Can I add an overflow (i.e. secondary) rainwater drain in an internal lightwell that feeds into a bathroom's soil pipe?

[LordWest]

I would appreciate some advice. I have a flat on the 3rd floor of a converted house, which has a lightwell in the middle of the flat. The bottom of the lightwell reaches the 3rd floor (my flat’s floor level) and has a roof lantern for the flat on the 2nd floor. I plan to build a small bathroom extension, which is highlighted in yellow, in the 2 square meters of the lightwell where there is no roof lantern. The lightwell has a drain (shown in blue) which goes to the back of the building. This is an old building (1850) and soil waste and rainwater are combined. Because the new bathroom will create less space for the rainwater to rest on the lightwell, I would like to create a second drain (shown in red below) on the lightwell acting as an overflow, in the event there is excess rain in the lightwell. The overflow would connect to the existing bathroom’s soil pipe. Do you think that would be ok according to building regulations? See floorplan below plus two photos of the lightwell.

Many thanks,

 

[SimonG]

Youd be better talking through your proposal with local building control to see what they want.

 

[WC1]

1. You can't connect a rainwater pipe directly to the soil because of sewer gas coming out.
2. Whatever construction you're doing should not compromise the rainwater drainage from the building.
3. You're better off with one drain working well than 2 which don't.

 

[LordWest]

ok thanks. I do plan to talk to the local control person. Also, the idea was for the new overlfow pipe to connect to the 40mm waste pipe for shower, not 110 soil pipe. It is difficult to mess with original drain which does the job, but need a backup in case of heavy rain...

 

[WC1]

Unfortunately you can't connect r/w to 40mm either or any other waste for that matter, they all run to soil.
If you need a "backup" rainwater drain then the existing drain is incontrovertably not doing the job properly.
I'd do a good bit more research and then speak to building regs.

 

[king of pipes]

I would check with building control before doing anything, the rainwater and soil are draining via that pipework already from your pictures, it probably can be done ? but will BC allow it ?? It needs signing off once complete presumably ?? Regards kop

 

[LordWest]

ok thanks

 

[Ric2013]

Worth considering that, as well as reducing the space the water can settle in, you are also reducing the area that the rain can land on, assuming your new bathroom has a roof with gutter that takes the water elsewhere. The new setup may be less prone to flooding than the existing?

 

[LordWest]

Worth considering that, as well as reducing the space the water can settle in, you are also reducing the area that the rain can land on, assuming your new bathroom has a roof with gutter that takes the water elsewhere. The new setup may be less prone to flooding than the existing?

You are indeed correct. It really depends on where the rainwater from the new bathroom roof goes to. I could in theory put a gutter and then route that water into the main drain in the patio (not elsewhere unfortunately), but instead I am thinking of creating a so called "blue roof" on top of the bathroom. A blue roof allows the accumulation of water on the roof and then with a special restrictor on the roof drain, it allows the water to setlle around the rooflight but in a managed way over a 24hr period. A blue roof controls and limits the rainwater flow from the roof ensuring that the drainage system below is not overwhelmed. It is a new concept used to control storm water.

"A blue roof offers a radical rethink in roof drainage; the emphasis is switched to utilising the space to provide attenuation capacity rather than quickly moving the water elsewhere. Water attenuated within the roof area can then be released at a controlled rate through a bespoke restrictor outlet designed specifically to offer variable discharge rates and keep the flow off the site within the levels set by the local authority as part of the discharge consent."

 

[Ric2013]

You are indeed correct. It really depends on where the rainwater from the new bathroom roof goes to. I could in theory put a gutter and then route that water into the main drain in the patio (not elsewhere unfortunately), but instead I am thinking of creating a so called "blue roof" on top of the bathroom. A blue roof allows the accumulation of water on the roof and then with a special restrictor on the roof drain, it allows the water to setlle around the rooflight but in a managed way over a 24hr period. A blue roof controls and limits the rainwater flow from the roof ensuring that the drainage system below is not overwhelmed. It is a new concept used to control storm water.

"A blue roof offers a radical rethink in roof drainage; the emphasis is switched to utilising the space to provide attenuation capacity rather than quickly moving the water elsewhere. Water attenuated within the roof area can then be released at a controlled rate through a bespoke restrictor outlet designed specifically to offer variable discharge rates and keep the flow off the site within the levels set by the local authority as part of the discharge consent."

Sounds like a good idea.