The 2020 edition of the National Building Code of Canada (NBC) introduced energy-efficiency performance tiers in Section 9.36. of Division B, with increasing levels of improvement for buildings and houses, to provide authorities having jurisdiction with the option to adopt the energy performance level most suitable to their needs.

Although performance modeling is common in the industry, many participants have requested that prescriptive compliance paths remain in the Code to provide simplicity in achieving energy compliance. However, there are no prescriptive paths provided beyond Energy Performance Tier 2 in Section 9.36.

Failure to develop a prescriptive compliance path for Energy Performance Tier 5 would force Code users to rely on the performance-based requirements that use energy modeling to achieve the energy-efficiency targets for Tier 5 performance. This would prevent compliance with Tier 5 for Code users who do not have access to performance modeling.

For the 2025 Code cycle, the Provinces and Territories identified “improved energy provisions leading to the adoption of 2030 net-zero energy ready model codes” as a priority. To provide a net-zero energy level of performance by 2030, authorities having jurisdiction could choose to adopt the highest tier of energy efficiency, which is Tier 5.

Prescriptive Tier 5 requirements would provide acceptable solutions for different components of the building to improve the total energy performance. Together with the tiered energy performance path in Subsection 9.36.7. and the tiered energy points-based prescriptive trade-off path in Subsection 9.36.8., the prescriptive path is one of three compliance options that provide an acceptable means of achieving the performance goal of reducing energy consumption by at least 70% for buildings over 300 m³ and by at least 60% for buildings under 300 m³.

In developing the Tier 5 prescriptive solutions, many different possible solutions were considered.

Building Envelope

Two Tier 5 building envelope packages were developed for each climate zone: one for buildings with conditioned internal volumes greater than 300 m³ and one for buildings with conditioned volumes less than or equal to 300 m³. This distinction was made to acknowledge the different requirements for tiered performance compliance based on conditioned volume, as described in Table 9.36.7.2. The 240 building archetypes were separated by volume, with 219 building archetypes having a conditioned volume greater than 300 m³ and 21 having a volume of less than or equal to 300 m³.

For each building volume group and climate zone, two criteria were used to define acceptable Tier 5 building envelope package solutions:

1. At least 80% of the building archetypes had to comply with the Tier 5 requirement for percentage heat loss reduction, as follows:

• 40% for volumes greater than 300 m³, and
• 25% for volumes less than and equal to 300 m³.

2. On average the building archetypes had to have a peak heating load less than their reference building.
There are numerous combinations of envelope measures that meet the criteria above. Therefore, additional selection criteria needed to be defined to reduce the number of prescriptive building envelope package solutions to one for each climate zone and building volume.

The two additional criteria were:

1. minimal incremental costs make a solution desirable, and

2. component performance of the building envelope must consistently increase across climate zones.

A fourth criterion was defined to ensure that, when going from a warmer to colder climate zone, the thermal performance of a building envelope component was not reduced. For example, a solution that uses 4.88 RSI for the effective thermal resistance of above-grade walls in climate zone 6 would not be used if the solution for climate zone 5 used 5.69 RSI for above-grade walls.

Airtightness

Mandatory airtightness testing is required in the Tier 5 prescriptive path, which follows the direction provided by the Canadian Board for Harmonized Construction Codes (CBHCC) to validate the compliance with airtightness level (AL) 4, considering that:

• Increasing the AL of the house is essential for achieving Tier 5 energy performance, as the energy loss due to air leakage/infiltration accounts for a significant portion of the overall building energy loss.
• It is difficult to verify whether the current prescriptive measures to minimize the air leakage of building components and assemblies were properly constructed based on a visual inspection alone without conducting a whole building airtightness test, especially for houses built to meet high energy performance tiers.
• Conducting an airtightness test would be the most economical way to achieve the energy-saving goal for Tier 5, as the cost of an airtightness test would be offset by decreasing construction costs for a Tier 5 design at increasing levels of airtightness.

HVAC and Service Water Heating System

Three fuel-sources (i.e., electric, natural gas and oil) were considered. Additionally, electric-only and dual-energy packages were proposed. A fossil-fuel-only package was not developed for mechanical equipment, as modeling results indicated that Tier 5 performance goals are not achieved with drafted packages (i.e., they missed the target by about 10%).

Heat-recovery ventilators or energy-recovery ventilators (HRVs/ERVs) were considered as an easy and economical way to save energy, especially for the Tier 5 prescriptive path; it was proposed that all Tier 5 houses should be equipped with HRVs/ERVs with minimum 75% sensible recovery efficiency.

Drain-water heat-recovery (DWHR) units were also considered as essential to a high efficiency house; therefore, it was proposed that DWHR units with minimum 42% heat recovery efficiency should be installed for all Tier 5 houses.

Based on the analysis conducted during the 2020 Code cycle for the tiered energy performance requirements in the NBC, a heat pump is required as the primary equipment for space heating to achieve the energy performance goal for higher tiers. Both air-source and gas-fired heat pumps were considered. As gas-fired heat pumps are mainly being used in commercial, not residential, applications at present, only air-source heat pumps were proposed to be used in the Tier 5 prescriptive path.

With well-insulated building envelopes and highly efficient space heating equipment, the performance of the service water heating system is another important factor that determines if the Tier 5 energy saving goals can be met. Heat pump water heaters, electric conserver water heating tanks, oil-fired water storage tanks and gas-fired instantaneous condensing water heaters were considered because they are the water heating equipment that is most commonly used available on the market.

It is worth noting that the fossil-fuel based mechanical systems (i.e., natural-gas fired or oil-fired systems) are still permitted through the use of the points-based prescriptive trade-off path or the performance path and when combined with a heat pump system in the dual-energy package.

This proposed change would improve energy performance by following the prescriptive requirements for building envelopes and, HVAC and service water heating systems to achieve Energy Performance Tier 5. Detailed costing data can be found in the supporting document.

Energy Performance Base Code versus Tier 5: Small House Archetype

The assumed building archetype is a small two-storey house of approximately 2 500 ft.² of livable space with a walk-out basement. The dimensions of the building archetype are provided in Table 1. The base case is a house that is assumed to meet the minimum requirements of Section 9.36. (Base Code).

Table 1. Total Area of the Building Envelope Components of the Small House Archetype

As shown in Table 2, the incremental cost by region varies by climate zone, described in Table 3.

Table 2. Incremental Cost of Tier 5 Compared to Base Code by Region

Table 3. Climate Zones by Region

Table 4 provides an example of possible incremental costs by region (and climate zone).

Table 4. Example of Incremental Costs to Achieve Energy Performance Tier 5 for Components of Building Envelope Assemblies and HVAC Systems in the Small House Archetype across Canada⁽¹⁾

Note to Table 4:

(1) The abbreviations that appear in this Table have the following meanings:

This proposed change could be enforced by the infrastructure currently available to enforce the Code.

This proposed change would facilitate the effective enforcement of high-performance energy solutions in jurisdictions where complying with the performance path is problematic.

Regulators, builders, designers, engineers, architects, contractors and consultants in provinces and territories where Energy Performance Tier 5 of the NBC  has been adopted for housing and small buildings.