Forum: Site Works
Topic: Switzerland renovation
started by: dave_in_gva

Posted by dave_in_gva on 06 Mar. 2019,11:58

A handy DIYer here but no trades person by any stretch of the imagination.

My wife and I are seriously considering buying and renovating a 2-storey house built in the 1950s here in Switzerland where we live.

The renovation would entail adding bathrooms with the attendant water and sewerage connections in new locations, including several on the ground floor.

My question is how complex is the work involved to lay new sewer and water conduits under an existing slab? Obviously this would be part of the work required for the new bathroom locations on the lower floor.

Thanks for any and all input, and do let me know if more information is needed. Much appreciate any guidance - here everything is in French and I am zero for that.... :)

Posted by Tony McC on 06 Mar. 2019,12:30
To install a new sewer beneath an existing slab is a bit of a task, and possibly not one best suited to a DIYer.

The two options are tunnelling or 'cut and cover'.

Tunnelling can be expensive, and you'd need to consider what the sub-grade is like, what length would need to be tunnelled, and how easy is it to find a willing contractor in that Switzerland. Getting a suitably experienced civils or groundworks contractor in Britain willing to take on a small, residential tunnelling job is fraught with difficulty. Most tunneller simply don't want to know.

So, that leaves cut & cover, but you would need a structural engineer to assess the slab to ensure it's suitable for cutting. Some slabs are so inherently structural that the cost of support works to carry loads while cutting takes place can be exceptionally scary.

In a simple case, it will be an unreinforced (unlikeley) slab or one that is only lightly reinforced for its own integrity, so you could cut through, excavate, install drainage, backfill and re-cast the cut section with appropriate tie-in dowels with relative ease.

If at all possible, the cut & cover would be the preferred option, but until you've explored the building's structure more fully, you can't really make an informed decision.

Posted by dave_in_gva on 06 Mar. 2019,17:54
Thank you Tony. Just to be clear when I mentioned I was an accomplished DIYer it was not to suggest I would be revising the sewer lines under the slab. It was just to make the point that I'm quite aware of the ins and outs of getting things done in construction.

I fully expect if we go ahead with this purchase that we will be engaging professionals to undertake the majority of the renovation - which will also include removing the main south facing facade and building an extension onto that side of the building.

So proper tradesmen are very much in the picture here. I just had no idea about the cost and complexity of cutting into the slab to lay new lines. Things are somewhat more complicated in the sense that we do not have proper plans for the site - best we have been shown are 1:50 drawings of an addition that was drawn in 1967 (the house was built in 1953).

Thanks again for your answer - very helpful.

Posted by jwill on 09 Mar. 2019,17:34
What construction method has been used? How did they build in Switzerland in that era? I've just cut a new drain into a slab but it's a ground bearing slab between two hallway walls with a screed on top... I would guess this is ideal scenario. You wouldn't want to be cutting into a raft
Posted by lutonlagerlout on 10 Mar. 2019,13:27
we have dug trenches through peoples houses before for new sewer runs,and then made good
but these were  just ground floor slabs i.e. 50 mm of screed on 100mm of concrete on hardcore
if its a structural slab and has rebar etc in  it you run the risk  of the slab failing if you cut it
another alternative for hard to get to bathrooms is a Saniflo,not ideal and a lot do not like them,but they work and we have fitted loads
cheers LLL

Posted by seanandruby on 10 Mar. 2019,20:26
Reinstated correctly, trench filled to underside of slab, dowelled, rebar, mesh etc: it should be sound. Done some headings, sank shafts, pipe jacking etc: all doable, just need the most  viable option.
Put in loads of internal drainage under very large  floors. Used cutters, breakers even hydro
cutting. Nothing is impossible, we even sank a shaft 30 metres down put a pipeline under Shoreham harbour by  pipe jacking. So don't be afraid of the work, just the cost  :;):   :)

Posted by lutonlagerlout on 12 Mar. 2019,08:43
very true Sean!
as I tell clients when they ask me is something feasible "anything is feasible with money "  :;):

Posted by dave_in_gva on 12 Mar. 2019,10:14
Thanks very much -  all very helpful. We still have a good deal more digging into the construction details to do before making a purchase decision. These comments have been a great help.

Thanks again,

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