French drain

[Flyfisher]

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.

That's a fair point, but I assume that it would be an annual check-and-cleanout thing anyway, a bit like gutters, which can't be seen either.

I was mainly thinking about how to keep the paving slabs supported though. Depending on the size of the paving slabs it probably wouldn't be necessary to fill the trench with 'milk crates' anyway - just at the join between the slabs.

Also, rather than use paving slabs, it might be easier to use concrete lintels stacked as high as necessary. These are available in varying lengths and could minimise the number of vertical joints and thus 'crates' required. Or they could be interleaved like a course of bricks, e.g. staggered 6-foot lintels with a 'crate' every 3-feet.

Just some random ideas really.

 

[MdB]

Another random idea which is simpler in the short term is get air flow down the pipe at the bottom of your drain. If you can arrange upright pipes at either end such that the prevailing wind blows through it then that may help considerably in drying it all out. Might not look too great depending on the location but it will save you a lot of work.

 

[Zebra]

The idea of crate thingies only at the joins is a great idea. As is staggered lintels! Really easy to do as well! And it wouldn't create any more sideways pressure on the wall, than the earth, or than the gravel-filled french drain that's there now, would it?

I think absolutely I'd do an annual, even twice annual, check up and clear out. And I'd have some sort of leaf-trap at the downward end.

Then in the bottom of the trench I might have an open gully, rather than a perforated land-drain. Any moisture coming from the ground would seep through the cracks in the slabs/lintels and into the gully. Air would circulate next to the wall, although it'd probably still be pretty moist down there....

The only snag I can see is that when the outside is rendered, rain run-off from the wall would drip from the render-drip-bead, splash against the grating and make the wall wet again...... But I suppose that's no worse than splashing against a gravel-filled trench.

MdB's idea of getting air into it could be difficult, my French drain is in the churchyard, and I couldn't really do anything that could be a danger to people or unsightly, besides, kids might shove things down it, and it's actually quite sheltered from the wind round there! Thanks though.

Also, the architect who did the spec for the external wall insulation said that this part of the wall ought to have a bitumen/polythene barrier and XPS insulation on the outside below ground level, which would negate any need for breathability anyway. I don't know whether I'm going to listen to him.

Hmmm, can't win, can you?
Thanks for ideas Feltwell, Flyfisher and MdB

 

[Penners]

No no. Milk crates is a really good idea.

Hertfordshire Milk Crate Mystery!

Dairies in Hertfordshire are scratching their heads over the sudden disappearance of hundreds of plastic milk crates. "Er... I was like, eh?" commented St Albans dairyman Hedgecroft Bulkenstorm. "One day we 'as 'undrids of 'em... next day they's gawn."

Authorities believe that , now that the last Hertfordshire church roof has been stripped of its lead and the last mile of overhead cable has disappeared, thieves are turning their attention to plastics, as the next valuable black market commodity.

 

[Flyfisher]

:lol:
You read it here first folks!

 

[Zebra]

:lol: :lol: :lol:

 

[worms]

Hertfordshire Milk Crate Mystery!
thieves are turning their attention to plastics, as the next valuable black market commodity.

...perhaps they'll be targetting uPVC next!

 

[Penners]

One can but hope....

 

[mr-squirrel]

Also, the architect who did the spec for the external wall insulation said that this part of the wall ought to have a bitumen/polythene barrier and XPS insulation on the outside below ground level, which would negate any need for breathability anyway. I don't know whether I'm going to listen to him.

My neighbour has allegedly had something similar done a few years back on a common back wall we share. How well it is performing i don't know, i'm going to send a camera under the floor to inspect when i get a miniute.

Modern solutions seem to be variations on this:

I've seen examples of the paving slab suggestion locally but only installed to a shallow depth - I assume because the majority of the slab is embedded in a footing for support.

 

[Penners]

IMO the above drawing needs some modification in the case of a period property that has no DPC continuous with a DP membrane under the floor. In such cases, the interior subsoil can risk saturation of the foundation wall, and a close-contact exterior waterproof coating on this wall could prevent breatheability to get rid of moisture in the wall.

In such cases, I would tend to use a vertical corrugated moisture barrier laid against the exterior of the foundation wall, to allow air movement against the outside face.

 

[Zebra]

i'm going to send a camera under the floor to inspect when i get a miniute.

Surely you'd be small enough Mr Squirrel to fit down there yourself, although you mustn't get your tail stuck...

Yes, the proposition the architect made was not dissimilar to that, although without the sump pump - the French drain takes the water away by a pipe on the outside of the building. I would be very glad to know how well you think it's working, and whether it would be better than the paving slab solution. Does your wall have external ground levels higher than internal then? What has been your solution on your side?

In such cases, the interior subsoil can risk saturation of the foundation wall

Sorry Penners, can I just clarify what you mean by the above bit? Do you mean moisture from under the slab will saturate the wall where there's no dpc? So there might always be a bit of damp in the wall, which is then prevented from evaporating by the moisture barrier? I think I see what you mean, and I think this is the key question in my case - whether the more serious source of the damp is coming up from the floor, which should therefore be allowed to evaporate outwards (no moisture barrier, open French drain), or whether the more serious source of the damp is penetrating through from the ground on the outside, in which case a moisture barrier in the French drain might be beneficial, and any moisture from the ground will just have to evaporate internally, as it does elsewhere with internal brick walls which have no dpc.

Unfortunately I've been unable to truly nail the answer to that question, because it's not been very long since fixing the last round of leaking gutters! My instinct so far is that I don't have a rising damp problem, it's not really coming up from the ground, because I've taken up the slab around the edges and (where I haven't had leaking gutters, there's no dampness down there. Where it's wet it's coming through the walls, I reckon.

I see what you mean Penners about a corrugated moisture barrier, although I think any air circulation would be restricted in my case by the XPS polystyrene external wall insulation that the architect proposes to have on the outside of the moisture barrier, up to 300mm above external ground level, where it would join with the breathable woodfibre external wall insulation....

The whole reason for the barrier really is that it would allow me to insulate the wall below ground and up to 300mm externally, otherwise I'll have a real cold spot. Hmmm, thanks both for your musings.

 

[Penners]

In such cases, the interior subsoil can risk saturation of the foundation wall

Sorry Penners, can I just clarify what you mean by the above bit? Do you mean moisture from under the slab will saturate the wall where there's no dpc? So there might always be a bit of damp in the wall, which is then prevented from evaporating by the moisture barrier?

Yes, Zebra, that's exactly what I meant. Obviously one can never be certain about these things - it's possible that the subsoil under the property may be unusually dry, in which case the risk that I mentioned is of course reduced. But as a matter of principle, if I was going to use some form of impermeable material to prevent contact between the outside face of the foundation plinth and the surrounding soil, I would always try to use a solution that allowed air to pass across the face of the wall. It may not be necessary, but it can't be wrong.

 

[Feltwell]

Anyway Zebra, I think you should just be pleased that scientists have discovered exactly why you are so stripey. It's not very glamourous but it is practical.

http://www.bbc.co.uk/nature/16944753

I think I should try evolving stripes. I taste like finest caviar to any annoying buzzy bitey thing. To a mosquito I have 5 Michelin stars.

 

[Zebra]

Oh, I always thought it was to confuse lions - that surrounded by a mass of moving stripeyness they'd get disorientated and have to sit down. If flies don't like it either that's a bit of a bonus.
Evolving stripes might take a while, but there's always the fancy dress shop!

But as a matter of principle, if I was going to use some form of impermeable material to prevent contact between the outside face of the foundation plinth and the surrounding soil, I would always try to use a solution that allowed air to pass across the face of the wall. It may not be necessary, but it can't be wrong.

Is there any point in doing both, do you think? Doesn't it kind of come down to a choice between one thing or the other? If you have an impermeable barrier on the outside of the brickwork, would it much matter what's up against it - whether it's air, soil, gravel or jam? (OK, maybe more research needs to be done before knowing whether jam is a good idea.)
I suppose as you say, it may not be necessary, but it can't hurt...

Anway, thanks for your views on my dilemma, very much appreciated!

 

[FamilyWiggs]

Anyway Zebra, I think you should just be pleased that scientists have discovered exactly why you are so stripey. It's not very glamourous but it is practical.

http://www.bbc.co.uk/nature/16944753

I was quite disappointed to read in that article, the solution to an age-old schoolboy query:

"Studies of zebra embryos show that, early in development, they are black and they develop their white stripes later".

The'll be telling us the egg came first next. :roll:

 

[LadyArowana]

I was quite disappointed to read in that article, the solution to an age-old schoolboy query:

"Studies of zebra embryos show that, early in development, they are black and they develop their white stripes later".:

I thought it was strange that when they first started cloning experiments they didn't start with zebras. Making copies of sheep was so boring, they all look alike anyway!

 

[mr-squirrel]

i'm going to send a camera under the floor to inspect when i get a miniute.

Surely you'd be small enough Mr Squirrel to fit down there yourself, although you mustn't get your tail stuck...

Yes, the proposition the architect made was not dissimilar to that, although without the sump pump - the French drain takes the water away by a pipe on the outside of the building. I would be very glad to know how well you think it's working, and whether it would be better than the paving slab solution. Does your wall have external ground levels higher than internal then? What has been your solution on your side?

I'm not sure i'd want to Squirrel around down there, only an inch below the joists to soil level at best.

I imagine the paving slab solution with grilles would be the best, you get ventillation to the wall and total seperation from the surrounding soil. Doubt it's an option for me though as the the land against the exposed gable end isn't mine. Good news is i have a rainwater drain at the front i can tie into if required.

Nothing has been done to my walls yet, other than that section i'm going to inspect. My floor is at best level with the external ground, and ground in areas is up to 400mm higher. There has been some water ingress, but not much as i'd have expected, i think due to the sheer thickness of the walls and some good luck. Some new guttering (though preferably a wrecking ball) on the neighbours ropey old shed would help too. Will post up some pics of what i have to deal with in a seperate post, i'm drawing a proper set of plans at the moment to get a handle on things.

 

[Penners]

I thought it was strange that when they first started cloning experiments they didn't start with zebras. Making copies of sheep was so boring, they all look alike anyway!

Whereas zebras all look completely individual, eh? :?

 

[LadyArowana]

I thought it was strange that when they first started cloning experiments they didn't start with zebras. Making copies of sheep was so boring, they all look alike anyway!

Whereas zebras all look completely individual, eh? :?

Yes, if you have the right barcode reader it will tell you each ones name, swipe a sheep and it will only say sheep :lol:

 

[worms]

Yes, if you have the right barcode reader it will tell you each ones name, swipe a sheep and it will only say sheep :lol:

That's because you need a baa-code reader.