French House buyers guide to fosse septiques (septic tanks)

We hope this little guide will give you a basic understanding on the fosse septic rules and why it is relevant when buying a French property.

“Fosse septique” translated to English means septic tank. In its simplest form this is the tank that collects waste from toilets, sinks, baths, kitchens etc. In practice it is a little more than just a tank and the term “fosse septique” is often used to cover the complete system which includes tanks, pipes, filter beds etc.  In this article the term fosse will refer to the complete system.

The Regulations

If you’re planning on buying a house in a town or a village then there is a good chance the property will be connected to mains drainage or will have a mains drains connection in the vicinity in which case a fosse won’t be necessary.

If there is no mains drainage available at the property then it will be important to find out whether there is a fosse and if so, does this comply with the latest regulations.

In 2012 the French government introduced a new set of rules relating to drainage and in particularly to fosse septiques.  These rules make the new owner of a property responsible for bringing the fosse up to current standards within a year of purchase.

Don’t worry though as long as you have budgeted for the work, if any is necessary, and understand some basics then there no reason to bypass a house with an older fosse. In fact, you may well be able to use this as leverage to negotiate a good price.

And the rules now also make it compulsory for sellers to provide buyers with a fosse inspection report prior to signing the initial sales document.

The report will detail whether a fosse is present, if it can be found (which isn’t always easy on very old properties), if it fully complies, if it needs reparation work or if it is otherwise non- compliant. The report will contain recommendations of works needed both compulsory and advisory.

What to ask?

Even before you have seen the report there are some questions, assumptions and steps you can make to protect yourself from any surprises further down the line.

Firstly ask the agent or owner whether there is a fosse present and if so what condition it is in.

If you are told yes there is a fosse and it complies with latest regulations then they should be able to provide you with receipts to show the fosse was put in recently or they already have a full report to hand. The report must be less than 3 years old.

If you’re looking at any property and it is clear that no major work has been done to the house over the past ten years and if there is no information relating to the fosse, then at this stage you should assume the fosse is non compliant and some work will be needed.

If the property is older than 30 years with no evidence of recent work then it is likely that a complete new fosse and drainage system will be required to bring things up to date.

If the house is newer then it is possible that the fosse system may just require some updates - the extent of which should come apparent when the fosse report is produced. A common fault is lack of ventilation and/ or grease traps which are relatively inexpensive to remedy.

Mains drainage – if the owner or agent tells you the property is on mains drainage then things are very straight forward. You can always check to see where this connection comes into the property. If there is a cellar you can often see a 10cm diameter pipe coming from the outside of the house and/or there should be a manhole just outside or near the property. If in doubt the local mayor’s office will be able to confirm if a property is connected to mains drainage or not.

The Costs

If you have settled on an older property that needs a complete new fosse – the cost of this system will depend on various factors i.e. accessibility, type of ground, size of land, size of property, usage (holiday home or full time home), number of inhabitants, etc.

There are two main types of fosse system that can be installed and these are a traditional system and a micro-station and there are variants on both of these. As a rule the traditional system has a larger filter bed, is cheaper and used more widely. The micro station costs a little more and requires a smaller filter bed.  This is often the only solution if the ground type and size isn’t suitable for a traditional system.  

A complete fosse system for your average 3 bedroom house will normally cost between 6 –12,000 Euros installed. The lower figure can generally be applied to a property with a decent size garden and easy access. If on the other hand space is limited and  there are other obstructions such as wells,  trees, swimming pools then we’d advise budgeting towards the higher end. If in doubt and things look as if they could be problematic, e.g. bedrock or very limited space, then we would advise getting quotes to be certain of costs.

The Work

It is possible to install a fosse septique and drainage system yourself but you must get permission and get the works checked off at various stages by a controlling body (normally the SPANC). Should you do the work yourself then costs (including materials) could be as little as a third of the prices detailed above.

However, unless you’re skilled with a mini digger and carry the necessary insurances we’d always advise our clients to use a specialist contractor. A good firm with the necessary diggers can get in and do the works within 2 – 4 days. You’ll get a ten year guarantee for the installation and normally they’ll organise all the necessary permissions.

Work is carried out from the outside of the property and it is unusual for contractors to need to go inside apart from maybe to test toilets are flushing once work is complete.

If you are planning to do other work that involves digging, e.g. landscaping , building pools, adding extensions, etc.,  it is best to tie this all in together.

Making your offer

We sometimes get clients saying they are only interested in a house if the fosse septic conforms. This is generally due to lack of knowledge or understanding of what’s involved and how the process works.

If you limit yourself to fosse compliant houses only you’re going to miss out on some fantastic properties and possibly bargains.

Our advice is simply this:-

  • Make sure the price you pay for the property allows you to do the necessary work.
  • Always ask what state the fosse is in,
  • Make some budget allowances using average fosse costs and then
  • Make your offer but make it clear to your agent or owner in writing that your offer is based on these assumptions.

Ask that they send you the fosse reports and/ or quotes for the work as soon as they have them - when you get them you are free to renegotiate if things are not as you had been told or assumed earlier on.

In France you’re not tied into a deal until 10 days after the ‘Compromis de Vente’ has been signed. The compromis de vente is an initial sales document and must be accompanied by a fosse reports as well as other diagnostics – a subject for my blog for another day. 

A good agent will be able to help and advise on all the above and put you in touch with fosse contractors - always wise to get two or three quotes before starting work.

If you have an particular questions relating to the above article or other property related questions please drop me Jon Boella an email and I’ll be happy to advise further.


SPANC (Le Service Public d’Assainsement Non Collective) – This is the organisation that comes and checks the condition of existing fosses and provides the report. They will also do subsequent inspections, control installation work (like building control in UK) and provide advice about installing a new fosse. If you are planning on purchasing a property were you think there could be complications on installing a new fosse then it will be wise to get confirmation from the SPANC as to what can and can't be done.

Traditional fosse septique -this type of system will have a tank which will collect the house hold waste, this waste will enter the the tank, then through gravity and the effects of natural bacteria working on the waste products,  the water that comes from the over flow will be clean enough to pass into the filter bed.
Micro station –this type of system treats the house hold waste more effectively than a traditional system, the water that comes out as over flow is basically clean water. As a result the filter beds can be reduced in size and in some instances the over flow can be directed into an existing land drain or soakaway. They do cost a little more than a traditional fosse but may be the only solution where space is an issue.

All types of fosse will require periodic emptying. The frequency will depend on the type of fosse and usage.

Epandage – this is the filter bed, the over flow from the fosse will need to run somewhere and usually this is into a filter bed. This will consists of perforated pipes which are laid on gravel and sand to allow the water to drain away into the land.

Entreprise de terrassement – these are ground working firms and will have the equipment to install fosse systems quickly. Always check they have “décennale assurance” ( a ten insurance back guarantee) and they are registered with a Siret number.
Bac à graisse – grease trap – this will be situated between the fosse and the kitchen to catch grease. It will need emptying on occasions

Tout-àl’égout – this is mains drainage – if a property is connected to mains then a fosse won’t be necessary .

Regard – manhole or inspection chamber