How to insulate a shallow water line
How to insulate a shallow water line
(OP)
Sorry for reposting, but I think this would be a better forum for this question than where I had origionally placed it.
I am working on an office building project which has been completed, however the contractor installed the water line for the building sprinkler system approximately 36" below grade due to shallow bedrock. The frost line here is approximately 42" and the water within the sprinkler system will not be flowing unless there is a fire in the building, so we believe that there is a real pottential for the water within the line to freeze.
My question is: how can i determine an R-value for the soil above the water line? I plan on using this information to determine how much foam, preferably sprayed, to place around the sprinkler system distribution line. Thanks for any help.
I am working on an office building project which has been completed, however the contractor installed the water line for the building sprinkler system approximately 36" below grade due to shallow bedrock. The frost line here is approximately 42" and the water within the sprinkler system will not be flowing unless there is a fire in the building, so we believe that there is a real pottential for the water within the line to freeze.
My question is: how can i determine an R-value for the soil above the water line? I plan on using this information to determine how much foam, preferably sprayed, to place around the sprinkler system distribution line. Thanks for any help.





RE: How to insulate a shallow water line
RE: How to insulate a shallow water line
RE: How to insulate a shallow water line
Other threads on similar topic:
thread378-217830: UG piping within Frost depth
thread164-196645: Buried Water Pipe - Blueboard Insulation
RE: How to insulate a shallow water line
RE: How to insulate a shallow water line
As I understand it, the frost line is the point underground below which where piping, subject to freezing, should be installed. It is due to the heat transfer from the "earth" to the above ground atmosphere.
Depending on location the "earth" is considered to be a set temperature - say 50 degrees. As you head toward the sky and colder temperatures, the temperature progressively drops due to conductive heat transfer. So at 6 feet, it is 50 degrees, at 5.5 feet it is 45 degrees, etc. So the frost depth is where the temperature will not be lower than 32 degrees.
If the soil temperature is less than 32, eventually the water in a stagnant pipe (fire water) will match the temperature of its surroundings, i.e. less than 32 degrees.
What am I missing?
RE: How to insulate a shallow water line
Or, create a pool of water on the surface in an area. The "cooling energy" necessary to freeze the water will reduce the frost penetration below the pool. The "frost depth" varies a lot from place to place, depending on soil conditions, groundwater levels, surface type, whether cleared of snow, wind effect, etc.
RE: How to insulate a shallow water line
So the depth of the 32 degree soil temperature line may shift depending on the temperature above the ground. And isulation will slow down how much the piping loses heat.
But I thought that the frost line was defined as the depth underground that is always above freezing - based upon the prevalent conditions.
Adding insulation will help, but may not be enough - depending on how deep you are and how far from the defined frost line you are. And with a life safety system such as a fire water main, I would not want to be the engineer that accepted an installation above the published frost line and just used insulation. I might consider it on a domestic water pipe, but not fire suppression.
RE: How to insulate a shallow water line
the basic concept being that the natural freezing of the ground uses the travel path from the edge of the insulation board to the pipe plus the vertical distance from the edge of the board to the surface. i'm not saying simple distance math but there is a relationship. the R-value of your total insulation cross-section and the distance that the blueboard extends away from the centerline are both important factors. there are other factors that can help but i would not be consider (1.if it is a yard area, you may get some insulation value from the snow 2. if it is a main line, the water may not have the opportunity to freeze. 3.anything to do with soil mechanics)
RE: How to insulate a shallow water line
It should be obvious that if you build a structure on the ground, there is no longer a "frost line". The frost line is also just a rule of thumb. Soil conditions will the depth of frost. In the same manner, putting insulation on the ground will raise the frost line.
RE: How to insulate a shallow water line
I was considering the piping outside the footprint. I agree that the "frost line" is subjective in that you could be below this depth and have an incredibly long and cold winter and all bets are off.
But to bury a stagant water pipe above the frost line with only insulation is risky.
But as I thought about it more last night, I would accept it if I calculated/approximated the heat transfer resistance of the 6" of the soil above the pipe and compared it to the heat transfer resistance of the insulation (considering the thickness and material) and the insulation was greater. All other things being equal, I could accept that.
RE: How to insulate a shallow water line
RE: How to insulate a shallow water line
RE: How to insulate a shallow water line
I beleive the best example may be in the IRC of all places. - Shallow foundation insulation may be the subject. Sorry, I do not have the code handy to provide a section to refer to.
Basically, it is the horizontal and diagonal use of rigid insulation to prvent the ground from feezing.
Dick
RE: How to insulate a shallow water line
Being that I am not the most experienced at this, I brought it up with some of the more experienced engineers at my office. After getting the scared deer in the headlights when I brought up not burying the pipe below the frost line, the following two suggestions were brought up.
1. For the length of the pipe, dig into the stone until you are below the frost line. Now depending on the type of stone and the distance of the pipe run, this might not be too easy.
2. Raise the grade elevation in the area so you have the 42" of cover. This will depend on what is going on at grade and if you are able to have more soil in that location.
As was stated before, talk to the insurance carrier. If they are willing to risk freezing by not burying the pipe at the frost line, then do it. Just get it in writing.