aj mccormack and son

Drainage - Page 06
The Brew Cabin


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Forum Question Crappy Access Chamber - Acrabat - Apr 4th 2003
Can anyone offer any advice on my Access Chamber? I am planning on installing a new WC and soil pipe but I am not sure my AC is up to the job. I have posted a short description of my problem on my web site at....

The black uPVC pipe entering the AC is the proposed new soil pipe.

forum answer Tony McCormack - Apr 5th 2003
I'd definitely opt for a new clayware or uPVC access chamber. There have already been alterations and amendments to the existing chamber, so a further bodge is not recommended. Building a brick chamber is over-engineering for such a simple connection, and would cost twice as much as a a pre-formed chamber of some type, if you have to bring in a tradesman especially for the job.

One of the circular polypropylene ICs from Hepworth might be a good choice, as they're easy to adapt to existing clayware, and provide you with up to 5 inlets and one outlet. The base, a single rasing piece and a ductile iron cover costs around 120-150 quid, depending on where you buy.

I'd have a look at that 'dead' tail, too, while the ground was open, and find out whether it really is dead and has been capped, or whether it's blocked, collapsed or some other problem.

Apr 5th 2003
Thanks for the reply. I'm going to get a plastic AC.
Forum Question Level of linear drains - Flashman - Apr 5th 2003
I'm putting a patio at the back of the house outside a conservatory. The local 'expert' came round today to have a look at the base and suggested putting a linear drain along the conservatory wall to catch any surface water. It would connect to a gulley already there. His suggestion was to place the drain one brick course down from the DPC. The reason being that the garden level is slighty higher, 60-70mm, than the patio level would be, if laid at 150mm below DPC. By installing the drain the patio would be 'almost' level.

Is this acceptable or am I going to have problems later, like surveyors etc?

Excellent site!!!

forum answer Tony McCormack - Apr 6th 2003
Some expert! The linear drain must be 150mm, that's 2 courses of brickwork, below dpc, to comply with Building Regs. If doing this means that the garden is higher than the patio, then you need some way to deal with the surface water, and my preferred method would be to omit the linear drain around the conservatory itself, and lay it (or some other form of drainage) at the garden/patio interface, with a step up to the garden if necessary, and fall from the conservatory to the linear drain. This would allow you to keep to the requirements of the Building Regs, keep any future surveyors off your back, and effect a workable solution to draining both the garden and the patio.

patio crossfall

Chris H
Jun 27th 2003
On the DPC page on this website it states that a linear drain may be laid to within 75mm of the DPC. Could you clarify which is correct?

I have a similar problem around a small extension where I want to install some paving, although the ground slopes up transversely across the house from left to right (looking towards the house) as well as sloping up fairly sharply towards the garden. The ground at the Right Hand Side is nearly up to the DPC but we have no problems with damp. The nearest drain is the LHS side of the extension.

It would be easier for me to install a linear drain against the house and around the extension to comply with building regs than having to dig out a load of earth to make the ground slope away from the house and ensure the finished paving level is 150mm below DPC.

Any advice would be most welcome and many thanks for the very comprehensive and informative site!

Tony McCormack
Jun 27th 2003
Laying a linear drain just 75mm below dpc is stretching the limit to the very edge of breaking point, and should only ever be countenanced when there's no other option - perhaps I should make that clearer on the dpc page.

The issue of using Linear drains in this manner is complicated, as some BCOs are quite happy to accept a linear drain laid in this fashion, while others will reject it out of hand. Part of the problem comes from the implementation of Document M of the Building Regs, which requires disabled access to new buildings. One of the supporting documents shows a linear drain laid to within millimetres of the dpc as one possible solution. Some BCOs I've spoken with, claim this is acceptable only for the width of the doorway (1200mm) and would not be acceptable for extended runs of a few metres, while others, as I said, are happy enough for it to be used wherever.

In your situation, where there's no overwhelming obstruction to complying with the 150mm below rule, I'd stick with that, as it's less likely to arouse the interest of a surveyor if you ever come to sell the property or make a claim on your insurance for any damp damage (even if it's nowt to do with the linear drain). Once the linear drain is in, you can backfall the paving towards the house, and save yourself a good bit of work (and a skip or two of spoil), as long as you have somehwre to outfall the linear drain.

Forum Question Pressure Testing - Nick - Apr 14th 2003
I have built a conservatory and connected the guttering to the existing storm drain at the back of the house. Due to changes in the builing regulations in Scotland the nice building control officer (BCO) wants me to pressure test the system in their presence. This length of drain already had 2 inlets, plus 2 rodding eyes and the outlet into the inspection chamber. I have added another branch to this, that makes 6 outlets. Therefore unless I am missing something do I really need to seal all 6 outlets to the system to pressure test it?

Thanks - Nick

forum answer Tony McCormack - Apr 15th 2003
'Fraid so, Nick, if it's an air test. If the BCO will accept a water test, and the layout of the system is advantageous, you can possibly get away with just stoppering-up the primary outlet, then filling the sytem till it's within 100mm or so of the top of the RE's/inlets/etc, but then, not all BCOs will accept a water test unless you have a sufficiently large head (of water, not on top of your shoulders!)

You might be able to get a loan of half-a-dozen bungs from a local builder in exchange for a few beer vouchers. It'd be cheaper than buying 6 of summat you're never likely to need again!

Forum Question Drainage near house wall? - Vinny - Apr 15th 2003
I have broken the patio, as it was level with the dpc. I would like to make a good job and wonder what to do re drainage? I guess to make a channel min 150 deep 200 away from wall, but where do I take the water in this channel as I am not near any drains?

Any suggestions?


forum answer Tony McCormack - Apr 15th 2003
Have you read the page "All about DPCs"? That gives some common solutions to the problem of levels, but, as for where you can drain to, I'm not sure, as I'm not familiar with your site. Would a soakaway be feasible?
Apr 16th 2003
Thanks for your site and info. Very detailed and informative.

I thought the soakaway had to be 10 meters away from the house? From reading your site, I thought the best way was to connect to a drain?

I have now found a clay pipe about 3 meters away but it is combined house and drain.

I have seen another reply re close to the conservatory which is similair to mine. There has been times where the water rises up from the ground/garden after heavy rain. The water runs down the alleyway. The garden is wet but does dry quickly. No puddles.

I thought that the best way would be to connect to a drain/gulley but the patio surface area is about 18 sq meters, L shaped with only 4 meters near the house wall which needs lowering.

regards - Vinny

Tony McCormack
Apr 16th 2003
If you have a drain within 3 metres, then forget the soakaway option (yes, it should be 10 metres from the house!) and form a connection to the existing combined system.

Did you decide on a 'method'? Would a linear drain be the simplest option?

Apr 16th 2003
I've just realised that to connect the linear drain to the sewer I have to incorporate a trap....

I was going to use your system of a pcc flag on edge. Construct the base out of concrete with a permeable pipe and pebbles on top. Again though I thought how do I connect/drain to a sewer re smell/trap.

I then thought about taking the hard option of digging out the patio to a level below the dpc. Dropping to a gulley?


Tony McCormack
Apr 16th 2003
It's not all that difficult. At the low point of the dry channel, install a single-piece trapped gully, and connect that to the existing drain.

But, if you really want all the work of reducing the level of the patio, and correcting the falls, then again, a trapped gully is the best solution, but you won't need the dry channel arrangement.

Apr 16th 2003
Thanks Tony, I have gone for the level of patio. I am in the process of buying the gulley etc. I would have liked to use your recommendations for shops but they seem all to be your way?

Thanks for the help!!


Tony McCormack
Apr 17th 2003
Most of the suppliers I recommend have a nationwide presence. The odd one or two might be limited to a particular region, but, for everyday stuff such as gullies and linear drains, you should be able to get these at almost any BM.
Forum Question Old land drain system - Antony Hare - Apr 17th 2003
I hope you can help us out with some much needed advice. I live in a 1900s cottage (block of four - garden slopes away from the house). Approx 2 weeks ago a large clear water puddle/pond appear approx half way down our garden (total length 200'). At the botom of the garden is a ditch running along the bottom of the gardens. Across the road from us is a ditch running towards the house into the drainage system. I hope this isn't too confusing!!!

We have been informed that this used to flow across the road towards us in some way, but was redirected to drain away down the into a public drain some way down the road instead of ours. The local authority have been out and dug holes in the garden and have said they found a large concrete slab which could indicate a septic tank was used for foul water in the past and that our clear water could be draining to that now.

Sewerage is now connected to main drainage system. I don't know what insight into the world of drains you can give me! Is this their (LA) responsibility or the residents of this block?

You may detect a slight hint of desparation, this is because three weeks ago we sold our house and on Wednesday after Easter the valuation is being carried out!!!!!!!!

What do you think. I am not sure I have explained this with any real clarity!!!


forum answer Tony McCormack - Apr 19th 2003
I can't follow your description 100%, Antony, but, from what you say, I can spot two possible get-outs for the LA.

1 - the age of the property. As this cottage was built before the 1936/37 Public Health Act, the sewer system is the repsonsibility of the property owner.

2 - preliminary investigation by the LA suggests that it is surface water (what you call 'clear' water) from your property that is being directed to the possible septic tank, rather than water from the ditch, which means it is outside their remit.

If there was some way of testing whether water from a public area, ie, the ditch you mention, was ending up in your garden, then it would be the responsibility of the LA (as agents of the Water Authority) to take any necessary remedial action to prevent water entering your property. However, the LA has already been on site and investigated, and, to be fair to them, if there is any suggestion that it is the LA's responsibility, they usually accept the work and get it done as soon as possible. If they are saying 'it's not us, Gov!' then, short of bringing in your own team of drainage inspectors, you have to accept their word.

All you can realistically do is wait to see what the Surveyor comes up with on Wednesday.

Antony Hare
Apr 21st 2003
The LA guy mentioned that the septic tank has not been used for some while but may have a split or hole in it. Therefore it has slowly been filling up over time and has now reach its limit and is spilling over.

He also said that there are granst available for this type of problem because of the age of the house. Have you ever heard of this?

Tony McCormack
Apr 21st 2003
I've heard of old septic systems rupturing, and I've heard of grants for new or replacement septic systems, but the grants tend to be a matter of local policy, rather than national standards, and, as far as I know, have nowt to do with the age of the house, but with access to existing sewer systems and public health concerns.

Still, if they're offering money to help fix the problem, snatch their hand off!   smile

Forum Question Patio Drainage Next to House - Scotty - Apr 18th 2003
I am soon going to be constructing a patio for a friend, however I have a few questions about drainage.

The patio is to run right up next to the house, however the dpc is only 4 inches from the proposed slab surface. Is it possible to put some sort of drain/soakaway between the house and the slabs in order to prevent damp?

Or one run of slabs next to the wall then a channel??

I was told that a gravel filled trench round the outside of the house would be suitable as long as this was kept 150mm below dpc. However this sounds dodgy.

Any help greatly appreciated


forum answer Tony McCormack - Apr 19th 2003
Have a look at the page on Dealing with DPCs which probably has the solution for which you're searching. If not, post back here and I'll talk you through other possibilities.
Apr 20th 2003
Thanks for your time Tony.

One further question.

Ensuring that the gravel filled trench is 200mm wide and 150mm below dampcourse. Does the channel need to be lined with concrete at the base? Could water not be allowed to pass through the gravel and drain into the ground below. The soil is very well drained. Or would this cause problems with foundations?

Regards - Scott

Tony McCormack
Apr 21st 2003
Scotty asked...

Does the channel need to be lined with concrete at the base?

Not nesser celery.

Could water not be allowed to pass through the gravel and drain into the ground below?

Yes, that's fine. smile

Would this cause problems with foundations?

Most unlikely, unless you were subject to regular floodings and extremely high levels of rainfall and/or surface water.

Forum Question Drain to Nowhere - Owen Ireland - Apr 22nd 2003
I have a house on a slide gradient facing the road, the road being lower than the house and garden. At the back of the house is a patio with a patio drain than runs under the adjoining garage and comes out at the bottom of the driveway, just next to the pavement into what looks like a normal roadway drain.

However, this drain doesn't lead anywhere - it's plastic, about 1m deep and the only exit/entrance is the pipe from the patio drain.

Is this a wierd sort of soakaway, (or evaporate away), or did the builder's forget to join it to the road drain (it was built 7 yrs ago).

Thanks! - Owen

forum answer Tony McCormack - Apr 22nd 2003
If the mystery drain is on a public highway, then it will be connected up to some form of approved drainage system, rather than be a direct soakaway. However, if this is on your own property (I can't tell from reading your message), then I suppose it could be a small soakaway access point.

Do you have a photo or a fuller description?

Owen Ireland
Apr 23rd 2003
Thanks - it's on my property - just at the end of the drive. I guess for the amount of water that comes through, it could just be allowed to evaporate, but it seems a bit odd!
Tony McCormack
Apr 24th 2003
It won't evaporate from a gully, or, at least, it won't evaporate sufficiently to control the water level.

Think about the road gullies on any public highway - we've had next to no rain for a few weeks, yet there's still water in the gullies. They may have lost 20mm or so due to evaporation, and, if left for long enough with no topping-up, then they will eventually be dry, but it'd take a long time!

I wonder if what you have is a little sand drain, which is, essentially, a deep, thin hole (think of it as a vertical pipe) filled with sand and/or gravel that allows the water to percolate to to lower levels and more permeable layers of the sub-strata.

Owen Ireland
Apr 28th 2003
Thanks for the reply. However, this is plastic, about a foot wide and 3 feet deep, and you're right it doesn't evaporate very fast at all!


Forum Question Multi-property soakaways - Dave Purcell - Apr 24th 2003
I am looking for data on soakaways to cater for 10 or more houses
forum answer Tony McCormack - Apr 25th 2003
You can get one of the manufacturers to do all the sums for you, Dave, on a project of that scale. The basic calculation is pretty much the same as that I give on the Soakaways page, but, because you'll end up with a sizable chamber, the manaufacturers of segmental soakways will help you design what is required and present all the relevant calculations to your BCO or development team.

Try Polypipe (for uPVC) or Marshalls (for concrete) - they are usually very helpful in this sort of thing. The contact details for both are given on the Drainage Links page

Forum Question Waterlogged Garden - Fat Dog - Apr 25th 2003
I stumbled upon this website shortly after purchasing my house. The two big projects I had planned for the new property (laying a new drive and patio) are covered by this site, which has given so much excellent advice that I am now full of confidence to go DIY rather than use expensive contractors. Well done on the sheer usefulness of the site and the abundance of information it contains.

So, drive and patio taken care of. Thank you. My main problem now therefore relates to the waterlogged back garden. The house is built right next to what was an old brick and tile works. So, below the top couple of inches of topsoil in the garden is an indefinite depth of extremely heavy clay. The whole garden remains waterlogged after rain (often for many weeks after the last fall of rain). I have planned the layout for the garden and will replace the top 500mm or so of clay with soil (so I can actually grow something in it). This would be an ideal opportunity to install some land drainage. I plan to use perforated plastic pipe layed in trenches. From your site I have easily been able to work out how to do this and work out a drainage layout. My problem is where to connect the new land drains to. There is a concrete inspection chamber ideally located in the garden. The main channel is about 500mm below ground level. I've checked and can advise that only toilet and kitchen sink waste flow into this system - definitely no surface water. Am I allowed to connect into this with my land drainage and is it an easy task? Other than that, there is a gulley in the corner of the garden/at the corner of the house which takes the surface water from the roof? Again, am I allowed to connect into this and is this an easy task? The trap water in this gulley only appears to be about 250mm below ground level, so I'm not sure it is low enough to connect into to still allow for the gradient of the drainage. I could probably just about manage it, but by only having the plastic pipes a few inches below the top level of the garden - probably not recommended.

I'm almost there (thanks to your website) but just need the last little push in the right direction.

Many thanks in anticipation.

forum answer Tony McCormack - Apr 25th 2003
Do you know if you have two separate drainage systems, ie, Foul and Surface, or is it one combined system?

The best option is to connect up to the surface water system, so that you're not sending what is, effectively, clean water to the ETW when it could be dumped into a river somewhere. You're concerned that the Rainwater Pick-up (RWP) you've identified is too shallow to accommodate the gradient of the planned land-drain system. Have you dug down around this RWP to determine just how deep it runs or to where it is connected? You will probably find that it is at least 500mm deep and that you could install an access chamber (AC) at some point which could then be used to connect-up the land drain.

Installing an AC is relatively straightforward and is already shown on the site with an animation. This is, by far, the best and simplest option. However, if you've a combined system, or you have no viable alternative other than to connect to the foul system, then you will need to use a trapped connection. Rather than go into all the detail about just how that is done, check your RWP and see if an AC is feasible. If it turns out that the Foul option is the only option, I'll explain the Foul Water connection method in greater detail at that time.

Fat Dog
May 2nd 2003
Hello again. Thanks for the reply. My investigations have been quite limited because of the rain, which as you know leaves the whole back garden waterlogged. Anyway, there is definitely two distinct systems - one for foul water (of which the inspection chamber belongs to) and one for rainwater. I think the rainwater drain pipe from the gulley does run away at around 500mm deep. I think I can therefore just achieve the gradient required. If the new drains will run under just lawn and patio, what would be the minimum recommended depth? I'll try and go for a surface water system connection and install an access chamber following the instructions given on your site.

Once I've connected an access chamber into the existing pipe running away from the gulley, how do I connect into the access chamber with the new drainage? Is it best done with a short rigid section of pipe (bearing in mind that the land drains will be flexible perforated plastic pipe)? Do I need any end cap over the last piece of drain pipe before it enters the access chamber, to stop any small bits of grit etc. entering the main drainage system? Is it necessary to install a trap? Hopefully nearly there now.

Thanks again.

Tony McCormack
May 3rd 2003
The minimum recommended depth for a land drain varies according to the contractor that laying it, but I would always make sure they are at least 300mm deep, and preferably 450mm, when it's in a private garden. Keep it as deep as possible, even if it means laying it flat with just 25mm or so fall over the last half-metre where it connects to the SW system to reduce the risk of backwash. On such a relatively small system, the hydrostatic pressure generated by water seeping into the system will provide sufficient force to 'push' the water towards the collection point.

When it comes to connecting the land drain to the new AC, then you should use a 'rocker pipe', which is a short length of unperforated pipe, usually around 600mm in length, and then use an adaptor coupling to connect the perforated flexible drain to the rocker pipe. There's no need for a silt trap if you've used a membrane to surround the land drains or if it's only a small system, and any small bits of grit finding their way into the pipework will be flushed along by the water flow.   smile

Forum Question Drain access spacings - Rik - Apr 26th 2003
Just wondering whether there is a standard for access on long drain runs for SW. I know foul has to have a manhole at least every 90m, is it the same for SW?

Cheers in advance


forum answer Tony McCormack - Apr 27th 2003
The standards are the same for FW and for SW. 90m is the max spacing for Manholes - IC's or access chambers (as used on residential drainage) have a lesser maximum separation distance (45m)
Apr 28th 2003
Many thanks Tony, I thought it might be. Now I know.
Forum Question Drainage and DPC - Danny SJ - May 1st 2003
I have been laying a patio along the side of my house from front to back (with the excellent aid of this site). The only drainage point I have is at the front of the house and have therefore inclined the patio towards that way. The highest point of the patio is around 170mm below DPC and the lowest point at the front of the property is around 250mm below DPC. My question really relates to the drainage issue and whether I should link up to the existing system via a linear drain and pipe section cut in to the existing downpipe or whether as I am well below DPC at the point of rain collection on the patio that it is necessary at all. At present the rain collecting at the front end of the patio just sinks through the soil.

Connecting to the down pipe would involve lifting of the street paving, which although reluctant to do, if deemed necessary would accept.

Any advise will be greatly appreciated.

forum answer Tony McCormack - May 2nd 2003
Normally, I would always send the surface water from a patio (or any other pavement) to a proper drainage point. Whether that drainage point is linked to a local outfall, to the sewer systemm or to a soakaway somewhere onsite doesn't really matter, as long as I was sure the surface water was gone from my paving.

However, if you have a situation where the water is finding its own way off the paving and is draining away without any problem, then maybe it's best to leave it for the time being - if it ain't broke: don't fix it! You may find, though, that after a year or so of draining the patio, this low spot becomes 'silted up' and the surface water starts to hang around after the rain has stopped. That would be the time to install a "proper" drain of some description.

Suck it and see, as they say!   smile

Danny SJ
May 2nd 2003
Thanks very much for the swift reply. The intention has always been to install the drain as mentioned (if a job is worth doing, it's worth doing well). Your points confirm my intention, only that now I can take the time to complete the project properly over the Summer/Autumn rather then rushing to get it done, (not that that will please her who must be obeyed).

Thanks Again.

Forum Question Riding arena - Amical - May 1st 2003
I'm planning to build a 60x20m outdoor arena for she-who-must-be-obeyed. I've looked at several designs and examples of professional installations and, frankly, I'm a bit concerned that sub-base and drainage arrangements may not be adequate - hollows filled with additional riding surface (sand) to compensate for collapsing sub-base seem all too common.

Our land is a hill farm on heavy clay and I've started by using cut-and-fill to create a large enough area with 2% slope. I was then planning to install Terram 700 followed by 100mm perimeter drains in 450x600mm trenches of 14/20 gravel, fed by 80mm drains in 300x300mm of 14/20 at 5m intervals. On top of this I was hoping to put 150mm of compacted DTp1 or 0/32, followed by 150mm of equestrian sand.

Would the compacted DTp1 be sufficiently permeable to allow the sand to drain properly, or would I be better off using 40mm drainage gravel? If I use the gravel, how can I get the strength of DTp1? Or can anyone (Tony?) offer a better idea? Thanks!

forum answer Tony McCormack - May 2nd 2003
Given all the drainage you're putting in, I'd hazard a guess that the area will drain fairly well and that the surface water will find its way through the DTp1 without too much trouble.

If you wanted to consider alternatives, then you might look at using a sub-base material with fewer or no fines (the 'drainage gravel' you mention), and then using another layer of the Terram (700 or 1000) between that and the Eq. sand (which seems inordinately deep to my non-equine experience) to prevent it being washed into the 'open' sub-base, or, more expensively, using a drainage composite to intercept the surface water as it percolates downwards, and so deliver it directly to the land drains.

What type of DTp1 are we looking at? If it was a limestone or a crushed concrete material, I'd be more concerned about possible blockages in the longer term than I would with, say, a gritsone or a granite.

May 2nd 2003
Very many thanks for your helpful and prompt reply.

I'm told that the riding surface is usually 150mm - either all so-called 'equestrian sand' (single size, fine, washed, sub-rounded and virtually free from clay, silt or grit - presumably also in several flavours..) or 100mm sand plus 50mm special topping of sand mixed with PVC or rubber granules. Ideally, the sand should be firm, like a foreshore, given the correct water content.

Re. geotextile between the sand and the sub-base, it seems this is controversial. Apparently there have been problems with horses putting their feet through it (despite the 150mm cover) - at best defeating the object and at worst causing trips and broken limbs (horses and riders).

The DTp1 (or 0/32 - 0/40) would be granite.

Do you think I've gone overboard with the drainage?

(Excellent site - I'd be lost without it!)

Tony McCormack
May 3rd 2003
Regarding the depth of the Eq sand - keeping the moisture content correct is going to be the difficult part. The construction you've envisaged is fine for ensuring the sand doesn't become waterlogged when it's lashing down with rain, but, in the dry summer months, this system could 'parch' the sand, reducing the moisture level to well below the ideal, turning it into a dust bowl rather than a riding arena. How this affects horses, I don't know, but it may be that you have to hose the area a couple of times a day in the dry months to make the surface rideable.

For the geotextile - if there are incidents of hooves ripping the membrane, then I would suggest either a stronger membrane, say Terram 4000 instead of Terram 700, or possibly the use of a composite which is much, much tougher, or, even overlaying the membrane with a reinforcing mesh. There is no reason for horses, or their riders, to be endangered by such a construction if a bit of thought is put into it.

Using a granite sub-base material should be fine. It's a stable, inert material and less likely to cause a problem with the sub-surface drainage.

As for going over the top with the drainage, I think you may have done, but without seeing full plans and understanding a bit more about the requirements of a horse riding arena, I couldn't be sure. Does the British Horse Riding Club (or whatever it is) issue any guidelines?

May 3rd 2003
Many thanks once again, Tony. I'll try to follow-up on the questions you raise.

Incidentally, did you manage to sort those b......s that stole your intellectual property?

Tony McCormack
May 3rd 2003
It's ongoing, but Northants Trading Standards have been pestering them and my pet solicitor is about to have another go at them. Their web hosting company closed down the site featuring the stolen material and quite a few folk have told me about their "experiences" when dialling the freefone number.   smile
Concrete Chris
Jun 17th 2003
I would think that the issue with the membrane will mostly be an issue if the surface you put down is not up to the job (as most that I have seen aren't). Common sense dictates that a ton of horse turning on a small surface area (its hooves) at more than walking pace exerts huge sideways pressure on the surface. If you are using the arena for any form of jumping or lunging the majority of surfaces will dig up very quickly - rubber or no rubber.   The only way I have seen around this is to pay for a properly bound surface material that is supportive to the horse yet gives when taking off / landing. There are some about, but like all good things in life you pay for what you get. The surface we used for our arena of 7 years is brilliant, but it cost more than everything else put together. We spent ages to-ing and fro-ing on this issue, but have never regretted the choice we made. Most of the reputable top surfaces have some form of vaseline coating to provide this extra strength - hence the cost.

The vast majority of people do not go for these surfaces (due to cost) and then act surprised when their lovely new arena looks like someone has been at it with a spade.

If you are saving on construction then I would spend the money you saved on a top surface. My experience is that you will never regret it.

Moral of the story is that horse maneges used for jumping etc take a beating - you pay for what you get.

Tony McCormack
Jun 18th 2003
Last month I had a meeting with one of the technical experts for the largest supplier of construction membranes in the UK, and he told me that the British Horse Society (is it??) issues a specification for riding arenas that shows a membrane being used but in the wrong position, ie, at too shallow a depth and without sewn lap joints.

There was also some discussion about the type of membrane being specified and the suggestion was that a typical geo-textile is insufficient in such circumstances and that a composite product would be a better option. However, there is no 'official' approval of such a construction, and so it remains the musings of two chaps over a couple of pints. The Tech Rep said that, if he got the chance, he'd sketch a spec and submit it to his bosses and the Horse people for their comments, but I've heard nowt since.

Do you know of a spec. from this Horse Society crowd, Chris?

Concrete Chris
Jun 27th 2003
I asked about and no-one knows of one. This does not mean that there isn't.

You could phone the BHS (British Horse Society)

Tony McCormack
Jun 27th 2003
I'll check with the good folk at Terram
Forum Question Drying out the sub-soil clay - David Nelson - May 6th 2003
I have a Victorian terrace built on heavy London clay. Having lowered ground levels which had been raised too high over the years, I discover that the foundations below the slate DPC are minimal - just two layers of brick, then some 2 - 3 inches of compacted rubble. As this is on clay, I do not want to over-drain the soil which would lead to cracking in dry spells and subsequent wall cracks. Further complications are introduced by the presence of the soil stack and a seperate rainwater drain by the wall. I am hoping to use the Marshalls Driveway 50 range, but advice on what to do up next to the house wall would be most helpful.
forum answer Tony McCormack - May 6th 2003
I did a design for an almost identical property in Stoke Newington last year. The construction you describe is known as 'Spreader Courses' and is common on older properties built on a stable clay.

On the Stoke Newington job, the paving finished 300mm or so short of the wall and the 'gap' was dressed with a decorative flinty gravel. Disturbance to the spreader courses and the immediate surround was kept to an absolute minimum, and it seems to have been successful.

Forum Question Draining a garden - dak uk - May 18th 2003
I need to lay a lawn, small wall 6mtr and with flagged path with kerbed edges the 16mtr length but the land is full of water. The owner has said it always floods when rains. So he covered his 16 mtr x 7 mtr garden with 25 ton of top soil, with no compaction. So you can imagine the state.

He dug a small found about 300mm but that is full of water too. I think the best way to sort out the water is to dig a large trench the width of the garden at the bottom and about 1 mtr deep, fill with large stone, then long trench's with perforated pipe and gravel leading to trench to disperse water.

Q1. Will this drain the top soil as I don't want to take it out?
Q2. The ground is soft - my wall is about 800mm high with four pillars with single brick between, how deep should my founds be?

There are no manholes to run pipes to.

forum answer Tony McCormack - May 19th 2003
Q1 - it would work if there was somewhere to outfall, but you say there is no drainage point that can be used, so to where would this planned interceptor drain go? Simply digging a trench and installing a land drain or a soakaway will not work unless there is somewhere for the water to go.

Q2 - You need to go down deep enough to find a firm base, preferably clay. You shouldn't pour a foundation over topsoil or suspect/iffy ground. Find firm, stable ground, then pour a 150x450/600 footing.

dak uk
May 19th 2003
Right I found out that were the trench is at btm of garden there is an underground spring or well of some sort so the water will seep into there.

About 1mtr down I hit clay. Will I have to dig down to clay level for perforated pipes and if so what level will the pea gravel be from the top soil level and dose the pipe needs to sit on the clay?

I'm also putting a 6ft fence with posts @ 8ft (2ft in ground using post mix down to clay with broken concrete to bring post up to height.) the ground is so soft I don't think it will hold posts, as the old 4x3 posts pushed over with medium force. HELP it's like working on a swamp.

I was thinking of fastening a couple of feet to btm of post's then hardcore around, then post mix? What u think as i need to keep cost down.


Tony McCormack
May 20th 2003
Water will not seep into a spring! The reason the ground is so wet is probably because the spring is flooding the ground, and you could spend literally thousands attempting to ameliorate the problem, involving the installation of a proper drainage system to carry the spring water elsewhere. I can't help thinking that you're peeing into the wind tryuing to overcome this problem on a tight budget, and you might be better off developing a strategy that makes the most of the spring, rather than try to turn a swamp into firm ground.

The standard spec for a collector drain is shown on the land drain page, but I repeat: unless you have somewhere to send the water, you're wasting your time.

For the fencing, you might need to consider using longer posts, say 2.7m posts, with 900mm buried, rather than 2.4m with 600mm buried. If there's still an issue, then lateral braces (aka "sprags", "rakes" or "outriggers" ) may be necessary. Your notion of fastening "feet" to the base of the posts, and then backfilling with inert hardcore will not work if the ground is loose. A longer posts and a good, solid backfilling of concrete, sufficient to counter the force of the wind on the panels, is the simplest option.

dak uk
May 20th 2003
Thanks. I'm also working at the neighbors' garden, I was informed that his father dug trenches, filled with hardcore then backfilled with soil and his is a lot drier.

Back to the garden in question, at the bottom there is a patch of grass about 3mtr's wide and the ground is a lot firmer, I read on this site that grass grows greener were the drainage-line runs and seen this in the past, (with out much thought,) anyway this is why I think the spring runs under this patch of grass, the rest is baron wet soil.

I've seen the spring at the neighbours' garden and I think it would take the water away. (Fingers crossed)

I think your right on the posts so I'll give it a try.

I'll let you know how I get on, Thanks.

I don't use the net much but must say that your site has been the most helpful and informative that I've personally have had the pleasure to have viewed
Also thanks for the very quick response to my problems.

dak uk
Jun 6th 2003
You're right that the water needs channeled away.

So what I'd like to do is: there are three gardens backing on to our garden which have manholes in them. 1 is council, then ether side is private. I have asked 2 of the tenants but they said I will have to get the relevant council permission??????  Could you fill me in with the law on this one?

Also I've installed my perforated pipes to a large sump trench, I wish to take an overflow pipe from this trench to one of the M.H. Would this method be all right as the lady in the private house was worried about silt from my pipes. Also if this method is ok is perforated pipe all right to run to the M.H.

Would it have to be a company or can any competent person do the work.

Thanx Dave

Tony McCormack
Jun 8th 2003
The law regarding connection to drains and sewers is somewhat complicated, but, if there are two access chambers on private property, then you may be able to connect to them, as long as you have permission from the property owner, and this may need to be some form of legal agreement to cover eventualities such as dealing with blockages, cleaning and maintenance, access rights, etc.

The first thing to establish is whether the manholes/access chambers are part of a private drain (which is the property/responsibility of the property owner) or a public sewer, which is most often 'managed' by the local authority. Just because a MH/AC is on private property it doesn't necessarily mean it is a private drain. The deeds and/or your LA should be able to clarify that point, and then you know who to approach to seek permission.

To overcome any problems with silt, you could construct a Catch Pit, which will trap all silt before it can enter the main drainage system. Silt is not usually a major problem with drains and sewers as the inbuilt falls are normally fast enough to ensure any silts and clays that do find their way into the system can be washed along by the flow of water.

Finally, when it comes to carrying out the work, it all depends on the layout. I would strongly recommend a drainage contractor, who has all the right tools, the right experience and the right training for working in sewers, but, if this is a private drain, on private property you could undertake the work yourself. Even so, I'd still get a drainage contractor to give you a no-obligation quote for the work, just to see whether you think it's worth all the hassle.

dak uk
Jun 8th 2003
This sounds like good news.

I think the manholes are under the council authority so would I need permission to use there M.H.

The best located M.H. would be the council property as the gentleman said if I got council permission he wouldn't mind (as he said he "would have no choice as to let me use the M.H.").

So do you think the person who has the problem water should get the permission then I can get on with the major work.


Tony McCormack
Jun 14th 2003
Yes - have a chat with your local council Technical Services Department and see if you can cajole them out of their office, while the weather is good, to come and have a look at your problem and advise you on the best or most practicable solution.
Forum Question Drainage suppliers in W London - K Meeres - May 19th 2003
I need to lay approx 3 m land drain to solve a waterlogged lawn. I cannot seem to find a supplier who will sell by the metre though. Anyone have some spare? In the W London area.
forum answer Tony McCormack - May 19th 2003
Try 'phoning a few local contractors (see your 'phone book) to see if they can let you have a length.

Most BMs sell in 25m rolls, and while the better BMs are often willing to split a roll on demend (albeit for a healthy price hike) the Nationals tend to be less co-operative.

Forum Question Patio drainage on garden sloping uphill - Deb H - May 22nd 2003

We are about to lay a new patio adjacent to the house. However, the garden slopes uphill away from the building. Immediately the other side of the patio is a ground level pond which will have stepping stones to cross it, so I can't drain it that way. The drainage has to run towards the house.

My question is, what type of channel would be most appropriate? We are using a textured concrete buff coloured slab, laid at an angle of 45 degrees to the house. As it is a new house, the builders have sealed the bottom of the downpipes - there is no open gully there, although I assume that this is easy enough to remedy?

Has anyone any idea on what type of gully and channel I can use that won't look too horrendous immediately adjacent to the house? And how do I link it to the sealed downpipe?

Thanks - Deb H

forum answer Tony McCormack - May 22nd 2003
Hi Deb,

it is pretty easy to replace the sealed rainwater pick-ups with a gully. There's a bit of digging involved, and some fiddling to persuade the gully to sit just where you want it, but it's an hour of a job, if that.

Once you have your gully in place, you could use a number of solutions to direct the water away from the brickwork of the house and into the drainage system. The two simplest options for diy'ers are....

1 - use a dished channel. Lay this tight against the house with endfall towards the gully and allow the patio to drain towards it. The surface water will trickle along the channel and disappear into the gully.

2 - use a linear drain. Again, this can be laid tight against the house, but there's no ned to lay it to a fall (unless you've more than around 10 metres or so). Also, it is possible to omit the gully if you use a linear drain, as it can be connected directly to where the rainwater pick-up was, and you can feed the downspout directly into the linear drain.

There's a good explanation of these techniques on the Drainage for Pavements page.

Forum Question Water running towards house - Matty Lad - May 27th 2003
I have just had a new block paved drive laid, and they done a lovely job except...

Originally my drive sloped down towards the house, but "kinked" back up about a metre or so away from the brickwork, and all of the water soaked into a central gravelled area. The contractor has, at my request, fitted some lovely kerbed edging to the gravel.

He has sloped the drive down towards the garage (with a narrow strip drain, which is fine) and similarly towards the bay window/door wall (three bricks down on the blue brick). The bit of path in front of the bay window is only 1m wide x 3.5m long

I ran a hose at the weekend, and noticed that water runs from the left hand side of my drive, avoids the grate in front of the garage, and ends up along the front of the bay window wall, and dissapears gradually into the sand joint between the blue brick/block paving. I cant tell where it would eventually end up, because the sand is still very porous

I believe he should have fitted a drain here, or channelled blocks to allow the water to run off into a rainwater pipe (which he has block paved around) which is at the other end of the bay window wall.

Am I being too picky? is a hosepipe sprayed on the ground a fair test?. What real damage could this do to my house from such a small area of path?

What can I reasonably expect him to do about it?????

Thanks for listening...

forum answer Tony McCormack - May 27th 2003
Have I got this right? The surface water from the entire drive falls towards the garage and the drain installed there, but never actually makes it into the drain as it is directed towards an area of paving beneath the bay window, where it sits, sulks for a bit and then finds its way through the joints to the sub-layers?

If that is correct, then you have a serious problem. The joints will self-seal over the next few weeks and then you'll have a puddle which will take longer and longer to disappear. It will also encourage the blocks to become green and manky with algae and other crud, and it can cause problems with settlement over the longer term.

It's relatively easy to rectify this problem NOW, but the longer it gets left, the worse it will become. I can't say which is the more feasible, but either the blocks need re-laying to re-formed levels that direct all the surface water into the drainage system, or the drainage system itself needs lowering to ensure the surface water finds its way in, or, possibly, a bit of each.

What you can reasonably expect is that your driveway drains properly to suitable drainage points. Areas of standing water are not acceptable and any decent contractor will gladly remedy the problem. Have you asked your contractor what they propose to do?

Matty Lad
May 29th 2003
Yes Tony, thats right!

I have had the chap back in, who has agreed to put channelled edge bricks around the bay window wall, ending up in a rainwater drain (currently sealed with a gutter downpipe)

He was a bit reluctant at first, he said that "there was not much he could do", and then he said that when sand sealed, it would run along the house, and he would open up the drain cap for it. I said that I wanted some form of channel or drain, as I had read that water against the house is not a good idea.

It was only when I actually demonstrated with a hosepipe that he finally relented.

Can I just say that if it wasn't for this site, and your advice, I might just have left it.....

Many thanks - Matthew

Forum Question Plastic drains - Paul Roe - Jun 5th 2003
I am extending (again) and I need to lay quite a bit of drainage, I was going to go with plastic for all the new stuff as there is so much. However I have 4 quesions

1. I have priced up a plastic inspection chamber and with risers and cover they are comming in at about 200 quid each!! Is this the going rate or is the builders merchant ripping me off?

2. Where the drain goes under the floor slab, do I bed it on the same bedding as outside and then put hardcore on top or do I also put the same bedding on top upto the bottom of the floor slab? The top of the pipe will be approx level with the bottom of the hardcore.

3. Do the inspection chambers need to go on a concrete plinth?

4. Can I put bends on the entry to the IC and how big 45deg?


forum answer Tony McCormack - May 7th 2003
Q1 - that sounds like list price to me. Contractors normally get 20-35% discount, but then, contractors are repeat buyers and spend several thousanbd quid per month, whereas you're a one-off customer, so you're not likely to be offered the same discount.

Q2 - Check with your BCO. Some will accept a bed and cover of A10 pipe bedding, but some will insist on concrete bed and haunch.

Q3 - Yes - it's actually easier to bed them on concrete, as you can ensure they are level/plumb, and be sure they won't settle or shift as soon as your back is turned.

Q4 - You can use whatever bends you require, but remember that you must be able to get rods or cctv kit around the bends. If you absolutely need to use a 45 bend, would it be possible to use 2 @ 22.5° or even 4 @ 11.25°? The slower the bend, the better.   smile

Paul Roe
Jun 8th 2003
It must be just the the builders merchants around here, I asked for discount and they usually say "how much ya buying mate" but all I got was "we don't discount that stuff"

Is there any brand that you can recommend over another? I have looked at Osmadrain, Hunter, Marley and Hepworth, Marley seem to be the cheapest and Hepworth the most expensive

Tony McCormack
Jun 8th 2003
Marley is plasticware; Hepworth is clayware - you have to cost out the whole system, and then take into account the different bedding requirements of clayware and plasticware to arrive at an accurate cost comparison.

For diy'ers, there's no doubt that plasticware is the simpler option, as the pipes can be cut with a handsaw, but, for shallow drainage runs beneath trafficked areas, I prefer clayware.

There's not a lot to choose between 'brands'. The all have to meet the relevant British Standards, so it comes down to range of fittings, ease of sourcing, and, of course, price. For plasticware, I usually find that Polypipe offer the best all-round deal.

Forum Question Draining gravel area - Nic - Jun 8th 2003

First off, I have to thank you for such a well presented and informative site. It's helped us no end with sorting out solutions for our very problematical driveway and front garden.

Our house is on the side of a hill, above the road by about 15ft. Consequently the driveway is very steep - too steep for block paving, so it's going to be concreted. The ground also slopes from left to right. Where the ground becomes less steep, the concrete will stop and we'll block pave the majority of the garden, apart from an area in front of the house measuring around 5 m x 6m. This is the most level part of the garden, with only a slight slope and we plan to gravel it.

So, after that long-winded explanation(!), the question I have is how to drain the gravel section? It will be 'enclosed' on one side by the house and on the other three sides by block paving kerbstones. What I wish to avoid is a big puddle of water gathering under the lower corner of the gravel area, where it meets the block paved area.

Will water just permeate across the whole area and gradually drain away or should we install some drainage system? The ground soil is almost solid chalk.

I hope that's not too rambling and vague!!

Cheers - Nic smile

forum answer Tony McCormack - Jun 14th 2003
Firstly, what makes you think your driveway is too steep for Block Paving? There are a couple of tricks that are used when using block paving on steeply sloping areas (tricks that I keep meaning to illustrate on the site but never seem to find the time!) and it's certainly easier to block pave a slope than to lay concrete, which has an uncontrollable desire to run to the bottom of the slope!

Anyway, that's by the by, and your main concern is draining the enclosed gravel area. Well, you'll be releived to know that it's actually quite simple - lay a perforated pipe beneath the gravel, wrapped in a piece of membrane as shown in the Land Dranage pages, and then connect that to a standard pipeline that runs beneath the new driveway to some suitable outfall point where it can trickle out and join the rest of the surface water running down the road.

Because this drain will actually run beneath a trafficked pavement, I'd strongly suggest using a rigid pipe such as clayware, rather than a flexible pipe which would be prone to collapse under the loading, unless you were happy enough to dig down about 750mm to give it adequate cover. If you prefer to use plasticware, then, for the section of non-perforated pipe beneath the driveway, encase it in concrete to prevent it deforming, leading to settlement of your lovely new block paving.

Forum Question Drainage beneath new pond - C Atkinson - Jun 11th 2003
Thanks for all the great info on this site.

Can anyone advise on this problem. I'm in the process of digging a new pond and due the high water table in my garden (only 12 ins of topsoil over heavy clay subsoil) I've had to locate the pond in an area I know will become waterlogged in the winter. I've read that the pond will therefore require drainage below the liner.

OK so I'll excavate another 8 inches or so and sandwich perforated pipes in a layer of gravel. I don't have anywhere to direct this groundwater other than to collect in a sump and then pump into the nearest (12ft away) surface drain. Two questions please - the pond area is only 3.4m x 2.4m what can I use as a sump - I had thought about burying a plastic dustbin, is this a ridiculous idea? Secondly any recommendations on a suitable pump - it would need to have a float switch and be rated for continuous use and need to lift the water around 1.5m?

Many thanks for reading

forum answer Tony McCormack - Jun 14th 2003
A buried plastic bin is fine, or you could buy one or more of the soakaway/storage units shown on the Soakaways page and use one or more of them.

Any pump with a float switch would be suitable. The Draper SWP 235ADW is a good choice as it can cope with larger particles that may, inadvertantly, find their way into the system. It can cope with a lift (head) of up to 8.5 metres and can thrash out a respectable 235 litres per minute. A 240v model costs around 120 quid (plus the dreaded VAT, of course)


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