Net-zero builds: How masonry leads the way

by sadia_badhon | March 26, 2020 10:09 am

By Dave Jackson

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The building codes and approaches to sustainability are changing rapidly with many manufacturers and construction professionals struggling to stay ahead of the curve. The industry is also facing severe labour shortage. This is why advancements in masonry and manufacturing technologies have combined with other materials to create ‘green,’ easy-to-install systems. They also meet evolving codes, such as the National Energy Code for Buildings (NECB) 2017, a transition to achieving net-zero emission targets by 2030.

“Due to the pace of change with energy codes, it has become difficult for designers and manufacturers to interpret, meet, and demonstrate compliance with the increasingly strict code requirements,” said Mark D. Hagel, PhD, P.Eng., executive director, Alberta Masonry Council. He explained the traditional building materials of wood, masonry, concrete, steel, and glass may not deliver the necessary properties, even in temperate climates, to comply with thermal requirements.

For example, steel-studded backup walls can offer far less thermal resistivity than masonry due to the former’s high thermal conductivity. Additionally, the majority of today’s HVAC systems only operate at approximately 85 per cent efficiency, which is fine for more temperate places in the world, but is less than the 95 per cent required to help building performance in colder climates. It is also becoming more difficult to tradeoff fenestration for opaque walls, especially without modelling. The requirements for increased accuracy in accounting for thermal bridging of all elements is also driving up the insulation demand, leading many architects to take another look at how masonry’s thermal mass and heat retention, durability, and sustainability can help meet today’s increasingly challenging codes.

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In 2013, the Masonry Veneer Manufacturers Association (MVMA) worked with the National Concrete Masonry Association (NCMA) to ensure their products were formally recognized as concrete masonry products. Two ASTM standards for adhered manufactured stone masonry veneer (AMSMV) were also developed to determine adhered manufactured stone unit properties and veneer installation procedures. The latest versions of these standards were published in 2018. These standards, along with Canada’s NECB requirements, have resulted in increased installation of thin masonry veneer products over exterior rigid or semi-rigid insulation.

The need to maintain an acceptable wall thickness coinciding with the increased depth of exterior insulation now needed to meet NECB requirements has made adhered masonry veneers popular material options. Thin veneers deliver the noncombustible properties and attractive look of full bed masonry while reducing the required wall thickness by several inches, as well as creating a thermal break between the structural wall and the exterior.

This lowers the thermal bridging that is typically not reduced when cladding is in direct contact with the backup wall, as in a wood-stud wall with siding.

However, the totality of the NECB code is yet to be realized as the transition to the stringent NECB 2030 draws closer. NECB 2017 can be interpreted as a transition code, representing a move to thermally broken (or at least improved) connectors for cladding with the goal of net-zero residential buildings by 2030.

As a result, one trend designers and constructors are anticipating, especially in the residential sector, is the use of exterior-insulated, 2×6 double-studded structural wall to comply with thermal performance requirements and a second 2×4 wall connected to the top and bottom of the structural wall to eliminate thermal bridging and serve as cladding support.

Masonry presents an alternative to this complex, multilayered system, as thermal breaks in adhered veneers require less thermal bridging, and the material provides an inherent thermal mass advantage that directly affects cooling and heating cycles.

“Masonry has been able to achieve Passive House targets with either concrete masonry or clay brick,” said Hagel. “There is a great opportunity for masonry to become much more viable than vinyl siding and traditional stucco. The new energy codes will also increase the square footage of opaque walls, which may cause a move to classic architecture that uses smaller windows and more masonry, as popularized in 1920s North American cities.”

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Further, full bed-depth or thin veneers can add to the thermal mass and R-values of homes and office buildings. During the winter months, it is common for homeowners to raise the thermostat when they first arrive, since many building materials do not retain heat well. Masonry’s ability to store heat can directly impact utility bills by offsetting the need to warm a home during peak demand periods by a couple of hours.

It is also important to consider the insulating value of materials alongside their thermal mass when assessing energy efficiency. Thermal mass absorbs energy slowly and stores it for longer periods of time, which reduces indoor temperature swings, and often leads to a reduction in the size of mechanical heating and cooling systems. The benefits of thermal mass are most accurately reflected when utilizing energy analysis programs that assess the building type, location, and temperature variations over a 24-hour period, 365 days a year. Thermal mass is also directly proportional to the weight and density of the material and is most effective when used on the interior side of the insulation in the building envelope. This includes using loadbearing concrete masonry as part of a wall system.

There is also now a requirement to address and minimize thermal bridging and its impact on overall thermal performance to get more accurate data than using the simple R-value of a wall system.

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“The impact of thermal bridging must be accounted for, not only for the backup, but also in all the components that attach the cladding to the backup wall to meet the requirements of NECB 2017,” said Hagel. “This makes it difficult to have a blanket solution as each building has a different type and number of thermal bridges that previously could be ignored.”

Eliminating the two per cent thermal bridging relaxation permitted in NECB 2011, which previously excluded ties and shelf angles, will make it more difficult for highly conductive building materials, especially steel, to meet the new codes. The latest thermal bridging calculations require measurement of the following elements.

Clear field transmittance or the heat flow from the wall, floor, or roof assembly

This transmittance includes the effects of uniformly distributed thermal bridging components like block ties, structural framing (e.g. studs), and structural cladding attachments that would not be practical to account for on an individual basis. (The clear field transmittance is a heat flow per area, and is represented by a U-value denoted as the clear field [Uo].)

Linear transmittance or the additional heat flow caused by details that are linear

This includes the slab edges, corners, parapets, and all of the transitions between assemblies. (The linear transmittance is a heat flow per length, and is represented by psi [Ψ].)

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Point transmittance or the heat flow caused by thermal bridges that occur only at single, infrequent locations

This includes building components such as structural beam penetrations and intersections between linear details. (The point transmittance is a single additional amount of heat, represented by chi [χ].)

Masonry’s ability to meet these requirements, the NECB 2017 code, and combine effectively with other building materials as well as its thermal qualities, have made it a highly competitive resource among the design-build community. Whether employed as a standalone material or in combination with wood- or steel-studded structures, the complete system approach to wall materials has not only grown in popularity, but also improved the cost-effectiveness, structural integrity, energy efficiency, and building strength, while achieving the desired look.

Sustainability and durability take centre stage

As the transition to NECB 2017 hits home, provinces are gearing up with building designs integrating sustainability and durability.

“Asset management plans incorporating the life-cycle costs of building components are becoming mandated, leaning toward durable materials,” said Hagel. “The intent is to codify sustainability as, according to Carl Elefante, ‘the greenest building is the one that is already built.’”

Moving to NECB 2017 requires the building envelope to increase thermal performance by 10 to 14 per cent, Hagel explained.

“Energy code targets will require more rigorous thermal analysis and insulation and cross-disciplinary co-ordination,” he said. “In addition to this, jurisdictions are moving quickly toward requirements for building materials and components that are not currently codified in the national or provincial building codes to have a Canadian Construction Materials Centre (CCMC) number or an engineer’s stamp.”

Subsequently, masonry is playing an important role in Leadership in Energy and Environmental Design (LEED) projects. Another great advantage for masonry materials is the ability of the Portland cement in these components to absorb carbon dioxide (CO₂). In clay brick veneer installations, only mortar joints absorb CO₂, while concrete block and concrete masonry veneers (including manufactured stone) absorb the gas. Both types of masonry reduce the carbon footprint of a building by offsetting the gas used to produce the products via CO₂ absorption either at the time of manufacture of the products (as with carbon-cured concrete products) or naturally over time through weathering carbonation.

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The life-cycle impact of masonry

When evaluating the environmental aspects of building materials and their ability to meet the latest code and sustainability requirements, specifiers should begin the process with a life-cycle assessment (LCA). This includes a cradle-to-grave or cradle-to-cradle evaluation highlighting practices that range from manufacturing and building maintenance to end-of-building-life projections and material re-use, repurpose, and recycling.

At a minimum, an LCA should ascertain steps ranging from the environmental impact of the raw material acquisition process (cradle) to the manufacture of finished product. The results of a LCA can be reported by a manufacturer or can be used to develop an environmental product declaration (EPD), which is a formal reporting of the life-cycle impacts of products, according to specific rules.

Other considerations should include:

• the cost of building materials over the entire lifespan of a building;
• fire-resistant construction and resistance to impacts and wind-borne debris;
• superior sound absorption with all frequencies; and
• designs that do not produce volatile organic compounds (VOCs) or the release of other hazardous chemicals.

Multiple disciplines for durability

These details are important for nearly all types of masonry installations, including their seamless integration into hybrid wall systems. Often used in multifamily residentials, shopping centres, and low-rise construction, brick veneer and wood or steel studs are paired to create façades that look like solid masonry and provide long-lasting brick exteriors.

There are also new options simplifying the path to a high-performing veneer system. One such path combines thin veneers inserted directly into profile-moulded expanded polystyrene (EPS) panels that are attached directly to the structural wall. The veneers are held in place with a specially designed anchor and finished using a proprietary, high-performance mortar.

This system provides:

• a steady-state R-value of 9.2;
• continuous insulation with extra layer of thermal protection;
• improved water management; and
• acoustical comfort.

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Since it can be paired with a number of structural systems that can accommodate the additional internal insulation, this system has helped building owners meet and exceed demanding energy codes, while creating the beautiful look of brick or stone masonry veneer.

Another consideration for mixed-use structures is sound transmission for interior walls, also known as the sound transmission class (STC) for new construction. The aforementioned wall system has an STC of 61 when installed over steel stud framing. Additionally, the performance improves if installed over structural concrete masonry blocks, depending on size, configuration, and adjacent room occupancy.

Likewise, a panelized stone system is also viable, as it eliminates the need for lath or mortar, and allows for application over a wider variety of substrates than adhered stone veneers. This particular product can be fastened directly to the substrate—whether concrete, wood, or fibreglass—and can also be installed over rigid insulation to enhance R-values. The panelized stone also has an integrated drainage channel that acts as a rainscreen, keeping the wall dry. “With panelized stone systems, one has eliminated the need for the substrate to be attached to z-bar or drainage mat product and still have the reduced thickness and esthetics of a thin stone veneer,” said Hagel.

Environmentally preferable materials and products

The careful specification of building materials and products is important in achieving the sustainable design strategies. Materials should be evaluated over their entire life cycle, from raw material extraction to end-of-life. In this context, environmentally preferred masonry products should incorporate:

• abundant and efficient use of raw, bio-based, recycled, or rapidly renewable materials;
• sustainable acquisition or manufacture measures;
• regionally available materials;
• regional manufacture or fabrication;
• recyclable, salvageable, durable, and nontoxic materials; and
• construction waste avoidance.

These building products have evolved tremendously in recent years to meet the performance and esthetic needs of modern construction. In terms of overall life-cycle costs, masonry veneer systems provide added thermal protection, moisture management, and mould resistance to a building, thus delivering beauty, performance, and long-term maintenance.

Known for their timeless appeal and enduring strength, today’s next-generation masonry assemblies are helping the construction environment achieve green, sustainable goals with enhanced building performance, installation efficiency, and flexibility—all without losing the unique character and appeal of traditional masonry.

[8]Dave Jackson is the brand manager for masonry and dry mix at Oldcastle APG, a CRH Company. Coming from an ad agency background with a specialization in building products, Jackson melds creativity and industry intelligence to help the masonry team remain a leading provider of modern masonry solutions to construction pros, architects, and builders across North America. He can be reached via e-mail at dave.jackson@oldcastle.com[9].

Source URL: https://www.constructioncanada.net/net-zero-builds-how-masonry-leads-the-way/

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