British Columbia

How do you choose between the ERS path and the 9.36.5 path?

Steps 2 through 5: The ERS Compliance Path

Please note: STEP 3 is proposed to be implimented imminently throughout british columbia. Please plan your projects to this level as to not incur any delays or unintended consequences.

When a builder is seeking to comply with Steps 2 through 5 of the BC Energy Step Code following the ERS path, the Energy Advisor may model the proposed building using the airtightness target of the respective step (Table 1). The building must achieve both the Performance Requirement of Building Equipment and Systems (either the Mechanical Energy Use Intensity or the % lower than EnerGuide Reference House target for the step) and the Performance Requirement of Building Envelope (the Thermal Energy Demand Intensity target for that step). The decision path for ERS for Steps 2 through 5 is shown in Figure 3.

9.25

How do you choose between 3.5 ACH & 4.5 ACH?

Buildings can be constructed to meet either 3.5 air changers/hour (ACH) at 50 pascals or 4.5 ACH@50 pa (if blower door tested) in accordance to NBC (below). The details below specify the differences required in order to meet the air tightness requirements. At 3.5 ACH, the building envelope will leak (if blower door tested) 3.5 x the volume of the home through the building envelope within one hour. At 4.5 ACH, it will leak 4.5 times. A 4.5 ACH built house will be leakier and have an energy penalty applied. This means that your project may require you to compensate for the additional heat/energy loss through various measures taken through performance energy modelling (increasing insulation, higher efficiency appliances, better quality windows, etc).

Airtight buildings are much more likely to have better energy performance and durability, and are more likely to comply with the BC Energy Step Code. While there is no minimum requirement for airtightness at Step 1 of the BC Energy Step Code, the reference house in both the ERS path and the Subsection 9.36.5. path assumes an airtightness of 2.5 ACH50. A building that is designed to and achieves an airtightness of 2.5 ACH50 may not need any upgrades relative to prescriptive code minimums. However, buildings modeled with a proposed airtightness higher than 2.5 ACH50 will likely need to incorporate energy efficiency upgrades relative to prescriptive code minimums to achieve Step 1 of the BC Energy Step Code.

An airtightness value of either 3.5 or 4.5. air changes per hour at 50 Pascals pressure differential (ACH50) must be used in the proposed house energy model, as per Sentence 9.36.5.10.(9). The value is determined as follows:

• If the builder chooses to comply with BCBC Section 9.25., “Heat Transfer, Air Leakage and Condensation Control,” the energy model must use an airtightness value of 4.5 ACH50.

• If the builder chooses to comply with BCBC Subsection 9.25.3., “Air Barrier Systems” and Articles 9.36.2.9., “Airtightness,” and 9.36.2.10., “Construction of Air Barrier Details,” they may use 3.5 ACH50.

If less than 3.5 air exchanges are used in the proposed model, provide vapour barrier installation details to the authority having jurisdiction. 

Notable differences between the two options:

• Section 9.25. states that, where a flexible sheet material is used as an air barrier, the joints shall be sealed or lapped not less than 100 mm and clamped between framing members. In contrast, the Article 9.36.2.10. requirement for the flexible sheet materials’ joints are that they must be lapped not less than 50 mm, sealed, and structurally supported;

• Article 9.36.2.9. contains more information on air leakage requirements and standards to be met for windows, and a requirement to restrict air movement through chimneys from fireplaces; and

• Article 9.36.2.10. contains more clarity on sealant materials and on sealing around penetrations in the air barrier, joints, chimneys, and where interior and exterior surfaces meet, among other items.

Sentences (9) through (11) of Article 9.36.5.10. state:

1. 9)  The airtightness value used in the energy model calculations for the proposed house shall be

   1. a)  4.5 air changes per hour at 50 Pa pressure differential, where the construction complies with Section 9.25.,

   2. b)  3.5 air changes per hour at 50 Pa pressure differential, where it can be shown that
      the air barrier system is constructed in accordance with Subsection 9.25.3. and Articles 9.36.2.9. and 9.36.2.10., or

   3. c)  tested in accordance with Sentence (11), and shall be,

      1. i)  the number of air changes per hour at 50 Pa pressure differential, and

      2. ii)  the equivalent leakage area (see Appendix A).

2. 10)  Where airtightness is measured in accordance with Clause 9.36.5.10.(9)(c), the applicable airtightness value in Clause 9.36.5.10.(9)(a) or (b) shall be assigned for use in the energy model calculations until the actual airtightness has been measured in accordance
   with Sentence (11).

3. 11)  Where measured airtightness is used in the energy model calculations, it shall be determined in accordance with CAN/CGSB-149.10, “Determination of the Airtightness of Building Envelopes by the Fan Depressurization Method”

   1. a)  as written, or

   2. b)  excluding Clause 6.1.6, which allows intentional openings for mechanical equipment to be left unsealed.