Staying Ahead of the Curve: Meeting Adhered Veneer Code Standards in 2021

Introduction

Building codes are constantly evolving to address the changing needs of construction, energy efficiency, and occupant safety. In recent years, there has been a growing emphasis on creating tighter, more efficient buildings that dry from the outside. This article will discuss the 2018 and 2021 code changes for the International Building Code (IBC) and the International Residential Code (IRC) as they relate to stucco and adhered veneer wall assemblies over wood-based sheathing.

Code?Trending?Toward?Rainscreen

As?energy?efficiency?continues?to?be?a?crucial?aspect?of?building?design,?the?construction industry is witnessing a shift towards more sustainable building practices. One of the most significant changes in recent years has been the increased emphasis on rainscreen technology in building codes. The usage of rainscreen systems is on the rise due to their ability to offer an extra shield against moisture infiltration by ensuring ample drainage area and encouraging efficient drying from the exterior.

What?is?a?Rainscreen?Wall?System

A rainscreen system comprises a series of components that work together to create an air?gap?betweenthe?exterior?cladding?and?the?underlying?building?envelope.?The?system typically includes a water resistive barrier (WRB), an air space, and a cladding layer.

The?importance,?that?it?creates?an?air?cavity?directly?behind?the?cladding?which?is?vented at both the top and bottom of the wall so it may help protect the building against moisture intrusion while promoting drying from the outside.

The trend towards rainscreen systems is particularly evident in the 2018 and 2021 updates?to?theInternational?Building?Code?(IBC)?and?the?International?Residential?Code (IRC). These code changes reflect a growing recognition of the benefits of rainscreen technology in protecting building envelopes and ensuring that structures are energy- efficient, durable, and safe.

Benefits?of?a?Rainscreen?Wall?System

One of the main benefits of rainscreen systems is their ability to protect the building envelope from moisture infiltration. This is particularly important for stucco and other cementitious?adhered?veneers,which?can?be?especially?vulnerable?to?moisture?damage. When water penetrates the cladding, it can become trapped, leading to significant damage to the building's structural components. In fact, a 2013 EPA study found that 85% of buildings surveyed had experienced water damage.1?Rainscreen systems provide an additional layer of protection against moisture by helping to ensure that the building envelope remains dry. Basic rainscreen systems provide enhanced drainage for the building envelope and often prevent water from ever reaching the primary WRB. This is easy to observe in a traditional brick veneer cladding system. In those systems the water may penetrate through the mortar very quickly, but it does not easily migrate across?the?airspace?to?the?WRB.?Instead,?water?drains?downthe?back?of?the?brick?until?it is directed out onto the face of the cladding utilizing masonry flashing.

With proper design and detailing, rainscreen walls can also incorporate ventilation into the exterior wall assembly. By incorporating an airspace between the exterior cladding and?the?underlying?buildingenvelope,?a?rainscreen?system?can?promote?effective?drying and allow for the removal of moisture utilizing air flow. This ventilation helps remove moisture that was unable to drain from the wall assembly. Dry claddings are more resilient and last longer!

Water?Resistive Barriers:?ASTM?E2556 Type 1?and?Type?2

To understand the building codes, we will first look at the test standards referenced. To better?regulatewater?resistive?barriers?(WRBs),?building?codes?reference?two?standards: ASTM E2556 Type 1 and Type 2.

Type 1?WRB’s offer basic protection against water intrusion and are considered the code?minimum.?Ten-minute?building?paper,?traditionally?asphalt?saturated?materials,?is the most common example of a Type 1 WRB. A 10-minute material provides a basic level of moisture protection, as little as 10 minutes.

Type 2?WRBs, such as DuPont??Tyvek?, provide significantly higher levels of water resistance?anddurability?compared?to?Type?1?WRBs.?They?are?considered?the?preferred choice for builders and architects who prioritize long-lasting protection against moisture?infiltration.

In?addition?to?Type?1?and?Type?2?WRBs,?there?are?also?coated?sheathing?products?that utilize tape to seal the seams.?While these products are not?tested to the low standard of ASTM E2556 Type 1, they are accepted into the building code as a Type 1?equivalent.

Utilizing?coated?sheathing?with?stucco?or?adhered?veneer?systems?in climate zones A and C will?require?additional steps and costs to meet the more stringent requirements set forth in the new IBC and IRC codes.

ASTM?E2273:?Drainage?Efficiency?Standard

The ASTM?E2273 standard measures?the drainage efficiency of?a?EIFS clad assembly. This?standard helps to ensure?that?water?and moisture?can effectively drain from?behind the?cladding,?thus?reducing?the?potential?for?moisture-related?issues?such?as?mold?and rot. To ensure drainable wall systems, products must have a drainage efficiency of greater than 90% to be utilized in some 2021 IBC and IRC wall assemblies.

Assembling?a Code Compliant?Wall?in?the 2018?IBC

When installing an adhered veneer over wood-based sheathing, the 2018 IBC requires the?use?of?adesignated?drainage?space?in?Climate?Zones?1A,?2A,?and?3A.?Climate?zone maps can be easily found by searching the web for "2018 IECC Map."

To create a code-compliant wall assembly under the 2018 IBC in the climate zones listed above, builders?must?use?a"ventilated?air?space"?between?the?stucco?and?the?Water?Resistive Barrier. Underneath the ventilated air space, there are essentially two choices.

Compliant?assemblies?can?incorporate?1?layer?of?Type?2?WRB,?like?DuPont??Tyvek?,?or two layers of Type 1 WRB. Utilizing any DuPont??Tyvek??WRB in conjunction with a rainscreen system?like Keene Driwall??Rainscreen will ensure proper?water?resistance, drainage, and most importantly, code compliance.

Assembling?a Code Compliant?Wall?in?the 2018?IRC

The?2018?IRC?does?not?require?the?use?of?a?rainscreen?in?any?climate?zone.?However, “designated drainage spaces” have been explicitly allowed into the code as an exception to the two-layer requirement since at least 2009. A Type 2 WRB used in combination?with?a?rainscreen,?like?the?assembly?describedfor?use?in?the?2018?IBC,?is an excellent and durable choice for buildings that fall under the 2018 IRC.

Assembling?a Code Compliant?Wall?with?the 2021 IRC or?IBC

The 2021 building codes continue to emphasize the importance of WRB’s and rainscreen?systems.?In 2021,?the?IRC?and?IBC?utilize?very?similar?language.?The?2021 codes split the requirements into "Dry" and "Moist or Marine" climates. See the 2021 IECC Map to determine which climate zone applies to your project.

When installing adhered veneer systems over wood-based sheathing in a Dry climate zone,?you?mustmeet?one?of?the?two?following?assembly?minimum?requirements:?(1)?Two layers?of?Type?1?WRB?installedindependently?utilizing?correct?shingling.?(2)?One?layer?of Type 2 WRB separated from the stucco by foam sheathing, non-water absorbing layer, or a designated drainage space.

In all Moist and Marine climate zones, you must comply with one of the two "Dry" climate assemblies. In addition, you must also do one of the following: If you picked option?one,?you?must?use?a?3/16"rainscreen.?If?you?chose?option?2,?then?your?assembly must?drain 90% of?the water?out?of?the assembly as tested by ASTM?E2273 or?Annex 2 of ASTM E2925.

Summary

Code compliant wall assemblies can be achieved across all climate conditions, Dry, Wet, and Marine, by utilizing a Type 2 Water Resistive Barrier (WRB) such as DuPont??Tyvek?, combined with a 3/16" rainscreen like Keene Driwall??Rainscreen. This combination provides an effective solution for managing moisture. By adhering to the most recent updates in the International Building Code (IBC) and International Residential Code (IRC) requirements, builders are better equipped to construct lasting high-performance durable structures.

For?additional?information?on?rainscreen?wall?systems?and?product?details,?visit?WeatherizationPartners.com

About?the?Author:

Evan O’Connell is the Business Development Leader at Weatherization Partners. Weatherization Partners covers the Southwest part of the U.S. from Tennessee to California. Evan has 15 years of experience in the building products industry, mostly focused on the building envelope. He currently represents numerous well-known companies including DuPont building products, Keene Building Products, Mortar Net Solutions,?and?Tower?Sealants.?Evan?can?easily?be?reached?through?his?LinkedIn page or at Weatherization Partners.