If You Install Up North, Lay Out Pipes to Prevent Freezing

With chilly winter on the horizon, slope and insulation are critical to avoiding those pesky customer calls about ice-dammed systems

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As we move from fall into winter, your clients are probably beginning to worry about whether their systems will experience freezing issues. Good installations can go a long way toward avoiding problems with freezing regardless of whether the system is in a cold climate. 

The first line in freezing defense is to establish a good vegetative cover over the system. Well-established vegetation, such as grasses, can help insulate the system and capture snow and hold it in place. Snow is a good insulator and if it remains over the system will provide protection. If installation has been completed late this year and a good cover has not been established, application of a mulch or straw will provide insulation and hold snow in place. 

Proper installation of house sewer and supply pipes to different parts of the system is an absolute must to prevent freezing and other blockages. Municipal water and sewer lines are installed deeper than expected frost penetration. In cold climates, this requires lines be located 6-8 feet deep or more. For our gravity systems where we want the soil treatment area placed 

Control the flow

It is key for supply piping to be installed so they remain empty between water-use activities. Standing water for whatever reason in supply pipes will be subject to freezing during prolonged cold periods. Proper installation requires laying pipes at the necessary slope to conduct water and bedding the lines to avoid low dips or bellies and to remain in place during backfill. In the winter where we live, these low spots are all identified because they do freeze causing backups and numerous homeowner calls wondering why their sewer line is backed up.

The house sewer line will carry raw sewage to the septic tank. The slope on this pipe should be between 1 inch per 8 feet of distance (1% slope) and 1 inch in 4 feet or 2 inches in 8 feet (2% slope). When the slope is too flat, the liquid will slow down allowing solids to settle out in the sewer pipe. When the slope is too steep, liquid runs away from the solids and the result is the same; solids accumulate and will pond some water which allows everything to freeze. 

For the outlet pipe from the septic tank to distribution or drop boxes, the slope should be 1 inch per 8 feet or greater to ensure the pipe runs free between events. This also goes for the slope on piping between drop boxes. There is no specified maximum because the pipes are carrying effluent without solids that have settled in the septic tank. 

This is the reason we promote the use of drop boxes instead of a distribution box with multiple lines where water sometimes can be held in the supply lines to individual trenches. We even specify drop boxes on level sites where distribution boxes would be allowed just to avoid the freezing potential if there is any standing water in any of the piping. 

Supply piping from a pump tank to either a drop box or a pressure distribution system in a mound or at-grade must also drain free between uses. When the pump shuts off, the liquid must drain back to the tank. It should not drain all the way back through the pump, so the pipe inside the tank should have a weep hole to allow this drainage. There should not be a check valve installed to hold water in the pipe between uses.

Insulation options

If soil cover over the pipes is less than 1-2 feet or the pipe passes through areas with compacted soil or lack snow cover, such as driveways or other hard surfaces, the trench or piping should be insulated. 

There are several ways the pipe or the trench the pipe is installed in can be insulated. It is possible to purchase pre-insulated pipe which includes one pipe embedded in insulation inside a larger diameter pipe. For our purposes, it’s usually either a 4-inch pipe inside a 6-inch diameter pipe for sewer lines or a 1- to 2-inch pipe inside a 4-inch pipe for effluent pumping. Of course, as an installer you can create this effect by placing one pipe inside the other and wrapping the small pipe with insulation or spraying foam insulating material to fill the spaces. 

Another approach is to insulate the trench using underground rated expanded polystyrene sheets over the top of the piping and for added insurance along the sides of the excavation creating a box-like effect. For even more protection depending on the application and the risk, the supply pipe can be embedded in a larger pipe as described above.

Polystyrene sheets can also be used to insulate sewage tanks and distribution or drop boxes. This can be done over the top and by cutting insulation to fit inside the access openings. Consider this option when tanks and boxes have less than 1-2 feet of cover and a lack of snow cover.

One final comment: We talk about the importance of having easy access to all parts of the system for maintenance purposes. It is important that access be provided in cold climates so parts of the system can be accessed and thawed if needed during the winter. For a happy client, you want to minimize the time spent locating, digging through the frozen soil and providing access to the frozen sections of pipe so the house is not left without service for long periods of time.  


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