×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Internal roof drains and freezing
2

Internal roof drains and freezing

Internal roof drains and freezing

(OP)
We are working stormwater projects involving the disconnection of impervious surfaces from the local CSO.  Some of the buildings associated with our projects are equipped with internal roof drains directly connected to the sewer system in the building basements.  We are looking to disconnect these systems and run them outside of the buildings to green infrastructure practices.  A concern has been raised relative to freezing of the pipe daylighting to the outside in our cold climate and whether that could lead to backups that could compromise the roof.  Given that the drains are within the heated structures and the above-freezing basements until they extend to a <6" length of pipe extending to the outdoors, we have considered freezing of the pipe to the extent that it plugs completely with ice, highly unlikely.  Icicles perhaps yes, but a complete ice plug, no?  Does anyone have experience or other knowledge related to this subject?     Thank you.   

RE: Internal roof drains and freezing

Flow through roof drains is generally too fast to freeze under the conditions you noted.  If backups occur on the roof from an obstructed drain, then yes, you could get freezing of the ponded area.

Provided the drains are sized properly and adequate conveyance slopes are available, I would not consider this to be an issue.  Make sure you have a good vertical drop in the roof drain outlet before turning to the horizontal.  Further, prior to making a 90 deg turn, increase the pipe size by two sizes to prevent a slow-down  in the flow.

RE: Internal roof drains and freezing

(OP)
THank you.  We have indeed incorporated such a feature into our designs that we have undertaken from scratch.  Unfortunately, we were designing on the fly for a previous project.  The contractor asked us where to set the outlet and we hadn't considered all of the plumbing issues at the at point.  I guess we'll have to keep our eyes on that one.  Thanks again!   

RE: Internal roof drains and freezing

(OP)
My first reply was to bimr.  

Thank you to Ron for that response as well.  I think the concerns have been less with fast flow associated with rain event, and more with snow melt that could refreeze at the outlet (i.e. the icycle phenomenon).  I don't see that as likely to freeze up to the point that it plugs the outlet.  And even then the concern would only be where that plug would remain even under a subsequent rain event wherein the rain water is backed up onto the roof causing a load exceeding the snow load typically experienced up here.  Again, this seems highly unlikely to me.  Thanks again!    

RE: Internal roof drains and freezing

If water can find a way to pond - IT WILL.  Mother Nature is a B&TCH and she always wins - sooner or later.

Just don't forget that.

RE: Internal roof drains and freezing

I think it's naive to assume that freezing will not be a problem, but it depends on how cold and how long your winter really lasts.

The one situation that I have dealt with that I can compare is with outside gutter drains.  Due to the heat produced from the roof and house, the water does not freeze in the gutters (asuuming they are clean of debris), or the downspout, but there is ALWAYS freezing at the outlet.  The only way I've seen to solve the freezing issue is to install heat tape or connect the downspout directly to a storm sewer system.  This freezing does block the entire pipe, but rather than backing up the water, it usually just busts the pipe (which should not be an issue for you since your pipe is inside).

For reference, the average daily low temperature where I'm at is about -10 F for about four months.  If anyone else deals with temps this cold for this extended period of time, and has other ways to prevent freezing at a roof drain outlet, I'd love to hear them.   

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources