If we ever want to turn the basement into a third unit, flood protection will be rather important. We have inherited a check valve protection, but I am not too sure if this is the best option.
What else can we do?
Option #1
We could create a vertical separation between the waste water system for the basement and the rest of the building. In other words, the 1st and 2nd floor waste water system is gravity fed, while the basement system is pumped. Here is how it would work:
We eliminate the check valve with the sump and have the main sewer run directly to the vertical stack that service the first and second floor. All the basement waste water is plumbed into an ejector pit with a sump, which pumps all waste up to the first floor level and over into the vertical sewer stack.
If the city sewer system backs up into the house, all flood and waste water will be contained in the main sewer pipe. There is no plumbing connection that would allow the goodness to spill into the basement.
Option #2
We could keep and repair the check valve system. The check valve prevents the city system from backing up into the basement. It would be placed in an ejector pit with a sump and a sewer overflow. The waste water for the entire building is thus gravity fed…
… with one small exception, and that is if city system floods and the check valve closes. Once this happens, the pump engages and all waste water from the house is pumped out of the building.
Pros and Cons
Option #1 (see sketch above) would give us the flood protection we seek. The bathrooms and kitchens on the 1st and 2nd floor are gravity fed and would always remain operable. Not so for the basement plumbing, where use would be restricted during any power outage, which would disable the sump for the basement waste water system.
Option #2 (see sketch above) also gives us the necessary flood protection and is highly efficient as all waste water is gravity fed. A power outage in this case would only affect us during flooding, disabling the sump when the check valve is closed.
Should this ever happen, we still would be in good shape because we plan to use low-flow fixtures throughout the house. I calculated that we could store about 30 to 40 gallons of waste water in the 4 inch main sewer line, before it would spill out the basement floor drains. With 1.1 gallons-per-flush toilets, we could use the bathroom up to 25 times.
This logic of storing waste water in the sewer line will only work if I am disconnecting the downspouts from the sewer, which the city won’t allow. If I keep the existing roof downspout connected, the roof runoff would certainly flood the basement – if the power is out.
Option #1, on the other hand, would avoid this problem altogether, as all roof runoff and waste water is contained in the main sewer line and nothing can spill into the basement.
I also have to look at the energy side of things, if I would like to keep the ultimate goal of a zero energy building alive. The beauty of Option #2 is that a law of physics does the work for us. The system runs on gravity. The sump at the check valve may only have to kick in once it floods, say once or twice a year if that.
Not so with Option #1, where the sump in the ejector pit will kick in each time a plumbing fixture in the basement is used. This, over the course of a year, could result in major kilowatt usage and would not help with lowering our energy consumption.
This is quite a pickle, isn’t it? If you have a good idea or the solution, please let us know!
Tags: city of chicago, drainage, energy, layout, utilities, water
The City won’t let you disconnect the downspouts? I thought they were trying to get us all to disconnect them. Did they give you a reason? Option 1 seems overly complex. Have you ruled out sumps with battery backup?
The Department of Environment is promoting downspout disconnection, but the Department of Building is still throwing up road blocks - is basically saying no.
Yes, the good old battery back up! I think it would only work if I can disconnect the downspouts. If the battery back up has to handle all the roof runoff, it would run out of juice pretty quickly…
Can the storm water be directed in a separate line to connect on the other side of the check valve?
It potentially could. It would, however, make the sewer layout rather complicated, I double the amount of material I need to use (cast iron sewers) and I double the material cost (cast iron sewer pipes are not cheap!). I love simplicity and hope to come up with a real simple but elegant solution…
Would the city require the down spout water part of the system to be made of cast iron.
While I was house shopping I saw a house that had PVC run in the ceiling of the crawl space which makes it easier to access if repair is needed.
Probably not code.
In #1 you could have a drain with a check below the the sump line in the the ejector pit, though I would not want to be around if that check failed.
The City of Chicago allows the use of PVC for DWV systems if it is not concealed (such as in the ceiling, the vertical stack in the walls, etc). My sewers run under the basement slab, are as such concealed, and must be cast iron… I can’t put them under the ceiling as I need to preserve the 7.5 feet ceiling height.
That idea of yours about Option #1 is worth while considering, if I can get the sewer elevations to work and line up. I will discuss this with my plumber!
I can think of 6 projects, designed and permitted in Chicago, that have disconnected downspouts.
Is there history of flooding in the neighborhood or on the block that would indicate you need a check valve?
What is the elevation of City sewers with respect to elevation of basement floor drains?
Municipal Code of Chicago:
“18-29-1101.2.1 Roof drainage and downspouts.
All roofs exceeding 750 square feet (69.7 m2) in area shall be drained to a sewer, where such is available in any adjoining public way, or public place. Every connecting roof downspout having the open roof connection, located nearer than 12 feet (3.66 m) to an inside lot line or any door or window on the same premises, shall be trapped on the downspout side of the connection to any sanitary sewer or any combined sewer or drain, and shall be set where not subject to frost.
Exceptions:
1. Nothing in this provision shall prohibit the temporary or permanent disconnection of the roof downspout of a building from the sewer or combined sewer so long as the disconnection does not result in the drainage of water beyond the property lines of the lot on which the building is located.
2. Roofs of single-family (Class A-1) and multiple-family (Class A-2) buildings may be provided with external downspouts discharging onto a paved or landscaped area, provided the water thus discharged can be drained directly to an area drain, catch basin or street gutter connected to a public sewer, without spilling over onto adjacent property creating a public hazard or nuisance.”
Thanks Eric! This appears to be a constant battle - some win it, some don’t.
The plan review comments I got back from DCAP asked me to re-connect the roof downspout to the sewer. I probably could fight it, but I don’t have all the stormwater treatments or volumes figured out yet. They also require me to install a check valve, believe it or not!
I am now thinking that keeping the connection to the sewer maximizes my flexibility. It is very likely that once I am done, I will have everything disconnected - so I hope. But it is good to know that I have the option of this last resort overflow, if I need it. And I don’t have to fight the city.
There is no history of flooding on the block, as far as I know. What worries me is that the block is under-developed with several vacant lots. Not sure if they will stay vacant forever (hopefully not).
As far as I can tell, the city sewer elevation is below my basement floor elevation. Our main sewer exits the building 42 inches below the basement floor (the invert that is). Assuming a 1% slope and 30 foot distance from the building to the city sewer, the elevation difference would be around 45.5″.
Thank you for these diagrams! I have been talking to too many plumbers about flood protection recently and just now understood how the 2 systems work.