It’s always a good idea to get this checked out and it will differ if you can connect to public systems or have to have the systems on your property.  It’s a good idea to get your draft plans and where you want to put the house checked by us (as Chartered Professional Engineer/s) before you finalise your position to make sure you have room for your wastewater system, as there are rules about where they can be put.  Soils, distance to houses, slopes, type of soils etc… all impact on where onsite stormwater and wastewater disposal can be put.

Under the current council regulations standard septic tank with trench disposal are still able to be used for onsite wastewater disposal. There are a number of restrictions to it and it is best to get us to view your proposal to see if you can have a septic tank.  If not, there are a variety of different systems, we can discuss with you and then design a system that will suit your needs.

There are a variety of different systems from the traditional septic tank with trenches and ETS beds (Evapotranspiration aeration systems) to systems which have a variety of treatment options known as AWTS (aerated wastewater treatment systems).  There are a variety of AWTS systems which can provide both primary and secondary treatment options with dripper-lines disposal.  The Council has requirements for different areas so it is important to tell your Civil Engineer the address of the property during the setup of the project so they know which Council requirements they need to meet.  Let us also know your own personal preference if you have been looking at systems so that we can talk it through with you.

Surfaces which are impermeable (rooves, concrete pathways, sealed driveways and the like) which are over 25m² will need to be assessed as part of building consent and the stormwater managed in such a way that the water can be controlled.   Managing stormwater will depend on your property size, location and limitations.  You may be able to connect to the Council system so will need a design that maintains the flowrate to pre-development levels. If you are rural you may need a soakage pit or you may choose to have water tanks to collect the water for use within the building.  There are a variety of different options for helping the stormwater flow from tanks above ground to ones that go under a concrete driveway so they do not take up room for small properties.

This means that the council wants to ensure that your development will not have a negative or any major effect on the environment due to stormwater runoff.  What this means is that you need us as Charted Professional Engineer/s to analyse the rain water flows which will be affected by your development and the possible impacts on the environment to come up with a solution, which we can do.  We take into consideration different types of rain fall from normal rain fall through to heavy storms.  Forward us your details and your proposed design or come into the office to discuss your development.

Council has extensive maps showing particular areas which are required to be checked for flooding, overland flow paths or coastal inundation and these are usually related to existing water systems such as streams and rivers, part of a valley system where water is caught in the higher hills or on flat land.  Sometimes the maps are not accurate so an onsite investigation is important to understand what is happening.  For a Flood Analysis the local water flows and possible storm events are examined along with the contours of the land and your proposed building site.  The report will then tell you what height the flood level will be at certain events and will often recommend a finished floor level above that flood height, or recommend changing the building platform so that it is not in the flood plain area. 

Getting a geotechnical report which looks at the soils that your house will be sitting on is generally required by Council for all building and if you are building in a new subdivision there will be some basic information on the site available which may cover the soil type so ask as part of your due diligence in buying land for this information.  For a geotechnical report it will take in to consideration the variety of different soils within the Auckland and Waikato regions.  For our Geotechnical reports by doing the testing we can find out what type of soil you have and if it needs any additional help to meet council requirements such as the strength of the soils. 

Peat is one of the complex soils which requires more detailed analysis and building design which we work with. When buying land keep in mind if you are looking in a flat area with hills above and around it you may be looking at peat.

There are a lot of different things that can affect your foundations including subsidence, stormwater flows and trees, to name a few.  Something as simple as problem guttering can mean that the water flows are changed and can upset the soils around the foundations.   

At one of our site investigations, we found tree roots and wind movements of the tree were impacting on the foundations causing cracking in the building at St Andrews Church in Pukekohe. At a house site in Green Bay we identified that changes to the surrounding area due to new developments effected the way rain water was moving across the property. Other reasons can be soil instabilities or altering of the land around the property.  We undertake forensic investigations to find out what the issue is and recommend solutions.

Steeper sites do have limitations on what can be achieved without blowing the budget. Steep sites generally require slope analysis to provide suitable subsurface (in-ground) retaining to maintain the stability of your site. Within our slope analysis we look at the proposed development and the soils within the area to come up with options to help retain the stability of the land and the dwelling. We work with Structural Engineers where appropriate to help to ensure an integrated design between the soils and the structure required.

The soil on your site will dictate what type of floor or foundation system you can have.   There are some changes to earthworks that can take place to help to make the soil more stable but this is not always the case as disturbing the soil may make the situation worse.  Generally, the main types of foundation are timber pile, concrete raft and conventional brick foundations. As part of our geotechnical report we provide recommendations on the type of foundations that will work best for your site.

Of the greatest importance in thinking about roads and driveways is the stability of the ground that they are put.  These are often high use areas and at Gibbons Civil Engineering Ltd we value ensuring that the base is strong and can take the wear and tear as well as meeting Council requirements.  If you are subdividing your land in the Auckland area Auckland Council has regulations that must be met for all new roading, which can include the main road outside of the proposed development as well. Discuss with us what you are planning on building and we can design a suitable road, driveway or access-way that meets your requirement while meeting Council requirements.  If the driveway is going to be made of an impermeable surface then it will also require stormwater analysis as well to meet Council requirements.

The Council have a list of requirements depending on which area your development is located. As part of your initial proposal for Council you will need to think about what type of development you are going to undertake. Once this is sorted you will require survey work of the development area, a geotechnical investigation for the proposed building platforms which includes soil testing, slope stability analysis, possible future stormwater management and wastewater disposal recommendations.   If your property has a stream running through it or Over Land Flow Paths you may also need a flood analysis but this depends on your proposed building platforms.   This is to give the council an indication on whether the site is capable of handling the development.  Compressive geotechnical report, stormwater and wastewater designs may be required when the properties are designed as part of building consent.

We recommend you talk with a planner, registered surveyor and us as civil engineers as part of your initial investigation as there are a number of rules you need to meet as part of the Council rules regarding subdivisions whether your subdivision is for 2 Lots or 100 Lots.