MaxClad

To explain the difference lets turn to Rainscreen Cladding: A Guide to Design Principles and Practices (Anderson, Gill).

“The main point to note about the drained and back-ventilated approach is that claddings are allowed to leak, and no deliberate attempt is made to minimize the effects of wind by means of pressure equalization. Instead, the cavity behind the cladding is drained and positive back ventilation is used to promote the rapid evaporation of any rainwater deposited on the inner leaf. The same process is used to evacuate the water vapour which permeates through the inner leaf and, if present, it’s insulating layer.”

By contrast, Anderson and Gill further offer the following differentiation to PERS:

“The essential defining attribute that differentiates PERS from D/BV is the design and use of compartmentalization within the cavity to allow pressure equalization that accounts for the constantly changing wind pressures across the face of any building. This makes these systems much more design intensive."

D/BV Rainscreen Components

1. Series of sheets, cassettes , or tiles in a range of materials (collectively called ‘Cladding’).
2. Vertical or horizontal support systems for the cladding.
3. A minimum allowable width of air space between the outer cladding and inner leafs to facilitate positive back ventilation
4. An air/water barrier at the rear of the cavity, generally on the outer face of the inner leaf. The inner leaf is generally the structural building enclosure wall
5. Water resistant insulation can be applied to the exterior side of the moisture barrier and is optional subject to the building’s thermal design requirements.

Designing A D/BV Rain Screen

The design of any D/BV rainscreen is usually a collaboration between the architect and either a façade engineer or a supplier of rainscreen support systems [Brackets; profiles; Primary and secondary fasteners and associated components] who also supply a systems package including shop drawings and a structural analysis of a specific façade.

The suppliers of rainscreen systems must ensure that the components used in their systems are certified and are fit for use in any specific environment. In the case of New Zealand this means the products are suited for use in a marine zone. While this is not always the environment it is best to use these systems as they have a high level of corrosion resistance.

Weather Resistive Barriers (WRB)

Weather resistive barriers are designed to protect building materials from moisture, which can penetrate through a variety of places including cladding joints, sheathing laps, penetration points and open joint reveals.

Weather resistive barriers:

• Allow moisture vapor to escape
• Resist air movement while ensuring building materials to remain dry and weather tight
• Increase building performance while decreasing maintenance costs
• reduce the risk of moisture-related problems such as mold, mildew, rot and sick building syndrome.

Weather Resistive Barriers vs. Air Barriers

Not all air barriers are vapor barriers and not all vapor barriers are air barriers, however, all weather resistant barrier membranes must resist entry of liquid water (rain/snow) into the wall system by providing a drainage plane.

Air Barrier Functionality:

• Air barriers and weather resistive barriers (WRB) are typically combined into a single membrane
• Air barriers are used to reduce air infiltration from outside into the building
• Air Barrier Membranes can reduce building energy losses by up to 40%.

Essentially, weather resistive barriers must resist entry of liquid water (rain or snow) into wall systems by providing a drainage plane.

Mold Damage

The value of a breathable weather resistant barrier is its ability to allow moisture to continue to filter from the interior of a building to the exterior where it dissipates. Trapped moisture can cause wood rot, swelling and distortion of lumber, corrosion of metal and a reduction in insulation thermal value.

Continual Drying Is Key

Moisture penetration creates a risk of mold, mildew, building deterioration, poor indoor air quality and health and safety risks to occupants increases.

VaproShield’s breathable membranes provide secondary waterproof protection, reducing the risk of condensation and promoting the escape of moisture through the envelope. Because they are breathable, they allow drying during and after construction—reducing the risk of damage.