granny flat drainage question
- Thread starter knightm
- Start date
It's for drainage only.
Thanks for that Serge. What do you do about sewage if the property slopes to the rear but the only sewer lines are at the front?
That never happens.
Sorry for for the short n sweet replies-busy busy little moneky is me!
It is doable although not common. The first preference would be to try and bring the sewer to the front under gravity still. If that is not possible then (for a single lot) a pump and sewer line (not a main) can be used to pump it back up to the street although you would generally need to cut in a manhole on the sewer main unless there is one you can hook into. Either way it is not a cheap option.
On larger subdivisions a rising sewer main can be used which is just a larger form of the above. Generally lots which can't be discharged to the main sewer network under gravity would flow (under gravity) to a common point pumping station where the sewage is then pumped up the rising main until it can connect back into the main gravity sewer network. Again, not cheap.
This is probably a silly question but can you link the storm water to the sewage line if its easily accesible?
EG there is a WC in the backyard could you just connect it there rather than linking to the storm water at the front of the house?
EG there is a WC in the backyard could you just connect it there rather than linking to the storm water at the front of the house?
Perhaps I am misunderstanding your question. A WC (toilet) would discharge to the sewer network, not stormwater network.
Generally you are not allowed to discharge stormwater into the sewer system.
I thought so, thanks for that.
What is the best solution when having a granny flat at the back of the block but the land is completely level with regards to natural run off to the street. There is no chance of having an absorption pit either due to size constraints. (based in NSW).
You're welcome.
The land is dead level you say. Well, tbo there's no such thing as 'completely level' land but the logic tree goes like this:
1. Connect to exiting dowmpipes if THEY drain to the street. The way to check this is go out on the kerb (dont get run over please!) and look for an Outlet hole.
2. See if there's an existing Drainage Easement serving the block (rare). The way to check this is to look at either (a) The Deposited Plan <look for a dotted line with a symbol keyed for an "easement to Drain Water x.xx Wide".>
(b) Read the 'Property Title' which will lists whether the block is burdened/benefitted by a Drainage Easement.
3. Design an absorption (dispersion) pit into the rear yard. This pit is generally 4m long x 0.6m wide x 0.6m deep and must be placed minimum 3 mtrs from all tree-trunks, boundaries and structures. It must of course not be located upstream from the granny flat.
lol...If I write this^^ 3 more times in Somersoft I get a free set of steak-knives right?
BrazenWater would generally be off the existing water connection, likewise with sewer. Power would need to go back to the switchboard of the main property and then could have a separate meter depending on the desired configuration.
Hi ok80,
If the block is dead-flat (quite level) you can still drain to the street. Your slab is 100mm above the ground anyway plus your rainwater tank outlet is a few hundred millimeters above that again; so its no worries just connecting to the nearest downpipe on the house. Just make sure (of course) that IT is connected to the street outlet.
The fall can actually be <500mm below the kerb and you can still drain to the street. This is a 'charged system'. Another option is to build on piers. This buys you even more fall.
It's all about velocities. That is, is there anough ooomph (charge) to the street? Imagine two glasses connected by a long tube. They are both half full. Now imagine lowering one of the glasses. This will make the water from the higher glass flow to the lower glass, until the water-level is horizontally identical. It's like that with roofwater drainage.
The rainwater tank is glass-1 and the kerb/gutter is glass-2. You want glass-1 to empty into glass-2.
If the block is dead-flat (quite level) you can still drain to the street. Your slab is 100mm above the ground anyway plus your rainwater tank outlet is a few hundred millimeters above that again; so its no worries just connecting to the nearest downpipe on the house. Just make sure (of course) that IT is connected to the street outlet.
The fall can actually be <500mm below the kerb and you can still drain to the street. This is a 'charged system'. Another option is to build on piers. This buys you even more fall.
It's all about velocities. That is, is there anough ooomph (charge) to the street? Imagine two glasses connected by a long tube. They are both half full. Now imagine lowering one of the glasses. This will make the water from the higher glass flow to the lower glass, until the water-level is horizontally identical. It's like that with roofwater drainage.
The rainwater tank is glass-1 and the kerb/gutter is glass-2. You want glass-1 to empty into glass-2.
