On 21 April 2026 the Roof Drainage Calculators were updated outside of the standard update sequence.
This update was to address the issue of the HIRDS tool from NIWA changing to a pay-per-use tool:
- There were no changes to recommendations or calculation methodologies.
- Existing project calculations and figures are unchanged for the same parameter.
- All calculators now enable selection of Location to utilise rainfall intensity figures from NZBC E1/AS1 Table A.
- Intensities determined from HIRDS or other methods can be entered as 'Custom'
19.1A v26.4 - April 2026
| Category | Clause Number (prior to update) | Clause (As of current publication) | Details |
|---|---|---|---|
| 2 - Editing and rearrangement | 5.3.2 | 19.1A v26.4 - April 2026 | Inserted mention that payment is now required to use NIWA's HRIDS tool. |
| 2 - Editing and rearrangement | 5.3.2.1 | 19.1A v26.4 - April 2026 | We have changed the recommendation for calculating rainfall intensity to using the new feature on our online calculators. |
| 2 - Editing and rearrangement | 5.4.7 | 19.1A v26.4 - April 2026 | Enable selection of Region/location per NZBC E1 Table A. Calculations are unchanged for a given Rainfall Intensity, and Rainfall Intensity can still be manually entered if determined from HIRDS or other methods. |
| 2 - Editing and rearrangement | 5.5.7 | 19.1A v26.4 - April 2026 | Enable selection of Region/location per NZBC E1 Table A. Calculations are unchanged for a given Rainfall Intensity, and Rainfall Intensity can still be manually entered if determined from HIRDS or other methods. |
| 2 - Editing and rearrangement | 5.7.3 | 19.1A v26.4 - April 2026 | Enable selection of Region/location per NZBC E1 Table A. Calculations are unchanged for a given Rainfall Intensity, and Rainfall Intensity can still be manually entered if determined from HIRDS or other methods. |
| 2 - Editing and rearrangement | 5.8.1 | 19.1A v26.4 - April 2026 | Enable selection of Region/location per NZBC E1 Table A. Calculations are unchanged for a given Rainfall Intensity, and Rainfall Intensity can still be manually entered if determined from HIRDS or other methods. |
| 2 - Editing and rearrangement | 7.1.4 | 19.1A v26.4 - April 2026 | Enable selection of Region/location per NZBC E1 Table A. Calculations are unchanged for a given Rainfall Intensity, and Rainfall Intensity can still be manually entered if determined from HIRDS or other methods. |
| 2 - Editing and rearrangement | 9.4.4 | 19.1A v26.4 - April 2026 | Enable selection of Region/location per NZBC E1 Table A. Calculations are unchanged for a given Rainfall Intensity, and Rainfall Intensity can still be manually entered if determined from HIRDS or other methods. |
| 4 - Clause Inserted | 19.1A v26.4 - April 2026 | Urgent update to introduce rainfall intensity calculator. |