Homestar Technical Clarification Rulings
| Technical Question Title | Clarification Type | Tool Version | Month Released | Credit Name | Amendment/Approved Ruling |
|---|---|---|---|---|---|
| TQ161 Bath capacity to overflow | Technical Clarification | V4.1 | In both v4 (WAT-1) and v5 (EF3) of Homestar, NZGBC advises that the capacity of any bath installed to be reported as ‘the capacity to overflow’. It is common for baths in New Zealand to be installed without an overflow (since the plumbing regulations require a floor waste anyway). As such bath capacities are often reported in product literature as the ‘working volume’ which is 50mm from the lip of the bath, rather than 50mm from the overflow where one is present. The equivalent ‘capacity to overflow’ of baths without overflows can be assumed to be 80% of the working volume and this figure can be used in the Homestar water calculators. | ||
| TQ213 HS v4.1 Extension Conditions | Project Specific | V4.1 | February 2024 |
An exemption beyond 31st January 2026 can be arranged under extenuating circumstances. This must be confirmed in writing by NZGBC. Updates to the building code (specifically H1 5th edition), finalised in November 2023 will require insulation levels to match or exceed the insulation requirements of Homestar v4.1 for heat loss. However the ventilation requirement of the building code have not changed, nor is there any requirement to consider the risk of overheating. In order to manage the reputational risk to Homestar, to incentivise improved design where possible, and to inform home occupants, NZGBC requires the following as a condition for granting an extension to the submission date of Homestar v4.1 projects: 1. A risk assessment of overheating is to be carried out. This should be done in accordance with CIBSE TM59, or similar. 2. The submission must included a summary report of the overheating risk assessment. The report should also include any planned or possible mitigation measures. Project teams are reminded that projects may be upgraded to Homestar v5 at any stage prior to submission, at no additional cost. Every effort should be made to fulfill the performance objectives of Homestar v5, which may include the application of further TQs. |
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| TQ204 Embodied Carbon Guidance | V5 | October 2023 | EN2 - Embodied Carbon | This is a broad guide for what to include when accounting for (custom) materials in the Homestar Embodied Carbon Calculator (HECC). When all materials in the “must include” section are included, it is estimated that 95% of the total embodied carbon for the most common construction assemblies in New Zealand will be accounted for. Must Include Walls : Cladding Structural framing Internal linings (e.g., GIB) External paint (e.g., applied to weatherboards, if included) Internal paint Cavity Battens Insulation Roofs: Cladding Structural framing Ceiling lining Internal paint Insulation Purlins Suspended Timber Floors: Flooring Structural framing (joists, bearers, piles) Pile footings Subfloor linings. Insulation Concrete Slabs: Concrete (slab and footings) Reinforcing steel Basecourse/fill Underslab insulation (e.g., EPS) Edge protection Membranes (e.g., DPC) May Exclude : Internal paint applied to cornice and skirting. Exterior primer Cornice Interior primer Cavity vent strips Building wrap Skirting Fixing straps Adhesives Fixings Interior primer Building wrap Adhesives Fixings Membranes Adhesives Fixings Sand blinding Flashings Edge insulation Formwork Accessories to slab (e.g., bar chairs, wire) Adhesives | |
| TQ217 HC4 Slab Edge Exemption | Technical Clarification | V5 | HC4 - Moisture Control | 6 and 7 Homestar homes are exempt from the HC4 mandatory minimum fRsi requirements stated in the Homestar v5 Technical Manual. Thermally broken window frames with a minimum R-value of 0.25 are still required for all Homestar v5 projects This ruling is in response to uncertainty regarding the real life moisture accumulation risk of certain junction thermal bridges in New Zealand climates. The fRsi guidance provided in the Homestar v5 Technical Manual is based on static modelling with the threshold of eliminating any moisture occurring at the junctions. The approach of eliminating moisture risk by fully insulating the junctions remains prudent however static modelling does not consider other factors such as the ventilation rate of the conditioned space and the thermal mass of the envelope components. More importantly, static modelling provides no detail regarding the length of time that moisture is likely to be present in any location or if the building envelope is more or less prone to either accumulating moisture or drying out over time. Additionally, there remains several market concerns about the available options for insulating the edges of concrete slabs and concrete mid-floors. These concerns include cost and durability. NZGBC has commissioned dynamic hygrothermal modelling research to re-assess the risk of moisture accumulation over time at specific junctions within typical building envelopes. While this research is being completed and the market continues to respond to any demand for slab edge insulation, NZGBC has made the decision to allow 6 & 7 Homestar v5 projects to proceed without specific fRsi requirements. While slab edge insulation will not be explicitly required for the duration of this Technical Clarification, insulation in this location may be necessary for achieving the requirements of EF4: Energy Use and HC1: Winter Comfort. | |
| TQ220 RPV for Sustainable Materials v4 &5 | V4.1, V5 | October 2024 | EN3 - Sustainable Materials, MAT1 – Sustainable Materials | In both v4 and v5 of Homestar, NZGBC advises that the Responsible Products Framework may be used in lieu of the NZGBC’s Framework for Product Certification Scheme. The following Responsible Products Value (RPV) may be converted to the previous levels A, B and C: • RPV 10 or above = Level A • RPV 7 – 9 = Level B • RPV 5 – 6 = Level C New Zealand suppliers and manufacturers who aim to be rewarded for their responsible products in Homestar projects should reach out to GBCA to check if their product's certification scheme is approved. If not approved, they can ask their certification scheme provider to approach GBCA for approval. GBCA Products website Responsible Products Framework | Green Building Council of Australia (gbca.org.au) is updating a list of recognized initiatives and in the interim, please email materials@gbca.org.au for the most current list. | |
| TQ223 Airtightness Measuring During Application | Technical Clarification | V5 | December 2024 | HC4 - Moisture Control | Where the application of an air control system involves a blower door and/or other means of testing building permeability, an airtightness measurement can be taken at the time of application of that system. The tester (who may also be the applicator) will be responsible for the airtightness test result. |
| TQ228- Multi-unit pathway for HC1,2 & EF4 | V-5 | June 2025 | HC1 - Winter Comfort, HC2 - Summer Comfort, EF4 - Energy Use |
The New Zealand Green Building Council (NZGBC) advises that for a contiguous However, in order to account for practical design limitations while maintaining The percentage of dwellings that exceed the credit thresholds should not exceed The onus will be on the project team to show that remaining dwellings (i.e. the next Note that this Technical Clarification does not apply to standalone dwellings or |
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| STC rating of apartment common spaces | Technical Clarification | V5, V-5 | June 2025 | HC6 - Acoustic Performance |
The intent of this prescriptive pathway is for the control of internal ambient noise levels from external environmental source of noise such as road traffic etc. Therefore, these specifications apply to the external building fabric (e.g. façade/roof) of an apartment common area. Such that the common area within the apartment is protected from external source of noise. This means that, when the technical manual talks about STC ratings of external walls and ceilings in common areas, it refers to the external wall or ceiling between the common area and the outside. |