Browse Forums Building A New House 1 Feb 02, 2017 9:49 pm We got an email today saying: I have am currently working now with our Hydraulic engineering to prepare your hydraulic stormwater design. One thing I would like you to confirm is your preference on either 1. Below ground modular tank for OSD - Or โ 2. An above ground basin We have noted we would be obtaining a design for an above ground design as this is usually the standard however you do have the option of either. Unfortunately at this stage I could not provide the cost difference until we get back your design and send away for quotes but normally the below ground system is the more expensive. If you have a look at our Hydraulic engineers website on the two types of systems and let me know what your preference is. http://www.stormwater.net.au/on-site-detention.html We are building in Ku ring gai. I am confused whether to go above or below ground. Can anyone advise me on pros and cons and what price to expect to pay? Re: Stormwater retention 3Oct 20, 2017 12:19 am I got same problem, finally how is it done, and how much. we build in ku ring gai council as well๐ Metricon Glendale 38 -ย https://forum.homeone.com.au/viewtopic.php?f=1&t=88854 Re: Stormwater retention 4Oct 20, 2017 10:08 am Are you having a retention and detention system or just a detention system? Below ground is always more expensive but other factors also need to come into it when making an informed overall decision, for example: Is the space needed for an above ground system at a premium? What is the lay of the land? I would have to assume that a below ground OSD is viable seeing as how it was mentioned in the Email but this also indicates a steepish slope to the LPOD which brings me to the next question...what are your landscaping plans/requirements? Will you have decking with available storage underneath for various water storage options and if so, would there be available slope to the LPOD? Have you been made aware of the possibility of using multi functional tanks? It seems like you have been treated like a mushroom and not informed of all commercial storage options or have I misinterpreted your post? The council requires a very large detention capacity but maybe a multi purpose option like Landscape Tanks which also serve as retaining walls and even garden beds and water features could be considered. This option can easily add value to a property. Thin Tanks may not offer a complete small footprint multi purpose solution due to their small volume but they may provide an in part multi purpose solution. https://www.landscapetanks.com.au/ http://www.thintanks.com.au/about.html The Ku-ring-gai council regulation of having a retention compartment only contribute 10% towards the detention capacity regardless of the retention capacity is absurd for several reasons but you have to accept it unfortunately. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Stormwater retention 5Nov 20, 2017 8:12 pm Do council's give you an option for OSD, whether it is underground or above ground ?
Our builder came back to us saying we have to do an above ground OSD. Then proceeded to give us a PCV for an additional 20K, we had an PA of 15K for an OSD. So our OSD will be 35K, not including the cost of rainwater tanks. I get the feeling our builder is trying to pump up their profit margins on us. Re: Stormwater retention 6Nov 20, 2017 9:08 pm I used a big rain water tank as OSD. The volume increase to 10K. The additional cost on top of the 5000L tank is about 2K extra. Hydraulic engineer should be able to work out the volume required. They will need from council the permitted site discharge rate later/s, the catchment zone I am in Ryde council on the council web site there is a stormwater-and-floodplain-management-technical-manual on section 8.2 Appendix 2 There is a work sheet and the hydraulic eng use this to calculate the OSD requirement. in section 1.4.5 Rainwater Tank Offsets Rainwater tanks do not generally substitute for the storage capacity required for on-site detention. However, where a rainwater storage tank for water efficiency is incorporated into a stormwater drainage system for a single occupancy development and the tank is connected to an internal re-use system, the volume of the required on-site detention may be reduced by an equal amount up to a volume of 5,000 litres for sites less than 3000m2. This provision will be in addition to any BASIX requirements. . . . Rainwater tanks (above or below ground) can be designed to form part of an on-site stormwater detention system. A dual purpose OSD/rainwater re-use tank that collects only roof water from the roof may however allow the majority of stormwater runoff from the site to be uncontrolled. When using a dual purpose OSD/rainwater re-use tank the design must still ensure that the permissible site discharge for the whole site is still achieved. Storage tanks below ground will need appropriate pumps for their intended re-use purpose Once it work out the OSD volume required and the allowable rain water tank reuse volume, than you can see if increase the rain water tank meet the council requirement. You just need the gutter and downpipe sizes to be compliant with the NCC for the roof area harvested and have the downpipes connected to a LPOD. You need to ask your… 1 2961 Plumbers 'can be' plumbers, made all the worse by self certification which the building surveyor invariably accepts as proof of compliance! The good thing is that you know know. 3 3237 Grab a hose, insert it at the top of the inlet/down pipe and turn the water on and see where the water is escaping from. Then you'll know. 3 6337 |