Wednesday, 11 February 2015

Application of the National Energy Code for Buildings 2011 to a Steel Building System

Dockside Green Power Generation Building - Victoria, BC

The National Energy Code for Buildings (NECB) was published in the fall of 2011. It is a National Model Code which will be adopted by the Provinces and Territories to the extent it meets their plans. It applies to the construction of new buildings that are required to meet the provisions of Part 3 of the National Building Code of Canada, or the applicable Provincial Building Code.

There are four paths through which building designs may comply with NECB 2011:
  1. The Prescriptive Path (Section 3.2) in which assemblies and components must meet minimum prescribed performance requirements.
  2. The Simple Trade-off Path (Section 3.3.3) in which certain assemblies or components may not meet the prescribed performance requirements, while other assemblies or components exceed the prescribed performance requirements, such that the overall performance of the building will not use more energy.
  3. The Detailed Trade-off Path (Section 3.3.4) in which a computer model is used to establish a reference building envelope energy target. Some components are permitted to be less energy efficient provided it can be demonstrated the building envelope will not transfer more energy than the building envelope energy target.
  4. The Performance Path (Section 3.4) in which the Trade-Off methodology is extended to include equipment inside the building, (i.e. fans, appliances, elevators, etc.) and a computer model is used to determine that the building assemblies, components and equipment in aggregate, will not use more energy than the reference building envelope energy target. 
The Prescriptive Path provides maximum overall thermal transmittance for the building walls, roof, fenestration and doors (refer to Section 3.2.2). The Prescriptive Path also allows certain percentages of total wall area for vertical fenestration and doors (Section For heating degree days (HDD) less than 4000, the ratio of area of doors and fenestration to total wall area can be a maximum of 40%. For HDD between 4000, and 7000, this ratio is calculated as (2000-0.2xHDD)/3000. For HDD over 7000, this ratio is 20%. As it gets colder, the allowable area for doors and windows decreases. The Prescriptive Path further allows up to 5% of the gross roof area to be skylights (Section

The Simple Trade-off Path demonstrates that the sum of the areas of vertical (or horizontal) assemblies of the building envelope multiplied by their respective overall thermal transmittance is not more than the corresponding assemblies in the reference building. The reference building for the Simple Trade-off Path is the same building used with the Prescriptive Path.

If certain components are more energy efficient than those prescribed in the Prescriptive Path, the trade-off calculation is permitted to take this increased performance into account.To perform the calculation, vertical (wall) portions of the building envelope can only be traded off against other vertical (wall) portions, and horizontal (roof) portions of the building envelope can only be traded off against other horizontal (roof) portions.

The Simple Trade-off Path cannot be used for semi-heated buildings, which require less energy than a reference building with a temperature set point of 18°C, and have heating capacity no greater than the heating load plus 5%. For semi-heated buildings, the Detailed Trade-off Path or the Performance Path, must be used.

The Detailed Trade-off Path and the Performance Path utilizes computer energy modelling and the services of a professional engineer proficient in this work.

To learn more about Steel Building Systems and the National Energy Code for Buildings, download our Fact Sheet #37: Application of the National Energy Code for Buildings 2011 to a Steel Building System

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