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A rainscreen wall controls rain by combining cladding, a drainage cavity, insulation, air and moisture control layers, and a supporting wall—not by asking one exterior surface to stay perfectly watertight. The approach assumes that some wind-driven rain will get past the cladding, then gives that water a continuous route back to the exterior while preserving opportunities for the wall to dry.
That distinction matters because the most damaging failures usually occur at interruptions: windows, doors, decks, penetrations, parapets, corners, and wall bases. The six-element framework described in Building Design + Construction’s 2016 AIA CES class is therefore best understood as a coordination method for the whole envelope. The class page is historical; its current availability and continuing-education status have not been verified.
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What is the rainscreen approach?
A rainscreen is a drained wall assembly in which the outer cladding is separated from the drainage plane by a cavity or gap. The cladding deflects much of the rain. Water that reaches the cavity is collected on the drainage plane, directed downward by gravity, and discharged through base flashing and weeps or drain holes. The wall is then designed to tolerate and release the smaller amount of moisture that remains.
Building Science Corporation describes the most reliable rain-control strategy as “Deflection, Drainage/Exclusion/Storage, and Drying” in BSD-013: Rain Control in Buildings. A rainscreen emphasizes deflection and drainage, but it still needs drying potential and materials that can tolerate occasional wetting.
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How does a rainscreen differ from other rain-control strategies?
Wall systems can control rain by storing it in a massive assembly, excluding it with a highly resistant exterior layer, or draining it after accepting that some water will pass the cladding. None is automatically right for every climate or construction type; the decision depends on drainage continuity, drying potential, material tolerance, and the quality of the details.
| Strategy | How it handles rain | Primary design concern |
|---|---|---|
| Mass or storage wall | Absorbs or stores moisture in substantial materials and relies on their capacity and drying rate. | Provide enough mass, durability, and drying so stored moisture does not accumulate. |
| Perfect-barrier or exclusion wall | Depends on an exterior layer remaining effectively watertight. | Maintain continuity at every joint, penetration, opening, and transition. |
| Drained-screened wall | Allows some rain past the cladding, then drains it outward on a dedicated plane. | Keep the cavity, flashing, weeps, and drainage plane continuous and unobstructed. |
The drained-screened approach is valuable because it does not require flawless performance from the cladding. It does, however, make detailing and construction quality decisive: a blocked cavity or missing flashing can defeat the concept even when the cladding itself is sound.
What are the six elements of a rainscreen wall?
The course overview identifies six coordinated elements. Their exact products and locations vary by wall type, but each has a distinct job.
- Cladding: The visible outer layer—such as masonry veneer, panels, siding, tile, or another rainscreen finish—deflects most precipitation and shields inner layers from ultraviolet exposure and impact. It is not assumed to be perfectly watertight.
- Cavity: The gap behind the cladding creates a capillary break and a path for gravity drainage. Depending on the design, it can also provide airflow and accommodate cladding tolerances. A cavity can be formed by furring, clips and rails, spacers, masonry detailing, or a rainscreen drainage mat selected for the specific assembly.
- Thermal layer or insulation: Insulation limits heat flow and affects the temperature of the other layers. Its location influences condensation risk, drying direction, fire performance, and how thermal bridges at supports are handled.
- Air barrier: A continuous air-control layer limits air movement through the wall. Air leakage can transport moisture, so the air barrier must connect across joints, corners, penetrations, windows, and roof or foundation transitions.
- Moisture barrier: Often called the water-resistive barrier or drainage plane, this layer receives water that passes the cladding and directs it toward flashing and discharge points. Its laps, tapes, membranes, and compatible sealants must remain continuous.
- Supporting wall: The structural backup carries gravity, wind, and attachment loads. It may be framed or masonry, but it must be detailed so anchors, fasteners, deflection, and movement do not interrupt the water and air-control layers.
These elements are not six independent sheets. A window sill, for example, must connect the cladding opening to the drainage plane, base flashing, air barrier, and supporting wall while allowing movement and directing water outward.
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How does water move through a drained rainscreen?
Rain first meets the cladding, where overhangs, laps, joints, profiles, and surface geometry deflect much of it. Wind can drive the remainder through joints or behind the outer finish. In BSD-013, Building Science Corporation gives an approximate order-of-magnitude estimate that rain deposited on the worst part of many low-rise buildings can be about 10 to 20% of the product of wind speed and rainfall intensity, for each orientation. This is not a universal design load; exposure, height, geometry, and local weather change the result.
Once water enters the cavity, gravity should do most of the work. It runs down the drainage plane, is collected by flashing, and exits through weeps or drain holes. The cavity also interrupts capillary suction so water is less likely to bridge directly from cladding to the inner wall. Drying then removes residual moisture by evaporation, diffusion, and—where designed—air movement.
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How should the drainage cavity be designed?
The cavity must remain a real, continuous route from the top and intermediate collection points to exterior discharge. Its required geometry depends on the cladding, attachment system, fire strategy, climate, and project requirements; cavity width by itself does not guarantee better drainage.
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- Preserve a capillary break. Keep cladding and drainage-plane surfaces separated so water cannot bridge the gap by surface tension.
- Keep the bottom open to drainage. Base flashing should project water beyond the wall, and weeps or drain holes should not be covered by mortar droppings, sealant, insulation, insect screens that block flow, or debris.
- Coordinate attachments. Rails, clips, shelf angles, shelf supports, and fasteners should not create dams. Where an attachment interrupts the plane, provide a compatible transition detail.
- Choose venting deliberately. A cavity may be drained only, vented at openings, or designed for more continuous ventilation. Airflow can assist drying, but it does not replace gravity drainage.
- Use a drainage mat only when it fits the assembly. A rainscreen drainage mat can create a reliable gap behind some claddings, but its compressibility, fire characteristics, attachment method, and compatibility with the wall must be checked against the project details and manufacturer instructions.
BSD-030: Rain Control Theory explains that a cavity can provide a capillary break, gravity-drainage path, and airflow path. It also notes that larger cavities may be needed for other purposes, such as ventilation or cladding tolerances, rather than simply to make drainage “better.”
Where do rainscreen walls most often fail?
Failures commonly begin where the outward water route is interrupted or where one control layer stops without a compatible transition. A wall can look complete in the field while still lacking a continuous drainage plane behind an opening or at a change in material.
| Failure point | What goes wrong | Design or construction response |
|---|---|---|
| Windows and doors | Sill flashing is missing, reversed, discontinuous, or not connected to the drainage plane; head and jamb transitions can also leak. | Detail sill pans, end dams, jamb and head transitions, and an exterior discharge path before cladding is installed. |
| Decks and balconies | Ledger attachments and waterproofing transitions interrupt the cavity or direct water into the wall. | Coordinate structural attachment, membrane laps, flashing, and the cladding termination as one detail. |
| Penetrations | Pipes, conduits, brackets, and fasteners create holes or dams in the air and moisture-control layers. | Use boots, collars, tapes, sealants, or formed flashings that are compatible with the membrane and allow movement. |
| Wall bases | Flashing terminates behind the cladding, weeps are blocked, or the wall discharges onto a surface that sends water back. | Provide a visible, protected outlet and coordinate it with grade, paving, and adjacent materials. |
| Parapets and terminations | Roof-to-wall and wall-to-wall transitions leave the drainage plane or air barrier unconnected. | Draw the control layers continuously through the termination and verify laps before concealment. |
| Blocked cavities | Mortar droppings, insulation, sealant, or incorrectly placed fire stops stop downward flow. | Detail cleanouts or inspection points where appropriate and inspect the cavity before closing the wall. |
Does pressure equalization replace drainage?
No. Pressure moderation may reduce some wind-driven forces, but it cannot substitute for gravity drainage, flashing, and capillary breaks. Building Science Corporation notes that instantaneous pressure equalization rarely occurs in real walls and that pressure equalization often offers only marginal benefit once a drained path is provided.
A pressure-moderated cavity still needs correctly located openings, a continuous drainage plane, and outlets. Calling a wall “pressure equalized” is not a guarantee that it is watertight, nor is it a reason to omit sill pans, base flashing, or weeps.
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How do air, moisture, and thermal layers work together?
Rain control is only one part of envelope performance. The air barrier limits moisture-laden air leakage; the moisture barrier handles liquid water; and insulation controls heat flow and surface temperatures. If these layers are discontinuous or placed without regard to climate, condensation can occur even when bulk rain drains correctly.
Map each control layer on drawings and at every junction. The air barrier should connect to window frames, roof membranes, foundation transitions, and adjacent walls. The moisture barrier should lap and drain over flashings rather than terminate at them. Insulation should be fitted around supports and penetrations so gaps do not create severe thermal bridges. The supporting wall and its fasteners must accommodate movement without tearing membranes or closing the cavity.
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What is a practical design and construction workflow?
Use the following sequence before selecting proprietary components. It is a coordination checklist, not a substitute for the project’s governing codes, climate analysis, fire requirements, structural design, or manufacturer instructions.
- Define the exposure. Review wind-driven rain, building height, orientation, overhangs, local climate, and the cladding’s joint and opening pattern.
- Select the rain-control strategy. Confirm why a drained-screened wall is appropriate compared with a mass or exclusion approach, and identify how the materials will dry.
- Draw the six elements. Show cladding, cavity, insulation, air barrier, moisture barrier, and supporting wall in section at typical areas and every change in condition.
- Trace water downward. Start at the highest joint and follow the drainage plane to base flashing and an exterior outlet. If the line stops at a window, deck, shelf angle, or penetration, resolve that transition before proceeding.
- Trace air and vapor control separately. Mark the air-barrier connection and assess whether the insulation and layer arrangement support drying for the project climate.
- Coordinate fire and structure. Verify cavity fire-stopping, attachment loads, movement joints, deflection, and thermal-bridge treatment without blocking drainage.
- Write installation requirements. Identify acceptable laps, substrates, tapes, sealants, fastener penetrations, cavity protection, weep locations, and sequencing.
- Inspect before concealment. Look for continuous flashing, open drainage paths, clean cavities, sealed transitions, and undamaged membranes. Photograph critical work where the finished cladding will hide it.
- Plan maintenance. Keep weeps and outlets clear, inspect sealants and exposed flashings, and investigate staining or dampness before it becomes a concealed-wall problem.
What should be checked during a design review?
- Is the drainage plane continuous in plan and section, including corners and material changes?
- Does every opening have sill, jamb, and head details that discharge water outward?
- Are base flashings, end dams, weeps, and outlets shown rather than left to field interpretation?
- Can mortar, insulation, fire-stopping, or sealant block the cavity?
- Do fasteners and supports preserve both the drainage path and the air barrier?
- Are the selected membranes, tapes, mats, and sealants chemically compatible?
- Does the wall have a credible drying path after wetting?
- Are pressure-moderation features being treated as supplemental rather than as a replacement for drainage?
- Do details address roof edges, parapets, foundations, decks, penetrations, and adjacent walls?
- Have code, fire, structural, accessibility, and manufacturer requirements been checked for the actual project?
What are the health and durability implications?
Persistent wetting can corrode fasteners, decay susceptible materials, reduce insulation performance, damage finishes, and support biological growth. Exterior-wall moisture can also contribute to indoor environmental problems when it remains concealed or enters occupied spaces. A rainscreen reduces risk by providing a robust liquid-water route, but it does not make poor detailing harmless.
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The most durable assemblies combine deflection, drainage, and drying with materials selected for the expected wetting and drying cycles. Because older guidance does not establish performance for a particular product assembly, final decisions should follow current project-specific codes, climate analysis, engineering, and manufacturer instructions.
What does the original AIA CES class establish?
The Building Design + Construction course page, published January 28, 2016, presents the six-element rainscreen concept and discusses rain entry, wall-system choices, durability, error sources, and health implications. It stated at that time that the course was free through BD+C University; current enrollment, pricing, and AIA/CES credit should be confirmed directly rather than assumed from the old page. The technical principles are supported by BSD-013 and BSD-030, which are explanatory references, not project-specific design documents.
Frequently Asked Questions
Does rainscreen cladding make a wall waterproof?
No. The cladding deflects much of the rain, but the design assumes that some water may pass joints or openings. The drainage plane, flashing, weeps, and drying strategy are what keep that water from becoming concealed damage.
Is a deeper cavity always a better rainscreen?
No. A small gap can provide capillary separation and gravity drainage, while a larger cavity may be justified for ventilation, fire detailing, or cladding tolerances. Width alone cannot compensate for missing flashing, blocked outlets, or a discontinuous drainage plane.
Can pressure-equalized walls omit sill flashing and weeps?
No. Real walls rarely equalize pressure instantaneously, and pressure moderation does not remove the need for gravity drainage or capillary breaks. Openings still need positive flashing and an exterior discharge route.
Can an existing wall be retrofitted with a rainscreen?
Often, but feasibility depends on the existing substrate, structure, fire provisions, window positions, and available thickness. A retrofit should begin by tracing the drainage, air, and thermal layers at openings, bases, roofs, and attachments rather than simply adding furring and cladding.
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