Fewer glass towers will be appearing in Canadian skylines if proposed changes to the National Energy Code for Buildings (NECB) are adopted. Consumer demand may be driving the proliferation of high-rise condominiums with extreme window-to-wall ratios, but recently released documentation from the Canadian Commission on Building and Fire Codes (CCBFC) contends that a flawed basis for determining a building’s thermal transmittance has played an enabling role.
A slate of measures addressing building envelope, heat recovery and lighting are now posted for public comment with a target for a 2017 code update. Of these, new criteria for calculating thermal bridging and a mandate for heat/energy recovery systems in a wide range of conditions could have the most significant impact on the design and construction of new buildings. Other proposed energy code changes of note include: calls for improved performance of roofs, window and doors; reduced allowance for skylights; and generally lower lighting power densities due to the emergence of more energy-efficient lighting products.
“This is a lot in one step, but I think this is where we need to get,” advises Andrew Pape-Salmon, senior energy and sustainability specialist with RDH Building Science Inc. “Definitely it will increase upfront capital costs (to comply with the code), but these are all economically justifiable from an operating cost perspective.”
In calling for a more comprehensive approach to gauging infiltration/leakage, the CCBFC maintains that currently accepted methods underrate the impact of thermal bridges — i.e. how heat or cold moves between various elements of the building envelope assembly.
Currently, a fairly limited number of elements are directly factored into the code’s allowances for overall thermal transmittance, while other elements that penetrate the envelope are addressed more generally as a percentage of the surface area or exempted from consideration if insulation is present. New evidence disputes these assumptions.
“With the NECB-allowed exclusions and unconsidered thermal bridges, the actual overall thermal transmittance of opaque envelope assemblies can be substantially higher (>2x) than the calculated overall thermal transmittance as assumed in the NECB,” the rationale for the proposed change states. “Because the impact of thermal bridges is not properly reflected in ‘base building’ assumptions, there is no credit or incentive for designers to incorporate design practices that reduce thermal bridging.”
For example, the insulated glass spandrel panels that create the opaque portion of a glass curtain wall can have a high insulation value when assessed as a stand-alone structural component, but any penetration or contact with other surfaces will diminish that performance.
“If you take into account all the thermal bridging, the R-20 degrades to R-5 or R-4,” Pape-Salmon notes. “That would be the best example of thermal bridging and the worst example of degraded thermal performance.”
To counter this, it’s proposed that designers would have to account for the thermal transfer at almost any place another element comes into contact with the envelope, including: studs and joists; penetration of floor slabs, beams, girders and columns; junctions with the roof or glazing; edges of walls and floors; ornaments; and appendages. This could be accomplished via prescribed ASHRAE or ISO calculations, computer modelling or laboratory testing, but Pape-Salmon speculates most developers will opt for modelling and the cost premium that goes with it.
“Fundamentally, this requires what’s called thermal analysis. The thermal bridging calculations mean everything is moving into the cost area of energy modelling,” he says. “It’s definitely increasing the cost of compliance, but it is also moving us into the direction of the compliant building actually performing in line with what the energy model has predicted.”
The proposed measure means that formerly compliant designs could fail to stay within the code’s allowable limit for thermal transmittance since developers’ calculations will almost automatically yield higher numbers — a result the CCBFC acknowledges amounts to a “major change in performance requirements”.
“This, in turn, will require major departures from current common construction practice in NECB-compliant buildings and associated increases in construction costs,” the code change rationale states. However, there may be relatively little cost impact for designs that already exceed the code.
On the plus side, the CCBFC argues that expanding the required input of information will help developers identify where gains can be made. “One benefit of this additional analysis is that it will make apparent where low-cost changes to details can generate significant changes to energy use over time,” it submits.
An accompanying consultant’s report commissioned by the CCBFC’s Standing Committee on Energy Efficiency in Buildings also stresses that this measure is the most effective among all proposed code changes. “Codifying infiltration would have a significant impact on energy savings (in the range of 20-40 per cent) for all building types in all six climate zones,” it concludes.
U value reductions
Meanwhile, the proposed code changes would explicitly mandate improved performance of roofs, windows and doors, equating to a 15 per cent increase in insulation values. Notably, associated studies conclude that there are fenestration products “currently available” in the marketplace that could achieve this target, resulting in modelled savings of 2.1 to 3.3 per cent of total building energy consumption depending on building type and geographical location.
The cost premium for this new window performance requirement, relative to the current NECB, is pegged at a maximum of $10 to $15 per square metre in all but the coldest of climate zones. Beyond that, the code change rationale also suggests the new stipulation “may force windows to be completely redesigned.”
“Each specific change may result in a very small cost to the builders, but when you add up all the changes, the cost increase can be very significant,” cautions Bob Finnigan, president of the Canadian Home Builders Association and chief operating officer with the housing developer, Herity. Yet, based on trends in the single-family and low-rise market, industry insiders do foresee more competitive product costs as market scale grows.
“The technology is there. The glazings are there. As production ramps up then costs usually go down,” observes Lisa Bergeron, government relations manager with the window and door manufacturer, JELD-WEN, and first vice president of the industry association, Fenestration Canada.
She commends Natural Resources Canada’s Energy Star initiative — a voluntary partnership with manufacturers supplying the residential and low-rise sector — and suggests the proposed regulatory prompt might spur similar progress in larger commercial/multi-residential buildings.
“It truly is a market transformation,” Bergeron asserts. “We went from doing clear-clear (in double pane assemblies) to using low-e argon in about a five-year period. Low-e was a rarity not that long ago. Now, a lot of the time, the regulations are trailing what’s happening in the marketplace. Now the residential sector is going to triple (pane).”
Pape-Salmon concurs. “In commercial buildings, performance of windows has not been tracking in step with the residential sector,” he says. “The proposed code change is very significant. It ensures windows will be high-performing, and Canadian manufacturers are capable of meeting this requirement.”
Together, the more stringent fenestration requirements and heightened scrutiny of thermal bridging will likely have the most impact in the multi-residential sector. As code drafters have intended, developers will either have to ensure their favoured architectural style is more energy-efficient or turn to something different to engage prospective homebuyers.
“The glass boxes would still be plausible, but they’d need better windows, and the balconies would have to be better insulated from the suite,” affirms Andrew Pride, an independent energy management consultant who serves as chair of the Standing Committee on Energy Efficiency in Buildings. “There are countless examples today of developers profitably constructing buildings, including glass boxes, that are designed to use significantly less energy than required by code.”
Tighter building envelopes lead somewhat logically to ventilation and the proposals for heat recovery or energy recovery systems in a much wider sweep of buildings. The code currently mandates heat recovery when the air exhausted from a building’s HVAC system contains at least 150 kilowatts of sensible heat, but code drafters suggest there are far greater savings to be captured and cost-effective technologies for doing so.
The proposed energy code changes establish varying triggers for requiring heat/energy recovery based on the climate zone and the volume of outdoor air that will be drawn into a building. They also introduce more stringent efficiency thresholds for heat recovery equipment, bumping up the current requirement for a minimum of 50 per cent transfer of energy to 60 per cent.
Effectively, heat/energy recovery systems would be required in almost all commercial buildings (except in Vancouver’s climate) where ventilation systems operate for at least 8,000 hours per year. Multi-residential buildings with self-contained in-suite HVAC systems would be exempted.
“This is a significant move for Canada and it actually puts our code at the forefront for energy performance,” Pape-Salmon says. Yet, in practice, HVAC industry insiders suggest the market is already there.
“We are sealing up buildings tighter and tighter and, as a consequence, ventilation is critical for air quality,” says Warren Heeley, president of the Heating, Refrigeration and Air-conditioning Institute (HRAI) of Canada. “Energy recovery is a mainstay of the commercial side of the building industry. It just makes sense to try to save on the costs of warming up the air you’re bringing in from outside.”
Other proposed energy code changes include: ventilation requirements specifically targeted to commercial kitchens; a reduction of the allowable area for skylights from 5 per cent to 2 per cent of gross roof area; and occupancy-triggered controls for lighting and temperature in hotel and motel guestrooms. All are posted on the Codes Canada website and are open for comments until December 9, 2016.
Barbara Carss is editor-in-chief of Canadian Property Management.