Water-resistant barrier for moisture protection
Key building code objectives are put in place to protect occupants from precipitation and prevent water penetration from the exterior through the building’s envelope. As the use of wood framing in mid-rise developments increases, water protection is of greater importance. After all, wood is susceptible to mould and rot. A properly designed water protection skin is an architect’s best defense against moisture. This is typically done with rainscreen cladding over a water-resistive barrier (WRB).
Typically, moisture problems occur because of moisture-sensitive materials and components. However, gypsum manufacturers have developed technologies to address the need for mould and water resistance. Glass-mat-reinforced gypsum board offers a mould and WRB face. High-performance exterior glass reinforced gypsum sheathings can achieve a mould resistance rating of 10—the highest possible rating—according to ASTM D3273, Standard Test Method for Resistance to Growth of Mould on the Surface of Interior Coatings in an Environmental Chamber.
Fibreglass mats used in lieu of traditional face and back paper are the highest-performance gypsum boards on the market. These durable boards are reinforced glass mats, fully embedded into a water-resistant gypsum core positioned beneath a paperless polymer-modified gypsum surface, and a protective acrylic coating on the exterior face. These best-case-scenario boards also handle like standard gypsum board and come with an exposure warranty—typically between six and 12 months, depending on the product and manufacturer. This guarantees the board will experience no loss of performance due to ultraviolet exposure or exposure to the elements. The glass-mat-reinforced gypsum can also be covered with a WRB complying with CAN/ULC-S741, Standard for Air Barrier Materials, and CAN/ULC-S742, Standard for Air Barrier Assemblies compliant WRB for a smarter skin that protects against moisture ingress and helps prevent moisture build-up in exterior walls.
Air barrier system
According to the National Research Council of Canada (NRC), about 100 times more moisture enters a building by way of air leakage than by vapour diffusion. As such, gypsum board’s airtightness makes it a suitable material for air barrier systems. Code-compliant mid- and high-rise buildings require high-performance wall assemblies that are continuous, airtight, and constructible. Recently, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) reported the best-performing air leakage system was sealed (including taped joints) exterior gypsum board. Ensuring joints and penetrations of the installed gypsum sheathing are installed with compatible code-compliant air barrier sealants and membrane materials will help maintain the durability of the air barrier system.
Specifiers should also seek out gypsum sheathing that will meet the manufacturing requirements and specifications of ASTM C1177, Standard Specification for Glass Mat Gypsum Substrate For Use as Sheathing. These boards are appropriate substrates in architecturally specified exterior insulation and finish systems (EIFS). Such compliant gypsum sheathing boards are designed for attachment to the outside of an exterior wall framing with the intent to control the infiltration of weather elements. They can be used in wood-frame as well as steel-stud commercial construction. Importantly, these gypsum materials have a uniform hardness across the entire board that assists in the prevention of screws from penetrating the fully embedded glass mats, creating less opportunity for moisture and air intrusion.
Indoor air quality
Indoor air quality (IAQ) is another top-of-mind consideration in the specification of any material. Currently, a few Canadian-appointed experts are participating in a joint International Organization for Standardization (ISO) working group on energy performance of buildings using a holistic approach to develop a new 52000 series of ISO standards—there have been 13 published. There is a draft standard, “Energy Performance of Buildings—Indoor Environmental Quality—Part 1: Indoor Environmental Input Parameters for the Design and Assessment of Energy Performance of Buildings,” for indoor environmental design and assessment of energy performance of buildings that includes the panels (wall) that clean the air. It is anticipated these standards, as well as the National Building Code (NBC), will adapt these health-related standards in the coming months to include low-polluting buildings for the well-being of people. In the meantime, architects and specifiers working on hospitals, schools, and other landmark buildings where healthy indoor environments are paramount can take advantage of world class ISO standards.
Gypsum board is a naturally derived building material. It is non-polluting to indoor environments, and can be certified by GREENGUARD for low chemical emissions per UL 2818, Certification Program for Chemical Emissions for Building Materials, Finishes, and Furnishings.
Further, innovative formaldehyde-absorbing gypsum board has been engineered to actively clean indoor air by absorbing circulating formaldehyde and converting it to inert compounds. This material has been measured for permanent formaldehyde absorption capacity of 0.4/m2 of surface area and has been tested to ISO 16000-23, Performance Test for Evaluating the Reduction of Formaldehyde Concentrations by Sorptive Building Materials, and validated by ULE through their Environmental Claims Validations program. This interior air-cleaning passive technology reduces the need for relying on mechanical ventilation systems to clean VOCs, and hence the energy required for a mechanical system to function.
