Which to choose – ASHRAE 90.1-2010 or NECB 2011?

As of December 20, 2013 the British Columbia Building Code incorporated a fairly substantial addendum that requires complex buildings (buildings other than housing and small buildings) to conform to either ASHRAE 90.1-2010 or the NECB 2011. Before this addendum, the BCBC referenced only ASHRAE 90.1-2004. The change to the two new alternate compliance paths is intended to reduce energy use, which all would likely agree is commendable. However, it will have an impact on construction requirements.

Like B.C., other Canadian provinces are choosing to reference either, or both, of these energy compliance paths in their building codes, but many building designers and building officials wonder which to adopt. Although the paths are similar, there are differences that can factor into which is the pragmatic path. The entire design team has to follow the same path and will likely need to determine which one early in the design process, so some understanding of the differences will become “need to know” information for design professionals, contractors and owners. The intent of this article is not to suggest which path to choose, but to discuss a few of the differences.

NECB 2011 (National Energy Code for Buildings, 2011) was developed by the National Research Council of Canada and volunteers from industry to provide minimum requirements for the design and construction of energy efficient buildings in Canada. 

ASHRAE 90.1 (full name “ANSI/ASHRAE/IES Standard 90.1-2010 – Energy Standard for Buildings Except Low-Rise Residential Buildings”) is published by ASHRAE, the international association focused on advancing building systems, energy efficiency, indoor air quality, refrigeration and sustainability. Written by a large group of members worldwide, ASHRAE 90.1-2010 is complex with specific requirements and exceptions for various applications. The goal of this standard was to cover the full range of construction approaches.

While there is a debate that ASHRAE 90.1 may be over complicated; it can also be argued that NECB does not have enough complexity, leaving ambiguity and potential challenges in interpretation.

Climate zones

One area in which the compliance paths differ is in how the climate zones are defined.  NECB is defined by degree days and broken into 1000 heating degree-day increments. (A heating degree day (HDD) is defined as the number of days the outside temperature is below the indoor set point temperature; for standard room temperatures these are defined in the building codes under climatic data.)ASHRAE uses a more complex system to define climate zones, intended to include heating, cooling, solar angle and latent loads. Climate zones for Canada are defined in Appendix B (Table B-2.)

In both compliance paths the building performance requirements are defined by the climate zone, and in one location the requirements in one standard might be more stringent than in the other. For example, Victoria is ASHRAE zone 5c and NECB zone 4, while Nanaimo, which is 100 kilometres away, is ASHRAE Zone 5c but NECB zone 5. Therefore, when deciding which path to follow the climate zone must be reviewed. 

Space classifications

Another area of ambiguity is the classification of spaces. For example, the NECB 2011 does not define a semi-heated space (warehouses, factories etc.). In ASHRAE 90.1 a semi-heated space is defined and has reduced requirements resulting in lower construction costs. While the NECB U-value requirements may be avoided using an energy simulation of the envelope, such an approach adds complexity and cost and would fall under the discretion of the authority having jurisdiction.

Although the structure of the compliance paths is similar, ASHRAE 90.1 contains a number of mandatory provisions that must be followed regardless of the path chosen. In the NECB, nearly all requirements are prescriptive and don’t need to be followed, but if followed are like a checklist to compliance. Alternatively, if it can be shown that equivalent performance can be met in other ways, the building is deemed to comply. While ASHRAE 90.1 mandatory requirements are typically good design practice, there can be some challenges in meeting them in specific applications. A good example of this is the mandatory requirement in many applications for vestibules in new construction.

Energy cost vs. energy use

The most significant difference between the compliance paths is the baseline of net energy cost versus net energy use. ASHRAE 90.1 was first written in 1975 as a response to the energy crisis and is based on an energy cost basis. The NECB was written to reduce energy consumption and therefore does not look at cost but rather the total energy used. This difference impacts a large number of factors. The most direct is that ASHRAE 90.1 has various U value requirements for different construction types to balance the increase in construction costs for the increased insulation, so a wood wall would have a higher insulation requirement than a mass wall. The NECB looks at building envelope performance, so only the calculated U Value is considered in compliance and has the same requirement for all construction types. The construction type needs to be reviewed when selecting the compliance path as some assemblies may be costly to insulate to the required values.

Both paths are similar in that you can use area weighted averages to show compliance for differing assemblies and they allow for some form of trade-off on the envelope. However, in the NECB you can only trade similar planes; if you want to trade off dissimilar planes you will require an energy simulation of the envelope. In ASHRAE 90.1 envelope trade-off can be done with calculations or using a program. The NECB also allows for trade-off options in all components of the building, whereas ASHRAE does not have trade-off paths for all building system components.

Due to these and a number of factors; when deciding which standard is the more practical, the answer is simple — it’s complicated! The decision therefore needs to be discussed early in the design process.cce

Kyle Hasenkox is a senior project manager with Rocky Point Engineering, in its Victoria, B.C. office. He is also Chapter president-elect and XI YEA Regional Coordinator with ASHRAE.