French drain

[Zebra]

I have a 17th Century cottage. Ground floor is brickwork, and external ground level on the back is about 300mm higher than internal, and I cannot lower it, since it is within the churchyard and not my land!
So a French drain seems in order. Any tips? How wide? Filled with pea shingle or gravel? Put a pipe in the bottom or not? And how effective are they really?
Many thanks for any advice.
Zebra

 

[MdB]

My tip would be to put the pipe in the bottom and make sure it drains somewhere useful.

I built a french drain into a soak away which was part of the trench my heat pump pipes were in. This trench is 60m long with 75mm of sand in the bottom so I thought that it should drain fairly well even though built into clay. It filled up completely with water the first rain shower.... (due to the ground water rising)

I haven't built a french drain right next to the house but I have dug the trench and left it exposed. This has greatly improved the damp problem in the house were it has been done and we still have issues were is hasn't. Another job to be done when I get time...

 

[Lime]

A french drain or trench works best if it is left unfilled.
Otherwise, the filling needs to be bulky and iregular so that there are many, quite large, air voids within it.
I'd also look for sources of water that may be wetting the soil next to the wall.
i.e. broken guttering and downpipes and particularly blocked drains and soakaways.

 

[johnandrew]

Hi Zebra

Maybe I have misunderstood but if the raised ground level is part of the Churchyard do you have permission to go digging on Church ground and installing a drain? Apologies if I am missing something here.

John

 

[Penners]

John's point puzzled me, too. In order to install a French drain you'd need to dig up church land, which I presume wouldn't be permitted.

But if you think the church would allow this, why not ask whether the trench could be made permanent, in order to reduce the ground level to below your internal floor level. The trench wouldn't have to be very wide - 500mm or so should suffice.

If the church's land slopes down towards your house, then you could usefully incorporate a French drain into the trench, leaving it permanently open, as Lime suggests.

 

[Zebra]

Hi Zebra

Maybe I have misunderstood but if the raised ground level is part of the Churchyard do you have permission to go digging on Church ground and installing a drain? Apologies if I am missing something here.

John

No, you've understood completely! Yes, it's on the Church's land, but they're ok with me digging a French drain, right next to the house. I've not asked them if it would be ok to leave it open, but I imagine not, as the public have access it could be a danger, possibly? Hence the question of what to fill it with!

 

[Gareth Hughes]

Something like that is likely to require a Faculty, even if it doesn't need any "secular" permission.
http://www.churchcare.co.uk/legal.php?GA
The parish may not be aware of that but it's worth making sure, before someone's great auntie Ethel turns up in the French drain.

(And I could go on to say, if you think getting planning permission or listed building consent is time-consuming and irritating, you ain't seen nothing 'til you enter the world of the CofE's own planning system...)

 

[Zebra]

Hmmm, that doesn't look like much fun! The church don't actually own the church yard. The council own it and look after it, and certainly weren't too interested when my neighbour wanted to repair his section of the boundary wall. The church warden certainly thought it would be fine to go ahead. So if the French drain were filled in again, with shingle?.... Thank you Lime for your tips...

 

[Penners]

Well, if you have to fill it in, I would certainly use coarse gravel. Create as much permeability as you can.

 

[AMc]

Thinking aloud - Is it worth using a geotextile to wrap under then over the aggregate to form a tube and minimise silting of the french drain?

The soakaway we nearly had to build was to be made using green plastic storm crates wrapped in geotextile. This creates a void which is unlikely to clogged and provides storage for flash amounts of water which can then drain off slowly.
Thinking about it with the soakaway you're putting clean(ish) rain water from the gutters into the soakaway and letting it permeate out so I suppose the textile isn't likely to clog as fast as trying to move dirty water into the void from the outside...perhaps you'd end up with a nice clean, dry tube of gravel?

 

[El Greyo]

Hi Zebra

This is how we installed a French drain behind our house last year. How much is relevant to your situation I don't know but it might be useful - it is all our land so we were reasonably unconstrained (and had the blessing of the CO).

The ground level behind our cottage was about 9in higher than the inside floor levels and was concreted for a couple of metres immediately behind the house. The garden then sloped up away from the house, so consequently our back wall was very damp - water running onto the concrete would sit against the wall, water in the ground underneath the concrete could also seep into the wall. We first broke up the concrete and lowered the ground levels to just below the inside (we didn't dare go further). We dug a trench about two feet from the wall, about 45cm deep and a spade width wide. We lined it with a geotextile, put in a thin layer of 10mm pea shingle, then a perforated 10cm diameter drainpipe. As ground levels slope down around the side of the house, we were able to run the pipe round there and connect it to the drainage system. The trench on top of the pipe we filled with small hard core to the surface then wrapped the geotextile around it. Then we laid a geotextile over the whole area previously covered by concrete and then pea shingle on top of that.

Seems to work very well. One of the key issues is somewhere for the water to drain away to and in that respect our circumstances made it relatively easy. Sorry about the complete mix of units.

 

[Zebra]

Thanks all. Glad to hear yours is still working El Greyo. Hope it still is in ten years! Apart from the fact that mine will have to be against the house, sounds like a good model to follow.

 

[El Greyo]

Good luck. I've thought of a couple of other things we did with our drain that you might like to think about:

We put an access point at the upstream end of the pipe to allow access for drain rods. We put the main French drain at a shallow (but constant) incline but at the end had an angle to bring it to the surface for the access point.

At the downstream end we connected the French drain to a trap, with an access chamber, before it went into dainage system. That way there was no problem with smells seeping out.

I found quite a lot of advice on the web through google, some very helpful, others not relevant for our site. I filtered that and drew up my own plans.

 

[Zebra]

I also have a small chamber to drain it into, which in turn feeds in to the drainage system. The gutters at the back of the house also drain into it. It is old and not working properly, but at least it is there, and there is also evidence of an old bitumen lined trench all the way along behind the house, so at least there is a precedent for remedial works for the house in that area of the churchyard.
Thanks El Greyo, good idea about bringing it to the surface for rodding at the upstream end. I hadn't thought of that. I could put a bend on the upstream end, bring it to near the surface, and cap it off with a screwcap buried just beneath the soil so I could get to it when needed. Good idea!

 

[Penners]

Thanks El Greyo, good idea about bringing it to the surface for rodding at the upstream end. I hadn't thought of that. I could put a bend on the upstream end, bring it to near the surface, and cap it off with a screwcap buried just beneath the soil so I could get to it when needed. Good idea!

Hmmm - bends can be a pain when it comes to rodding. Do make it as slow a bend as possible.

 

[LadyArowana]

Hmmm - bends can be a pain when it comes to rodding. Do make it as slow a bend as possible.

Indeed, wouldn't want to risk a back injury, so debilitating.

 

[Penners]

Funny you should mention that, Milady. I was thinking only the other day that one can become debilitated*, but I've never heard of anyone being bilitated.

Likewise gruntled.





*As I know only too well, but I bear it like a brave little soldier.

 

[LadyArowana]

Funny you should mention that, Milady. I was thinking only the other day that one can become debilitated*, but I've never heard of anyone being bilitated.

Likewise gruntled.





*As I know only too well, but I bear it like a brave little soldier.

I like this story about gruntled, don't know if the quoted examples are correcthttp://www.worldwidewords.org/qa/qa-dis1.htm

 

[Penners]

I absolutely believe that good old P. G. was the first to use the word in literature. Wonderful!

if not actually disgruntled, he was far from being gruntled

 

[Ushy M]

Zebra, we have done exactly this. Our house (17thC limestone walls,) flanks the front churchyard of a Victorian church. The ground level of the front aspect of the church was raised for appearance's sake (the Churchwarden was able to show us the accounts which costed the works at £22 in 1867!) increasing the new ground level to approx 1 metre above our internal ground level at the highest point. When purchasing the house our Surveyor expressed concern over the effectiveness of what seemed to be a rudimentary French drain and under the gypsum plaster on the inside of the gable end wall some damp was evident, initially through electrical sockets on that wall. (Before you worry, we're talking smell rather than a torrent! Mr M is a trained electrician among other more dubious skills...)

Investigation of the drain showed it had no outlet and although Geotex had been used to line the Church face of the trench the top fill was very small (and dirty) gravel and the fill was large broken common brick, probably from demolition of a garden shed. This type of brick is very porous and was acting as a mass of sponges holding moisture in the trench. Over a very hot fortnight Mr M removed the brick carefully by hand a small section at a time, (to prevent the trench collapsing, the nearest headstone was only 18" from the edge,) laying a 6" land drain in the bottom and re-filling with large beach cobbles approx max 6" in size and then topped with a 3" layer of small pebbles, 2" dia max.

The drain was gently sloped down to the front of the churchyard and out from a new hole at pavement level in the front wall. The repair has worked very well, the only re-used parts being the geotex in situ and the gravel layer at the bottom of the trench. Perforated land drain is cheap from your builders merchant (but you will have to buy 25 metres minimum) and cobbles can be bought by the bag from online garden stone suppliers. Ours were covered in thick red mud and had to be individually washed, probably the worst job! Keep the Churchwarden on your side, they are the ones who give permission for access and ours has been a real help over several issues and become a friend. It cuts a lot of red tape if you do. There are unlikely to be burials right up against your wall although since we've done ours cremation burials have crept along this side and they are much closer to the walls than a grave.

Our situation allowed a clear fall to the end of the pipe which is best as it allows air in and water out (although we've never seen water exiting) but if you can't, run it to a soakaway sump. Don't close the top with too small gravel as this will choke with earth quite quickly and then weeds and grass will grow, your enemy! Keep the top layer weeded, an autumn job really. All in all, easy to do but sadly, all by hand!