The best way to insulate a septic system post-installation

October 25, 2021

By Sara Heger, Ph.D.

For those of us who live in colder climates, winter is right around the corner. Both during construction and with existing systems there are measures that can be taken to reduce the likelihood that systems will freeze.

In a past article we discussed insulating piping and tanks, but what about once the system is built? In colder climates we often get a layer of snow that helps insulate the system, but what if we have a winter with less than average snow with cold temperatures? What can be done to protect the system?

The items below can be checked during service visits or recommended to property owners:

  1. Make sure all risers, inspection pipes and manholes have tight covers on them to prevent cold air entering the system. Placing insulation in the lids can help prevent heat loss through needed at-grade maintenance access. 
  2. Let the grass/vegetation over the system get a little longer in the late summer and fall, primarily over the tank and soil treatment area. This will provide extra insulation and help hold any snow that may fall.
  3. Place a layer of mulch (8-12 inches) over the pipes, tank(s) and soil treatment system to provide extra insulation. This mulch could be straw, leaves, hay or any other loose material that will stay in place and not compact. This is particularly important if you have had a new system installed late in the year and no vegetative cover has been established. This needs to be removed in the spring to assure vegetation is able to grow.
  4. Place an insulating blanket on the surface over the pipes, tank(s) and soil treatment system. This insulating blanket should be placed in the fall before frost has started and removed once frost is out of the ground, which may be after all the snow has melted.
  5. Keep all types of vehicles and high-traffic human activities off of the system. Compaction of soil or snow reduces the insulating properties of the material as the air/void space in the soil or snow is what actually helps insulate the system. This is a good rule to follow year-round, as the soil treatment system must get oxygen from the surface.

Things to not do:

  • Unless it is an emergency, do NOT clean out tanks during months with freezing temperatures.
  • Do NOT add antifreeze, salt or a septic system additive into the system.
  • Do NOT place sheets of insulation permanently above a soil treatment area as it will limit oxygen transfer and evaporation.
  • Tell homeowners NOT to run water continually.

In extreme situations, tank heaters, heat tape and other measures may be needed for very low use or special circumstances.