Building over stormwater pipelines is not a recommended practice and will only be considered by the council in exceptional circumstances where no suitable alternative exists.
Build-over guidelines also apply to cantilevered buildings. Approval from the council is required before undertaking any physical works activity over or within the zone of influence of the public stormwater network which may cause damage to the network. This includes removing existing cover material or placing additional material. Refer to drawing SW22 in Appendix B for construction clearance requirements and for definition of the zone of influence.
If a diversion will definitely be required in creating new lots, the developer of the original site shall effect the diversion at the time of initial development.
If building over a pipeline is proposed then the following requirements shall be addressed:
a) Engineering Approval is required for ALL stormwater relay and diversion works.
b) Alternative options such as relocating the building or diverting the pipeline around the building shall be thoroughly investigated. Diversion of pipelines will not be considered where the diversion will result in more than one change of direction of 90 degrees or more, or significant loss of grade, either of which may reduce the hydraulic capacity of the pipeline. In such cases it will be at the council’s discretion as to whether building over is acceptable.
c) Stormwater pipes are frequently located beneath overland flow paths. Careful attention shall be paid to the consequences of building in such locations and the need to maintain overland flow paths clear of obstructions. Applicants shall submit a detailed design of the overland flow path where the catchment exceeds 4000m2, or for smaller catchments at the council’s discretion.
d) Accurate location of the existing pipelines shall be required. Pot holing may be required to prove pipe location prior to works. Adjacent services shall be adequately protected and supported during construction.
e) The pipeline shall be inspected using CCTV both before and after the works. The pre-construction CCTV inspection shall confirm the condition, pipe material, depth and location of the pipeline and shall be conducted not more than six months prior to construction. Note that the council’s GIS information shall NOT be relied upon in regard to any design or build-over decisions.
f) The CCTV footage and inspection report of the pre-construction condition of the existing pipelines shall be submitted together with detailed long sections and cross sections of the proposed build over. The detailed long sections and cross sections shall clearly indicate the relation between the proposed foundation works (including any piles), the pipeline, any other existing or proposed services and the proposed ground levels either side of the building footprint.
g) The post-construction CCTV and inspection report shall be completed immediately following construction of the foundation and prior to the laying of the floor slab to verify that the pipeline has not been damaged as a result of the construction works. An additional CCTV inspection and report may be required at the completion of construction.
h) If the pipeline is either not in satisfactory condition, not in compliance with the council’s standards for public stormwater infrastructure or the council is in any doubt as to the functionality and condition of the pipe, then the pipeline shall be replaced by the developer at their cost to the required Auckland Council standard.
i) As-built records shall be provided in accordance with the Auckland Council document Development Engineering – As-built requirements.
j) Any existing earthenware/clay pipes, asbestos cement pipes and corrugated iron culverts shall be considered to be beyond their useful working life and shall be replaced at the cost of the developer irrespective of existing condition.
k) For deep pipelines, where the existing pipe is found to be in a satisfactory condition with only minor defects, in-situ repair techniques may be considered for approval. All associated costs shall be met by the developer.
l) The council may require that an assessment is made to cater for anticipated future development or increased level of service, at the developer’s cost.
m) Selection of the pipe material and the length of pipe to be relayed shall be at the discretion of the council.
n) No horizontal or vertical deflection of pipelines as a result of being built over is acceptable.
o) The support structure for the building shall be totally independent of the pipeline so no additional loading is applied to the pipeline.
p) Piles shall be constructed where there is a need to bridge the pipeline. Piles shall have a minimum separation distance of 1000mm from the outside of the pipe to the edge of the pile (refer to drawing SW22 in Appendix B).
q) For pipes with diameter greater than 375mm or depth to invert greater than 2m the separation distance shall be increased. This situation shall be subject to specific design.
r) For manholes with diameter ≤1200mm and depth ≤4m, piles shall have a minimum separation distance of 1000mm from the outside of the manhole to the edge of the pile (refer to drawing SW22 in Appendix B). A minimum clearance of 5m to any overhanging structure above the manhole shall also be maintained. Manholes larger than 1200mm diameter or deeper than 4m shall be specifically designed, including specific design of required construction clearances.
Note that meeting the above criteria does not necessarily mean that a build over will be approved.
Where pipelines are to be diverted, the following shall apply:
- Where a diversion is necessary, curvature in the pipeline will be considered in order to minimise the number of manholes required. Design will be subject to specific design and approval by the council.
- The pipeline is to be on an even longitudinal grade.
- Diversion pipelines shall be designed to the requirements of this code and in particular Section 4.3.5.