STEEL FRAMING ALLIANCE | FRAMEWORK ONLINE
  November 3, 2010
MARKETPLACE
 
Energy Efficiency Standards Could Change Building Methods In Canada

Construction and design methods could be in for more than a few alterations in the next five years as building codes move to toughen energy efficiency standards.

One of the top priorities will be how to improve the building envelope. Builders shouldn’t underestimate the significance, especially considering that by 2015 the Model National Energy Code for Buildings could call for buildings to be 50 percent more energy efficient than they are today.

The once-common solution of adding more insulation batts to cavity walls won’t cut it in many building types anymore. Exterior insulation will play a bigger role, with how much to use depending on building type.

Two inches of exterior insulation such as extruded polystyrene foam is a “fairly common practice” in some types of commercial buildings, but it is difficult to apply with some cladding types — brick for example. Careful planning is required to incorporate it properly, says Laverne Dalgleish, principal with Building Professional Consortium (BPC), a building science consultancy based in Winnipeg.

If future energy code updates stipulate even more exterior insulation, as is expected, builders might have to completely redesign wall assemblies to make it feasible, he adds.

There’s no need to panic, however. While the 2011 update to the Model National Energy Code for Buildings will call for about a 25 percent increase in energy efficiency, that is still within the bounds of “normal construction” and design methods, says Dalgleish.

Some experts question how much of a difference the 2011 update will make because many provincial and even municipal code authorities have been addressing energy conservation for years, says Mark Lawton, principal with Morrison Hershfield Ltd. Ontario, B.C. and other provinces, for example, reference ASHRAE 90.1, the U.S. energy standard for buildings over three floors tall, and a lot of governments have incorporated LEED requirements into codes.

Still, many of today’s highrises are clad in curtainwalls and windowwalls, which don’t compare to a well-insulated opaque wall for energy performance.

So why are so many new buildings, even those billed as energy efficient, constructed with windowwalls or curtainwalls? A key reason is money. Opaque walls can be expensive and time-consuming to install, Lawton points out.

To compensate for the energy deficiencies in a wall with windows, designers might have to use higher performance HVAC systems.

“The root to energy savings is, yes, to build better envelopes,” says Lawton. But building the envelope that best suits the building type and usage is rarely straightforward.

Factors such as “plug loads” — heat generated from electronic equipment such as computers — have a significant impact on energy performance of large commercial buildings.

Lawton says that too often the energy modeling for large buildings has been “fictional” because of thermal bridging, a phenomenon in which materials that are poor thermal insulators allow the escape of heat, even though they are surrounded by insulation.

It is not unusual, he says, for builders and designers to measure the energy performance based on the amount of insulation installed in cavity walls.

That’s not an accurate measurement in many commercial steel-framed wall systems where thermal bridging can occur, he says.

Lawton points out that a cavity wall rated R-20, for instance, might in reality only be R-4 when thermal bridging calculations are made.

To complicate matters even more, it might not matter if a wall is rated R-20 or R-4 in part because opaque walls in many large commercial buildings represent a small portion of the overall wall assembly. Moreover, heat generated from office equipment might be enough to justify less insulation.

Canada’s updated energy code will shift from R-values to U-values as the standard for measuring energy performance for walls, says Dalgleish. U-value is the rate of the heat flow while R-value measures the resistance to heat flow. U values take into account the framing assembly type, thermal bridging and a host of other wall details that aren’t measured through R-values.

Source: Daily Commercial News, October 14, 2010

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