House on the side of a hill

Can anyone offer any advice on this please? We’re considering buying a house that has been built on the side of a hill, so that on one side one floor is below ground level. We would like to know more about how it was constructed to resist any movement in the land, and also damp. The house is only about 20 years old but it has changed owners and the immo seems to think the builder’s plans will not be available anywhere. Any ideas?

Probably worth contacting the mayor’s office as they would have to have given planning permission.

Probably not wholly relevant to your situation, but the two lower storeys and foundations of our house were built into a schist cliff, probably some time in the 1300s, andeverything’s still fine. But of course schist is very stable and they knew what they were doing in those days!

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Here in the Vendee the type of construction design you mention is very common, and the lower semi-basement level is intended for use as a garage, workshop, utility room, and wine storage area, with all the living accommodation on the upper level.
If the lower level is now in use as living accommodation, the important question to establish is whether the house was built like that in the first place, or has the semi-basement been improved at some later date. If it is a later improvement there may be problems with damp if the appropriate measures were not taken to prevent it, as if the original build was as a ‘sous-sol’, a bit of damp in the garage or workshop areas would not have been a problem.

If the house is situated in an area known to be subject to seismic activity, then you need to establish if it was built in accordance with the special requirements for such areas. The Mairie will be able to clarify this for you.
Here in Vendee we are in a seismic zone, so in addition to the foundations, all the corners of the building, the joints between major dividing walls, and the tops of the walls have to be of steel re-inforced concrete, and the load bearing walls have to have a horizontal steel re-inforced row of concrete blocks, at not more than 2 metre intervals up the wall. If the seismic zone rules were followed then it is unlikely that the resultant reinforced concrete frame would be affected by land movement unless the slope is very severe indeed.

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Many of the ‘new’ type of houses are built like that to put the garage and the services away from the living quarters.
It really depends what you are describing as a hill.

Thank you Robert that’s a very helpful reply. Considering the house layout I’m sure the lower level accommodation was in the original design and construction. Hadn’t thought about seismic activity but will check it out !

Thanks Nigel, we checked with Mairie and they do have the original permissions - the immo thought they didn’t but they do. We will go and have a look.