Stucco has been commonly used in North America as an attractive, durable, fire-resilient, and affordable cladding material. When applied as part of an exterior insulated wall system with stone wool insulation, stucco can support evolving energy code requirements in new and retrofit residential, commercial, and institutional construction.

Stone wool is an excellent choice for high-performance exterior insulated stucco wall assemblies because it has the compressive strength to support the weight of plaster, is noncombustible, has negligible thermal expansion to provide a stable long-term substrate, and offers reliable, long-term energy efficiency.

Continue reading to find solutions for designing a complete exterior insulated stucco wall system with stone wool.

What are insulated stucco systems?

Stucco cladding is a rendered construction material commonly made up of a mixture of cement, sand and water, and is currently one of the most commonly applied cladding materials in North America.

As energy code requirements are increasingly driving toward the need for continuous exterior insulation (ci), designing assemblies that combine commonly used cladding materials, like stucco, with a high-performance thermal strategy   contributes to construction of a durable building envelope.

ROCKWOOL stone wool insulation boards have been tested and approved to work in a variety of exterior-insulated stucco solutions.

Stucco Cladding Installation - Amity Construction
Completed Buidling Imagery - Residential

 Photo Courtesy of Amity Construction


Fire resistant

  • Noncombustible stone wool insulation is a critical component in fire-rated wall assemblies, with tested systems per ASTM E119 (CAN/ULC S101)
  • NFPA 285 solutions that may eliminate the need to encapsulate the insulation board at openings
    View one-coat systems
  • Well suited for high-density construction including urban areas with zero- and reduced-lot line installations, WUI (wildland-urban interface) zones, and in noncombustible construction  
  • Resists transfer of heat in a wall assembly that causes layers on the other side to begin burning or smoking, making it part of a strategic solution to a growing risk for all building types
  • ROCKWOOL Comfortboard products are listed in the California State Fire Marshal’s Building Material Listing (BML) as ignition-resistant products for WUI zone construction 
    View the listings

Sound absorbent

  • The non-direction fiber orientation and increased mass of stone wool insulation effectively reduces exterior sound transmission across the wall system, creating quieter, more comfortable spaces.
  • ROCKWOOL has developed a series of assemblies tested for Sound Transmission Class (STC – ASTM E90) and Outdoor-Indoor Sound Attenuation (OITC – ASTM E1332) to support the design of healthy and comfortable buildings.


  • Dimensionally stable: changes in temperature have a negligible impact, making stone wool a stable substrate.
  • ROCKWOOL Comfortboard® has a high maximum-use temperature of 1200°F, meaning it won’t warp or crack as a result of exposure to reflected light or ambient temperatures.
    • Permits the use of darker finishes from stucco manufacturers 
  • Stone wool is proven to resist termites and other insects, even in regions with very heavy pest pressure on building structures  
  • Stone wool boards may be exposed to UV light for up to three years with no significant negative effects — providing greater flexibility with project schedules, even in hot, sunny climates.

Vapor permeable and moisture resistant:

  • Stone wool insulation is moisture resistant and vapor permeable, allowing for a high drying potential and mitigating the risk of mold and mildew while reducing the risk of condensation within the wall assembly, contributing to healthy, comfortable indoor environments.
  • When used in exterior walls, the vapor permeability of stone wool minimizes the risk of decay, rot, deterioration, or corrosion, supporting the durability of the assembly. 


  • Stone wool insulation is manufactured from one of the world’s most abundant raw materials without the use of blowing agents or toxic flame retardants. And because of its ability to support high-performance assemblies that reduce energy consumption, stone wool can contribute towards LEED credits for your project.
It is predicted over the next decade, 2/3 of stucco used in the U.S. will be an insulated system. Due to verifiable code compliance, one-coat stucco will make up a significant portion of the future stucco market.

Stucco Manufacturers Association 2019 U.S. Stucco Market Report

One-Coat Stucco

One-coat stucco installations can be traced back to the 1970s energy crisis and are often applied over rigid insulation boards and lath for energy efficiency to help meet thermal code requirements. This approach must adhere to stucco manufacturer (system holder) instructions as they are not generically described in the building code.

  • One-coat stucco systems are proprietary, with each system owned be a stucco manufacturer (system holder)
  • Combines the scratch and brown coats into a single layer
  • Features a minimum 3/8” thickness of material that is embedded into lath
  •  Completed with a separate finishing coat to offer a wide range of finish colors and textures
  • Can provide labor efficiencies when compared to a traditional three-coat application
  • Reduces the weight load from the cladding on the assembly by approximately 50 percent

Through partnerships with stucco one-coat system manufacturers within the North American market, ROCKWOOL stone wool insulation is a component of code compliant plastering systems that may be installed over open framing or various approved sheathing surfaces.

These systems provide increased energy efficiency that creates a long-lasting exterior cladding for residential and commercial projects. These systems are used as alternatives per ICC-ES Acceptance Criteria for Cementitious Exterior Wall Coatings (AC11) to code prescribed conventional stucco systems compliant with ASTM C926. The stucco systems outlined below must be installed in accordance with the code, ASTM C1063, and the manufacturer’s published installation instructions, as applicable.  



Stucco Cladding Installation - Ci Labs Testing Imagery
Direct Applied Stucco Installation
During construction of the stucco wall assemblies no cracking was observed after the curing process. Compared to EPS foam, there were no extra efforts or modifications to the stucco mix required when using stone wool insulation.

Kenyon Plastering

Three-Coat Stucco

Three-coat stucco systems have been used for more than 100 years to create long-lasting, attractive, and durable cladding for buildings of all types. The use of continuous insulation (ci) in three-coat systems is becoming more common with evolving building codes that require greater thermal performance from exterior wall assemblies.

  • Three-coat stucco systems are non-proprietary and are designed to meet various code requirements, such as
    • International Building Code (IBC) Chapter 25
    • International Residential Code (IRC) Chapter 7
  • Typically applied in three layers
  • Heavier than one-coat stucco systems
  • Classified as noncombustible under the IBC

In a traditional three-coat system, typically the first layer is a 3/8” scratch coat, followed by a 3/8” brown coat, and the assembly is completed with a 1/8” finish coat for a total thickness of 7/8”. The three layers are applied over an approved water resistive barrier (WRB) and metal lath either by hand with a trowel or by machine. 

ROCKWOOL stone wool insulation boards can be used effectively in three-coat stucco systems in a variety assembly types and attachment strategies to meet building code requirements. These can include:

  • Drainmat over thermally broken clip-and-rail
  • Vertical hat channels over Z-girts and stone wool insulation
  • Vertical strapping over stone wool insulation
Stucco Multiunit Residential - Stock
iStock-184341017 - Modern Townhomes stock photo

ROCKWOOL Comfortboard®

Comfortboard is a rigid, high-density stone wool board designed for exterior continuous insulation applications. It offers improved energy efficiency, increased fire resistance, enhanced acoustic comfort, along with vapor permeance and moisture resistance for a durable enclosure.

Available in two product options;
Comfortboard 80 or Comfortboard 110, providing compressive strength to meet specific structural requirements, these products may also be used below-grade, under concrete slab, in floor-ceiling assemblies, and for sloped roofing applications.

Comfortboard is an approved component of both one-coat and three-coat stucco assemblies. Comfortboard can also be used with ROCKWOOL Comfortbatt thermal batt insulation in a complete insulated stucco assembly to provide increased thermal, fire and acoustic performance. 

Learn more about these stone wool insulation products:

R-Class builder product photos

Looking for answers? Let us help!