2.9. Topic 6: How the areas of roofs, walls and floors should be measured is unclear
Discussion topic on how the areas of roofs, walls and floors should be measured is unclear
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2.9.1. Reasons for the change
With all compliance pathways for the H1 energy efficiency insulation provisions, designers need to determine the areas of building elements. These areas are used to establish which compliance methods can be used for a proposed building, and as inputs for the calculation and modelling methods.
For the areas of roofs, walls, and floors there can be big differences depending on whether they are measured on the inside or on the outside of a building. This is because external measurements include the thickness of external building elements, whereas internal measurements do not.
Acceptable Solution H1/AS1 and Verification Method H1/VM1 currently do not specify how the areas of roofs, walls and floors should be measured. This creates inconsistency and uncertainty of compliance.
2.9.2. Proposed change: Roofs, walls and floors to be measured using overall internal dimensions
The proposed change involves amendments to Acceptable Solution H1/AS1 and Verification Method H1/VM1 Energy Efficiency for all housing, and buildings up to 300m2 to require the areas of roofs, walls and floors to be measured using overall internal dimensions. Similar amendments are proposed for Acceptable Solution H1/AS2 and Verification Method H1/VM2 Energy Efficiency for buildings greater than 300m2.
As shown in Figure 2-1 below, overall internal dimensions are measured between the internal surfaces of a building’s envelope and include the thickness of any interior walls and floors.
Figure 2-1: Overall internal dimensions
For more details of the proposed wording, please refer to Appendix A for H1/AS1 and Appendix B for H1/VM1.
Appendix A: Proposed changes to Acceptable Solution H1/AS1 [PDF, 4.4 MB]
Appendix B: Proposed changes to Verification Method H1/VM1 [PDF, 3.3 MB]
2.9.3. Analysis of the proposed change
For this issue, the primary objective of the proposed changes is to support better consistency and certainty for designers, Building Consent Authorities and building users that buildings have sufficient insulation for achieving Objective H1.1 of the Building Code, Functional requirement H1.2(a) and Performance H1.3.1(a).
For this issue, MBIE considers that the proposed changes will best achieve this objective by providing a clear requirement on how the areas of roofs, walls and floors are to be measured. MBIE does not expect this proposed change to result in any additional work or costs.
2.9.4. Other options MBIE considered
As part of the analysis, we also considered other options that were not further pursued on the basis that the proposed changes were considered to address the issue more effectively.
These discounted options included:
- Requiring the use of external dimensions.
Whilst external dimensions are used in some industry building certification schemes like Passivhaus, MBIE does not considers the use of external dimensions appropriate for the H1 compliance methods. This is because the schedule and calculation methods have limits for the glazing area that are expressed as glazing area to wall area percentages.
The assumed glazing area in the theoretical reference building of the calculation and modelling methods also depends on the wall area of a proposed building. The use of external dimensions would result in inconsistent compliance outcomes depending on the thickness of the roof, walls and floor of a building.
- Requiring the use of internal dimensions that exclude the thickness of interior walls and floors.
Compared to the proposed option, this would require more work for designers to establish the areas of roofs, walls and floors, and would be less accurate given that interior walls and floors are part of a building’s overall heated or cooled space.
We determined that the proposed approach of amending Acceptable Solution H1/AS1 and Verification Method H1/VM1 to require roofs, walls and floors to be measured using overall internal dimensions is the most reasonable and effective option for achieving the objective.
2.9.5. Questions for the consultation Topic 6
6-1. Do you support amending Acceptable Solution H1/AS1 and Verification Method H1/VM1 as proposed to improve certainty and consistency of compliance by requiring the areas of roofs, walls and floors to be measured using overall internal dimensions?
- Yes, I support it.
- Yes, with changes.
- No, I don’t support it.
- Not sure/no preference.
6-2. Please explain your views.