Daylighting Pipes in Cold Climates 2

[Forensic74]

I'm trying to get a feel for what the standard of care is when daylighting small diameter pipes in cold climates. In particular, a 6-inch foundation drain that also accepts downspouts. I often see these systems form ice plugs at the discharge point, whether its discharging into an open swale or a shallow open grate inlet. Once plugged, the system fills up and then bad expensive things can happen at the building. I dont see much in the way of code requirements, but feel that there has to be some sort of standard rule of thumb. If anyone can comment and/or provide reference to any useful documents I'd be grateful!

 

[cvg]

foundation drains should never be connected to downspouts. downspouts should be large enough that they will not freeze solid

 

[dhengr]

Forensic74:
I agree with cvg on the account of the down spouts not being connected to the found. drain system. Normally, during the winter the found. drainage volume settles down, so you may not have much flow. Two ideas, and I’ve used the latter one with success. Up-line from the outfall, could you run your line through a deep enough dry well so that the smaller volume during the winter would most likely never get to daylight, and would not freeze? We used to put some straw insulation over the open end of a similar drainage system at the outfall. This kept the pipe end and the ground from freezing so the drainage could continue to work.

 

[Forensic74]

CVG are you quoting a code requirement or a general civil standard of care?

dhengr, I agree straw insulation is a good approach. as it pertains to a design drawing, is that something you would specify to the owner as a yearly maintenance requirement?

 

[CarlB]

A brute-force method, self-limiting electric heat trace, some distance upstream of daylight, and to a few feet downstream.

 

[cvg]

just common sense

 

[Forensic74]

Regardless if the system drains downspouts, back to my original question, what is typically accepted for daylighted drain pipes outlets in cold climates? Do PE's design these knowing the outlets will probably freeze up and essentially screw over the owner??? Maybe the standard practice is poor practice? I've seen this several times now, so it's not a random occurrence. It seems idiotic to expect a daylighted drain system to work in the winter; however, i'm just not finding any publications that talk about it. Stormwater BMP Design Supplement for Cold Climates (1997) seems to be as close as it gets.

 

[bimr]

Perhaps you can make a sketch? What size building are you talking about?

 

[Forensic74]

warehouse, approx 150' by 150'. No basement, but they supposedly installed a buried preforated drain around the perimeter of the building that accepts downspouts and daylights into an onsite detention basin via two separate runs of pipe. Ice plugs formed at both outlet ends, and the system filled up with water and saturated the grade around the building, froze, and heaved many of the adjacent walks. Outlet ends were smooth 4" PVC.

 

[bimr]

I don't believe that it is covered by a code requirement.

This has been discussed:

http://www.eng-tips.com/viewthread.cfm?qid=352222

In the north, people run the roof drains underground and have them daylight downstream, but the pipe is not perforated near the building or foundation. It is possible to drain a residence into a french drain (also located away from the structure). However, your structure will have too much roof runoff for a simple French drain.

As the others have posted, it is not a good idea to run the roof drains into the foundation drain. That is asking for trouble.

 

[cvg]

first of all, it is very bad practice to introduce more water from the roof into the foundation. even if it doesn't freeze, you are putting more water (and sediment) into the foundation. down drains should be disconnected and run in a separate system from the foundation.

good practice to reduce the chance of freeze up is to use larger pipes, steeper pipe slopes that can accommodate more ice buildup without plugging. if you want to eliminate the ice totally than you might need to heat trace it or possibly drain to a covered and insulated dry well. An overflow can be provided to allow flow to continue if the pipe plugs at the end.

I would not expect much flow from a foundation drain in the winter.

 

[civilman72]

Forensic: I've designed numerous outlet structures in the Rocky Mountains and yes sometimes they do cause the owner long-term maintenance issues. But I've never tried to hide the potential issues from a Client and I take the time to discuss more expensive options to properly address the potential freezing problems. But often the owner makes a conscientious decision to spend their money on maintenance and not up-front construction costs.

If the owner decides to go with the cheap option, which is basically a 4" plastic pipe daylighted to the surface, I highly encourage the following:

1. Make sure the pipe daylight is located away from snow storage and roof drainage areas.
2. Install a DIP or steel pipe at the outlet, because (whether they want to or not) they will have to chip away at ice blockage and will destroy the plastic pipe in the first winter.

If they want to go a more expensive route, I try to get the roof drain system to connect to a public storm sewer system and put the foundation drain into a dry well that discharges well below the frost line.

 

[Forensic74]

Thank you civilman, I think that paints a great picture of the standard method to approach this. Obviously, memorialize those discussions with the owner or else this can come back to haunt you!! FWIW, I would be cautious of recommending option #1. I have seen entire 300 foot runs filled with water. Also, be careful to assume that connecting to a public storm will solve the problem. On more than one occasion, I have seen ice plugs form in a roof drain system where it emptied into an open grate manhole. One plug held back three stories tall worth of water that backed up onto the roof!

CVG, you would be surprised at how much flow can occur in the winter. Get a sunny day with a high of 30 degrees and you usually have something flowing in the system through the night. Trickle of water is the worst to build up a plug.

 

[dicksewerrat]

Roof drains in cold climates FREEZE. If you want to have them work all winter, they have to be inside a heated bldg. and discharge to pipes that are totally below the frost line. Even roof drains that are a rectangular with an opening all the way back to the roof still will freeze above the roof line. The foundation drain should probably be 'heat taped all the way from the sump to well past the outlet. They should be in the lake/ pond well under the ice. If that pond freezes solid there is no solution except pump into barrels and haul away.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com