Wood in civic buildings

by sadia_badhon | January 14, 2021 9:53 am

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By Jim Taggart, FRAIC

In April 2019, John Horgan, then Premier of British Columbia, announced a new program to incentivize the use of wood in public buildings in an attempt to mitigate the impact on the forest industry of climate change-related phenomena as the rising population of mountain pine beetles and the increased frequency and severity of forest fires.

For public projects, as for other types of buildings, new engineered mass timber products, supported by new legislation, make wood an economic and functional choice in both rural and urban areas. Two recent projects illustrate this point.

This article, based on a newly released case study by Wood WORKS! BC and the Canadian Wood Council (CWC), examines two recently completed civic buildings in British Columbia using wood. In Vancouver, Fire Hall No. 5 is an innovative response to rising land costs and the shortage of affordable social housing. In the Village of Radium Hot Springs, a wealth of local wood products, manufacturing capabilities, and craft skills combine in a community hall and library that can truly be called a ‘100-mile building’.

Fire Hall No. 5

Vancouver has the highest land costs of any city in Canada and, as a consequence, faces the challenge of maintaining an adequate supply of affordable housing. One strategy employed to address this situation is to reconsider permissible density and co-location of uses on city-owned property. Fire Hall No. 5, which combines a new station with 31 units of supportive housing, is one such example. The mixed-use project replaces an aging facility rendered obsolete by new seismic codes and the introduction of larger ladder trucks.

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The new fire hall includes three apparatus bays, crew dormitories, washrooms, fitness areas, a community training room, and a self-contained breathing apparatus (SCBA) maintenance room serving the entire Vancouver Fire Rescue Service (VFRS). Through a partnership with the Metro Vancouver YWCA, 31 units of safe, affordable housing for low-income, woman-led families and their children became the second component of the project.

Johnston Davidson Architects (JDa) faced the challenge of maximizing the program area within the 18-m (59-ft) height limitation on a tight site, while facilitating fire truck access and separating the fire hall and residential uses. Moreover, the entire building had to be designed to meet current post-disaster standards.

With the corner site facing two streets, it was possible to create two distinct entrances to the building—one for the fire hall off 54^th Avenue, and another for the YWCA housing off Kerr Street. This ensures the two organizations are understood by those accessing the building to be separate and distinct. VFRS occupies the first two floors and YWCA occupies floors three to six.

Most of the main floor is taken up by VFRS operational spaces and the apparatus bays where the emergency vehicles are stored. These vehicles leave and return through overhead doors located off 54^th Avenue.

The glazed fire hall entry is denoted by its coloured interior and proximity to the traditional concrete hose tower. The entry gives access to a community/training room and washroom, separated from the remainder of the hall by a secure point, making it accessible for community groups. The Kerr Street entry to YWCA residences is also at this level. The second floor is entirely occupied by VFRS and houses the crew dorms, washrooms, and fitness facilities.

Above the fire hall are four floors of housing for YWCA’s tenants, the suite layouts are almost identical on all floors with the exception of the third floor, which also incorporates a common room and laundry. Certified Leadership in Energy and Environmental Design (LEED) Gold, the building provides YWCA, the City of Vancouver, and the occupants with an energy-efficient solution for affordable housing.

The colour and texture of the materials used throughout the building play a role in the well-being of all occupants, and together with large-scale graphics, contribute to easier wayfinding. On the main and second floors where the fire hall is located, access to natural light, exterior views, and operable windows was a key component of the design. This increases the comfort for fire crews and reduces the requirement for artificial light and related energy demand.

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The residential floors are constructed in light wood frame, a highly efficient building system that utilizes a renewable material, harvested from sustainably managed forests. Solid sawn lumber is also inherently low in embodied energy.

All of the apartments have abundant natural light and access to generous balconies and in many cases, panoramic views of the city. The common roof terrace has both a children’s play area and large planter boxes that serve as a community garden, accommodating the City of Vancouver’s urban agriculture mandate and giving tenants an opportunity to contribute to their own well-being.

Just as this project broke new ground in terms of its mixed-use program, it also posed structural engineering challenges not dealt with in the current B.C. Building Code (BCBC). Although Herold Engineering had considerable experience with both fire halls and multi-storey, light wood-frame construction, there were no precedents to guide them through the design of a hybrid structure of this type that was also required to perform to post-disaster standards.

In such circumstances, the engineer-of-record is required to consult with professional peers to confirm the validity of the design assumptions being made. In concert with the City of Vancouver, an independent technical review was undertaken and design parameters agreed on before the final structural design phase.

While the decision to construct the fire hall portion in concrete was made at the outset of the project, the material of choice for the residential floors was reviewed with several options being put forward for cost analysis. Cross-laminated timber (CLT) and steel were both considered, but with each iteration of the design, the consulting team returned to traditional light wood frame as the most flexible and economical choice.

Creating a hybrid structure that behaves harmoniously under seismic, wind, and other dynamic loads is a challenge when the concrete spans are long, such as in a fire hall. This is in contrast to the more common situation of a commercial podium or parking garage, where the close spacing and repetition of column and beam elements enables imposed loads to be distributed more evenly throughout the podium structure. Additionally, the overall height restriction meant floor-to-floor heights on all levels had to be minimized to ensure the required residential program could be accommodated. A further complication was the need to provide three large apparatus door openings in the north wall, limiting the number of columns that could be used.

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To create consistent diaphragm action at the third-floor level at the base of the wood frame structure, the concrete slab was strengthened with a series of integral down-stand ‘joists’ that also help transfer loads evenly. These joists also provided the additional thickness necessary to cast in the multitude of screw anchors required to hold down the light wood building above, against seismic and wind uplift loads.

Additionally, because of the long span, there was a requirement to cast the 18- and 17-m (55-ft) slabs over the fire hall with a crown in the centre, in anticipation of the deflections occurring during construction and over time. This posed challenges for the four-storey, common wood-frame construction with gypsum board paneling being erected above the slab.

Comparing the predictions from several analytical software applications, the decision was made to camber the slabs accordingly and to monitor deflection during construction. Shims were used to level the prefabricated light wood-frame wall elements as they were installed. As construction proceeded, measurements were recorded confirming deflection of the long span suspended slabs was small enough to avoid excessive cracking in finishes.

Vancouver is in a very high seismic zone, so considerable analysis and design is required to ensure fire hall structures meet the building code requirements for post-disaster use. As this building makes use of wood framing for the four-storey residential portion, the wood structure makes use of conventional 2×6 frame construction with single- and double-sided plywood-sheathed shear walls along the corridors, at demising walls between suites, and for bearing walls within each suite. The higher than usual number and cumulative length of shear walls and seismic tie downs were needed to meet the more rigorous code requirements for this type of building.

Concrete and wood frame have decidedly different ductility and over-strength parameters, which are predictors of performance in a strong earthquake. After much consideration and professional peer reviews, it was decided to modify the wood-frame ductility and over-strength co-efficients to rationalize the requirement for force resistance between the two distinctly different framing systems.

The floor structure on levels four through six comprises wood I-joists and, where loads are greatest, laminated veneer lumber (LVL) beams. In the third-floor common room, where spans are greatest, steel beams were used in concert with wood beams and joists. These measures were required because
of the height restriction noted previously. This limitation also required the elimination of suspended ceilings and the careful routing of mechanical ductwork through and between the I-joists.

The use of hydronic heating also added complexity, as the 50-mm (2-in.) concrete topping on each floor added to the dead weight of the building and also to the magnitude of the lateral forces that had to be resisted and resolved.

At roof level, the provision of a play area in the centre portion of the roof required the mechanical units to be located around the perimeter, rather than positioned directly above the zone of the building they served. As a result, additional lengths of ductwork were required to connect the units with the appropriate zone below, and the structural engineer and I-joist manufacturer worked collaboratively to optimize wood-frame layouts.

The success of this highly innovative project is, in part, due to the adaptability and affordability of contemporary light wood-frame construction. Faced with height restrictions, post-disaster seismic requirements and unusual loading conditions, it nonetheless proved the most viable choice for the residential portion of the building.

Radium Hot Springs Community Hall and Library

The Village of Radium Hot Springs is located in the Columbia River Valley, East Kootenay region of southern British Columbia. The area is known for the natural hot springs in nearby Kootenay National Park, the Columbia Valley wetlands, and the Rocky Mountain culture. Perched on the edge of a natural kettle hole and lined with pine trees, the site of the new 800-m² (8611-sf) community hall and library is a microcosm of the valley. Vancouver-based Urban Arts Architecture (UAA) was selected to design the project following a request for proposals (RFP) issued by the village.

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The RFP required the project comply with the Wood First bylaw recently adopted by the village, and aspires to the creation of a “100-mile building,” (the Wood First Act was passed by the British Columbia government in October 2009 with the aim of generating demand for wood products, promoting climate-friendly construction, and stimulating economic activity in forest-dependent communities). Maximizing the use of locally harvested wood, processing capacity, manufacturing, and fabrication capabilities and craft skills would combine to provide the greatest possible social and economic benefits to valley communities.

Accordingly, UAA set up an integrated design process, in which various municipal departments, user groups, local industry representatives, and members of the broader community were invited to contribute their ideas and expertise to the conceptual development of the project. In bringing the community together, the meetings and open house events also helped build a broad consensus and strong commitment to the project.

By identifying the wealth of local materials, resources, and labour that could be incorporated into the project, the consultation process also ensured that, by reducing the effect of transportation, the embodied energy, carbon footprint, and life-cycle impacts of the building would be minimized. The result is a building incorporating approximately 288 m³ (10,171 cf) of wood products harvested mostly from forest licenses within 50 km (31 mi) of the site and processed at a local mill.

The building is organized and oriented to maximize the effectiveness of passive design strategies, with a long linear form on the east-west axis, permitting natural daylighting and cross ventilation. Strategically located roof overhangs control solar exposure. Window locations are carefully calibrated to capture  views of the mountains and connect to the park while maintaining less than 40 per cent window-to-wall ratio for energy efficiency.

The formal inspiration for the building came from the simple utilitarian sheds dotting the Columbia Valley. Unlike chalet-style roofs, low-pitched roofs allow snow to build up over the winter, with little danger from shedding snow or large icicles.

The building is clad in charred wood siding, a reference to the agricultural and ranching traditions of the valley. The charring machine, created by a local millwright took the form of a pizza oven fitted out with propane burners. The depth of char was controlled by varying the speed at which the material was run through the oven.

The interior spaces are defined by the variegated dowel-laminated timber (DLT) roof structure, and are layered with minimal wood detailing at key areas (DLT is a mass timber structural panel constructed of standard dimensional lumber, friction-fit together with hardwood dowels, not requiring the use of nails, screws, or adhesives. This combination results in a structural system with a high potential for demountability, adaptability, and reuse). The ramp down into the hall is lined with a wood screen, filtering views into the hall, and referencing the pine forests. Composite wood and acoustic panels provide sound attenuation at the stage.

Beyond its energy-efficient design and locally sourced materials, the building acts as the living room and social heart of the community. Co-locating the library and community hall provides cross-pollination and increases overall use. The community kitchen was designed with the local seniors’ group to ensure accessibility and ease of use.

The siting of the building creates a variety of exterior rooms within the public realm that can be occupied throughout the year. Indoor-outdoor connectivity promotes social well-being and expands year-round use of the adjacent park.

The building structure is relatively simple, with a post-and-beam frame supporting a shallow shed roof. With a tight budget, it was important to give the various product suppliers in the region equal opportunity to participate in the project. Accordingly, structural engineers Equilibrium Consulting, Inc., created a schematic design and performance specification that could accommodate either glue-laminated (glulam) timber or LVL columns and beams and CLT, nail-laminated timber (NLT), or DLT panels.

DLT panels of 1220-mm (48-in.) wide and lengths up to 6000 mm (236 in.) using 2×4 and 2×6 Douglas fir dimensional lumber were prefabricated. The panels were hand assembled using jigs to ensure accuracy and consistency, with the members fastened together using beech dowels. Adhesives were not employed to fabricate the panels. The tolerances achieved were in the order of 2 mm (79 mils), much finer than those for cast-in-place concrete foundations, and remarkable given that no computer numerically controlled (CNC) machinery was used. When completed, the DLT panels were transported to the site in a choreographed sequence to maximize efficiency.

Alternating the 2×4 and 2×6 timbers created a self-finished ceiling with a variegated texture. By spacing the panels 600 mm (24 in.) apart, the modular system was able to integrate lighting services in the gaps, which were later bridged by smaller removable panels finished with sound-absorbent material to enhance room acoustics.

Interior light wood framing was prefabricated onsite and installed in panels. The use of prefabrication for all elements of the structure reduced the overall construction time and helped the project stay on budget.

A high-performance building envelope, combined with passive design strategies and energy-efficient mechanical systems were used to minimize the building energy loads. A heat recovery ventilation system is augmented with large low-velocity fans and passive ventilation strategies to reduce cooling demand. Air source heat pumps and high efficiency boilers provide heating for the building, switching between systems to maximize efficiency.

A participatory design process has been shown to instill pride of ownership in a new building, encourage ongoing care and maintenance of the facility and improve its overall life-cycle performance.

The past decade has seen a number of important changes in the size and types of buildings permitted to be constructed in wood. It is important to remember the requirements for the specification of structural wood products and wood building systems are set out in the model National Building Code (NBC), which is concerned with health, safety, accessibility, and the protection of buildings from fire or structural damage.

In the 2015 edition of NBC, changes were made to increase the permitted height limit of wood construction for some buildings. These changes, which are the result of a rigorous scientific and engineering process by expert committees of the Canadian Commission on Building and Fire Codes, were incorporated into BCBC in 2018.

Whether built with light wood framing materials or engineered mass timber products, the added height and area of these buildings has given designers new options for an expanded range of occupancy types. These changes reflect the broad consensus that wood is a safe, economic, and more environmentally friendly alternative to concrete or steel construction. Additionally, the local availability of wood and wood products in most regions of the country means the majority of Canadian communities can benefit both economically and socially from the expanded opportunities offered by the new code provisions (the full case study, titled Wood in Civic Buildings, can be viewed at www.wood-works.ca/bc[6]).

[7]Jim Taggart, FRAIC, is a Vancouver-based journalist who has written on the subject of contemporary architecture in wood for over 20 years. His credits include more than 100 articles for national and international magazines, numerous technical case studies for wood industry organizations, and the books Toward a Culture of Wood Architecture (2011) as well as the recently released, Tall Wood Buildings: Design, Construction, and Performance (Second and Expanded Edition), written in collaboration with architect Michael Green. He can be reached at architext@telus.net[8].

Source URL: https://www.constructioncanada.net/wood-in-civic-buildings/

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