Cold Weather Storm Sewer Design

[Jeamon]

Hi,

We live in a relatively cold climate (ontario, canada) and our company has had issues in the past with a Storm Sewer freezing. This sewer was slightly above the recommended depth of bury for frost but was adequately insulated. The pipe froze between the building connection and a catchbasin manhole. The conclusion was that the building roof drain interior piping (for the second story roof) was creating a stack/chimney effect that resulted in cold air being drawn in through the CB manhole, through the pipe and out the roof drain. The cold air resulted in the pipe freezing.

As a result, our company has standardized on not connecting building storm sewers to CBs or CBMHs. I'm wondering if anyone else has had similar experiences?

My issue is, assuming there really was a stack effect that caused the freezing, I'm unclear how not immediately connecting to a CB or CBMH, when there are CBs and CBMHs downstream, solves the problem. Any input would be appreciated.

Thanks,

 

[CarlB]

I've heard of roof drain lines freezing at or near location of tying into a CB or CBMH. I had thought the explanation was that freezing was due primarily to the proximity/exposure to the cold air. I didn't think of the stack effect baut can see how that would exacerbate it. It may be the effect is limited to a short distance from the CB (of course depends on air flow). The manhole being further away should improve the situation, decrease the air flow.