Diagnostiques part 3: risks, pools, septic tanks and dry rot

Don't panic when you see that the house you're about to buy is in a flood and earthquake zone so ar

Don't panic when you see that the house you're about to buy is in a flood and earthquake zone so are very large parts of many regions - Credit: Archant

In the conclusion to his mini series on diagnostic reports, John Marshall discusses the final four you may have dealings with


Since 1 June 2006, it has been mandatory to provide the État des Risques Naturels et Technologiques report to all buyers and tenants. It basically states whether or not the property (with or without buildings) is within an area where there is a risk of a natural or technological disaster, or accident.

The standard natural risks are flooding, avalanche, earthquake, forest fire, flash floods, earth movement, cyclones, rising water table, drought and volcano. The standard technological risks from nearby industry are thermal, high pressure and toxic. The report will direct you to sources of further information. There is a central online registry of the risk zones at prim.net

I have heard that there are still some communes who have not registered their information yet, so when you search there is a possibility that the answer will be blank. Also, you may need to enter the INSEE number of the commune rather than just its name – this is not its post code. You can often find the INSEE number by searching for the commune on Wikipedia, if not there, look in the online census. As an example, have a look at my local town Quillan in the Aude, postcode 11500 but whose INSEE No. is 11304, you will see not only a list of the risks but also a schedule showing the last occurrence of a disaster and how long it lasted etc.

There is also information available on the website about the purpose of the report and how to compile one yourself, if you need one to give to a tenant. A lot of this information is published in English. You will find the report useful if, for example, you have only ever viewed the house at weekends, and you would not be aware that during the week a constant stream of heavy quarry lorries pass the door.

Please do not panic when you see that the house you are about to buy is in a flood and earthquake zone, so are very large parts of many regions.

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Major earth tremors are rare, for example the last serious one in the Pyrénées-Orientales was in 1986. For some time in areas prone to significant risk new housing has had to be built to withstand major tremors and reinforced escape routes are built into the structure. Minor tremors are quite frequent, though they are so deep underground that they are hardly noticeable on the surface.

While a lot of towns and villages can be susceptible to flash floods, the risk for the vast majority is very small. Places that are most susceptible have special planning rules that apply to conversion and new builds that either completely ban development or stipulate that living accommodation has to be a certain level above the most probable height of a flood.

If the house you are hoping to buy is older look out for channels or grooves fixed to or cut out from the doorways. They are there to take panels that can be dropped in the event of a flood warning. If you are buying a holiday home that has provision for flood panels, then it is a good idea to make an arrangement with a permanent resident neighbour to keep and drop them in if you are absent.


Sometimes there is a separate report and sometimes there is just a paragraph in the compromis about the pool and whether it complies with the safety regulations. The simplest and cheapest way for a pool to comply is for there to be a battery-operated alarm that sits on the pool edge. A tube runs from the alarm into the water and if the surface is disturbed, the alarm goes off. These can now be bought for about €300. More sophisticated and expensive are laser beams around the pool, a safety cover able to take the weight of a person, and fencing. Fencing has to be ‘unclimbable’ and gates must have a child-proof catch. Proper security is a legal requirement for in-ground swimming pools under the 2003 loi Raffarin. It is essential that pool safety is in place, especially if you propose to let the property. In the event of an accident, it is possible for your insurer to decline a claim from a tenant and you would be personally liable.


If the property is not connected to a mains sewer you should be given a report from SPANC that states whether it complies or, if not, details what needs to be done to make the system comply. In the latter case, a period is often given after the inspection to get the works done. It is not obligatory for the current owner to have works done to make the system comply, however, it is obligatory for the new owner to fulfil the demands in the report. The property is normally re-inspected to verify the completion of the works.

Sometimes a system does not comply because the tank is too small. It should be 1,000 litres or 1m³ per bedroom. The size is not verified by inspection, the inspector merely needs to see the invoice from when it was last emptied, which shows the volume of how much was pumped out. A tank should always be full of liquid and solids; the percentage of each changes with use.

If it is not a fosse toutes eaux there should be a grease trap; if it is, and is a good distance from the kitchen, there should also be a grease trap as fat can cool and collect in the pipes before reaching the tank. There should be secondary filtration after the tank plus inspection covers and air vents for the tank and filter bed.

If the inspector thinks that the system may comply if proof is provided, a certificate subject to reserve can be issued. On the next visit the inspector may wish to see an invoice confirming the tank size, exposed inspection covers or a soil test confirming that the secondary filtration is working.

Bringing an old system up to date can cost several thousand euros and a new system over €10,000, so it is prudent to obtain a quotation (devis) from a contractor for the required works before signing the compromis.


This is now often mentioned in the compromis de vente, with the vendor declaring that they have no knowledge of any being present in the property.

Contrary to the name, dry rot actually requires moisture; it can grow in unventilated spaces where condensation gathers. It is related to bracket fungi, toadstools and mushrooms and, like them, it produces a large fruiting body which releases spores (a rusty brown dust that can lie dormant for years), which germinate to produce hyphae (strands). These elongate and entwine to create the mycelium which ultimately creates the fruiting body (sporophore) and so on.

Wood is gradually destroyed by enzymes produced by the fungus. In damp, dark places, soft, white cushions or silky tassels of mycelium can grow on the surface of the wood. Drops of water may be seen on the tassels. In drier areas the mycelium can be no more than a grey skin tinged in small parts with a lemon yellow or lilac colour.

The wood remains a lighter colour than if it had been attacked by wet rot, and areas of cubes appear which are larger and wider than with wet rot. As with wet rot, this can occur beneath a supposedly good surface veneer.

The decayed wood is powdery when dry. It will not only live on hardwood and softwood but also on damp paper, cardboard and carpets, and likewise will cause severe damage to chipboard.

The optimum temperature for growth is 22°C but it can exist from 5-26°C. It is called ‘dry’ rot because it can exist in timber with a moisture content of only 20%, whereas ‘wet’ rot requires 30%.

The bad news is that while most wet rots are restricted to the timber on which they feed and cannot penetrate masonry, the bundles of dry rot hyphae are capable of growing over and through non-woody substances to get to fresh timber. I have even seen them grow through two metres of concrete.

John Marshall is a chartered valuation surveyor and ‘expert immobilier’ in Languedoc-Roussillon

Tel: 0033 (0)4 68 20 26 48