If you are considering building a new shed, you may be wondering what you will need to do to comply with the council stormwater regulations. The answer is, it depends.
In this blog, we discuss 5 ways to dispose of the stormwater, however, the best option for you will depend on your property location, shed site location, and other council regulations.
Stormwater is the water that runs off surfaces such as roofs, roads, and driveways. In an urban area, stormwater flows down the drain, through stormwater pipes and out to sea. However, in rural areas, stormwater disposal is left for the owner to manage, and all buildings require a statement as to where stormwater will go. Therefore, you must consider where your stormwater will go before building.
One of the key requirements for stormwater is to ensure that any collection or discharge of stormwater doesn't enter buildings or cause a nuisance to any other property. This means that buildings and siteworks should be designed so that water cannot pool and flood the building, and also so that stormwater discharge cannot cross over a property boundary and negatively impact neighbours.
A soak pit is an underground pit to which stormwater is directed. The design consists of a drain below the ground, emptying into a hole with 100-150mm sized rocks and surrounded by filter cloth. These pits are designed and engineered specifically to hold the water and slowly release it back into the ground, thus preventing flooding.
Most councils will require that an inspector checks the soakpit before it is covered up. A good stage for the inspection is when the soakpit is half full of rocks, so they can check the filter cloth, rock size, and drainage fall. Taking plenty of photos during excavation and construction is also a good idea, as these can be used to show it has been constructed correctly.
Soak pits must be site-designed, and because of this, some tests may need to be carried out. A test hole (100-150mm diameter) is required to be bored to the depth of the proposed soakpit, filled with water and maintained full for 4 hours to pre-soak the ground. The soakage level is then measured by recording the drop in water level on a graph and determining the soakage rate from this.
It is important to note that soak pits are best suited to sites that have sufficient soakage available underground, as materials such as heavy clay make drainage slow, or do not drain at all.
We recommend talking to your inspector at the first foundation inspection to see what their requirements or expectations are.
In large, remote rural areas, especially in areas of low rainfall and high soakage soils, it may be an option to install 1.0m long 'kick-outs' at the base of the downpipe, to direct the roof water away from the building. The kick-out is essential to save the water from pooling and entering the shed
In some areas around the country, the council may not allow this option. For example, if your building site is situated next to a natural watercourse as this can cause water contamination in some cases.
Many rural clients like installing tanks to capture the rainwater from the roof so it can be reused during the dry summer months.
It is important to note that these tanks still need to have a method of disposal for when the tanks get full. This means another method of discharge is required to dispose of the overflow water e.g. soakpit, flow dispersal pipe, or council network.
This is a viable option for areas that have a good stormwater drainage system on the property, especially in areas of high clay/low soakage soils.
It is a requirement to prevent erosion at the outfall or where the pipe empties into the drain. Some councils may require evidence of this at the design stage or the final/drainage inspection. The simplest way is to create a Rock Riprap at the drain outlet, which is a layer of rocks 100-150mm in size, used to slow the water down before it enters the drain or swale.
Connecting to council stormwater networks is generally considered the best method of stormwater disposal for buildings in residential or industrial zones, where there is limited space for soak pits and there are smaller distances to neighbouring boundaries.
There are often options to discharge stormwater to the curb and channel along the roadside, or to connect the drain directly to the council stormwater pipes under the road.
Some councils or specific properties may require any stormwater discharge to meet Greenfields rates. This can be to minimise concentrated discharge to streams and rivers, or because the council stormwater system is already at capacity.
The best way to have a compliant design for this is to have the roof water connected to a detention tank, which could also be a dual-purpose tank if storage is required as well. This involves having a slow-release valve installed at a set height on the tank, allowing the water to drain slowly as it fills up during the rainfall event. Calculations are required to determine the tank size, valve size, and location/height. The Easy Kit team can point you in the right direction here, or you could engage with a civil engineer.
If your shed does not require a concrete floor, site preparation is easier. You will still need to level the site to make it easier for the builders. However, this does not need to be as exact as you would need if you were doing a concrete floor.
Scrape the topsoil away and spread 200-400mm of gravel around — this will stop the site from becoming too muddy, especially in winter. It does help the builder if the pad is compacted as it provides a more stable work platform for elevated work platforms when the builder is working at height.
If you have any other questions or want to discuss stormwater disposal further, you can give the Easy Kit team a call at 0800 428 700 or visit our website: easykit.nz.
Alternatively, price your shed instantly with our shed configurator to find the right fit for your upcoming project.