aj mccormack and son

Drainage - Page 03
The Brew Cabin


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Forum Question Drainage for retaining wall - Dave Yearsley - 4 Jun 2002
Hi Tony,
Just taking a break from flagging due to rain. Thanks to all your advise things seem to be going well, I first laid my marshalls sets sloping away from the house and then proceeded to lay my flags. My query this time is: I have a retaining wall the full length of my patio, the wall is 500mm high and is built from marshalls walling with a second skin behind of concrete blocks. Behind the wall is the garden. Do I need to install any type of drainage, the garden never seems too wet.

P.S. I have taken some piccies and when the after pics are taken I will send them to you.

Thanks again
Dave Yearsley

forum answer Tony McCormack - 4 Jun 2002
You might not need drainage behind the retainer wall, Dave, if your garden is fairly dry, but it's good practice to incorporate weepholes in a wall like this, just to alleviate any pressure building up behind the wall.

However, if you do this, is there anywhere for the garden groundwater to drain to?

Dave Yearsley
4 Jun 2002
Hi Tony,
Thanks for your prompt reply. I have already incorporated weep holes in the wall and the water can drain across the patio towards a gully.

Thanks again
Dave Yearsley

Forum Question Garden renovation - Wossie - 12 Jun 2002
Can anyone help me? the answer is probably in here some where but at the minute im not taking any thing in as ive had a few tins while going through the whole internet. im converting my back yard into a garden. ive got a manhole at either end and at the outside edge in the middle. i have a surface water drain that leads into the sewer. under the concrete is a very thick layer of clay that is not draining away a single drop of water, is it possible to take away all of the surface water drain which is about 1.5feet deep and dig a trench around the remaining pipe, fill it with hardcore and level off the rest of the area with hardcore. would this be enough to drain away water from the lawn and topsoil that i want to put down. i hope this makes sence.
forum answer Tony McCormack - 12 Jun 2002
I can't quite follow your plans, Wossie, but it's not a good idea to remove any existing drainage unless you are 110% certain that it is redundant.

If you're worried about the clay layer impeding the drainage of the planned garden, then installing a land drainage system and connecting it to the SW system would seem to be the best solution, as far as I can see. This can then be burried beneath your topsoil and no-one need be any the wiser.

Does that help at all?

13 Jun 2002
My yard is in two parts, one part is the drive the other part is the yard, where i want the garden. The drive is higher than where i want the garden. The surface drain that i want to use drains all the water away from the drive and the yard. What i meant about taking away the drain is, the part itself that i want to take away looks like a chimney pot, with a small outlet at the bottom ( house and pipes are 100 years old ). This pot is joined to a pipe about 4ft long this joins into the house sewer pipe. By digging a trench the length of the edge of the garden as thats where the drain is, filling in with hardcore then leveling the rest of the area with hardcore. Is this suitable , as i feel that is i have to leave the pot in place i will loose the depth of the top soil that i want to put in, and feel that i will not get proper drainage either. I hope this makes sense  as i am trying to put my thoughts into words, so you can understand what i am trying to do.
Tony McCormack
17 Jun 2002
I think what you are describing is a filter or interceptor drain, but I'm not sure why all that effort is required.

The drive is higher than the planned garden, so it could crossfall to the garden and the surface water coukld be collected by a channel which then delivers the water to a single collection point, such as a gully.

There's no need to remove the existing 'pot' as its level can be adjusted by using a raising pice or building up the pot with brickwork and then setting the grating to the new level.

17 Jun 2002
the yard/drive way has been concreted over in such a manner that all rainwater/surface water falls to the centre, which is where proposed drain is. at present after taking away crazy paving ive got a step down into the lawn area i cannot give exact dephs as concreting is not to clever ie it goes from a few inches high to 1'6"in a 90 degree manner,all lawn area water drains away into this drain.concrete is approx 4"thick,so take away rest of concrete im now 4 "lower that drain cap where does pool of water drain away?.cant add hard core to this level as height of path along house/along drive way will not allow,so i must dig down,to bottom of the pot where underground pipe meets sewer pipe.this is where the thought about using this underground pipe to drain water off top of clay surface by having a trench dug the lengh of the drive way (garden/drive way are side by side) have this filled with hard core bottom being bottom of under ground pipe,then adding more hard core on to rest of clay with a slight fall to the trench so that rain water will drain through the top soil into hardcore then seep into trench then from the trench the rain water will then enter the underground pipe then flow away into the sewer system. can this be done i can only go down i cant build up,ive got the drain but i dont know if this is the correct way of doing this. i dont know about using a trap as this will give me problems as it is adding height i need to go as low as poss to the bottom of this underground pipe would be i feel enough its only about 24"deep maybe more from the top of the drive way i understand about what you say on land drains i think that this is the same principle , is this more understandable, i wish i had a scanner lol i could draw area and show you idea instead
Tony McCormack
18 Jun 2002
You need an Interceptor Drain, as shown on the Land Drainage page, and it is essential you use a filter membrane, such as Terram 1000 to prevent the soil being washed into the drain.

The depth of this drain can be altered to suit your site conditions, but I'd strongly recommend the use of a 80mm dia pipe at the base of the drain. Also, I'd dress the top of the drain with a larger decorative gravel or cobbles, rather than cover it over with soil, but the final decision must be yours.

Connecting the Interceptor Drain to the existing sewer is a relatively easy job - you could use the existing branch junction that will have been used to connect to the now-redundant gully. A flexible-throat coupling is the simplest way of connecting flexible land drainage to clayware.

22 Jun 2002
thankyou for your help.i had alittle difficulty in understanding terminology. but i now understand the principles of land drainage. i have only a few questions much pipe do i need for an area of 22' x 8'4". how are the pipes joined together to form the herinbone pattern and how do i lay the pipes,(sewer pipe is 2' deep)do i dig down to a level surface of 18"then dig the trench`s to the deph of 2' how deep should the gravel be and how do you use the terram 1000 is it layed in 1 piece over the whole area then top soil put on top,or do you use it only around the pipes.
Tony McCormack
23 Jun 2002
how much pipe do i need for an area of 22' x 8'4"?

That's roughly 6.7 x 2.5m, so you could just lay one single strip down the centre. So, a 10m length would be more than enough.

How are the pipes joined together to form the herinbone pattern?

You don't have sufficient room to form a herringbone pattern, but, if you did, the jointing detail is given on the Land Drainage page.

how do i lay the pipes,(sewer pipe is 2' deep)do i dig down to a level surface of 18"then dig the trench`s to the deph of 2' how deep should the gravel be and how do you use the terram 1000 is it layed in 1 piece over the whole area then top soil put on top,or do you use it only around the pipes.

Again, all this is shown in the drawings on the Land Drainage page. If you intend to outfall into the sewer, then you cannot lay the perforated pipe lower than that - try as you might, water won't run uphill smiley

The Terram (or similar) is used to line the trench and kep the gravel separet from the surrounding earth.

26 Jun 2002
im totaly lost now ive been given so much different advice i dont know where to turn. somebody has said that i cant connect the 80 mm perforated drain straight to the sewer system because of the gases and that taking out the gully drain i would loose the trap is this right? also i have read on other gardening sites that land drainage should be put in when garden is in but ive only got a space of clay soil so what is the best way to put in the drains,can i buy a new gully drain with a back inlet with a trap built in ive got a catalogue frompoly pipe ,they only have these as seperate items i havent got the thought now is to have one of these and to connect the 80mm pipe into this new gully drain.thanks from a totally lost and braindead diyer
Tony McCormack
27 Jun 2002

somebody has said that i cant connect the 80 mm perforated drain straight to the sewer system because of the gases and that taking out the gully drain i would loose the trap is this right?

You can't connect directly to a Foul or Combined system without a trap, but you can connect to a surface water system. Removing the gully may well eliminate the trap, if it is a trapped gully - not all gullies are trapped.

Are you connecting to FW, to SW or to Combined?

I have read on other gardening sites that lland drainage should be put in when garden is in but iI've only got a space of clay soil so what is the best way to put in the drains

Let the gardening sites advise on planting, and leave the construction work to those with actual site experience, not some cack-handed half-baked concept of how things are actually done. Land drainage should be done BEFORE creating your garden. The best way to lay land drainage, in my opinion, and that of more or less everyone I've ever worked with, is that detailed on the land drainage pages.

can i buy a new gully drain with a back inlet with a trap built in ive got a catalogue frompoly pipe ,they only have these as seperate items i havent got the thought now is to have one of these and to connect the 80mm pipe into this new gully drain

How would this work? If the B.I.G is set higher than the land drain, how will you persuade the water to run uphill? The trap has to be at the lowest point between the perforated pipe and the sewer to which you are connecting. You could use a simple S-trap or even a P-trap laid into the line at this point, and that would prevent sewer gas and odour escaping back via the perforated pipe. Having a trap at the head or high point of a land drain system is nonsensical.
3 Jul 2002
i have purchased all that i need,back inlet bottle gully,2 risers and i have to put land drain into a trench or can i lay it on the clay surface then bury it with gravel then add top soil.also at the bottom of my yard/garden i have an inspection chamber it has an old branch leading away from which i think was from an old outside question here is that whether or not i can bury the manhole cover with soil/turf as otherwise it shall have to be raised,i wont have a problem with rodding it as i can still get acsess to it from yhe inspection chamber which is closer to the house.also what is a cheaper alternative i can use to hardcore i have priced this and its a few quid short of 30.00 a ton,the land drain i have got has holes right around the curcumference is this ok  wont water drain into the ground as opposed to draining away in the gully.
Tony McCormack
4 Jul 2002
The land drain should be laid in a trench, unless you cane ensure it will have at leat 300mm of cover.

You should never bury old MHs or ICs. You may well know where they are, but, if you came to sell the property, the new owners might not be aware of their existence.

You need to use a 10-20mm clean gravel around the perfoarted pipe. In full loads (20T) it costs around 12-15 quid per tonne, so 30 quid per tonne in agg bags would be about right.

9 Aug 2002
lawn has been down a month now and have no probs with boggy soil even with all this rain.ended up burying man hole cover. looks great im quite exclusive now by the only 1 in a very long street of terraced houses to have a garden may of even added a bit more cash to the property.
Tony McCormack
10 Aug 2002
Good to hear you got it all sorted. smiley
Forum Question Football pitch drainage - Farmfootie - 21 Jun 2002
Great site, my first visit, Im a general builder and secretary of Hannakins Farm Football club in Billericay Essex.

We have a football pitch which runs adjacent to a stream but gets boggy when wet in its lowest area, 1/5th of its total area. One of our committee members had a landscaper look at it and he proposed a perforated pipe drainage network, discharging into the stream. the overall network consists of 300m of pipe, laid in what I think you call a herringbone pattern. His sketch implies that the pipes are the same size throughout. Our problem a the club is that we cant afford his or the other quote that we have had and propose doing the job ourselves. Ive printed off and read your article on drainage, but need to know some more technical detail and where I might buy materials? Im thinking along the lines of 100mm polypipe in 100m rolls.

Is normal peashingle ok and what membrane should I use. Money is tight so any cost saving advise would be helpful.
Thank you

forum answer Tony McCormack - 21 Jun 2002
You can use 80mm dia or 100mm dia perforated polypipe, which should cost no more than 1 quid per linear metre from a BM, or half that from a proper Civils or Drainage Merchant such as Cooper Clarke or WT Burdens.

For gravel surround, use whatever is available locally at a reasonable price. A10 pipe bedding is OK or any clean (ie, no fines) gravel that is 10mm or above, up to around 30mm maximum.

For a separation membrane, you can't beat Terram 1000 which you can buy via Greenham Trading or some of the larger BMs, or even online from the Terram Website for under 1 quid per m².

Careful consideration is needed for the outfall, and to the sequence of works. You need to minimise disruption to the un-excavated sections of the field, or you'll be playing all your matches 'away' next season. Use decking sheets or similar to keep the site clean and to prevent the mini-excavator from chewing up the pitch.

It's not rocket science, but it does take some planning and thinking ahead. If you can get a local groundworker to help out, it should be a doddle.

Good luck!

22 Jun 2002
Thanks Tony
I'm off now to see what I can buy for the job locally. Should I use pipe without holes for the final section that runs 20-30 thru scrub into the stream?

Cheers Kev

Tony McCormack
22 Jun 2002
It's not essential - a solid clayware or uPVC pipe is a good idea for the outfall pipe, but you can use the perforated pipe for everything else.

While I'm thinking - it's worth checking with your local Building Control, as agents for the Water Companies, that there would not be a problem outfalling to the ditch you mentioned. Most would have no problem with such a proposal, but they sometimes have an Outfall Detail that they prefer such schemes to use. This usually involves 'dressing' the outfall with a bit of rock or summat to make it look 'decent' and not just a pipe sticking out of a bank. smiley

Forum Question Manhole cover heights - Darren M - 24 Jun 2002
Are there any regs regarding the height of a manhole cover above a drain ? I need to lower a ridiculously raised manhole for my block drive project . Common sense tells me to check splash etc but I wondered if there were any regs.

Secondly, what would be the best type of cover to incorporate blocks and allow Transit to drive over it ? Thanks.

forum answer Tony McCormack - 25 Jun 2002
There are no specific regulations governing minimum height of a manhole cover over a chamber, but there are regulations covering maximum. Basically, as long as the cover isn't obstructing the channel, I would guess it's ok.

The best type of cover to use on a block paving project is a Recess Tray Cover - there's a page on the site that describes their installation.

Forum Question Sunken garden and pond - Simon B - 3 Jul 2002
I have taken it upon myself to excavate a sunken garden and pond (remember Blue Peter garden??) in my townhouse garden - and I am a novice at these things (too ambitious maybe!). The area is in the centre of the garden and away from the house. I have dug a trench around the area to be paved to build a retaining wall but I am a little unsure wether i should incorporate an element of drainage (maybe a gulley all around the area to hold standing water ?) How would you tackle this situation and would you incorporate some kind of land drain??

I would very much appreciate your help

forum answer Tony McCormack - 4 Jul 2002
With a sunken garden, unless you're on very free-draining ground, you need some sort of drainage at the lowest point to prevent it flooding. This drainage will need to be connected to the SW system, a ditch/stream, or to a reliable, working soakaway.

However, with a pond within the sunken garden, then the drainage point should be an overflow system, that prevents the water in the pond rising above a certain level. Again, you need to consider the outfall point.

Is the pond at the lowest point within the sunken garden, or is it, effectively, a raised pond in a sunken garden?

Simon B
4 Jul 2002
Thanks for responding so quickly. The pond is sunken within the sunken area.
I am thinking of making a gulley around the sunken area which would be filled with shingle/hardcore. I agree with you about a drain away/ overflow from the pond and I could install an overflow pipe out to the gulley area
The soil is heavy (clay-ish) but from last two days downpours it didn't seem to be retaining water (even in the lowest part of the pond)

I welcome your thoughts and advice

Tony McCormack
4 Jul 2002
Would the base of this gravel-filled gully be lower than the the base of the sunken garden, though?
Simon B
4 Jul 2002
Yes, the gulley will be as deep as the centre of the pond although it will be fill with shingle. the gulley also forms part of a trench for the laying of foundation for the retaining wall
Tony McCormack
5 Jul 2002
So where will this gully drain to?
Simon B
5 Jul 2002
I was hoping just into the ground - is that a bad idea?
Tony McCormack
5 Jul 2002
Mmmm...depends on the porosity of the ground. I know you mentioned it's not particularly prone to flooding or waterlogging, so it should be ok.

Have you dug a trial pit to see if you can find the water table? If you can get down to, say, 500mm below the lowest point of the planned sunken garden and there's no sign of the water table, I'd take that as a good sign.

Forum Question Do Patios need drains? - Fergus Byrne - 5 Jul 2002
I am just about to start laying my slabs but I had no plans to put drainage in. It is about 30m². Do I need to put drains in or not. The only option open to me is to dig out a soakpit.
I have never seen drains in a patio around a house before that's why I felt I didn't need any.


forum answer Tony McCormack - 5 Jul 2002
Depends on the ground conditions, Fergus. If you're on heavy clay and prone to waterlogging, then drainage into the SW system is the best solution, but, if a soakaway is your only option, it will have to do.

At 30m², you need to think about where you will send the water. It all depends on the layout - a 5x6 patio, with only 5m against the open ground, could struggle to drain in heavy rain, while, at the other extreme, 18x x 2m with 18m against the garden should drain into the garden fairly simply.

Tell me what the ground is like....

Fergus Byrne
8 Jul 2002
The patio is being laid up against the footpath from the house. It is approx 7m x 4m with the seven along the edge of the footpath. The ground condition is hard and gravelly and drains well.

I am going to lay the slabs on a mix of 8x1 mix of sand and cement(the sand is builders sand), will this be ok?


Tony McCormack
9 Jul 2002
The ground sounds as though it will be OK, Fergus. Just make sure you create adequate falls with the paving to get the surface water to a free edge.
Forum Question Fixing a recess tray - David H - 8 Jul 2002
Firstly, may I congratulate all associated with this site and its excellent advice it gives. Well done.

Q. I need to remove one of two brick courses to enable me to replace a light duty manhole cover with a block paving recess tray of the same size whilst achieving the correct crossfall for my new patio. Can I bed the the new tray on concrete to achieve the correct levels rather than mortar and slate packing? The thickness of the concrete will vary between 30-60mm. I was going to use an all-in-agregate concrete mix with ply shuttering in the opening to prevent spill into the manhole. Are my proposals OK? Any advice would be gratefully received. Thanks.

forum answer Tony McCormack - 9 Jul 2002
Yep - you can use concrete, David, but it's hard work, setting up the formwork. When it's that sort of depth, we would use slate for the 'thin' end, concrete roof tiles for the mid points, and broken flags for the 'deep' end.

Spread a bed of mortar over the reduced brickwork and then place the frame. Pack each corner of the frame to bring it to 3mm below Finished Paving Level in all directions, and then pack the 'gaps' between the corners with other hard, inert material (tile, flags etc) and fill all gaps with mortar.
Haunch the outside frame flange with concrete and then place the tray. Don't fill it with bricks for 3 days, to give the mortar/concrete a chance to set.

If you still want to do it your way, I'd like to hear how you get on....with pics, if poss. smiley

David H
9 Jul 2002
Tony, thanks for the speedy response. Probably will try and go down the concrete route because I have all the materials to hand. Also, the precast concrete reducing ring is visible in the corners just below the last course of brick work - this would help me support the vertical ply shutter. Attempt to do it at the weekend and will send pictures if I don't make a complete arse of it.

Thanks Again.  David.

Forum Question Digging a soakaway in a clay garden - Mrs M - 8 Jul 2002
Yesterday we dug out a hole 7ft x 7ft x 4ft 3inches in the garden and seemed to go past the clay layer and into some grey matter, believing that going down this far will enable the water to soak away. Do you think this will be far enough?

I read your webpage last night and you said that if water does not come into the hole after 24 hours this will work and work well, nothing much has appeared even after the rain last night, only a few puddles and hopefully this will be the case.

What do you think we should fill this in with, I don't really fancy the concrete soakaway you advise in your web pages, I was thinking more like large cobbles on the bottom two thirds of the hole and pea gravel on the top third of the hole?

Where can I buy the above from at a reasonable cost, the building centres charge a fortune and the quarries only seem to want to deliver 20 tons?

Also how much cobbles/pea gravel do you think we will need taking into consideration the above sizes

Thank you
Mrs M

forum answer Tony McCormack - 9 Jul 2002
I can't say whether your trial pit is suitable as a soakaway as I can't see it. What's this 'grey matter' that you've found? Is it sandy/gravelly, or is it clayey?

Assuming it is suitable, why would you then want to fill it with cobbles and pea gravel? That only occupies the space and reduces the storage capacity of the hole. Besides, using large cobbles at the base and pea gravel at the top is a waste, as the pea-gravel will trickle down into the voids between the cobbles.

If you don't fancy the concrete ring soakaway depicted in the Drainage section, then there are PVC units that you can buy that perform a similar function, but are lightweight and easier to handle. Filling a hole with all sorts of rubble is not how modern soakaways are constructed.

Quantity wise, if you were daft enough to backfill the hole, you're looking at around 2.1m x 2.1m x 1.25m (metric is so much easier to use!) which is 5.5 m³ which, in turn, is around 10-12 tonnes of rubble/rock/hardcore.

Your cheapest source depends on where you live. I could tell you to go to Charlie Love's Quarry where you can get 10 tonnes of 'cobbles' for around 80 quid, but then, you might not live in the same village as me! wink

Forum Question Leak in Cellar - Adele - 9 Jul 2002
I have an area of pavement which needs to be re-surfaced as I have a problem with rain water leaking into the cellar. There is currently a cobbled pavement which sloops slightly towards the terrace house to a drain. The water flows very slowly to this drain, and seems to disappear before reaching the drain.

I would like to get a quote for the work which would need to be carried out. Should I replace the cobbles with new block paving or re-lay the existing cobles? Perhaps an extra drainage gully is needed? Any advice gratefully received!

I live in Levenshulme, Manchester M19. Could you help? Is there someone local you could recommend?

I have never undertaken a job like this would it be easy for me to do if I can't find a builder to do it?

forum answer Tony McCormack - 9 Jul 2002
If groundwater is leaking into your cellar, it suggests the cellar itself needs remedial work over and above whatever needs doing with the paving itself.

You say the paving is 'cobbles'. Is it really cobbles, or is it setts? I can't think of anyone over that side of Manchester that undertakes sett/cobble work, but there are umptillions of so-called Block Paving Specialists, some of whom may be able to take on this type of work.

While not being familiar with the job, I'd guess that stripping out the cobbles/setts and replacing with concrete block paving would probably work out cheaper than relaying what you have. Just how feasible it would be to DIY depends on how fit and competent you feel yourself to be, and the size of the area. DIY block laying is much easier than DIY setts/cobbles.

9 Jul 2002
I have just had an appointment with Trace Water Systems who are suggesting laying drainage pipes around the edges of the cellar to collect the water & then pump it out. Also laying a plastic floor & chip board over the existing floor.

What remedial work would you see as appropriate in the cellar?

Yes the paving could be setts, there is a lot of concrete over them. The house was built in 1900.

Here is a sketch of the house!
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Do you have any other ideas for solutions?

Tony McCormack
10 Jul 2002
I wouldn't be happy with installing a drain within the cellar - this only ameliorates the problem once the water has found its way in. A better solution would prevent the water getting in in the first place.

I'd get another builder in to have a look and see what they have to say before committing to one option or t'other. I can't say what the best option would be, without seeing the site for myself, but a cellar drain would be my last resort.

Remember that these companies are more interested in flogging their so-called solution rather than finding the best solution for your property. That's why it's important to take more than one opinion.

Forum Question Gully and Water Meter in patio - Jon - 10 Jul 2002
I am in the process of rebuillding a rather scruffy patio with block paviors. I have dug out, levelled the site and installed some kerb edging, of which more later.

My question relates to how to incorporate a small drain and small inspection cover for a water meter into the paving. Both the grid of the drain and the inspection cover are quite small - only 6" square and so would not merit the use of a recessed tray cover, even if they are available in such small sizes. The grid of the drain is currently 'housed' in a tatty piece of concrete which sits on an 8" square gully, the top of which is maybe a couple of inches proud of the dig level/ sub-grade. How do I mount/ connect the grid to the gully and fit it into the block paving?

As for the water meter its inspection cover sits on top of a plastic tube (height adjustable using a threaded wall - clever eh?) can I just put hardcore (Dpt2 is it) and sand around this or is it likely to collapse? Should it have protective concrete overcoat or concentric cylinder?

Finally, the edging kerbs I have laid are supported by concrete below and behind them, but not in front, in fact the front of the edgings stand a little proud of their footings. Does this matter and will the action of the wacker plate tend to push the sand up beneath them and unseat them?

I hope you manage to make some sense of the above - your advice would be gratefully received.

An excellent web site, by the way, packed full of useful information.

forum answer Tony McCormack - 10 Jul 2002
I'm not sure what you mean with the gully/grid problem. If it's tatty, then replace the complete unit and set it to the correct level within the paving (3-6mm below paving level). It's a nonsense to spend hundreds or thousands on block paving and then skimp on installing a new gully that costs only 30 quid.

With the water meter cover, set it to the correct height, then haunch it with concrete to hold it in place, but make sure the haunching is (thickness of paver + depth of bedding) below the top of the unit.

Finally, don't worry about the edgings. As long as they are haunched at the rear, and bedded onto concrete, they should be fine. There's absolutely no need for concrete at the front.

10 Jul 2002

Thanks for the prompt reply and for setting my mind at rest re: the edgings.

As regards the gully/grid problem closer investigation reveals that the grid should sit directly on top of the gully. Presumably, the drain was installed before my old patio went down so that when the patio was built it raised the level of the original backyard. To allow the old drain to be used the grid was elevated on what was effectively a square shaped tube of concrete bringing it level with the newly installed patio.

Is replacing the old gully the only solution? It seems a pity to break up a perfectly serviceable unit, install a new one and reconnect it to the existing drain. It's also the type of job I would prefer to leave to a professional - any idea how much this work might cost?

Another question has just occurred to me. The patio is roughly 5.6m wide x 4.3m front to back and will drain to a point midway along its width and about 1m along the shorter dimension. Initially, I had thought to feed rainwater into the drain via dished channel blocks running front to back.
It's difficult to descibe without a diagram, however, the real question is are these dished blocks necessary I have seen no mention of them on your web site and my patio may be too small to warrant their use. Secondly, I am slightly concerned that they might not fit in very well with the Regatta blocks (from Top Pave) that I am intending to use and that the dish might be a "tripping" hazard.

Tony McCormack
12 Jul 2002
The gully/grid - you can buy raising pieces for some gullies that allow the grating to be set to a higher level, but they are not available for all types. Your local BM might know. Alternatively, you can elevate the grating yourself by building a raising piece from brick or concrete flags, or even casting one in-situ as seems to have been done before.

If you did replace the gully, then I suppose the materials might come to 50 quid, and then the labour would be perhaps 100 quid for such a small job, but, if you don't mind getting your hands dirty and enjoy a bit of a dig, it really is very, very simple for you to DIY.

Dished channels look fine with block paving. They are mentioned and illustrated on the site on the Road Kerbs page and on the Draining a Pavement page, which also shows how a channel can be formed in the blocks themselves.

There's no trip hazard with these dished channels - they are specificall designed for use on pavements and as long as they are correctly laid, they are as safe as can be.

14 Jul 2002
I have managed to "raise" the mouth of the drain on which the grid sits in the manner you suggested and I think it looks OK, but then I would say that wouldn't I?

I have got the sub-base down (compacted mill waste - those wackers vibrate like hell!) and am in the process of putting the sand down ready for screeding. Of course, I now have another(!) question. I shall be using the rear wall of the house as a reference "line" laying rows of paviors parallel to it. However, there are a couple of obstacles along this wall, namely, the drain pipe and a drain for the kitchen waste. I guess I can just miss a block around the drain pipe and fill in with compacted sand or even concrete.

The kitchen waste is more of a problem as I really need a raised border around it to contain liquids. However, I can't put kerbs around it as these would interfere with the pipe coming out of the gully and into the main drain.  I can't compact the hardcore around it either for fear of fracturing the drain. Is there a standard solution or product for this problem and how should I pave around it?

Once again many thanks for the advice.

Tony McCormack
15 Jul 2002
If you omit blocks in the edge course to accommodate the drains, then patch-in with coloured grano or concrete, rather than with sand. Sand will just wash away and leave a hole in the pavement.

I can't quite visualise the problem with the KW - is the 'pipe' of which you speak the discharge pipe from the sink itself, or do you mean the pipe that connect the KW gully to the FW system? Any chance of a picture?

Assuming you mean the discharge pipe, then you could use paving bricks laid on edge on a bed of mortar, and omit the section where the pipe feeds in, then patch that up with coloured mortar or grano.

Compacting the sub-base around the gully is a delicate business. We normally use a punnel (see Tools page) but you could use a sledge hammer or even just a lump hammer to consolidate the area, a bit at a time. Once the blocks are in place, you should be able to run the wacker plate over the lot, as the sand bedding will 'cushion' the buried pipework.

Forum Question Manhole under extension - Paul Roe - 10 Jul 2002
I have to construct a manhole under a new extension.
The extension will have a solid floor.
Could someone advise me on what sort of manhole to go for, i was hoping that i could use one of the pre-fab plastic ones.
forum answer Tony McCormack - 10 Jul 2002
Your local Building Control will tell you what they are happy for you to use. Some will permit a polypropylene chamber: some want brick or concrete.

It's the cover they are normally most concerned with - you'll probably be required to fit a double-sealed airtight cover. You should discuss this with your BCO.

Forum Question Do soakaways need to be inspected? - cwatters - 13 Jul 2002
Do I need to demonstrate that soakaways will work and do they need to be inspected by the buildings inspector?

On my clay site some surface water flows down the gentle slope into a surface water drain in the road. If I build a house I'm not allowed to connect directly to the surface drain but one practical solution would be to locate soakaways so that if/when they overflow the water will continue to flow down the gravel driveway into the drain. The net impact on the drain will be zero but would the  buildings inspector put a stop to this if he spotted the scheme?

I may also need to build a cut-off drain (land/french drain) to prevent my foundations causing surface water to go nextdoor. Could consider discharging this down my driveway as well? I don't think the volumes of water involved are very large.

forum answer Tony McCormack - 14 Jul 2002
Soakaways for private properties are a bit of a grey area. I know one local authority that simply doesn't want to know about them and lets you get away with almost anything, while the neighbouring authority insists on a percolation test and inspects the pit before passing the drainage to the plot as acceptable.

In areas where soakaways are common, then the BCO is less likely to need convincing of their viability, but if you're in a clay spot, then it may be wise to seek the advice of the BCO - they're not there to make your life hell, despite what you might think, but are often a damned useful (and free) source of very good advice and often have years of experience with regard to local conditions.

In your situation, I would discuss your plans with the BCO and see what interpretaion they will put on it. Personally, I wouldn't be happy with the soakaway being designed to surcharge into the gully on the public highway, and the same goes for the interceptor drain you're considering around the foundations.

Have you done a percolation test yourself? How confident are you about the viability of the soakway? Given the push for Sustainable Urban Drainage Schemes (SUDS) in modern developments, it's well worth considering an extra large soakaway facility if you have the right conditions. It's much better for the environment than relying on a public SW system that dumps everything in the local river.

David H
15 Jul 2002
This thead was of interest to me. Last year I put in a perforated pipe land drain system to my back garden and connected it to the end of a run (rodding eye) on the surface water drain. Should I have sought permission and approval to cover up from someone? Oops?
Tony McCormack
15 Jul 2002
No, you're ok, David, because you are connecting to an existing SW system, whereas cwatters is looking at using a soakaway in place of a connection to the public SW sewer.

On new-build or extensions, the local authority may require proof of the viability of a soakaway before passing the drainage scheme as acceptable. Adding a relatively small amount of land drainage to an existing SW system is nothing to concern them. smiley

19 Jul 2002
I've done a bit more research and what I had assumed was a surface water drain is actually a pipe ditch. eg it was an open ditch that was partly covered when the road was made up. Much further down the ditch is stil open.

I've done a lot of ringing round and the local water company say they don't own it (just the seperate foul sewer in the road).

The council say they don't own it but were quite helpful. They told me that they dug out or at least cleaned out the open section of the ditch a while back. They also mentioned that I may have "Riparian" rights (rights to discharge into an adjoining stream/river). Any idea how I confirm this? I guess it's a question for a solicitor?

I've not done my own percolation test yet but the soil is a heavy clay and I've seen a soil condition report that states something like "soakaways are unlikely to work" or "not ideally suited to soakaways".  Hence my interest in discharging into this pipe/ditch. On a practical level it should be ok because that's where all the water currently goes.

I'll think I'll speak to the BCO as you suggest.

Tony McCormack
20 Jul 2002
The LA, as agent for the Water Co will be able to confirm your Riparian rights, but, from what you say, discharging into that culverted ditch would be the best way to go. The BCO might be able to offer more advice, but, if you can't get any sense from the LA about the connection rights, then I'd put in writing your intention to connect and send them a copy by recorded post.

Riparian rights are a bit of a legal minefield - not that they are always contentious, just that they can be a right abstrad to track down, just the sort of work a solicitor loves to assign to the spotty office junior and charge you 75 quid per hour for the privilege. sulk

You'll get more sense from the BCO or the Tech Services Dept than you will from a solicitor!

20 Jul 2002
Sorry to seem a bit dim but by 'LA' I assume you mean the Local Authority (eg drainage dept of county council)?
Tony McCormack
21 Jul 2002
Yes - sorry, but I sometimes forget to switch from Trade Talk to normal English . smiley

LA = Local Authority
BCO = Building Control Officer
BM = Builders Merchant
BoQ = Bill of Quantities

...I'm sure there's more! Maybe a page covering all my many acronyms is required? smiley

Forum Question Flexible land pipe - Tribs - 16 Jul 2002
I bought some perforated flexible pipe for a land drain for a waterlogged lawn. I asked the builders merchant for some branch connectors but he told me that all I would need to do is run the branch up to the main pipe and that the water would just find its way into the main pipe from the branch. I'm not too sure about this. Can anyone clarify things?
forum answer Tony McCormack - 17 Jul 2002
The BM is basically right, although you can make your own branch junctions as shown on the Land Drainage page, or, if you're really keen and need to provide rodding/cctv access, you can actually but pre-formed oblique junctions from Polypipe.
17 Jul 2002
Thanks for the reply. I've just had a search around and I can't find anything on the land drainage pages about creating your own branch junctions. Could you point me in the right direction?


Tony McCormack
17 Jul 2002
My mistake - the drawings to which I referred were on the old version of this site and I've never replaced them on this new version. Anyway, this is the gist of it.....

Step 1 - Cut ellipse shape out of main pipe using a sharp knife or junior hacksaw. The hole needs to be approx 80mm across the short axis and 150mm along the long axis...

cut hole in land drain

Step 2 - Make a straight vertical cut, approx 300mm long at the end of the branch pipe, ie the pipe that is being added to the system.

cut slot in branch pipe

Step 3 - Fold over the end of the branch pipe, to form taper as shown

fold over

Step 4 - Insert tapered end of branch pipe into elliptical hole in main pipe, ensuring it penetrate by about 50mm at least. Trim the hole or the tapered end to fit.
The tapered end of the branch pipe will expand to fill the hole in the main pipe. Cover with gravel to hold in place.

slot into place

....I'll have to remember to update that page as soon as I get a chance. smiley
Forum Question Main collection chamber - John Davis - 17 Jul 2002
I have a main collection chamber which collects all of the outlets for the house, near the house. The outlet runs under a new extension to another chamber (inspection?) at the bottom of the garden. We're having problems with blockages and flooding of the collection chamber. I've rodded-out the pipe between chambers. However, the inspection? chamber seems to have a constant level of water in it. When flushing through the level then rasies and discharges through an outlet which is higher than the inlet. The inlet does have a level outlet which seems to be blocked-up with silt - after a lot of prodding the situation hasn't much improved. Is this normal? Does the level outlet need unblocking? How best do I sort out?
forum answer Tony McCormack - 18 Jul 2002
It doesn't sound right, John, but without seeing it for myself, I can't say what the best approach would be.

Just confirm that you have rodded the downstream section from the permanently flooded IC, haven't you? And that's made no diff?

My first suggestion, which might not be what you want to hear, is to call in a drainage specialist to see if they can resolve the problem. As a DIY'er, you're limited in what you can acheive with rods and it might just need a blast from the jetter unit to clear the problem.

Two further Q's - have you located the next IC/MH downstream from the flooded one? And is this FW or SW?

Forum Question Pipe Bedding for Filter Drain - Chris Brand - 17 Jul 2002
In your pages on Land Drainage for Fields and Gardens, you have some great diagrams showing what goes into the trench, but I can't find a description of the bottom layer - "Pipe Bedding". What kind of material is this?
forum answer Tony McCormack - 18 Jul 2002
It's usually a 20-5mm clean gravel, but, as different gravels are sold throughout the UK/RoI, the actual spec varies from region to region. Use whatever is reasonably priced in your area - as long as it's in the 20-5mm grading envelope (eg, a 10mm or a 15-8mm would be OK), and it's 'clean' (ie: no fines) it will do.
Forum Question Linear Drains, are they easy? - Old Dog - 18 Jul 2002
I'm just starting to dig up our old patio as I'm building a conservatory. At the moment we have no drainage at all at the back of the house and the existing concrete path is literally just one brick below the dpc. The back faces North and is always damp and wet in winter and so I thought now would be a good time to sort out the levels and drains.

I am thinking of laying linear drains right around the conservatory and along the back of the house and then joining to a manhole we have at the side of the house. They seem like a great idea and would give all the drainage we would need but I'm not sure how difficult they are to lay.

Does anyone have any comments or suggestions. I was hoping to start at one side of the thouse and have a fall around the conservatory and to the other side of the house to a gulley that matches the linear drains then use a normal pipe to join to the existing drain. Is it possible to go around corners with these type of drains? I can't seem to find info about it in the literature and wondered if anyone had any experiences or tips.

Thanks for any advice

forum answer Tony McCormack - 18 Jul 2002
Linear drains are a doddle to lay. All you need is a spade for the digging and concrete mixing, a trowel for levelling out the bedding, and a spirit level to check the falls.

Corners can be mitred, as shown on the Linear Drain page, although some of the more expensive makes offer angle/corner units ex-stock.

Take your time, and just ask here if you have any other queries. smiley

Old Dog
18 Jul 2002
Thanks a lot

I really must congratulate you on a brilliant site.

Forum Question Landscaping a slope - Vincente - 18 Jul 2002
Tony, Good Luck!
I have cut into the down gradient at the top of the garden for landscaping, which has lead to percolation of water looking for a route down the slope (heavy clay).
Could I install the 80mm perforated pipe at the appropriate depth to deal with that water, and then further down the garden, bury the pipe a few inches below the surface all the way down to the outfall (which will be the rainwater gulley)?
Would that have the effect of collecting the water and then as it makes its way down the pipe, soak into the dryer areas down the garden.
I am pretty sure it is my landscaping that has made the problem worse and if it had been left, the excess water would have drained away without the need for the land drainage.
Please, also I am remaking a sunken pond at the top of the garden, near where the water is showing. Before, I made a bit of a feature of allowing the ground water to trickle into the pond. The water brings the fine clay with it and clogs up the pond. That's why I am remaking the pond. Would there be any other issues as the shallow dug land drain will be passing the pond. Lower, of course, than the brim of the pond?
forum answer Tony McCormack - 20 Jul 2002
A perforated land drain will 're-distribute' the groundwater, Vince, but it's not as effective as you might be tempted to think. It's far more efficient at collecting excess than irrigating, but it will work to some extent. It's imperative that you keep a connection to a proper outfall, such as the gully you mentions, as, when it's really wet, the 'drier area' might not be all that thirsty!

To cut down on the amount of clays and silts washed out by the land drainage, use a separation membrane - Terram 1000 is fine - as this will filter out the smaller particles. In a year or so, as the ground settles after all your recent landscaping work, there will be much less clay/silt being carried by the system, so your pond should clear.

Vincente - 21 Jul 2002 1) Can I assume then, that water collected in the pipe has more of a tendency to pass down it to the outfall, than pass out to the "drier" areas and cause saturation locally?

2) How would I overcome the problem of a terrace of two steps deep when running the pipe. would it be acceptable to have a short vertical run down the terrace (in the corner hidden with bushes). If I tried to maintain the run, I think I would be digging down about 6 feet. Not an option!

3) I had been trying to get my LA to take responsibility for this water for the last 2 years. There is a park across the back (higher elevation) and I know the surface water drainage system is not working properly. They had CCTV in the drains and reckoned tree roots had blocked them. They backed off though, saying that there will always be ground water to some degree. Tony, I was wondering how you have found LA's attitude to this sort of thing. I can't chase them anymore now. I've got to finish this garden!

Regards Vince........................

Tony McCormack
21 Jul 2002
1 - water will always take the path of least resistance, which is, usually, an outfall to the sewers system rather than absorption by the surrounding ground.

2 - rather than a short vertical run, try to 'ease' the level change a couple of metres either side of the steps. So, from the vevel of the drain 2 metres from the steps on the uphill side, dig your trench to the required level at a point  2 metres downhill from the steps - do you understand that, or do you want a quick sketch?

3 - LAs are a law unto themselves and, if you get stroppy, they can always get stroppier still. If you could show, without a doubt, that the Park was draining into your property and causing damage, then you could compel the LA to install an interceptor drain at the boundary. However, they are right when they say that there will always be some groundwater, and it's only in cases where you can prove that some change they have made to the park, such as surfacing or digging out tree stumps, has caused a worsening of the problem on your property that you would have a viable case.

It's always a more productive policy to be as nice as ninepence to the LA. They can be very, very helpful and save you a small fortune, as long as you handle them correctly. If you can make a reasonable case for them to install an interceptpor drain, 9 out of 10 LAs would do so, but, if you start stamping your feet and threatening this, that and the other, they'll just drag the whole thing out for years.

Forum Question Planting near drains - Max Ali - 19 Jul 2002
Hi Tony,

I want to plant a climbing hydrangea on my north facing house wall. This is near gulleys/pipework which takes waste away from the house. Can you tell me if I will affect any of the drains/pipes by planting nearby. I had them all renewed about 2 years ago in plastic by a reputable local building company (who have been around for 80 years).

Thanks very much

forum answer Tony McCormack - 20 Jul 2002
Hydrangea are real water lovers (Hydra-ngea - geddit??) but the petiolaris you fancy planting isn't to aggressive and your drains should be fine.

Only a couple of weeks ago, my brother dug out a H.petiolaris that had been planted about 15 years ago at the side of a garage. It had become a bit of a bind for the owner, who is elderly and not into trimming and pruning as she once was, and was finding the H.petiolaris was interfering with the garage door.

Anyway, Our Kid hacked the bugger down and dug up the rootball and, although it had sent roots down about 500-600mm into the soil and a good metre all around, not a single one had attacked the pipework for an adjacent Rainwater Pick-up. smiley

Luvverely plants, too. I put one in on my N-Facing front wall a couple of years back. The only trouble is that Earwigs love to nibble the newly-emerged leaves, so it's worth setting a few earwig traps.

Max Ali
22 Jul 2002
Thanks very much Tony. One final question is re:the ariel roots on a hyrdangea. I had an ivy on the back wall and when I removed it, it left a lot of the old "roots" stuck to the wall. I have been advised to leave these and let the elements remove them over the years. I am concerned that the hydangea will give me the same problem and may also damage the mortar/bricks. Did your brother find lots of old ariel roots stuck to the wall when he removed the hydrangea? Also I have half tiled walls so I'm not sure if the tiles could be lifted by this plant.

Thanks for your help.

Tony McCormack
22 Jul 2002
There are some aerial roots, but they are quite fine and nowhere near as bad as those usually found with Ivy. Maybe it was because the brickwork was so hard (Accrington Stock Bricks) but Our Kid says that what few roots were left behind came off quite easily when scrubbed with the wire brush.
1 Aug 2002
Just a footnote..... When I started to prepare the ground for my block-paved path, the first unexpected thing I found was that a hydrangea petiolaris was well established with its root system nearly 3 metres down a rain pipe. I shall never know whether the monkeys who laid the original Hepsleve 10 years ago cracked it in their final tamping, and the plant seized the opportunity for better boozing, or it actually insinuated itself, root tendril by root tendril between a joint. Anyway the pipe itself ended up being cracked open, so in situ replacement was the order of the day. Not quite what I expected, so I didn't have the presence of mind to photograph the long and substantial root beard I pulled out. But this shot shows the relative positions of the pipe and plant, post repair.\petio.jpg
- Mike -

Max Ali
5 Aug 2002
Thanks very much Mike. I just had my plant delivered this weekend but didn't get a chance to plant it due to other commitments. It's quite a mature plant and expensive as a result.  I am a bit concerned to hear what you've written but I think I will risk it now. A couple of people I have spoken to have said it will be alright as long as the new pipes were laid correctly. I trust the company who did the job to have done this. Thanks for your feedback.
Forum Question Channelling water from a spring - Jan - 22 Jul 2002
I have a spring in the garden which is waterlogging what used to be my grass.  I want to channel it to make a stream further down the garden. I intend to lay a perforated pipe in 20mm shingle encased in Terram to take the water to the head of the stream.  At the end of the stream I will make a catch pit and then lay an overflow pipe to take excess water on to another drainage ditch at the bottom of the garden.

>question 1: What is the best way of channelling the water from the spring into the pipe - should I dig a pit at the site of the spring?
>question 2: If I use perforated pipe will I lose as much water as I collect on the way down to the stream?

This is a fantastic web site site Tony!

forum answer Tony McCormack - 23 Jul 2002
1 - depends on the nature and situation of the spring. A small pit just below the level of the spring would be one way, or you could simply sink in a hopper and rest bend and connect that to the pipe that delivers the water to the head of your planned stream.

2 - Using a perforated pipe depends on the nature of the ground (how porous and thirsty it is) and the amount of water emanating from the spring. If you think you might lose a significant volume of water between the spring and the stream head, then use a solid pipe rather than a perforated one.

I'm glad you like the web site. smiley

3 Aug 2002
I have tried to dig below the site of the spring but it's coming up from the ground and as fast as I dig it fills with water so I'll call it a day and fill it with shingle now and lay my pipe into the middle of the pit.

At present the water from the spring drains haphazardly across my garden  as well as down an open ditch towards an area which I have planted with bog loving plants.  I really want to preserve this boggy area and I am concerned that by diverting the spring water to my stream I may cause the bog to dry out.

I had thought of putting a Y joint in the pipe that I'm planning to lay and putting a cap on the section of pipe that leads to the boggy area so that I can open it now and then to allow water to drain back into the bog.  (I would, I suppose, also have to cap the section that runs to the stream head when I open the bog section).

Are there any mechanisms like sluices or such that I could install so that I haven't got to go groping into the trench to remove or replace the cap?

Tony McCormack
3 Aug 2002
The 'sluice' is usually known as a "Penstock" and, while they are available, they aren't cheap and they're a bugger to install. The usual method would be to construct a chamber into which would come the water from the spring. There would be two outlets - one for normal use, ie, down your stream, and the second would lead to the bog garden. When you deemed it necessary, you could open the penstock (they are winding vertical mechanism) and allow some of the water to flow to the bog garden for half a day or so, then shut it again as required.

Seems like a lot of work, to me, but, that's the only 'cleans hands' solution I can think of. Much simpler, and much cheaper, would be to install a Y-junction (we call them 'Oblique' or 'Square') and run a pipe to emerge just above the bog garden. Put a bung/stopper in the end of the pipe (these stoppers are less than a fiver) and just release it as required. If you look at the construction of a typical stopper on the Testing Drainage page, you can see that there is a simple screw cap that cane be undone to allow water to escape, and this would be easier than releasing the entire stopper.

Of course, this second solution relies on you having adequate falls to allow the bog-feed pipe to emerge above ground level above the bog garden, or, for there to be a sufficient 'head' of water to feed it via gravity.

Forum Question Grass manhole covers? - Rob - 30 Jul 2002
Have had a quick shufti through previous posts but found no reference to this...

I have two very rusty, unsafe and unsightly 2' x 1.5' manhole covers in my lawn. Are there such things as grassy manhole covers or less obvious green plastic ones and where can I get them (and doesn't the grass die)... or any other ideas?


forum answer Tony McCormack - 30 Jul 2002
There was a fibreglass insert, sold during the late 80s/early 90s, that could be filled with soil, planted up with grass or bedding or whatever you fancied, and used to replace the standard cover on a 600x450mm Inspection Chamber.

Brilliant idea, you'd think! And it was, until some kiddie jumped up and down on top of a grass-filled unit and the fibre-glass gave way, sending the kiddie down into the chamber, scratching legs, denting pride and incensing parents.

They were withdrawn shortly after, but you can acheive more or less the same by using a steel recess tray cover, safe in the knowledge that, as they are tested and approved to carry the weight of your average family Armoured Personnel Carrier, they are more than capable of withstanding even the most determined of kids jumping up and down. smiley

Drill half a dozen 10-15mm holes in the tray, line the base with a membrane of some type (Plantex, Terram or an old pair of tights will do) fill with a sandy soil, and turf it! Fix the frame as described on the Recess Covers page, and, once it's set, just lift the tray into place and voilá. smiley

A 600x450mm galvanised recces tray and frame will cost you less than 50 quid from most BMs.

Good luck!


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