What Makes a High Performance Wood-Framed Wall for Sunset Green Home?
21st century building scientists have developed new technologies to ensure that wall assemblies control rain, air, water vapor and heat, which makes new homes today more airtight and watertight than ever. And tighter building envelopes can lead to healthier and more energy efficient homes. With a goal of LEED Platinum certification, Sunset Green Home needs to have a high performance wall assembly. Here’s a look – from the outside in – at Sunset Green Home’s exterior wood-framed walls.
Cladding
Exterior cladding is a home’s first line of defense. The best performing cladding is designed to resist wind and water, and is made of renewable or recyclable resources. Sunset Green Home has purchased G&R “Choice Brand” #1 R&R (rejointed and rebutted) Western Red Cedar wood shingles from Liberty Cedar for their high quality and consistency with the historic shingle-style homes in the region. Proper installation is critical to prevent moisture from penetrating the walls.
Partial installation of Sunset Green Home's Certi-grade Western Red Cedar shingles from Liberty Cedar
Drainage Plane and Rigid Sheathing
Even the best cladding is vulnerable to water intrusion, so building scientists recommend including a drainage plane (also known as a water resistive barrier, or WRB) behind the cladding. Behind the WRB, a layer of rigid sheathing provides structural integrity for wind-resistant building. Traditional wood frame construction typically includes a sheathing layer of plywood or oriented strand board (OSB). Experts recommend sheathing of at least ½” thickness to protect the building envelope from damage by wind-borne debris in a severe storm. Sunset Green Home is using ½” ZIP System sheathing from Huber Engineered Woods, which includes a WRB integrated into the structural sheathing. When sealed with ZIP Flashing Tape, the assembly is water-tight and airtight.
Sunset Green Home's 1/2" ZIP System sheathing with integrated water resistive barrier
Advanced Framing Techniques
It is difficult to meet the insulation requirements of increasingly stringent energy codes using conventional 2x4 framing. High performance wood framed wall assemblies like the one found in Sunset Green Home use at least 2x6 framing. Sunset Green Home has also used material efficient framing techniques, such as ladder blocking where interior and exterior walls intersect, to allow for greater insulation to be placed in the walls.
2x6 framing with ladder blocking at the intersection of Sunset Green Home's interior and exterior walls
Mold Inhibitor
Sunset Green Home has included a protective mildewcide coating to inhibit mold growth inside the walls. Cary Insulation has applied CertainTeed’s proprietary FortiCel™ product, a mold inhibitor that is sprayed onto the interior wall cavity after framing and sheathing is complete and before insulation is installed, to prevent mold growth on structural framing surfaces.
CertainTeed's FortiCel protective mildewcide on Sunset Green Home's interior framing
Insulation and Smart Vapor Retarder
Insulation minimizes heat transfer through the wall assembly and contributes to a home’s energy efficiency. A high performance wall assembly will include high R-value wall insulation to meet the home’s energy efficiency goals. However, while insulation will reduce heat transfer through walls, it cannot prevent mildew-causing moisture from moving through a wall assembly. 21st century building science has given birth to smart vapor retarders that allow a wall cavity to dry out under humid conditions and deter moisture from moving into the walls under dry interior conditions.
Sunset Green Home’s walls will be insulated to R-21 with CertainTeed’s innovative SMARTBATT™ insulation, which combines insulation with a smart vapor barrier in a single kraft-faced fiberglass batt product and eliminates the need for installation of separate insulation and vapor barrier products. By blocking moisture from entering the wall cavity when humidity is low and allowing the wall to breathe when humidity is high, SMARTBATT helps reduce the potential for mold and mildew growth.
CertainTeed's SMARTBATT with smart vapor retarder will be installed to R-21 in Sunset Green Home's exterior walls (photo courtesy of CertainTeed)
Gypsum
Gypsum board is interior sheathing that acts as a fire-resistive barrier and encloses the home’s framing and insulation. Specialty gypsum products have been designed to reduce noise transmission, fight mold and mildew, and withstand abuse in high traffic areas. And, a high performance wall assembly can even actively contribute to healthy indoor air quality. Sunset Green Home has selected one of the most innovative gypsum products available. AirRenew by CertainTeed uses a patent-pending, independently tested, technology to clean the air by absorbing Volatile Organic Compounds (VOCs) such as formaldehyde that may be present in other building materials or home furnishings.
Sunset Green Home will use CertainTeed's AirRenew gypsum throughout the project (graphic courtesy of CertainTeed)
Low/No VOC Paint
Paint is Sunset Green Home’s final line of defense in its high-performance wall system. Earlier generations contained VOC-emitting solvents with associated health risks. All major brands now offer GREENGUARD certified low/no VOC interior latex paints. Sherwin-Williams’ Harmony paint with Formaldehyde Reducing Technology may even reduce VOCs from other sources in the air. In spaces where Sunset Green Home doesn’t have AirRenew gypsum, formaldehyde reducing paint could be a helpful final layer. And choosing paint with integrated mildewcide will complete the high performance wall assembly in Sunset Green Home’s bathrooms and laundry rooms.
If you're renovating or building a new home, make sure you understand what's in your walls! Harness 21st century building science to include a high performance wall assembly. Want to learn more? Check out the slide show we wrote for bobvila.com: What Makes the Ultimate Wall?