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WALL PERFORMANCE BY DESIGN:
The Role of Rainscreens in
Moisture Management
Laverne Dalgleish
Building Enclosure Moisture Management
Institute (BEMMI)
Today’s Agenda
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BEMMI Background
Exterior Wall Science: As I Live and Breathe!
Traditional Rainscreen Design
Engineered Rainscreen Design
Absorptive Cladding
Building Code Requirements and Compliance
Bibliography
Building Enclosure Moisture
Management Institute
• Founded in 2009
• Founding Members:
– Advanced Building Products
– Benjamin Obdyke
– Cosella-Dörken
– CavClear/Archovations
BEMMI Mission
To promote the growth of the engineered
rainscreen products industry to improve
moisture management in building enclosures
through technical advocacy
Exterior Wall Science:
As I Live and Breathe!
• Exterior Wall Assembly
– Wall Covering Assembly
– Water-Resistive Barrier
– Insulating Sheathing (continuous insulation)
– Structural Framing, Sheathing, Cavity Insulation
– Interior Finish Materials
• Air Barrier Requirements
• Penetrations
Traditional Rainscreen Design
• Ventilated Cladding
– Anchored Brick and Stone Veneers
– Wood Shakes and Shingles
– Clapboards
• Drainage and Drying
Traditional Rainscreen Design
Absorptive Cladding
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Masonry and Stucco
Adhered Veneers
Wood Siding Materials
Engineered-wood Siding Materials
Cement-based Siding Materials
Absorptive Claddings
Engineered Rainscreen Design
• Bulk Water Drainage
• Ventilation –
– Precipitation, Condensation
– Evaporation, Respiration
• Capillary Break Space – Isolate Cladding
Engineered Rainscreen Design
Types of Rainscreen Materials
• 3-dimensional membrane
• 3-dimensional mesh style
• Polymer-based products
• Roll out similar to water-resistive barriers
• Continuous airspace
Engineered Rainscreen Design
Engineered Rainscreen Design
0.25 in (6mm)
0.40 in (10mm)
Meets Canadian
Building Code
Engineered Rainscreen Design
Engineered Rainscreen Design
Code Requirements: 2012 IRC
SECTION R703
EXTERIOR COVERING
R703.1 General. Exterior walls shall provide the building with
a weather-resistant exterior wall envelope. The exterior wall
envelope shall include flashing as described in Section R703.8.
R703.1.1 Water resistance. The exterior wall envelope shall
be designed and constructed in a manner that prevents the
accumulation of water within the wall assembly by providing a
water-resistant barrier behind the exterior veneer as required
by Section R703.2 and a means of draining to the exterior
water that enters the assembly. Protection against
condensation in the exterior wall assembly shall be provided
in accordance with Section R702.7 of this code.
Code Requirements: 2012 IRC
Exceptions:
1. A weather-resistant exterior wall envelope
shall not be required over concrete or masonry
walls designed in accordance with Chapter 6 and
flashed according to Section R703.7 or R703.8.
Code Requirements: 2012 IRC
Exceptions (cont.):
2. Compliance with the requirements for a
means of drainage, and the requirements of
Sections R703.2 and R703.8, shall not be
required for an exterior wall envelope that has
been demonstrated to resist wind-driven rain
through testing of the exterior wall envelope,
including joints, penetrations and intersections
with dissimilar materials, in accordance with
ASTM E 331 under the following conditions:
Code Requirements: 2012 IRC
2.1. Exterior wall envelope test assemblies shall
include at least one opening, one control joint, one
wall/eave interface and one wall sill. All tested
openings and penetrations shall be representative
of the intended end-use configuration.
2.2. Exterior wall envelope test assemblies shall be
at least 4 feet by 8 feet (1219 mm by 2438 mm) in
size.
Code Requirements: 2012 IRC
2.3 Exterior wall assemblies shall be tested at a
minimum differential pressure of 6.24 pounds
per square foot (299 Pa).
2.4. Exterior wall envelope assemblies shall be
subjected to the minimum test exposure for a
minimum of 2 hours.
Code Requirements: 2012 IRC
Pass / Fail Criteria
Exception 2 (cont.):
The exterior wall envelope design shall be
considered to resist wind-driven rain where the
results of testing indicate that water did not
penetrate control joints in the exterior wall
envelope, joints at the perimeter of openings
penetration or intersections of terminations
with dissimilar materials.
ASTM E331
Water penetration test.
Simulates 8” rain / hr.
with 50 mph wind.
Code Requirements: 2012 IRC
• IRC Provides Basic Performance Measures
– Minimum Code (minimum legal requirements)
• Beyond Code:
– Durability
– Drainage and Drying
– Moisture Management as Preventative Measure
Performance Expectations
• Help Remove Bulk Water
• Promote Drying of Incidental and Absorbed
Water
• Improve Condensation Management
ICC-ES (Evaluation Services)
• Meeting the Intent of the Code
– ICC-ES Acceptance Criteria: AC356
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Drainage Test
Accelerated Aging & Weathering
Durability / Fungi Resistance
UV Exposure
Fire Resistance (optional)
Blower-Door Testing
Problem Areas
• Tighter the wall, the less it dries
• Penetrations and openings create moisture
movement issues
• Less expensive to address upfront than to fix
later
Engineered Rainscreen Performance
• Drain bulk water from behind the cladding
• Provide ventilation drying for other incidental
moisture
• Separates cladding from WRB
– Capillary break
– Surfactant issues, enhance WRB durability
• Continuously over entire wall surface
Engineered Rainscreen Details
Rainscreen Material
Review
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BEMMI Background
Exterior Wall Science: As I Live and Breathe!
Traditional Rainscreen Design
Engineered Rainscreen Design
Absorptive Cladding
Building Code Requirements and Compliance
Bibliography
Questions?
Bibliography
Advanced Building Products
Air Barrier Association of America
CavClear/Archovations
Building Enclosure Moisture Management Institute
Benjamin Obdyke
Cosella-Dörken
International Code Council, Evaluation Services
International Code Council
Masonry Veneer Manufacturers Association
NAHB Research Center White Paper
www.mortairvent.com
www.airbarrier.org
www.cavclear.com
www.bemmi.org
www.benjaminobdyke.com
www.cosella-dorken.com
www.icc-es.org
www.iccsafe.org
www.masonryveneer.org
www.toolbase.org/PDF/DesignGuides/RainScreenDesigns.pdf

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