Subfloor soakaway issue

13 Jan 2016
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United Kingdom
I've read lots of threads with similar problems to this issue but still struggling to find a solution.

Context...I live in a 1930s semi on a hillside. Some neighbours have reported have soggy gardens/water under floorboards and one neighbour has a pipe in their garden which gushes groundwater.

Our floorboards came up for building work and a lot of water was found in the sub-floor. Built into the sub-floor is an opening leading to a broken clay pipe. Presumably, an old-style soakaway.

We dye tested every drain I could and found the neighbours gully leaked some in so the water company came out and CCTV'd their rainwater line but only found the gully was broken so renewed it. They couldn't work out where their rainwater pipe went as it was 25m+

After, there was still quite a lot of water coming in and the builders were rightly worried about replacing the floor with UFH going down, plus there are footings for new steels.

I've suggested renewing the clay 'soakaway' pipe with 4inch plastic as it is clearly a historical issue and if the water table rises, there will be a soakway to drain the subfloor. They've put a gully in the subfloor.

What concerns us all, if that when digging the trench outside for the clay pipe the trench is filling quickly with water and the water smells stagnant. Would groundwater smell stagnant? Would groundwater refill a hole in 5-10 minutes? Builders obviously not keen on working on this trench in case it's sewage. However, the water company have dye-tested foul sewer (runs under patio) before and it didn't come through.

I've arranged for water company to come back to CCTV the foul sewer to look for a displaced join. If they don't find it, do you think replacing the clay soakaway and running the pipe through a retaining wall to pour into the garden will help drain the sub-floor?

How else can I keep this house dry? ACO drain at the front of the house and the back? Could we just increase the height of the slab in the sub-floor?
Is a plastic pipe the best idea to drain the sub-floor or would it be better to put in a perforated pipe in membrane and gravel to run away from the subfloor?
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Sorry I can’t answer this, but a family member has just bought a house with what appears is a similar problem.

I happened to pop round a day or so ago, and took a look under their floorboards... about 100mm of water. It’s a suspended floor around 1.7m above the water.

i don’t think this is correct.

know it all Neighbour has said everyone on the street has this, as water table is high and they are a few hundred metres from a pond, and on a slope.
So not the panic :eek:!

I had a quick glance around Families house and the downpipes just direct water to back garden and side of house... made me wonder if this is the cause?

K-I-A neighbour said one guy on the street has there are a couple of houses that have had concrete floors instead of suspended and have done away with the issue... or moved it next door. :cautious:

Good luck diagnosing yours, I’ll watch this post.
I've thought about creating a French drain from interior to exterior (gravity-led) but I fear drying out the clay-soil too much and causing problems with the foundation so will probably stick with the plastic soakaway route and then put a French drain in the front garden in case it's surface water flowing through the soil?
It's probably been like this for decades and not caused any mega-problems as far as we can tell.

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