Dampness / neighbours soil high above dpc

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Hi wondered if anyone could give some ideas.

Bought a 1960s bungalow, its built on a downward slope, and its had a couple of rooms added at garden level, I understand around 25 years ago, so you walk down to these 2 rooms and the garden.

One of the 2 downstairs rooms just feels a bit damp / musty. Previous owner has left receipts of work done for dampness i.e painting bitumen paint, adding air brick, refurbing the musty room.

It's evident that the big part of the problem is the garden ground level which is at the dpc of the downstairs rooms, and the side wall where neighbour has their garden / hedges (we own a small strip down the side, its 40cm over dpc (neighbours garden is higher)

I've dug a trench down that side below dpc and was going to put some concrete slabs against the neighbours soil / higher ground level, put weed membrane and backfill with large gravel for drainage. However I have read that this will eventually fail? as the gaps get clogged with soil.

Any ideas? theres a lot of clay in the soil I've noticed, Im thinking I need a soak away
 
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Djks, good evening.

OK as I understand it?? you have a trench your house wall on one side and the neighbours garden [soil] on the other.

Are you intending to place paving slabs against the neighbours earth? will the slabs be embedded below the bottom of your trench?? or?? will the gravel provide some "support" to the slabs? If you do not embed these slabs they will fail quickly, by beginning to lean over into your property and cause issues with the neighbours ground. you are creating a "retain wall" such walls need foundations and purpose designed walls with drainage behind, a concrete paving slab is liable to fail quite quickly??

Do you intend to place slabs on top of the gravel? if so can I suggest lay these slabs to a fall where the rain water runs of to the open end of in effect the path you are making.

As for your concern about the gravel being blocked by mud / silt Etc? there is a solution, that is wrap the entire excavation in a "Geotextile" material, various types on the market, Google Terram, this material holds back mud / silt and keeps the gravel free draining. Such gravel drains [called French Drains--- Google again?] work best with a perforated drain pipe at their base, but as you have a clay soil a Soak away may not work??

Ken.
 
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Appreciate the reply. I take your point on the gravel holding the slabs up (and holding soil back) failing after time. the geotextile is what I have, wrapping the gravel sounds like a great idea!

I've found a soil pipe at the back not far from where I have dug the trench. I questioned the previous owner if there was a soak away as the proper drains are higher up to the front of the property said they had a basic (i assume gravel) soak away half way down the garden for the discharge from a sink and washing machine. They don't know details as their husband passed away.

They omitted this info during the sale! I'm guessing no issues running a perforated drain pipe at the bottom of the gravel, to the soil pipe? I'm assuming the soak away is functional.

Should I paint the black bitumen paint on the wall below the dpc before putting in the gravel etc
 
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Djks, good evening again.

From the top---

As for the Geotextile, in effect you are wrapping the aggregate on all sides, top and bottom in the Geotextile. if needed, the slabs can be placed over this wrapped aggregate.

As for a "Soak away" taking sink waste and washing machine waste ? it would concern me that food particles going into a soak away could block it quite fast?

As for a discharge point, the perforated pipe can be led into a solid walled pipe then into the soil discharge, if possible in a manhole or similar, provided the soil drains are also taking storm, rain water ?

As for painting the external wall with Bitumen, my opinion, no? because the bricks below ground and especially below the DPC in the wall will be wet / possibly soaking?? and as such even Bitumen will struggle to stay on the wall. Also this sort of paint in this area is not needed, it makes no "Buildings" sense.

Ken.
 
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