2.10. Topic 7: NZS 4214 includes ambiguous instructions for determining the R-values of roofs, walls and some floors
NZS 4214 includes ambiguous instructions for determining the R-values of roofs, walls and some floors.
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2.10.1. Reason for the change
With all compliance pathways for the H1 energy efficiency insulation provisions, designers need to determine the thermal resistance (R-value) of the proposed building elements that form part of a building’s thermal envelope. Designers can either calculate the R-value or use tools with pre-calculated values such as the BRANZ House Insulation Guide.
For roofs, walls and floors, Acceptable Solution H1/AS1 and Verification Method H1/VM1 currently require R-values to be determined using the methods described in New Zealand standard NZS 4214[1].
From discussions with technical experts MBIE identified that clause 5.7.1(a) in NZS 4214 does not clearly define the boundaries of the bridged portion of a building element for the purpose of calculating its R-value. This can lead to incorrect results and creates uncertainty and inconsistency of compliance with the H1 energy efficiency insulation provisions.
2.10.2. Proposed change: Provide clear requirements on how to apply NZS 4214
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 provide clearer requirements for defining the boundaries of the bridged portion of a building element when calculating its R-value to NZS 4214. Similar amendments are proposed for Acceptable Solution H1/AS2 and Verification Method H1/VM2 Energy Efficiency for buildings greater than 300m2.
MBIE proposes to add a modification to the current citation of NZS 4214 to H1/AS1 and H1/VM1, with replacement wording for clause 5.7.1(a) in NZS 4214. See Table 2-2 below for a comparison of the status quo and the proposed modified wording.
Table 2-2: Modified citation for clause 5.7.1 (a) in NZS 4214 (status quo and proposed)
| Status quo wording in NZS 4214 | Proposed wording |
|---|---|
| (a) Select two planes to the plane of the wall, which enclose the portion of structure within which thermal bridging occurs |
(a) The bridged portion of the structure encloses the layers within which thermal bridging occurs. Where multiple bridged layers are immediately adjacent, they shall all be included in the bridged portion. Where multiple bridged layers are separated by homogenous layer(s), they shall be treated as separate bridged portions. On each side, the bridged portion is defined to end at the nearest face of the next homogenous layer (parallel to the plane of the building envelope component), except where: i) that next homogenous layer is an insulation material or air cavity, in which case the insulation material or air cavity is to be included in the bridged portion ii) that next homogenous layer is in between two bridged layers, in which case half of the intermediary homogenous layer is included in each of the adjacent bridged portions |
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]
2.10.3. Analysis of the proposed change
For this issue, the primary objective of the proposed change 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).
MBIE considers that the proposed changes will best achieve this objective by providing clearer requirements for defining the boundaries of the bridged portion of a building element when calculating its R-value using NZS 4214.
MBIE does not expect this proposed change to result in any additional work or costs. BRANZ have confirmed that the pre-calculated R-values in the House Insulation Guide already conform to the proposed new requirements.
2.10.4. Other options MBIE considered
For this issue, apart from retaining the status quo MBIE did not identify any other options.
2.10.5. Questions for the consultation Topic 7
7-1. Do you support amending Acceptable Solution H1/AS1 and Verification Method H1/VM1 as proposed to improve certainty and consistency of compliance by providing clearer requirements for defining the boundaries of the bridged portion of a building element when calculating its R-value using NZS 4214?
- Yes, I support it.
- Yes, with changes.
- No, I don’t support it.
- Not sure/no preference.
7-2. Please explain your views.
Footnote
[1]NZS 4214:2006 Methods of determining the total thermal resistance of parts of buildings.