The Model National Energy Code for Buildings (published in 1997) gets its first revision this year. The 2011 update calls for buildings to be 25 percent more energy efficient, so changes to the design and construction methods of building envelopes can be expected.
Will those revisions significantly impact designers and builders in the wall and ceiling industry? Probably not, says one expert, but 2011 is just the beginning. “We’re starting to get up to the limits of normal construction (with the new energy code),” says Laverne Dalgleish, principal of Building Professional Consortium based in Winnipeg.
A member of the Canada’s standing committee on energy efficiency buildings, he says builders and designers will have to start rethinking the way they do things because when the code is updated again in 2015, energy efficiency requirements could be 50 percent higher than they are today.
The building science specialist – also a participant in hearings into the US’s 2012 International Energy Conservation Code (IECC) – believes one of the most difficult challenges facing both Canada and the US is the building envelope. The era of filling cavity walls with insulation batts could be coming to an end. Exterior insulation could become the norm.
Currently, installing up to two inches of exterior insulation such as extruded polystyrene foam is a “fairly common practice” in Canada, but with some cladding types – brick for example – forethought and careful planning is required. More challenging will be future energy code revisions stipulating up to four inches of exterior insulation. To meet that end, builders might have to completely rethink how walls are built.
Designers and contractors will face other challenges as the method for measuring energy performance in walls changes from R-values to U-values. U-value is the rate of the heat flow while R-value measures the resistance to heat flow. U-values have been used for windows in Canada but the new code will make it the standard for walls as well, says Dalgleish. Framing, thermal bridging, and a host of other wall details are taken into account to determine U-values.
Why the change? U-value is a more accurate measurement of energy performance but it could dictate new demands on wall systems, including EIFS-clad assemblies, says Dave Johnston, executive director of the US-based EIFS Industry Members Association (EIMA). Still, if there is one wall assembly that stands to meet the new US code easily it likely will be EIFS.
Dalgleish says unlike the US, there is no panic in Canada over its new code because Canadian builders and designers are further ahead in energy efficient construction methods. Air barriers, for example, are still a new concept to many US builders; not so in Canada.
It will be difficult but not impossible to meet U-value requirements without using continuous insulation on the building exterior in the 2011 code. However, in 2015 cavity wall insulation might not be an option.
Glazing that meets energy performance criteria has always been a challenge. Today’s windows aren’t energy efficient by comparison to a well-insulated opaque (windowless) wall. So why are so many new buildings (even those billed as energy efficient) constructed with windowwalls or curtainwalls? By and large the answer is that they are easier to install and less expensive than opaque walls with “punched out” windows, explains Mark Lawton, building science specialist and principal at Morrison Hershfield Ltd.’s Vancouver office. To compensate for the energy deficiencies in a wall with windows, designers might have to use higher performance HVAC systems.
“The root of energy savings is to build better envelopes,” says Lawton. But the right formula is never straightforward. Such variables as “plug loads” (heat generated from electronic equipment such as computers) have a significant effect on energy performance of large commercial buildings.
The US National Multi Housing Council (NMHC), which represents large apartment building owners, suggests that the US’s energy code in 2012 could result in startling amortization periods of five decades or more. The Council’s findings are based on computer simulation studies it conducted on about 500 apartment buildings through eQUEST (used as a reference for the California energy code) and 500 through WUFI, a computer program for realistic calculations of heat and moisture movement in multi-layer building components exposed to natural weather. The objective was to figure out best ways to design and construct energy efficient building envelopes.
Ron Nickson, vice-president of building codes, NMHC, says in some cases, the computer simulations concluded that entirely new methods of construction would have to be devised to meet some of the proposed energy requirements.
For example, the addition of a few inches of expanded polystyrene foam insulation on building exteriors would be difficult, if not impossible, to do in combination with a number of cladding materials such as brick, vinyl siding and cementitious fiber board. EIFS is one of the systems that would meet such a standard, but not every building can be constructed with EIFS.
Lawton says many building science experts question whether Canada’s 2011 energy code update is even necessary because provincial and even municipal code authorities have been addressing energy conservation for years. A number of provincial and some municipal governments in Canada reference ASHRAE 90.1 – the US energy standard for buildings over three floors tall – and a lot of governments have put in requirements for LEED. So the question arises: Is there a need for a “separate, nationalistic model energy code?”
The Vancouver-based building science specialist adds that often the energy modeling (calculations of energy values) for the building envelope in large buildings has been “fictional” because the impact of thermal bridging and other factors are difficult to accurately measure. “For years, people have been just inputting things like the nominal value of insulation in a wall, which could work for wood frame but does not work for many of the commercial type wall systems.”
That is because commercial buildings are framed in steel and the insulated wall cavities often include major elements (shelf angles made of iron, for instance) that cause thermal bridging, he says. A cavity wall rated at R-20, for instance, might actually be only R-4 because of thermal bridging. “If you are honest, you can put that number into your program or you might just say it is an R-20 wall. Unfortunately, the latter has been fairly common practice.”
In the end 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 part percentage of the overall wall assembly.
To sum it up, the building envelope in large buildings may not be significant to the overall thermal performance, he says. “We always know that the mechanical systems are significant and we always know that the glazing is significant but the opaque part of the envelope may not be significant.”
The proposed changes to the energy code will be available for public review soon. Final changes will be made in February. While meeting the new code will involve changes to building envelopes, designers and builders still have a few years to sort things out. As of 2015, it is another story. “That is because by then we’ll have exhausted most of the cheap and easy ways of doing things and we’ll have to build buildings properly,” says Dalgleish.
Article By: Don Procter
This article originally appeared in the October / November 2010 issue of The Trowel Magazine
