Proposed Change 1653

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1653
Page: Last modified: 2023-11-16
Code Reference(s):
NECB20 Div.B 3.2.3.2.(1) (first printing)
Subject:
Building Envelope - General
Title:
Use of the Term "Grade" in the NECB
Description:
This proposed change clarifies Note A-3.2.3.2.(1) by using “ground” instead of “grade” to refer to the finished ground level.
Related Code Change Request(s):
CCR 1391
Related Proposed Change(s):
PCF 1840, PCF 1962
This change could potentially affect the following topic areas:

Problem

In the National Building Code of Canada (NBC), “grade” is a defined term used to determine a building’s height in storeys, which in turn determines requirements for the construction and protection of that building. The NBC defines “grade” as the lowest of the average levels of finished ground adjoining each exterior wall of a building. Therefore, at any point along the length of a wall, grade may be above or below the adjacent ground level. As such, the defined term “grade” does not necessarily refer to the finished ground level.

If Code users determine the requirements for the insulation of a building component based on the definition of grade provided in the NBC, which is reproduced in the National Energy Code of Canada for Buildings (NECB), this could lead to the installation of thermal insulation that is insufficient to minimize heat loss.

Justification

In the NECB, the main purpose for references to “grade” is to establish requirements to reduce heat loss. In most instances, rather than using the defined term “grade,” the NECB should refer instead to “ground,” which more accurately describes the building level intended to be used to determine the required thermal resistance of the building element. The use of the defined term “grade” to determine thermal insulation requirements may lead to building elements having a thermal resistance that does not meet the objectives of the NECB.

Moreover, the titles to Article 3.2.3.2. and explanatory Note A-3.2.3.2.(1) refer to “Roofs in Contact with the Ground,” while the content of the explanatory Note uses the term “grade.” Replacing “grade” with “ground” would therefore improve the consistency and accuracy of the Note language.

PROPOSED CHANGE

[3.2.3.2.] 3.2.3.2.Thermal Characteristics of Roofs in Contact with the Ground

[1] 1)Except as provided in Sentence (2), the overall thermal transmittance of below-ground roofs that are part of the building envelope and are less than 1.2 m below the exterior ground level shall be not greater than that shown in Table 3.2.3.1. for the applicable heating-degree-day category taken at 18°C. (See Note A-3.2.3.2.(1)PROPOSED CHANGE A-3.2.3.2.(1).)

Note A-3.2.3.2.(1) Roofs in Contact with the Ground.

Sentence 3.2.3.2.(1) refers to structures that are normally below gradeground such as walkways or storage garages. It does not refer to structures with vegetative roofs as might be built at elevations above gradeground.

Impact analysis

The proposed change has no cost implications, as it is not a change to a Code requirement. The change would have the benefit of clarifying the explanatory Note.

Enforcement implications

This change can be enforced by the infrastructure currently available to enforce the NECB without additional resources.

Who is affected

Designers, engineers, architects, builders and building officials.

OBJECTIVE-BASED ANALYSIS OF NEW OR CHANGED PROVISIONS

[3.2.3.2.] 3.2.3.2. ([1] 1) [F92-OE1.1]
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