Improving Drainage, Image, and Quality of Living
The Need for Better Drainage
Traditional Water Resistant
Barriers (WRBs) are not failproof. They run the risk of not
providing sufficient moisture
drainage in some cases,
especially when not properly
Traditional WRBs also
deteriorate over time with
prolonged exposure to
moisture causing an increase
in water migration and a
deterioration of underlying
Water Intrusion
3 Factors must be present for water intrusion to occur in
a building enclosure:
An Opening
A Force
Drainage Planes minimize the intrusion of water into
building enclosure
The Drainage Plane is defined as a point at which
water is diverted and either drained out or drained
downward, away from the remainder of the wall
Rainwater Control Strategies
3 types of rain water control strategies:
Face Sealed Barrier wall
Concealed Barrier Wall
Rain Screen Wall
All three strategies use “drainage planes” in
different locations to control moisture penetration.
• Face Sealed Barrier Wall
Face sealed barriers elude
water at the outermost face.
No provisions are made to
collect or redirect water
should it penetrate the
exterior wall.
Water Entrapment behind
exterior face can cause
serious problems.
Barrier-type EIFS (Exterior
Insulation Finishing System) is
a common example of facesealed barrier wall
• Concealed Barrier Wall
Concealed Barriers resist
penetration in two ways:
Exterior cladding sheds
most of the water at the
outer surface.
It protects against water
that manages to penetrate
behind the exterior surface
with the use of a WRB
(water resistive barrier)
If water manages to
penetrate the WRB, it can
trap and hold the water
behind the absorptive
cladding causing decay.
• Rain Screen Walls
A Rain Screen resists penetration in 3
Like “face sealed” and “concealed”
barrier walls, it sheds most of the water
at the outer surface.
It intercepts any water that crossed the
outer surface with a dedicated air
space/capillary break.
The space is then vented to the outside
to not only assist drainage but to
encourage drying as well
The addition of an air break provides
the wall with more free drainage and
drying than the “concealed” barrier,
diverting water downward by gravity.
If water were to cross the air break, the
rain screen system also employs a layer
of WRB on the back side of the air
space… just in case.
The Rain Screen Wall System
Three Types of Rain Wall Systems
Factors Affecting Rain Screen Design
Advantages and Disadvantages
Summery of Critical Features
Product Examples
Types of Rain Screen Systems
The Drained Cavity Wall System
In this system, water penetrating the
outer wall must be collected and
directed out of the cavity through the
use of flashing and weep holes
The drained cavity wall system has
some aspects of a rain screen but
can not be properly called a rain
screen wall because it does not
address air pressure gradients.
If the outer wall is more airtight, then
pressure will build in the lower air
pressure within the cavity causing
rainwater to infiltrate through the
interior wall surface and cause
Simple Brick Veneer Rain Wall
System on Metal Studs
Simple Cladding Rain Screen Wall
System on Wood Studs
Types of Rain Screen Systems
The Open (or Simple) Rain Screen System
The open rain screen system differs from the drained cavity wall system in the placement of the air
The outer screen layer is intentionally vented to the exterior, while the air barrier is located at the
inner layer or backup wall
The inner surface bear the brunt of the wind pressure loads since it is the most airtight. This relieves
the pressure gradient across the outer wall, which would otherwise tend to draw moisture inward.
Types of Rain Screen Systems
Pressure-equalized Rain Screen Wall
Pressure-equalized rain screen
walls work with the existing
external wind loads to promote
pressure equalization within the
Pressure-equalization minimizes
the force which drives moisture
through the outer wall.
The external cladding must be
able to perform structurally
against wind loads until pressureequalization occurs.
Pressure Equalization Concept
When outside air pressure is transferred to an air space behind exterior cladding,
the cladding is exposed to a near-zero pressure differential. The air chamber
compartments must be small enough, the air barrier system must be airtight enough,
and the area of the venting through the rain screen must be large enough to allow
sufficient air to move in and out of the compartments under the applied air
The strategy lies in the control of airflow within and through the wall assembly.
The higher cavity pressure brought about during gusting wind conditions creates a
negative (outward) load on the rain screen. This tends to force water out of
openings in the cladding, providing further defense against rain penetration.
Perfect pressure equalization across the rain screen at all times is neither achievable
nor necessary for adequate rain penetration control. Pressure equalization
strategies do not eliminate the need for sufficient drainage and drying capacity.
More information and specific guidelines regarding rain screen wall components can
be found at :
 www.cmhc-schl.gc.ca
Advantages and Disadvantages
Most reliable choice for applications
exposed to significant rain and wind
Rain shedding by the use of cladding
Drainage and venting to speed the
removal of water that passes through
the rain screen
Air pressure equalization in the cavity
to minimize forces drawing water
through the cladding, with the
cladding also providing a capillary
A second layer of moisture protection
at the backup wall
Requires less maintenance over its
service life compared to traditional
rainwater control strategies
The detailing and construction to
achieve a pressure-equalized rain
screen wall or joint may be complex
and expensive compared to other
wall systems
Rain screen wall systems are not
always the best solution in every
instance – In some climates and some
applications, face-sealed walls
perform well, and rain screen
construction might be unsuitable due
to expense, space, structural
considerations, etc.
Summery of Critical Features
Provision for water shedding at the outer cladding, away from joints, with drips under any projections
to prevent water collecting at the building face.
A cavity of appropriate width to allow pressure equalization across the cladding system and prevent
capillary movement (allow for construction tolerances!).
A continuous and effective (for example, airtight to a maximum air leakage of 0.1 L/s/m2) air
barrier within the backup wall.
Drainage of the cavity through continuous flashings and weep openings, and proper management of
drained water.
Adequate venting of the cavity provided through properly located openings in the cladding
(appropriate ratio achieved between vent area and leakage of air barrier and seals).
Additional provision for drainage at the backup wall (located on the “warm” side of the insulation to
avoid condensation problems).
Effective compartmentalization of the cavity at each building face with airtight seals, and
additionally across the width of the façade as required (refer to calculations).
Sufficient rigidity and/or structural support of the air barrier to resist wind loads and limit deflection.
Sufficient rigidity of the cladding to limit deflection and resist wind loads as required.
Special attention paid to water-resistance and drainage at building edges and parapets (areas
subject to heaviest rain-wetting and wind pressure differences, where pressure equalization not be
Dri-Design is a dry joint, pressure equalized rain-screen, metal wall panel system.
Panel manufacturing is highly automated and the installation is fast and simple, which
makes Dri-Design an economical choice.
More information at: http://www.dri-design.com/company.asp
PaperStone rain screen is made with a natural
phenolic resin and 100% recycled paper that
is virtually impervious to water. As a result it
sheds it quickly on the outside reducing
infiltration. For water transported by
mechanical forces behind it, the venting and
draining holes in the mounting brackets quickly
expel or evaporate the moisture.
The PaperStone rain screen is a pressure
equalized rain screen. This is a system that
prevents migration into the inner wall by
removing the pressure differential behind the
outer wall, making it equal the pressure on the
outside surfaces.
More information at:
NorthClad® Exposed Fastener Panel System
Tested for air, water and
structural performance (ASTM
283, 330 331)
Choose painted material or
natural finishes including wood
Cost savings are generated by
minimizing routing and forming
Panels can be installed out of
sequence and are easily
replaced if damaged
Complete flashing systems
available in matching colors
Field modification of most panel
materials is possible and simple
Vented rain screen design for the
health of your building
More information at:
Copper Rain Screen Wall System
More information at: www.copper.org
VaproShield Membranes, Rain Screen Design
Components and 3D Window Flashing Elements
provide an affordable and innovative solution to
build a breathable building envelope.
Rain Screen Design Components include
VaproBatten and VaproVentStrip. Combined with
WallShield or WrapShield, these components
create a very effective, easy to install rain screen
design. They are engineered to ensure trapped
moisture moves quickly through the building
envelope ensuring maximum ventilation within
drying cavity.
More infromation at:
http://www.vaproshield.com/media/A new standard for rain screen design
Project Name: Emergency Operations Center
Location: Springfield, Illinois
Architect: DeStefano and Partners, Ltd.
Contractor: River City Construction, LLC
Copper Applications: Exterior rain screen

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