigidity must also ensure that deformations (e.g., caused by stretching holes around fasteners) do not alter the barrier’s air-permeance and ability to prevent air through unintended gaps in the building enclosure.
A high-performing air barrier has the strength to maintain its integrity during and after construction. Specifically, a strong air barrier is designed to withstand structural wind loads and pressures that allow air flow within and through a building. A strong air barrier must also be properly installed and ensure adhesion of the sealants, self-adhered membranes (SAMs), tapes, etc.
Air flow through the building’s enclosures occurs if there is a pressure difference between two points and an opening connecting the two points (continuous flow path). The strength of the air barrier must control the three mechanisms that generate pressure difference: mechanical air handling equipment, stack effect, and external wind forces.
Mechanical pressures happen from the movement of air within a building due to the heating, cooling, exhaust, and other ventilation systems. For example, if the bathroom exhaust fans remove more air from the building than air supplied to the building, a negative pressure is created inside the structure.
The negative pressure will cause air and moisture from the outside to flow into the building, through cracks, windows, doors, etc., until the pressure inside the building equalizes. To reduce air infiltration, the mechanical systems of a building should equally exhaust and supply air.
Stack action is the movement of air in and out of a building due to thermal convection. During colder periods, thermal convection happens when warm air rises (by the flow of air and liquid molecules) to the upper areas of a building. Once the heat reaches the ceiling, it can escape through gaps in the building envelope.
Holes in the ceiling often happen near plumbing, ceiling lights, mechanical, and electrical installation chases (areas meant for tubing and piping), etc. when not adequately sealed. The rising warm air further lessens the pressure in the basement or crawl space of the building. As a result, outside cooler air can push its way through even the smallest gaps into the basement until the air pressure inside is equal to that outside.
During warmer periods or in hot climates, the stack effect is in reverse; the cold, dense air inside leaks out of gaps in the lower level of the building, which lowers the pressure in the ceiling. Therefore, if there are defects in the air barrier of the ceiling, warm air will get sucked into the attic.
Air pressure difference between the outside and inside of a building cause external wind forces. Positive wind pressure causes air to leak into a building, and negative wind pressure cause air to leak out of a building.
Correct installation of an air barrier system is critical to its strength. For example, sealing house wrap joints with manufacturer’s tape can improve the wrap’s performance by about 20 percent. A strong air barrier system includes attention to the adhesion of the sealants, SAMs, tapes, etc. especially at junctions between the air barrier and adjacent construction. Design consideration must determine adequate resistance to these pressures by fasteners, tapes, adhesives, etc.
Barricade® Building Wrap is a continuous air barrier over the entire building enclosure. Barricade® Building Wrap is also durable over the expected lifetime of the building and has the strength and stiffness to resist the forces that act on it during and after construction.