Have you read the FAQ on Improving Clay Soil? The suggestions therein are much cheaper and easier than installing land drainage.

However, if drainage seems to be to only solution, you should use a collector-type drain, but bear in mind that you have to drain it to somewhere. Have you an outfall in mind?

A soakaway can only work in well-drained ground, which you haven't got. What you need is a Surface Water drain that you can connect to, or a ditch, stream, river etc, to which you can outfall.

Read the section on soakaways for a fuller understanding.

As for the simple plain concrete sections, try a Civils Merchant, rather than a Builders' Merchant. Jewson and TP tend to stock only the most commonly used items in the building trade. For owt a bit out of the ordinary, a smaller local co is often a better source. If you have a branch of Burdens locally, or, if you live in the NW and can contact Cooper Clarke in Bolton, they have HUGE stocks of concrete sections.

I'd always go for the larger sections. 300mm is even better than 225mm and really shouldn't be all that hard to source. I know that I could get as few or as many as I needed at less than 48 hrs notice. Whereabouts are you?

That part of the SW Midlands is not an area I know too well, so I can't suggest any local Civils Merchants. However, it might be worth giving Cooper Clarke a call, as they do deliver down there or they may well be able to put you on to a local Merchant with whom they have a reciprocal arrangement.

Cooper Clarke Drainage Division - 01204 862222
Milton Concrete - 01795 425191

Your slab cover probably needs to be stronger. I'd go for 150mm thick, with A193 mesh top and bottom, and then use a C30 concrete vibrated into place. Alternatively, you might be able to get a 'biscuit' ex-stock from CC or Burdens.

The 110mm plastic pipe will definitely need encasing. Even a vc pipe at that shallow depth should be encased if it is to be trafficked.

you can use plasticware if you like, but they tend to be more or less the same dimensions as their vitrified clay cousins. If it fits, it'll do, basically!

Generally speaking, there's no need to roughen the outside of plasticware - it bonds to concrete or mortar well enough. I'd pack all around with a 1:2:4 concrete outside the chamber. On the inside, you can prime with PVA or similar before sealing any joint with a 1:4 mortar and then repairing the benching with grano.

a French drain is a 'catch-all' term for a land drain. In the trade, there are quite a few different types of land drain, but a French drain is, correctly, a Fin Drain, and you can read about them on the site.

However, what you actually need is probably a collector drain. Have a look at the pics on the Land Drainage page and you'll see what I mean.

It can be done, it's relatively simple, as long as you're fit and active and don't mind hard graft, and you will save a fortune by DIYing as contractors are not overly keen on coming in to residential properties to do this type of job, unless there's more than 50m or so.

Have a read of the page mentioned above, and post back if you've any further queries.

I would strongly suggest you get a builder to look at this. Pre-war houses are pretty much a law unto themselves and it's impossible to say what you might find or what you might not. A soakaway in the sub-floor wouldn't be all that unusual, but there's no way of saying there will/should be one.

Any water hanging under the floorbaords is not only a potential threat to your property, it's a potential health hazard. Get a good local builder, or call the Building Control Officer at your Local Authority. It definitely needs checking out.

Let me know how you get on.

Is my 1ft square hole in the clay filling because of water pressure in the clay forces it to the open hole where only atmospheric pressure is present? or is this likely to be the water table?

Why doesnt the water drain away through the clay to my existing drainage trenches which should have been surrounded with shingle?

Could I cheat a bit<S> and just trench out 1sq ft across the yard below the raised lawn, fill with large gravel and do the same to a point where my existing drains are bedded in?

Further, if you make a proper connection at this stage, and then install an interceptor drain, any future additions to the interceptor are a comparative doddle - you just tap into the existing interceptor with the new lengths, safe in the knowledge that a proper connection to the SW system is in place and that any groundwater collected/intercepted is being disposed of properly, not just shifted to another part of the garden.

Now finding a water table just 8.5" from the yard surface has me worried for my home foundations, the detached house was built in 1962 on clay before the latest regs for foundations on clay.
Should I be worried (i am already) about the water?

And a water table isn't always 'level' - it can follow the lie of the land and actually be lower in your front garden than it is at the back!

You could call in a builder, but bear in mind that they would be dead set on selling you summat, if only to cover their call-out costs, and other than the interceptor drain I mentioned, there's nowt you really need.

If you feel you could install that yourself (it's really not that difficult), you'll probably find it ameliorates most, if not all, of your problems.

Trust me, I'm a groundworker!  

If the LA are recommending a soakaway, it suggests that you have no SW system or that you have a combined system and an overworked ETW. Given that you're reporting saturated ground, impermeable clay and a shallow water table, I'm surprised they're recommending a soakaway in the first place!

Do you know if you have a SW system?

The important thing is to ensure a trapped gully is used to prevent smells escaping from the combined system, and incorporate a sealed rodding eye if you're not breaking into an existing Inspection Chamber. A trap before the IC is not essential as long you're using properly trapped gullies, or a P-trap hopper arrangement.

taking your points one at a time....

Plantex is nowhere near as good as Terram 1000. Plantex is a landscape fabric intended to keep bark/gravel etc separate from a sub-grade (ie, the bare earth), or make life hard for weeds; Terram is a geo-membrane and is tested and approved for use as a filter membrane for land drainage.

I have no data sheets for Plantex, but I seem to recall that it's nowhere near as tough as Terram, and therefore there's a real risk of puncturing it, which then compromises the integrity of the drain. Further, when I've seen Plantex on sale, it's always been more expensive than Terram 1000.

You can buy a Terram equivalent online at the Terram Garden website. It's sold as 'Patio Partner'.

The choice between a 10mm and a 20mm is somewhat academic on a small project like this. A 20mm is better, but a 10mm will be ok, as long as it is CLEAN, ie, not mixed with fines.

I'm not sure what you mean about the 'tube' (I think you mean 'pipe') going through the membrane. The membrane is wrapped around the the gravel surrounding the pipe. The pipe and the mebrane don't come into contact with each other. Can you do me a sketch and email it to me?

If you have an open end to your pipeline, that can wrapped in membrane to keep out the gravel, or you can use an end cap.

So, if you're just using a small 'tail' (as we call it), wrap a length of Terram around the open end of the pipe, then, line the trench with Terram, push the pipe into the hole in the wall, cover with the gravel, then draw the Terram over the gravel to 'warp it', and then back fill with excavated material.

Does that make sense, or do you want a sketch?

Do you have a SW system? You could put some drain tracing dye into the candidate pipe and see if it flows through one of the Inspection Chambers on your property.

If it's going to a soakaway, it all depends on how efficient the soakaway is. Although you're only adding a further 16m² of drainage, it could overload the soakaway, causing it to surcharge. Given that you've never experienced any problems with drainage to date, it's a good bet that it would be ok to use, as long as it is a proper soakaway and not just a 'tail'; that is, a pipe that leads into the garden and just dumps the water there.

Can you trace the shallow pipe while you've got the ground open?

With regard to the linear drain, what sort of clearance do you reckon you could get between top of drain and dpc? If you can get 100mm, I reckon you'd be ok on such a small project. But, will you be able to get enough fall from the outlet of the Lin drain to the the drain pipe?

If there are any other large trees or <spit> Leylandii in the vicinity, you could encase the new pipeline in concrete with flexi-joints (as shown in the drainage section), or you could line the trench with a root-barrier geo-membrane, such as Terram

the best way of dealing with this sort of scenario is to install a linear drain or a dished channel about a metre or so from the house and make that the low point...

...if you use a dished channel, you'll need to incorporate a gully at some point, bit that should worl out cheaper (and easier) than using a linear drain.

Note how the paving falls from the house to the channel at around 1:40 and then the rest of the paving backfalls from what was the garden.

Does that make sense?

They are sold in Ireland, as I've seen them used on a relative's property in Co. Wicklow.....

...they come in red, brindle (red/black] and charcoal, and they are a doddle to lay. The 'dish' is only 25mm or so deep.

The larger, 915x250mm units in concrete grey (shown on the Road Kerbs page) cost around 3-4 quid apiece, but are not really patio-friendly.

The B&Q DIY Shed's in the UK are selling a Recyfix linear drain, complete with galvanised steel grating for 10 quid per 1 metre length. There may be something similar in the Republic, but it's a couple of years since I was over and I'm not sure what's available.

In the UK we prefer soakaways or leach fields (which is more or less what you're proposing) to be at least 10 metres away from the property to avoid potential problems with the foundations and/or damp. Things may be different in your part of the world, but I have no experience of practices outside Britain and Ireland.

Also, from your description, it sounds as though you will be piling up earth against the garage wall. This, too, is something we would not do in the UK/RoI.

If you discharge directly onto the driveway, where would the water run to? Back to the house or out to your 'sidewalk'?

this has become something of a FAQ, so I've created a page showing the various ways of resolving this particular problem. Anyway, here's a sketch showing how your partiular situation could be dealt with...

...does that help? Just ask if you need further explanation.

Notes:

• The perforated land drain will need to be connected to the SW system or a soakaway at some point.
• The Terram 1000 membrane  helps prevent the gravel becoming silted-up with crud and whathaveyou over time.
• The impermeable membrane could be a drainage composite, or you could use bitumen 'tanking' or similar. It could actually be omitted unless there is an exceptional water flow regime and you have regular inundation of this wall.
• The flag-on-edge ensures the sub-base or sub-grade beneath the existing concrete doesn't fall into the drainage channel. I've shown a 450x50mm pcc flag, but you could use almost anything to suit you taste/pocket.
• By cutting back into the existing concrete, you give yourself more working space and it can be patched in with fresh concrete or grano once the flag-on-edge is in position.
• The gravel on top of the permeable membrane could be a decorative type, rather than the larger 20-50mm clean gravel used within the channel as backfill.

thanks for the compliments. It's good to know that you find the site useful.

Right then, your questions....the Rodding Eye - this is best positioned at the head of a run, so, if you have a line coming up the side of the house, serving the downspout and the Kitchen Waste, then the rodding eye should either be adjacent to the last upstream fitting, or at the end of the straight run.

The key determinant is that you must be able to get to ALL parts of the system with rods. If you have access from downstream via an IC or MH, then a rodding eye might not be essential, but I can only really say what is best if I had a sketch plan of your layout. If you want to send me a sketch, as a gif file or similar, I'll upload it to this thread and add my comments accordingly.

Secondly - the foundations over an existing drain. This is covered by Part H of the Building Regs and you need to speak to your local Building Control Office to see what they recommend. The usual craic is a lintel bridge over existing sewers, but, as you say, it all depends on depth. Where a sewer/drain would run through a concrete footing, rocker joints can be used to isolate the section of encased pipework, but again, you need to ok all this with the BCO.

To be honest, I've never seen a proper construction drawing for this type of drain, but we built one for a client in my village following the instructions from a book on garden design he had been reading. I can't recall the name of the book, but if I see him in the alehouse tonight, I'll ask if he still has it. All I can remember is that it was a 'coffee table' type book on building a Japanese Garden and featured many photos and descriptions, including the ever-popular 'deer-scarer' yoke for water features and a really elegant downspout arrangement for small roofs that consisted solely of a length of chain!

For the drain we built, we used stone roofing tiles bought from a salvage yard and filled the interstices with a 6mm local river gravel. The whole affair was about 450-500mm deep with a half-perforated clay pipe at the base which was then linked to the existing SW system of the property. If memory serves me right, we used 6 tiles, each around 30mm thick, and the overall width of the drain was about 250mm. It was used at the edge of a paved patio and was only about 4.5m in length.

As far as I know, it's still working. I'm sure that if there had been any problems with it, I'd have had my ear bent long before now!

I'd ask a professional for on-site advice. They might be able to spot a solution I can't see (obviously!)

As for choice of brick; why reclaimed? There is a very small market for reclaimed pavers and the quality ones are bloody expensive. All the rest are concrete or cheap clay seconds. Have a look at Tegula/Drivesett from Marshalls, Priory from RMC or Woburn from Charcon, to name but 3.

For diy'ers, a problem may arise if they come to sell their property, as it's the sort of thing spotted by the buyers' surveyor, and you're faced with having remedial work done or reducing your asking price.

Steps from a doorway can be brought up to internal floor level (as in the relatively new Document M of the Building Regs) but a threshold drain or cavity of some form is required to 'isolate' the outside from the inside, or vice versa.

I'm not sure what you mean about the car port -a dpm beneath the car port? Do you mean a membrane laid beneath the planned paving? And does your 'concrete base with paviors' mean you're planning to use rigid paving?

If I was going to all the trouble of using rigid paving, I wouldn't skimp by using broken brick as a sub-base - I'd play safe and use a 'proper' sub-base material, preferably DTp1, and you definitely need a dpm - all concrete slabs should have one.

At 8x6m, I'd say you ought to use reinforcing mesh, a simple 6 or 7mm mesh would be sufficient, but a 75mm thick slab doesn't provide adequate cover - you need at least 100mm thick to give the minimum required 50mm cover all round. You could consider using fibres instead, if you stick with a 75mm thick slab.

I'd split the area into two slabs, each 4x6m, with a movement joint between the two. You definitely need an expansion joint where the slab abuts the house wall.

I can't help feeling you're making this job far more complicated than it need be. Why do you feel you need rigid paving?

A simple low-back P-trap would do the job - connect in with a 90 degree knuckle bend, then the P-trap and then the connection to the FW or Combined system. Can you follow that or do you need a sketch?

If you have the choice between connecting to a FW or a SW system, land drainage should always be connected to SW as first choice (assuming there is no ditch/stream etc). Connection to FW is a last resort.

If you're connecting to a SW system (or FW/Combined) you should be able to rod up from some downstream point to the trap. Further, depending on how large an area is being drained by the land drain, a catch pit upstream of the trap may be worth considering, not only to reduce sediment in the sytem, but to provide access for maintenance both downstream to the trap point and back upstream along the drain field.

I wouldn't bother with a catchpit unless I was draining more than 100m² of silty or sediment-heavy ground or 200m² of clayey ground.

Position your new IC where you want it away from the conservatory (at least 1m away, I'd suggest), then connect it up with the appropriate pipework, test it, then disconnect the old brick MH and pipework.

I'd dig out the old drainage and backfill rather than leave it in situ, but this may not be feasible. The old brick MH can be backfilled with a lean mix concrete and left as it is.

read the page on Soakaways and the link to the FAQ I wrote for uk.rec.gardening on Improving Clay Soil. I'm sure they'll help you think up more questions, which you can post back here after you've read about the basics.

The various bedding classes are more to do with soil mechanics and the various types of pipe material but the reasoning behind them would take a day to write out - take it from me that you really don't need to worry yourself about them.

If your pipewoirk is beneath a graden, path or patio, then surround it with 100-150mm of pipe-bedding and it should be fine. If it';s beneath a driveway or other trafficked area, then it ought to be concreted in, especially if it's uPVC. Clayware is much stiffer and can look after itself at shallow depths. If you plan to sell up, though, it;s worth iusing marker tape to warn any future occupants of the shallow nature of your new drainage.

Next - the damage to the chamber. If the mortar repair is holding, that will be fine. Under site conditions, we might use a granolithic mortar to repair, or, in some cases, an epoxy 2-part mortar, but for what little damage you seem to have done, a mortar repair should be fine, as long as you've packed in plenty of it into the gap and it's not just a Rizla-thickness skim.

Now - get back into that trench!

This separation membrane could be a layer of 125 micron visqueen, if you have any available, or even old polythene rubble sacks, sand bags ftrom the BM or anything like that. The idea is to prevent the bedding material bonding directly to the pipe haunching so that, if, at some future date, the setts need to be lifted for whatever reason, they are not directly 'stuck' to the pipework and can be removed without affecting the drainage system.

There's no need for a sub-base where the pipe haunching is close to the surface. It can be re-introduced where levels permit, but it's not essential in this one spot.

The very generous concrete around the existing may be for any of a hundred reasons - they may have had loads left over from another job; they may have needed to protect the pipework from heavy loads; there may have been a worry about settlement - who knows? If you try to work out what the groundworkers were thinking when they did every strange thing you come across, you'll end up going mad!

Looking forward to the pics.

Anyway - the mystery pipe. It sounds like a Cast Iron feed pipe to a soakaway, probably constructed from bits and bats of leftovers, possibly by a previous homeowner, as CI is not a cheap option for drainage.

Is it still functional?