scope:

Application

This Standard provides requirements and guidelines for the thermal simulation and calculation of thermal bridges in new and existing Part 3 and Part 9 buildings, as defined in the National Building Code of Canada (NBC). This Standard describes the requirements for simulating heat flow through building enclosures, and can be used to justify the opaque envelope U-values used for demonstrating prescriptive or modelled compliance with building energy codes.

Thermal simulation does not guarantee the in-situ heat flow or temperature performance of a building enclosure detail. Actual performance can differ from the simulated outputs due to variations in construction, weather, and other factors.

Note: Annex D provides normative language for authorities having jurisdiction (AHJs) or other specifying authorities considering referencing this Standard.

Items covered

This Standard sets out the specifications for two- and three-dimensional geometrical models of thermal bridges for the numerical calculation of heat flows to assess the thermal performance of a building enclosure or part of it, and to determine surface temperatures to allow for assessment of other performance factors, including condensation risk and occupant comfort.

The procedure outlined in this Standard makes the following simplifying assumptions:

a) Heat transfer is conductive and steady state.

b) All physical properties are independent of temperature, including thermal conductivities and dimensions.

Note: Optional project-specific temperature correction for thermal conductivity (Clause 8.4) is excepted.

c) Heat sources within the building element are not included in the analysis.

d) Heat transfer due to air leakage or ventilation is not included in the analysis.

e) Insulation layers are installed tight to adjacent construction to avoid air looping around the insulation.

Items not covered

Items that are not covered by this Standard include

a) one-dimensional hand-calculation approaches described in the 2017 ASHRAE Handbook - Fundamentals;

b) simulation of fenestration products for the purpose of determining U-values or temperatures, which are covered by NFRC 100 and AAMA 515, respectively;

c) moisture transport through building enclosure assemblies or details;

d) solar radiation or shading;

e) phase-changing materials;

f) thermal mass storage effects or transient thermal analysis;

g) air leakage effects; and

h) computational fluid dynamics (CFD).

Note: Impact from weather events are not included in the simulation procedure. See Annex E for a simplified procedure for accounting for rainfall on an inverted roof.

Simulator qualifications

Performing simulations in accordance with this Standard requires for the simulator to be proficient with the specific software tool being used to carry out the simulations. Additionally, the simulator requires a working knowledge of building physics, building industry codes and standards, and construction practices.

Note: Annex D provides a more complete list of the modeller/supervisor qualifications that may be considered by AHJs or other specifying authorities considering referencing this Standard.

Terminology

In this Standard, "shall" is used to express a requirement, i.e., a provision that the user is obliged to satisfy in order to comply with the Standard; "should" is used to express a recommendation or that which is advised but not required; and "may" is used to express an option or that which is permissible within the limits of the Standard.

Notes accompanying clauses do not include requirements or alternative requirements; the purpose of a note accompanying a clause is to separate from the text explanatory or informative material.

Notes to tables and figures are considered part of the table or figure and may be written as requirements.

Annexes are designated normative (mandatory) or informative (non-mandatory) to define their application.

Units of measurement

The values given in SI units are the units of record for the purposes of this Standard. The values given in parentheses are for information and comparison only.

Note: The values given in parentheses are in IP (inch-pound) units and are often inexact rounded values. Users of this Standard/Specification are to simulate only to the SI values or to exact conversions of the SI values.

Common conversion factors used in thermal bridging analysis are included in Tables H.1 and H.2.