Traditional Fosse Septics and Filter Bed Systems – a winter warning

How To Stop Your Sewage System From Freezing

fosse-freezeOK, so it’s not often you can get me talking about traditional fosse septic and filter bed systems (other than in association with the phrase “prone to clogging” or attached to the word “outdated”) but I do know that many of you are still living with systems that have a septic tank or some kind of filter bed so this article is just for you.

Every winter, many people have to deal with the frustration of a frozen septic system when the temperature drops well below zero. Lack of snow cover, frozen soil conditions and very cold air temperatures can all contribute to the problem, but, with a little forethought, you could prevent this from happening and ensure your system continues to function well whatever the weather.

In this article I hope to

    • help you identify potential problems with your sewage treatment system
    • show you how to minimise any risk that the winter weather poses to that system, and
    • let you know what you should if a problem occurs


Why would my fosse, filter bed or septic tank freeze?

Fosse and filter bed systems and septic tank systems are made up of several parts including the pipes, fosse or septic tank, draining area or filter bed and, in some cases, a pumping system, and any or all of these parts are susceptible to becoming frozen. There are many reasons why your system, either wholly or in part, might freeze but the most prevalent causes are


    • lack of insulated cover – depending on how deep your tank or your filter bed are, they may be susceptible to becoming frozen if there is nothing with an insulation value covering them. Natural insulating covers include uncompacted soil and plant cover and if your system does not have this cover it can be that freezing will occur
    • irregular use of the system – when homes are unoccupied for extended periods of time and there is either no sewage or very little sewage entering the system, the temperature of that system may not be sufficient to avoid freezing
    • leaking or faulty appliances – a leaking tap, toilet shower head can cause problems for your sewage treatment system as they often result in a small amounts of water entering into the system which may freeze within the pipework


  • leaking, badly laid or clogged pipework – sewer pipes that are leaking or which are installed without proper fall will not allow the water to run freely through and out of the system, and this water is prone to freezing. Likewise, anything in the pipework that clogs the system will have the same effect of stopping the free flowing of the water.
  • cold air entering the system – anything that allows cold air to enter the system such as an open, broken or uncapped risers, inspection chambers or manhole covers allow cold air into the system increasing the chances of the system freezing
  • poorly maintained systems – a system that has not been correctly maintained can easily become clogged and this again can prevent the free flow of water through the system. The water can then settle either on the surface of the filter bed or somewhere in the pipes and this can easily freeze and prevent the system from working effectively.


How can I prevent my system from freezing?

Depending on your system, it’s location and frequency of use, you may never have a problem with any part of your system becoming frozen. However, if for any reason it should happen the could not only be inconvenient to you but it could also pose a threat to public health or the environment. There are however several steps that you can take to help prevent such an occurrence.

  • Carry out some basic maintenance on your system. A well maintained system is less likely to have problems. Make sure that your septic tank or fosse are not over full and, if you have one, check that your filter bed or drainage area is not clogged and is still working effectively.
  • Try to insulate you system as best as possible. This could involve lagging the pipework, placing polystyrene or other insulating material over your tank or fosse (making sure that any points of access are not concealed) and ensuring there is a thick layer of mulch or soil over the pipes, tank and drainage bed.
    During colder weather, spread the entry of warmer water into the system throughout the day. You can do this by scheduling your use of the washing machine, dishwasher and shower throughout the day to help maintain the temperature of the water in the system.
  • Try not to leave your system unused for long periods of time. If however your system needs to be left for an extended periods pump out your tank before leaving and try to have someone check on your system on a regular basis.
    Fix any leaking fittings and appliances around your home. This will help prevent small amounts of water entering into the system which could then freeze and create problems.
  • Try to keep vehicles and people away from all parts of the system. This will help prevent the soil covering the system from compacting and helps prevent freezing as uncompacted soil is a better insulator than soil that has been compacted.
  • Make sure all risers, inspections pipes and manholes have covers on them and are in good condition to limit the flow of cold air into the system.
  • Keep an eye on your system. You will be the first to notice any problems with your system and by checking it on a regular basis you could find and deal with small issues before they become a bigger problem.

What should I do if my system does freeze?

coldIf your septic system does become frozen your first step is to switch off any pumping system you have and contact a company that deals with sewage treatment systems. If the freezing has occurred within the pipes, they may use devices such as steamers, heaters and high-pressure jets to try to unfreeze system piping. Other than that, in truth, there is very little that can be done other than for them to identify the reason the system has frozen and take remedial action to prevent the problem reoccurring. Unfortunately, if it is the actual tank that has frozen there is probably nothing that can be done other than to wait for the system to thaw out naturally and deal with fixing the problem then. In this case you should try to reduce the amount of water entering the system and ensure that the system does not become over full.
There are also, however, several things that you should not do such as

  • Don’t add antifreeze, salt or a septic system additive into the system.
  • Don’t pump sewage onto the ground surface.
  • Don’t start a fire over the system to attempt to thaw it out.
  • Don’t run water continually to try to unfreeze system
  • Don’t attempt to dig up any part of the system.


All fosse and filter bed systems and all septic tank systems are made up of several parts and each or all of these parts are susceptible to becoming frozen. The problem is more prevalent than you would care to imagine and, when it does happen, it causes no end of inconvenience and can even pose a threat to public health and the environment. However, there are several things you can do to help prevent your sewage treatment system from freezing and both basic maintenance and upgrading the insulation needn’t cost the earth. If there is ever a time of year to think about your fosse then this is it, so take the time to go and check your system now, it may save a whole whole of hassle later on.