2.5. Topic 3: Where underfloor heating is only used in bathrooms, the minimum R-values for heated floors may cause unreasonable upfront costs
Discussion topic on if underfloor heating is only used in bathrooms does the minimum R-values for heated floors cause unreasonable upfront costs.
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2.5.1. Reasons for the change
Building elements that are part of the thermal envelope and have embedded heating systems, such as floors with inbuilt underfloor heating, must meet certain minimum R-values. These R-values are higher than the schedule method minimum R-values, and also higher than the minimum R-values of the calculation method discussed in subsection 2.4 above.
The minimum R-values for building elements with embedded heating apply irrespective of the chosen compliance pathway. They cannot be reduced by using the calculation or modelling methods. These higher minimum R-values aim to ensure that heated building elements have adequate thermal resistance to prevent excessive heat loss, enable efficient and effective operation of the embedded heating system and limit heating energy use and costs.
Achieving the minimum R-values for heated building elements typically requires more insulation and upfront building costs. Where the embedded heating is used for general space heating across large parts of a building, these additional costs are generally outweighed by the ongoing energy cost savings from the additional insulation.
However, it is common for new homes to have underfloor or undertile heating solely in bathrooms. Where underfloor or undertile heating covers only a very small part of a building’s floor, the additional costs from achieving the minimum R-values for heated building elements may not be justified.
In particular, common insulation solutions for slab-on-ground floors, such as underslab and slab-edge insulation, cannot be isolated to just the part of the floor that is heated. Instead, to be effective such insulation needs to be applied to the entire floor.
2.5.2. Proposed change: Exempt embedded heating solely used in bathrooms from additional insulation
The proposed change includes exempting buildings from the higher minimum R-values for heated building elements where embedded heating systems are solely used in bathrooms. This proposed change involves amendments to Acceptable Solution H1/AS1 and Verification Method H1/VM1. For more details of the proposed wording, please refer to Appendix A for H1/AS1 and Appendix B for H1/VM1.
Similar amendments are proposed for Acceptable Solution H1/AS2 and Verification Method H1/VM2 Energy Efficiency for buildings greater than 300m2.
For clarity, when using the calculation method, the minimum R-values discussed in subsection 2.4 above would still apply to all roofs, walls and floors and are not affected by this proposal.
Equally, if MBIE was not to proceed with the proposed removal of the schedule method discussed in subsection 2.3 above, the exempt bathroom heated building elements would still need to achieve the schedule method R-values.
2.5.3. Analysis of the proposed change
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).
For this issue, MBIE considers that the proposed exemption for embedded heating solely used in bathrooms will best achieve this objective. Compared to the status quo, MBIE considers that the proposed exemption will reduce upfront costs for some buildings, whilst still achieving ‘adequate thermal resistance’ as required by Building Code clause H1.3.1(a).
MBIE expects that the impacts of this proposal include:
- Lower upfront building costs.
The proposed change will enable building designers avoid disproportionately complex insulation solutions that create costs that may not be justified.
- Higher energy usage (running costs and carbon emissions)
Reducing thermal insulation under embedded heating reduces energy efficiency by increasing heat loss. However, as bathrooms are typically small this impact will be modest.
On balance, MBIE considers that the benefits of the proposed exemption outweigh the costs.
2.5.4. 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 option was considered to address the issue more effectively.
These discounted options included:
- Removing the higher minimum R-values for building elements with embedded heating.
MBIE considers that this option would not achieve ‘adequate thermal resistance’ as required by Building Code clause H1.3.1(a). It would result in excessive heat loss, energy use and heating costs, particularly where embedded heating covers large areas.
- Reducing the minimum R-values for building elements with embedded heating.
MBIE does not consider this option reasonable because the status quo minimum R-values are generally appropriate, except where embedded heating only covers a small area.
- Extending the proposed exemption to other areas, such as kitchens.
MBIE does not propose this option because spaces other than bathrooms would typically have larger embedded heating systems where the additional insulation to meet the minimum R-values for building elements with embedded heating is generally justified.
We determined that the proposed approach of amending Acceptable Solution H1/AS1 and Verification Method H1/VM1 to exempt heated building elements where embedded heating systems are solely used in bathrooms is the most reasonable and effective option for achieving the objective.
2.5.5. Questions for the consultation Topic 3
3-1. Do you support amending Acceptable Solution H1/AS1 and Verification Method H1/VM1 as proposed to reduce upfront costs and improve the cost-effectiveness of insulation by exempting building elements with embedded heating from higher minimum R-values where embedded heating systems are solely used in bathrooms?
- Yes, I support it.
- Yes, with changes.
- No, I don’t support it.
- Not sure/no preference.
3-2. Please explain your views.
2.5.6. Additional questions for topics 1 to 3
SQ1. What impacts from the proposals for topics 1 to 3 do you expect?
These may be economic/financial, environmental, health and wellbeing, or other areas.
SQ2. Is there any support that you or your business would need to implement the proposed changes if introduced?
SQ3. If there are other issues MBIE should consider to better balance upfront building costs and longer-term benefits of insulation in housing and small buildings, please tell us.