French drain

[Zebra]

Thank you, very useful advice! My Churchwarden is very helpful too, and not at all against my installing a French drain. Luckily too, there are now no graves nearby because they moved them all when the ground was deconsecrated (although they may have missed a few, who knows!) and besides I don't have to go as deep as you.

 

[Penners]

there are now no graves nearby because they moved them all when the ground was deconsecrated (although they may have missed a few, who knows!) and besides I don't have to go as deep as you.

I thought we all went the same depth - 6 feet.

 

[Zebra]

We'll see if it works, but here it is....
View attachment 1

 

[Keithj]

The chaps are just finishing our French drain too - pictures probably in this weekend's update to the blog. Nice idea, they are.

 

[Zebra]

Oh dear. Exactly how far towards the base of the foundations can you go before you start to undermine them?
I thought I had four courses beneath the internal floor level, so dug down two, levelled off the bottom of the trench, and filled up my French drain.
However now it seems that there are four courses only in the corners. There are only two in the middle sections, so my drain is level with the bottom course.
It all looked very nice and solid with the bricks and the mortar all in good condition. Will it be OK?

 

[MdB]

My understanding (which is limited) is that the important ground that must not be disturbed is that going down at a 45 degree angle from the bottom of the bottom brick. i.e. what you have done is fine so no need to worry.

If you think about it, when the wall was built, the soil would have been dug away in a trench wider than the wall. When back filled, it does nothing to support the wall and this is all you have removed.

 

[Penners]

My (amateur) understanding is the same as MdB's. Provided you don't dig vertically below the bottom course of masonry, you'll be fine.

 

[Schoolmarm]

So I can fully expose the side of the very bottom course before soil?

 

[Penners]

That's as I understand it (in my inexpert way). MdB explained it well - the soil under the bottom course of bricks/stone is holding up the wall; the soil against the side of the bottom course isn't doing anything important.

I think I might revise that view if the plinth was deformed so that it bulged outwards, but if it's still "as built" then I believe that principle applies.

 

[Lime]

So I can fully expose the side of the very bottom course before soil?

Where there is only direct downward thrust in the wall there should be no problems.

However at least two scenarios may exist that would cause problems.
The first is where a substantial and/or sustained outward/sideways/lateral thrust is taken by the wall footing.
This could be created by internal structures or the design and construction of the internal floor.

The second is where the subsoil is "live" such as in moving silt areas.

 

[Schoolmarm]

Hmmmm I am still nervous then.

 

[Zebra]

I should be fine then, thanks very much MdB and Penners...

 

[Penners]

Hmmmm I am still nervous then.

Oh dear - do you bulge, 'Marm? :wink:

 

[Schoolmarm]

Not any more

 

[Penners]

I wish I could say the same...

 

[Zebra]

My French drain doesn't appear to be working as well as I'd thought. I still have damp patches low down on that wall. Of course, it may be due to other causes (I did find a guttering problem recently). But I think that it doesn't really get any air down there, so isn't really allowing the wall to breathe.

I used 20mm gravel to fill it in with, wrapped in landscaping fabric. Perhaps this is too small, and the 6 inch beach cobbles that Ushy M used would be better.

Just pondering, how could you leave it open so that the soil didn't collapse into it, and at the same time cover it with a grille so people don't fall in it? I've been trying to think of a system that would keep the trench upright, and hold a grille, and allow the wall to breathe. I wonder whether I could have something made by the local forge. Or should I not have it made out of metal, against the soil? I can't think of any off-the-shelf system, it'd probably have to be specially made. Perhaps paving slabs on edge could retain the soil, but how would you keep them spaced away from the wall, at the same time spreading the load on the wall so it doesn't damage the brickwork?

Any ideas from you clever people?

 

[Feltwell]

Paving slabs on edge as you suggest, partially buried so they stand up by themselves - then a metal grid on top, something like you get on Aco channels?

A grid could be made with bracket on 1 side that you can screw to your wall, with the other side resting on top of the paving slab - and small downstand beneath to stop the paving slab falling towards your wall.

Or - perhaps better - a bracket that you screw to the wall with a grid resting on top, so you can lift the grid off easily to clear the trench.

I hope you appreciate the hours of technical wizardry that have gone into getting the fine technical drawing below onto the forum

Also - get yourself a copy of J & JW Longbottom's catalogue, they do drainage channels with nice cast iron covers - they'd probably sell you just the covers if you asked nicely, with a bit of ingenuity you may be able to put some bolts through to act as the "downstand" to retain the paving slabs. This would look quite "period" as well. You'll need to ring them up and ask them to post you a catalogue, they don't have much of a website.

http://www.longbottomfoundry.co.uk/gutters-pipes-fittings.htm

 

[Flyfisher]

Along the same lines, dig the trench, use paving slabs to hold back the earth, fill trench with milk crates to hold back the paving slabs, cover with a nice cast iron grill to keep people out.

OK, I don't really mean milk crates, but something like this might be suitable: http://www.ppsonline.co.uk/stormflo.htm

 

[Feltwell]

Only thing with that FF is that it won't be so obvious when the trench needs the top taking off to clear the cr@p out.

 

[Zebra]

No no. Milk crates is a really good idea. Or something like that, becuase it'll spread the load from the paving slabs onto a larger area of wall. I like it!!
And I like the idea of the grille sitting on the slab with some sort of thingy on the bottom, as per technical drawing... thanks for the link too, I'll look into that.