How to Insulate Exterior Walls with Rigid EPS Foam
Insulating exterior walls with rigid foam is a highly effective method for enhancing the thermal performance of buildings. Rigid foam board insulation, such as Expanded Polystyrene (EPS), is one of the most effective ways to improve the thermal performance of a building and reduce energy consumption. By applying insulation on the exterior, these products create a highly efficient building envelope, resulting in improved energy efficiency, lower heating and cooling needs, and increased indoor comfort. Alleguard’s rigid EPS foam board insulation products, such as non-perforated SilveRboard®, perforated SilveRboard®, SilveRboard® Graphite, Envirosheet, Envirostrap, Amdrain, are designed to provide stable long-term thermal resistance with easy installation.
Read this guide to learn the best practices when using rigid EPS foam insulation on exterior walls, focusing on maximizing thermal efficiency, minimizing air leaks, and ensuring durability.
Benefits of Rigid EPS Foam Insulation
Rigid EPS foam insulation offers several key benefits when used in exterior wall applications:
High R-Value: Rigid EPS foam provides excellent thermal resistance, reducing heat transfer through the building envelope.
Moisture Resistance: Rigid EPS foam insulation is resistant to moisture, preventing mold growth and ensuring long-term durability.
Eco-Friendly: Rigid EPS foam insulation boards are made from materials that can be recycled, contributing to sustainable building practices.
Ease of Installation: Lightweight and easy to cut, rigid EPS foam boards are simple to install, saving time and labor on construction sites.
Vapor Barrier Potential: Products such as non-perforated SilveRboard® can be a vapor barrier when installed with an approved sheathing tape at the seams, in accordance with the authority having jurisdiction.
Choosing the Best Rigid EPS Foam Insulation for Exterior Walls
Choosing the right rigid EPS foam insulation for exterior walls and foundations is critical to ensuring optimal thermal performance, moisture resistance, and long-term durability. Alleguard offers a range of high-performance rigid EPS foam insulation products designed to meet the needs of various construction applications, including SilveRboard® and Envirosheet. The following factors can help guide you in selecting the appropriate insulation for your specific project:
Application Type
Above-Grade Walls: For walls exposed to external weather conditions, you need insulation with high thermal resistance, moisture protection, and durability. Non-perforated SilveRboard®, perforated SilveRboard®, and SilveRboard® Graphite, with their reflective lamination provide an added layer of thermal protection in above-grade applications. Unfaced insulation is also available, and includes products such as Alleguard’s Envirosheet, and Envirostrap.
Below-Grade Walls: Insulation used in below-grade applications requires high compressive strength to withstand the pressure from below-grade elements and water. High-Density Envirosheet, High-Density SilveRboard®, and Amdrain are excellent choices for these heavy-duty applications due to their moisture resistance and robust performance under stress.
Thermal Resistance (R-Value)
Higher R-Values are necessary for climates with extreme temperatures.
For moderate thermal resistance needs, Envirosheet EN12 and SilveRboard® SB12 provide excellent performance at a lower cost.
Compressive Strength
Areas that endure high loads require insulation with higher compressive strength. Products like High-Density Envirosheet and High-Density SilveRboard® are designed to withstand these stresses.
For less demanding applications, Envirosheet EN12 and SilveRboard® SB12 offer adequate strength with lower compressive requirements.
Moisture Resistance
For applications prone to moisture exposure, such as below-grade walls, Envirosheet and SilveRboard® products offer excellent moisture resistance in addition to preventing prevent mold growth.
Overview of Our Exterior Rigid EPS Foam Insulation Board Products
Overview of Insulating Exterior Walls with Rigid EPS Foam
Above-Grade Walls
Proper insulation of above-grade walls is essential for maintaining thermal efficiency and ensuring the building is airtight. This process can vary slightly depending on whether you are working with sheathed or open stud walls.
Sheathed Wall Assemblies
When installing rigid EPS foam over sheathed wall assemblies, SilveRboard® or Envirosheet boards are installed over the exterior sheathing to provide a continuous layer of insulation.
Secure the rigid EPS foam boards using fasteners in a grid pattern to ensure a strong, even attachment. Pay close attention to fastening around the edges to prevent movement or gaps.
Open Stud Wall Assemblies
When dealing with open stud walls, the rigid EPS foam insulation can be attached directly to the studs. In these assemblies:
Rigid EPS foam boards are fastened directly to the studs. The fastener heads should be large enough to avoid puncturing the foam.
Vertical installation is preferred due to the ease of aligning the foam boards with the studs, however horizontal installation is also possible.
Below-Grade Foundation Walls
Installing rigid EPS foam insulation on below-grade foundation walls provides excellent thermal protection and prevents heat loss into the surrounding below-grade elements.
Exterior Foundation Insulation
Exterior insulation protects the foundation from temperature fluctuations and moisture ingress. The installation process includes:
Apply a waterproofing membrane to the foundation wall before installing the rigid EPS foam insulation.
After the waterproofing membrane is applied, adhesive or mechanical fasteners are used to attach the foam boards directly to the foundation wall. Ensure that the surface is clean and smooth before applying the insulation.
Provide covering/protection with proper flashing at the top of the insulation to ensure water doesn’t get behind the insulation and protect at grade from impact.
Interior Foundation Insulation
In cases where exterior insulation is not possible, rigid EPS foam can be installed on the interior side of the foundation wall.
This approach is less effective than exterior insulation, however interior foundation insulation may be more practical in many cases.
In humid environments or when the interior space has high moisture levels, an additional vapor barrier may be required to protect the insulation and foundation from condensation.
Exterior Cladding Installation
When insulating a home with rigid EPS foam, it is important to follow best practices for installing exterior cladding to ensure both the insulation and cladding perform optimally. Alleguard’s rigid EPS foam insulation boards are compatible with virtually all common cladding systems, but installation methods will vary depending on the cladding material. Below are guidelines for installing different types of exterior cladding over rigid EPS foam insulation. The following should be followed in accordance with the manufacturer’s guidelines and installation instructions.
Masonry Installation
Masonry or brick veneer is a popular finish in both residential and commercial construction. When applying masonry veneer over rigid EPS foam insulation like SilveRboard® or Envirosheet the choice of fastener needs to be considered:
In low-rise residential applications, a sheet metal anchor combined with a 2” (51mm) plastic washer and a screw is commonly used. The screw length must be at least 1” (25mm) longer than the combined thickness of the insulation board and sheathing.
Corrugated ties may be used for thinner insulation boards (up to 1¼”).
There are various proprietary anchors available, such as the barrel screw, which allow lateral loads to be transferred directly through the foam to the framing behind.
Siding Installation
Various types of siding such as wood, vinyl, fiber cement, or metal siding can be installed over SilveRboard® or Envirosheet. The installation process may vary depending on the material:
For wood and fiber cement siding types it is recommended to use vertical strapping, typically wood or metal, attached directly through the rigid EPS foam insulation and into the sheathing behind to provide a siding attachment surface. The siding is then installed over the strapping, ensuring there is a pressure-equalized air gap between the cladding and insulation along with appropriate flashing, trims, vents, and bug screens, to help facilitate proper water drainage.
Vinyl siding can often be installed directly over the insulation, provided it is fastened securely into the sheathing. Always ensure local building codes and manufacturer’s guidelines are followed, particularly concerning the use of a weather-resistive barrier.
Stucco
Stucco is an exterior finish that has been used for centuries all over the world and has evolved over the years in its application and composition. Stucco can come in various textures and colors. Currently, in North America, there are two main types of stucco finishes: traditional stucco and synthetic stucco. SilveRboard® and Envirosheet are both compatible with these systems.
Prepare the surface by installing a wire or expanded metal lath fastened through the rigid EPS foam board insulation into the wood framing. Additional lath materials (such as a fiberglass mesh) can be used with synthetic stucco. There are two common contemporary methods used to create a rainscreen wall; one method involves applying a water resistive barrier (WRB) over the sheathing, followed by the rigid EPS foam, dimpled/drainage membrane, wire lath, typically 17 gauge, fastened through the insulation, and into the sheathing and layers of traditional stucco. An alternative method involves the dimpled/drainage membrane being installed prior to the rigid EPS foam. The stucco layers commonly involve stucco, scratch coat, brown coat, and finish coat.
When installing synthetic stucco, if a fiberglass mesh or 20 gauge wire lath is installed instead of a 17 gauge wire or expanded metal lath, the assembly could be built without a drainage cavity, depending on the project and building code requirments. If installing traditional stucco without a dedicated drainage layer, it is recommended to use a WRB with a crinkled surface.
Always check local building codes for the requirements regarding WRBs, approved mesh types as well as requirements for drainage before beginning any stucco application.
When using fasteners to attach cladding, it is critical to ensure that fasteners are long enough to penetrate through the insulation and into the structural sheathing or studs behind it. Use screws, nails, or anchors that are at least 1” longer than the combined thickness of the insulation and sheathing. For heavier cladding like brick, consider using specialized anchors that help reduce thermal bridging and ensure a secure attachment. Follow the manufacturer’s guidelines and instructions, along with ensuring local building codes are followed.
Best Practices for Installation
Proper Sealing: Sealing all seams and edges with high-quality approved sheathing tape or caulk is essential for preventing air leaks and maintaining energy efficiency, where applicable.
Avoiding Gaps: Ensure that the insulation boards are installed tightly against one another and around openings to avoid thermal bridging.
Vapor Barrier Considerations: Depending on the climate and site specific building codes, a vapor barrier may be required to prevent moisture from compromising the insulation.
Rigid EPS foam insulation such as perforated SilveRboard®, non-perforated SilveRboard®, SilveRboard® Graphite, Amdrain, Envirosheet, and Envirostrap, provide a robust, energy-efficient solution for insulating exterior walls. For both above-grade wall and below-grade foundation assemblies, following best practices ensures that the building envelope is airtight, moisture-resistant, and thermally efficient. With proper installation, rigid foam insulation can significantly reduce energy costs, improve occupant comfort, and contribute to the sustainability of a building.
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