3.3. Topic 12: The schedule method may lead to less cost-effective construction than the more flexible calculation and modelling methods
Proposing the removal of the schedule method.
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3.3.1. Reason for the change
When using the schedule method, designers do not need to consider what insulation levels (R-values) are most appropriate and cost-effective for the various elements of a particular building.
Designers can simply specify constructions that achieve the prescribed minimum R-values. Building Consent Authorities can easily check if a building complies by comparing the specified construction R-values against the schedule method R-values. This provides a high degree of certainty whether a proposed building design complies.
Whilst the simplicity and certainty provide an incentive for designers to use the schedule method, this can come at the expense of higher building costs ultimately faced by building owners and businesses.
The calculation and modelling methods provide more flexibility that enables the use of different insulation levels (R-values) than the schedule method. This can help reduce upfront building costs and improve the overall cost-effectiveness of the insulation in a building.
Industry feedback indicates that for large buildings it is already more common for designers to use the calculation and modelling methods to demonstrate compliance with the H1 insulation provisions. Large buildings other than housing are more varied in design and less likely to fit within the scope of the schedule method.
3.3.2. Proposed change: Remove the schedule method
The proposed change includes removing the schedule method, leaving the calculation and modelling methods as compliance pathways. This proposed change involves amendments to Acceptable Solution H1/AS2 Energy Efficiency for buildings greater than 300m2. For more details of the proposed wording in H1/AS2, please refer to Appendix C.
Appendix C: Proposed changes to Acceptable Solution H1/AS2 [PDF, 4.3 MB]
3.3.3. Analysis of removing the schedule method
The primary objective of this proposal is to reduce upfront building costs and improve the cost-effectiveness of the insulation required for achieving Objective H1.1 of the Building Code, Functional requirement H1.2(a) and Performance H1.3.1 (a).
MBIE considers that removing the schedule method will best achieve this objective by better encouraging building designers to optimise insulation levels for each building they are designing.
Removing the schedule method will increase the use of the remaining calculation and modelling methods. Compared to the schedule method, the calculation and modelling methods enable reductions in upfront building costs from optimised insulation levels tailored to the individual building, whilst still achieving ‘adequate thermal resistance’ as required by Building Code clause H1.3.1(a).
MBIE expects that the impacts of removing the schedule method include:
- Lower upfront building costs.
Removing the schedule method will encourage designers to optimise their insulation solution for each building, reducing upfront costs while maintaining compliance.
- Higher energy usage (running costs and carbon emissions) for heating and cooling in new large buildings.
This is because the calculation and modelling methods can enable compliance with less insulation than the schedule method. However, MBIE expects that the estimated costs from additional energy use by using the calculation or modelling methods instead of the schedule method are relatively modest in comparison to the savings in build costs.
- More work for designers and Building Consent Authorities when establishing compliance.
The removal of the schedule method will require designers to calculate or model the insulation required.
Alternatively, designers may choose to hire specialists or invest in software tools capable of performing complex energy modelling, which could increase costs.
Increased use of the calculation and modelling methods may also require more detailed in-depth checks by Building Consent Authorities. This could add a small amount of time to the processing of consents. MBIE expects that these costs will be less than the potential savings in upfront costs from optimised insulation.
- Upskilling required by the industry.
Removing the schedule method may feel like a big step for some designers and MBIE would work with the industry to support this transition and help designers become competent with the use of the calculation method, including supporting the creation and use of user-friendly online tools that implement the calculation method for large buildings.
- More innovation.
Removing the schedule method could encourage innovation within the industry as practitioners explore new ways of achieving compliance. This could lead to increased development and uptake of innovative products, technologies or design methods that improve building performance.
On balance, MBIE considers that the benefits of removing the schedule method outweigh the costs.
3.3.4. Other options considered
As part of the analysis, we also considered other options that were not further pursued on the basis that the proposed option was considered to address the issue more effectively.
These discounted options included:
- Providing multiple combinations of R-values for the roof, walls, windows and floor in the schedule method that designers could choose from:
- Currently the schedule method only provides one combination for each climate zone. MBIE considers this option less practicable and effective than the proposed removal of the schedule method.
- The most cost-effective combination of insulation for achieving compliance depends on many factors, including the material supply and labour costs applicable to a particular building, a building’s shape and size of glazing areas.
- Using the calculation or modelling methods was identified as being more effective for providing the flexibility to optimise insulation.
- Increasing awareness and providing education for building designers about other compliance methods:
Given that the calculation and modelling methods have been available for over twenty years MBIE does not consider a lack of awareness of the other compliance methods to be a current barrier. Whilst additional education would help some designers switch away from the schedule method, the proposed option is considered to be more effective.
MBIE determined that the proposed approach of amending Acceptable Solution H1/AS2 to remove the schedule method is the most reasonable and effective option for achieving the objective of reducing upfront building costs and improving the cost-effectiveness of the insulation required for achieving ‘adequate thermal resistance’ as required by Building Code clause H1.3.1(a).
3.3.5. Questions for the consultation Topic 12
12-1. Do you support amending Acceptable Solution H1/AS2 as proposed to remove the schedule method?
- Yes, I support it.
- Yes, with changes.
- No, I don’t support it.
- Not sure/no preference.
Please explain your views.