Drainage issue beside wall of house

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Hi,

On one side of my 1850s house, the exterior ground level is higher than the internal floor level. So, there was a flowerbed full of damp stone and soil sitting against the first 60cm of the wall. As damp problems are materialising internally, I am in the process of digging this flowerbed out.

My plan was to fit a kind of "French drain" using graded stones and pea shingle alongside the wall. However, I have found an old drain pipe at the bottom of the flowerbed, which is what the roof guttering on that side of the house leads to. On a rainy day, it carries a lot of water. It is a clay pipe which is in lots of 12" (approx) segments, with small gaps between. A lot of the segments are in very poor condition, so I am going to replace it.

I was wondering what kind of pipe I should buy to replace the old pipe. PVC seems sensible, but I wondered whether I should get a perforated or half-perforated pipe (with the perforations facing upwards to collect rainwater as part of the French drain). Or would this simply leak out the water coming into from the gutter down the downpipe?

It is a 4" pipe, so presumably I should buy a 110mm pipe with an adapter for coupling it to the sound clay pipes at either end?

I have also discovered that externally the wall seems to sit on a flat bed of concrete. The drain pipe runs along the concrete bed. I think this may be a strip foundation, but I'm not sure. This has made me wonder whether my plan for a French drain will work, as the rain water will drain through the shingle and stones to a concrete base, especially if I don't install a perforated pipe. But as the wall in question is very sheltered, and is overhung by the eaves, it might be OK.

Any thoughts on what to do with the French drain, especially if I don't get a perforated pipe?

Thanks.
 
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I've thought about this a bit more since posting. I'd be grateful for any thoughts on anything in my above post, but I think it boils down to this-

Can I use a half or full perforated pipe along the bottom of the French drain AND have two downpipes connect to that pipe?
If so, should I get a half-perforated pipe and fit with the holes pointing up?

Thanks
 
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Your dampness may be caused by the the existing drain being in poor condition. Why not replace the existing drain with new pipe to carry away all the storm water from your gutters/downpipes, that ensures that is carried away, then if you want to lay an additional "french drain" to deal with the ground water. French drains can get blocked up, imagine where your rainwater is going to go if that happens on a shared perforated pipe!
 
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Thanks for the replies to this.

I thought I’d add an update. I decided to do as Blagard said and sort out all the drainage. It was a fairly big job in the end as we needed to dig across a tarmac path, round a corner and into a part of the lawn, which was dug out and a herringbone series of perforated pipes laid down to provide a soakaway.

We haven’t (yet) bothered with a french drain; we don’t think its needed as very little groundwater indeed gets into the trench, but we will keep an eye on things.
 

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