Browse Forums Building A New House 1 Jan 31, 2014 9:32 pm Hi, Our builder advised that we will be unable to drain roof water in the new (planned) house without either a rainwater 2000L tank or a concrete pit at the front of the property.. both with pumps. Around $5K and $15K respectively. But... we are on a block that has about 40cm angle towards the street. This is an older area and roof gutters could only be drained to the street kerb. This works pretty well with the existing house. We heard the problem was because that long underground pipe to drain to street could not "achieve 1:100" fall angle otherwise. But I guess that water pressure coming from the roof (say 3.5 m high) would easily push the water through the pipes to the street. The council, Glen Eira, advised this subject was not something they were interested in. They were interested in "site drainage" and said that with our angle they see no problem with that anyway. So what is the problem we seem to be against here? if we have a real problem with our block there must be hundreds and thousands houses in the similar situation. Is there a simple explanation and perhaps a simpler solution to this... we simply have no space for the above ground tank and no desire to have a pit with electrical pumps! Thanks in advance for advice Built a 2 storey house... hebel, proctor, pvc windows, aiphone, deck roofs, louver covered patio Re: Alternative to charged system moving rainwater to street 2Feb 01, 2014 1:35 am Rudy we are on a block that has about 40cm angle towards the street. What do you mean by the above? Rudy Our builder advised that we will be unable to drain roof water in the new (planned) house without either a rainwater 2000L tank or a concrete pit at the front of the property.. both with pumps. Around $5K and $15K respectively. Suggesting a pumped pit system is an option but amateurish. What happens in the event of a power failure during a storm? There has to be pumps in duplicate that alternate at each start and a host of hydraulic calculations made to determine the pit size etc. Rudy We heard the problem was because that long underground pipe to drain to street could not "achieve 1:100" fall angle otherwise. Plenty of places 'drain' uphill with a charged system. You would need a flush valve fitted to the pipes lowest point that flushed the retained water to an area that did not run off to a neighbouring property. A lawn is ideal. Rudy we simply have no space for the above ground tank and no desire to have a pit with electrical pumps! Then you won't be building! There are many different shaped tanks available and you don't need to restrict yourself to one tank. Two or three linked ultra thins might be ideal but it is impossible to suggest anything without knowing the topography, roof area, distances, landscape plans/potential etc etc. It appears you need a charged detention system. 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: Alternative to charged system moving rainwater to street 3Feb 01, 2014 8:04 am I remember seeing a house in St Kilda where the owner got over this issue by fastening the pipe to the side fence of the house above ground. Looked ugly, but if the pipe was inside a raised flower bed it could look OK. The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Alternative to charged system moving rainwater to street 4Feb 01, 2014 8:51 am I think what you are seeing is builders using their own "designers". They don't have to be registered and in most cases don't have the vision and the right expertise to solve a problem. The fact that your old house could drain to the street is an indication that new design could do the same Bashworth is on the right track and the pipes don't have to be on the outside. A good design with a bit of vision could solve the problem for you.(don't like raised flower beds against house because they are termite risk) Tell your builder to try harder or get someone else that can solve the problem for you. Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Alternative to charged system moving rainwater to street 5Feb 01, 2014 9:53 am building-expert Bashworth is on the right track and the pipes don't have to be on the outside. A good design with a bit of vision could solve the problem for you.(don't like raised flower beds against house because they are termite risk) I'd agree with not liking the raised flower bed against the house . . . . . so If I was designing a solution like this I would look to running the pipe in a hollow wall from the house to the boundary and then in a flower bed to the street. Or even a hollow wall all the way to the street. The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Alternative to charged system moving rainwater to street 6Feb 01, 2014 9:59 am We always thought that slope would be ideal for building. Ha ha seems might be not quite. Thanks for your comments so far! But I still do not understand WHY sealed pipes without tanks could not just drain direct to kerb just fine in our situation (with some water maybe left at the bottom of the pipes after rain)? Speed too low? Silting? Illegal as for some regulation...? How does a tank make it better? @SaveH2O - To clarify "40cm angle towards the street" - The kerb is the lower that our block. The block is gradually raising away from the street... about 20 cm in first 10m and then is about 40cm above kerb some 20m in to the block... after that is not raising much to the end of the block. The demo plan is to scrape to +30cm above the kerb. So we are "downhill" to street. @SaveH2O - We also do not want any pumps exactly for these reasons. @ building-expert - The builder is looking to get a 2nd opinion from an engineer that designs stormwater drainage for their multiunit sites. So we will know a more. In the meantime we trying to learn enough to have a meaningful conversation. We read all other formus here and elsewhere mostly about uphill situations. I get the idea in these situations (except for the tank role). But our is downhill so would really hope for simpler solution... Built a 2 storey house... hebel, proctor, pvc windows, aiphone, deck roofs, louver covered patio Re: Alternative to charged system moving rainwater to street 7Feb 01, 2014 10:52 am If your block will be scraped to a level 300mm above the street I find it hard to believe a gravity system wouldn't work. The problems with a charged system are explained a bit more at this link: http://www.anewhouse.com.au/2013/03/cha ... ge-system/ The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: Alternative to charged system moving rainwater to street 8Feb 01, 2014 12:06 pm Rudy But I still do not understand WHY sealed pipes without tanks could not just drain direct to kerb just fine in our situation (with some water maybe left at the bottom of the pipes after rain)? Speed too low? Silting? Illegal as for some regulation...? How does a tank make it better? I have previously been surprised at the Glen Eira council's lack of regulations in these situations....which makes it easier for you. Most councils mandate a detention tank so that the maximum flow rate diverted to the kerb during a storm is not excessive. REGULATIONS The amount of water diverted from the gutters is dependent on your roof area (including the gutter overhang) and your region's 1:20 Average Recurrence Interval (ARI). The 1:20 ARI is used to determine eaves gutter roof drainage compliance and I will assume here that you will have eaves gutters and not (the dreaded) box gutters. Your 1:20 ARI is factored as 2.17 mm/min for a 5 minute duration. 90 mm PVC stormwater pipe is flimsy whereas the stronger 100 mm PVC DWV pipe with 46% more volume may be your requirement (I don't know your roof area) but you might not want high velocity of water blasting out to the street during a storm. This is one reason why most councils mandate detention tanks but for you, it will be a personal decision. There is also surface drainage to consider if it needs to be captured. You cannot divert surface drainage into a charged system (for obvious reasons) and you cannot let it run off to a neighbouring property. This needs to be assessed and it might be why the builder also mentioned a pumped pit solution. As mentioned previously, you also need to occasionally flush the pipe and a wet system can easily retain several hundred litres of water. You need to plan where this will go. Mosquitoes love open pipes that retain water. All things being good, there is no reason why you cannot run a charged system to the kerb in Glen Eira. The downpipes will have to be PVC, not metal, so don't go optioning special downpipes. You should also have an air gap near the top of the downpipes so that in the event of a blockage, the gutters still drain. The best way to do this is to install a quality leaf diverter on each downpipe. Having a detention tank with a 2,000 L retention capacity connected to sanitary flushing would satisfy your 6 star requirement to have either a water tank or a solar HWS. The $5,000 quoted by the builder is reasonable provided that the quote included all plumbing to the toilet(s) but it sounds like he was only discussing a tank with a pump that pumped the water to the street. 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: Alternative to charged system moving rainwater to street 9Feb 01, 2014 4:38 pm Guys this is very useful. @bashworth - this link is good. The charged/wet/pressurised system illustrated is exactly what I imagined I would have needed. @SaveH2O - "a detention tank so that the amount of water drained to the kerb during a storm is not excessive" - this explains what the tanks are for well. Thanks. From speaking to the council building staff it seems outside of their concern. So as you said that might be helpful. We do not need tanks for 6 stars as we are way over insulated and have solar water. With tanks (not pit) the pump might have been to pressurize the mains to toilets. Not sure with the scant detail available at this moment. " you need to check as to whether the council is ok with this size pipe being plumbed to the kerb but a 100 mm" - I will check next week. "you will have eaves gutters and not (the dreaded) box gutters" - we have all metal deck GF and 1F so I think most or say half would box gutters - some areas will have parapets some will not... we have not finalised it yet. E.g. half of the 1F would use gutter. What is the problem with box gutters? Does it change anything? My calculation of the roof - total 213sqm GF 89sqm 1F 124sqm. (The house is on 9m front easement and is 19m from that point in the longest (roof covered) part. So that point is about 28m from the street. Imaging the house is a rectangle 19mx14m (it has some courtyards but lets ignore it) and has (at this moment) ground-level downpipes in 4 main corners plus one extra somewhere in the middle. Would 100mm work for that? Would 2x90mm make any practical sense here at all? (edited numerical errors) (corrected box gutter / eave gutter comments) Built a 2 storey house... hebel, proctor, pvc windows, aiphone, deck roofs, louver covered patio Re: Alternative to charged system moving rainwater to street 10Feb 01, 2014 7:37 pm A detention tank has a small overflow pipe fitted about 1/2 way up the tank and an 'emergency' larger overflow pipe at the top. The storage area below the overflow is called the retention compartment (there is no actual compartment) and you can use this water however you like. The storage area above the overflow pipe is called the detention compartment. When the tank starts overflowing, the initial flow will be slow and the tank will gradually fill but as it fills, the flow rate continues to increase as the tank fills. The detention compartment storage capacity is calculated to handle a set amount of rain during a 1:20 ARI. For your roof area, it would be +2,000 litres. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Rudy SaveH2O - "you will have eaves gutters and not (the dreaded) box gutters" - we have all metal deck GF and 1F so I think they are box gutters. What is the problem with these? Does it change anything? You really don't want to hear my opinion about box gutters. As far as compliance goes, box gutters are calculated for a 1:100 ARI, not a 1:20 ARI as for eaves gutters. This means that the calculated flow rates are about 50% higher. The builder would know this EDITED 08/07/2018. Added photo. 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: Alternative to charged system moving rainwater to street 11Feb 01, 2014 8:43 pm I love this thread as I had the same issue. I'm now flipping my crossover to the other side and not cutting my block. I have 600mm fall right to left which meant the garage down pipes were 300mm below my kerb and channel discharge point if I cut the block 300mm. Flipping the house means that I can build the slab up 600mm on the left hand side and the down pipes can achieve the required fall to the kerb. I too considered the charged system and believe the pump system is a load of cr*p and cannot be relied upon! he'll we had storms last week and had a blackout!! Sent from my iPad using Tapatalk Re: Alternative to charged system moving rainwater to street 12Feb 01, 2014 9:57 pm Crazyk I too considered the charged system and believe the pump system is a load of cr*p and cannot be relied upon! he'll we had storms last week and had a blackout!! Once would be one time too many. 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: Alternative to charged system moving rainwater to street 13Feb 02, 2014 10:12 am I am thinking if that makes any sense... 1) could discharge the front of the house using traditional approach (dry?) with metal downpipes. I have +30cm (scrape over the nail in the pathway) to play with... 10cm to bury the pipe plus say 15cm for a 1:100 fall... and I still have 5 cm left above the nail... speaking about the top of the pipe. As the kerb discharge is lower than the nail say another 5cm there is 10 cm left. With this extra 10cm (ie 10m 1:100 fall) I might be able to connect one of the other downpipes. 2) the 2 downpipes at the back of the house could use a smaller charged system perhaps. Still without detention tank. So if that made any sense I would have two 90mm pipes draining - one front+mid house and one the rest. @SaveH2O - thanks for detailed explanations. So it looks the detention with tanks with the overflow pipe would only be half full at best on not rainy days. So they are not as "useful" as water tanks with the overflow pipe at the top used to save water. If we could avoid the detention tank we might still be interested in a water tank. I understand that would be relatively easy to connect to the charged system at the back. The reason I am thinking future is that we would have more control over the project. Or would that be better to do it together? I am going to the council again to ask if 2 pipes discharge is something they are concerned about. Will see the builder too... maybe they have an update already. We asked the builder about any past cases and there seemed to be at least one house in a *very* similar situation and they did not have a charged system. The reason was apparently their back downpipes were not as far as ours... I need to get the plumbing plans for it. Built a 2 storey house... hebel, proctor, pvc windows, aiphone, deck roofs, louver covered patio Re: Alternative to charged system moving rainwater to street 14Feb 02, 2014 10:33 am @SaveH2O "You would need a flush valve fitted to the pipes lowest point that flushed the retained water to an area that did not run off to a neighbouring property. A lawn is ideal." How does this get done? Given that charged pipes are underground is a pit installed under the lower point with gravel? For example looking at this diagram http://www.anewhouse.com.au/2013/03/cha ... age-system ... how would that valve be organised? We have garden at the back (but little space for any tanks between windows). Built a 2 storey house... hebel, proctor, pvc windows, aiphone, deck roofs, louver covered patio Re: Alternative to charged system moving rainwater to street 15Feb 03, 2014 9:50 pm Just be aware that the (metal) downpipes have to connect to PVC pipes. If the system is charged, a simple hydraulic calculation will tell you the head needed. You can use metal downpipes without it looking too odd when you only require minimal head as you will but there will need to be be some vertical PVC pipe above ground. It will be a matter of the plumber making the above ground connection nice and neat and a bit of paint. The pipes are required to have a minimum depth and there are variances applicable. AS/NZS 3500.3:2003 table 7.1 states: "For a single dwelling, if the (PVC) stormwater pipe is not subject to vehicular loading and there is no paving, the pipe must be buried a minimum (from the finished surface at the top of the pipe) to a depth of 100 mm. For other than a single dwelling, it is 300 mm." If the plumber can get a slope to the front, you won't need a flush outlet. Sediment flushing velocity through a 1:100 slope pipe is considered a minimum of .7 metres per second. From memory, this is about 240 lpm through a charged 90 mm DIN PVC stormwater pipe. If you read the thread I linked and the link in that thread to the Gov doc I have previously mentioned, you will see that the roof slope is also factored for wind driven rain. The example I used in the other thread was for a standard 23 degree slope which is factored as a 1.21 multiplier. It is fairly simple to fairly accurately work out your multiplier; just think in terms of relating 90 to 100. A 15 degree roof for example has a multiplier of 1.13. As you will read, your 213 sq m roof (which must also include the gutter area) will be calculated as being more, primarily due to the roof slope. The plumber must calculate the roof and your 1:100 ARI (for box gutters) for all plumbing requirements. In real life, the plumber rarely does it, it is left to someone further up the food chain but mistakes are frequent, even by hydraulic engineers. It isn't hard to do it yourself. If you have a 23 degree slope, your roof (213 sq m) + gutter width + a 1.21 multiplier will factor your roof as being somewhere around 259 sq m. The slope doesn't increase the total amount of rain that falls on the building, only the amount that falls on the slope that gets the wind driven rain. This in turn delivers unequal volumes of water to pipes on opposite sides of the building and is why the pipes have to be sized accordingly. A single 100mm DWV pipe (the internal diameter is 104mm) would suffice. EDIT: The roof slope drainage calculation tables are found in AS/NZS 3500.3 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: Alternative to charged system moving rainwater to street 16Mar 05, 2014 7:35 pm I have an update on my side. Had some further conversation with the builder and now I am told the house needs to be raised only 200mm (improvement from the earlier 500mm) to get the discharge working or... I need the (dreaded, as we have no space where it is supposed to go to) water tank in the system. I am still not convinced and will meet with the contract drainage engineer to discuss. We do not fancy raising the house at our expense. My (simplistic) view is that: 1) if 200mm would do the trick... that would mean... that I do not need the detention tank. Does this view make sense? 2) if 200mm would work (note: without the tank) then the system the builder is proposing is "dry pipes". If that is correct... perhaps I could just have a "wet pipe" system? Or am I completely confused? Built a 2 storey house... hebel, proctor, pvc windows, aiphone, deck roofs, louver covered patio Re: Alternative to charged system moving rainwater to street 17Mar 05, 2014 9:31 pm Have you signed a building contract? Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Alternative to charged system moving rainwater to street 20Mar 09, 2014 7:32 pm "...Drain in front of the garage..." The driveway would have a small fall towards the footpath so I would assume the water would not sit there. Built a 2 storey house... hebel, proctor, pvc windows, aiphone, deck roofs, louver covered patio Once you know the basics, the rest is easy. Read my post in the thread linked below. viewtopic.php?p=1919271#p1919271 2 19522 Might cheaper to changer your idea of what makes a home, have you considered building a porch? 2 51809 Hi all. I'm thinking of installing an electric gate in front of this street front villa (link below). The gate would be between the bush on the left and the letter box on… 0 2780 |