aj mccormack and son

Drainage - Page 04
The Brew Cabin


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Forum Question Drain backs up in heavy falls - Silicone Man - 8 Aug 2002
Hi Tony

Congratulations on a brilliant site.

I have been having some problems with drainage on my property. My surface water at the moment goes to a ditch 60 mts away,the problem is that the pipe (4 inch Dia ) cannot seem to take the volume when I get heavy rain, this backs up causing problems

This run of pipe also goes under neighbouring property making access difficult .
I have re-routed half of my roof water into a natural water course (not an option for surface water) and hope this will alleviate the problem . Next winter I will know for certain .

I have got a large drain in the road outside my house and I could get a fall into this, the problem is that this is a Road drain not a mains drains will I need permission from the highway agency to access it.

I cannot drain into a soak-away because of a high water table.

My only other alternative is to pump it into the garden via Tank and float pump (could I use this system for watering my garden in summer?)


forum answer Tony McCormack - 9 Aug 2002
Hi Nigel,

firstly, why does this 60m run of pipe back up? Is it silted up, or is it because the outfall is restricted or submerged during wet episodes? The pipe itself has a capacity of over 450 litres, which isn't a massive amount, but, depending on the size of the area being drained, I would expect it to offer some level of storage without surcharging.

Anyway, the option to connect to the main sewer under the road. For this, you must get permission from your Local Authority, who act as agents for the Water Company, and they will impose certain conditions, assuming they sanction the connection. These may include use of their own work force or an approved contractor, construction of a drag-out MH prior to the connection, construction of a Sewers for Adoption 4thEd. MH on the connection can all get to be quite complicated and well beyond the remit of a DIY'er. A typical connection beneath a public highway would cost something in the region of £5,000-£10,000, and considerably more if it's a busy road, or there are other factors to consider.

Your notion of pump storing the water is technically possible in most cases, but you first need to know the sort of volumes involved, and you still need some provision for overflow discharge. What we're you planning to use for storage? A pond or a tank of some form? If you consider the volumes involved in storing surface water, especially if you have a largish area, then any tank has to be HUGE.

From what you've told us so far, I reckon your best course of action is to find out why the existing pipe and outfall are not performing as they should. It might be that a good clean out with a high-pressure jet, or a bit of ditch-clearing is all that's needed.

Forum Question Draining a Riding Arena - Ian P - 10 Aug 2002
I am going to build an outdoor riding arena 45m x 25m. The arena will comprise 150mm of 40mm drainage stone and then 100mm of sand and rubber for the riding surface. I intend to put a drain around the the perimiter comprising 100m perforated pipe at a depth of 1m and more drainage stone.

Do I need a herringbone system as well across the surface of the school? If I make a mistake it will cost £,000s to fix but the additional drain will also cost a bit. This is a diy project to keep costs down. I am not an expert so can any replies be free of jargon.

forum answer Tony McCormack - 10 Aug 2002
I'd put cross-links in as well, Ian, with a maximum 10m spacing between them (or 9m for convenience). So, you;d have your perimeter, plus cross links at 9,18,27,and 36m along the long axis. This will involve and extra 100m of drainage, but it's not terribly expensive, and, as you say, it would be more expensive to try to correct it retrospectively.

If you're on heavy clay that's very slow to drain, you might want to reduce the separation between the cross-links to, say, one every 5 metres, or, even consider the use of a drainage composite layer beneath the sub-base.

Forum Question Blocked Drain - Sparky - 11 Aug 2002
The piece of clay pipe in the Photo is where the downpipe from my guttering drains into. The downpipe and guttering were completely backed up with all the rain we have had and the pipe just disappeared into the concrete path. I broke away the concrete around the downpipe and found a small piece of angled downpipe just sitting in the clay pipe you can see in the photo.

The clay pipe was completely silted up I have cleaned out as much as is possible and I have had my pressure washer on it but all to no avail - water does not even begin to drain away (I think it is a P-trap) In Cambridgeshire we get a lot of Lichen growing on the roofs and it has had 35 years of this.


I have dug down in the flower bed the other side of the path and found the clay pipe on the way to the soakaway.

I am now wondering whether to cut into this pipe and try rodding it back towards the P-trap so as to avoid damaging the concrete path.(There is no rodding eye anywhere)

My questions are is this the best option if so what do I need to ask for in the BM to rejoin the clay pipe (the inside diameter of the pipe is 3 inches and the widest point of the pipe you can see in the photo is 6 inches)

When I have it cleaned out I would like to fit a hopper will I be able to get a modern plastic one to fit into the imperial clay pipe?

forum answer Tony McCormack - 11 Aug 2002
You need to establish that the pipe from this P-trap is serviceable, so, I reckon you're going to have to break into it somewhere, and that might as well be where you've got it exposed under the flower bed.

Rod upstream and downstream to ensure the pipeline itself is not blocked or silted-up. Flush a bucket of water down the P-trap and see if it emerges at the 'break' as a trickle or as a full flow. If the P-trap is silted-up, you might be able to unclog it with the pressure washer now that you have an open point nearer to the unit itself. However, if the P-trap remained steadfastly blocked, then your only option is to break it out and replace with new.

Turning to the rest of the pipeline, you need to make sure it's running clear. The pressure washer will help for the first couple of metres, but what's really needed is a jetting unit, which you'd need to hire in.

The final link in this particular drainage chain is the soakaway itself. Old soakaways have a limited lifespan and they eventually silt up to such an extent that they cease to function. That may be the problem with yours. Only by sending water down the pipeline into the soakaway can you determine whether it's functioning, and, if it is, just how well it's functioning, in terms of litres per hour.
It may be that a new, modern soakaway is required, which means finding a suitable site on your land, digging the pit and installing the soakaway before diverting the existing pipework, but let's take one step at a time, and determine just what is the problem with the existing set-up.

When it comes to re-joining the system where you broke in, then most BMs carry a selection of adaptor couplings that will enable you to piece-in a new section as required. If, for example, you were connecting from the old 4" salt-glazed to a new length of 110mm uPVC, the BM will have a coupling to suit.

Sparky - 21 Aug 2002 As promised I thought I would let you know how I got on

I broke into the pipe with a large angle grinder and rodded back to the P trap but it was still solid

So there was only one option left to dig a channel across the path about eight inches wide to the P trap I hired a small breaker for the job and this soon made light work of the path as it was only about three inches thick - in the path there was some steel reinforcing under the path was just rubble and soil

I cut the reinforcing out of the way and got down to the pipe which when I removed was full of  of concrete and causing silt to back up I guess there since the building was new I replaced with a piece of new pipe after testing the soakaway and now it is working well

I am a little worried about my channel across to my P trap as I believe the house is built on a raft foundation and the reinforcing mesh appears to disappear under the house I haven't dug under the house in any way but I am wondering how to go about reinstating my channel - should I get the reinforcing bar welded back in and then lay my concrete or is such a small area of reinforcing bar missing not a problem and just lay my concrete - is this area known as the apron of the raft ?

Also if you could give me an idea as to what a raft is all about in terms of construction it would be appreciated

Many thanks once again for all your help

Tony McCormack
22 Aug 2002
This reinforcing steel mesh - is it part of the path concrete or is it part of the raft itself? I'm not quite clear. I doubt it's part of the raft, if it's exposed, as just having rebar steel exposed to the elements (even underground ) does far more harm than the good brought about by having steel within the concrete in the first place. Great care is taken during construction to ensure all rebar is totally encased within the concrete, by at least 50mm.

That's why I ask for clarification - I suspect that, if this steel is NOT part of the path reinforcement, it may just be a bit of 'scrap' steel chucked in the backfill once the raft was constructed.

Anyway, a raft is basically a big concrete slab that spreads the load of a structure over a larger area. They are common in areas with bad ground or where mining is known, hence we get a lot of them here, in what was the Lancashire coalfield. Cutting into the raft is not an easy task, and is something that should be avoided at all costs - this also makes me think that what you've found is not part of the raft.

A raft apron is an access structure, put in place to aid working, but not an essential part of the structure. they are wasteful and rarely used, although some architects use them as 'add-ons for larger rafts when they want to provide for later lightweight buildings, such as a conservatory.

Can you get another photo?

Sparky concrete raft
Tony McCormack
22 Aug 2002
Thanks for the photo....

It's a bit hard to tell but I reckon that just might be rebar from the raft. Best to play it safe and concrete it all in. You can create a joint on the building line, if necessary, and then everything around the gully up to the joint should be concreted - solid concrete, and a reasonable mix such as a C20 equivalent.

On the other side of the joint, where it's just path, you can backfill with decent hardcore or sub-base material, and then lay 100mm thickness of concrete over a small piece of damp proof membrane.

It's really important to ensure you get that steel totally encased once again, otherwise air and water will start to corrode it and then it will start spalling the concrete...I'm not saying the house is in any danger, but it's best to get that steel covered and protected.

If you need any further explanation, or a drawing or concrete 'recipe', just ask.  smiley

24 Aug 2002
Thanks for that Tony

I've had a look at the concrete page and I'm OK with the recipe for a C20 mix

Thanks again smiley

Forum Question Water under floorboards - atkinben - 11 Sep 2002
Whilst having the flooring up in our dining room we found to our horror when it rained that water came up in the room in the corner near the front wall.Outside the house is a concrete drive with a strip about 1ft wide running the width of the house and then different concrete for the rest. We think surface water is being wicked down the join and emerging under the floor. Also the driveway although below the DPC is only one bricks depth.

What should we do, digging the whole lot up seems a good idea, but then what and who by? Also could a clogged up soakaway be involved? The house is 1930's with extensions.

forum answer Tony McCormack - 12 Sep 2002
Water hanging on the sub-floor can be caused by many different things, and without seeing the property, it simply isn't possible for me to say what the cause may be. You could be right that the water is being carried in by porous brickwork or this 'different' concrete that you mention, but I can't say one way or t'other from this side of the computer monitor.

You need a building surveyor to look at it, and then a number of simple tests can be arranged that will identify the source problem. Once that's done, a remedial plan can be prepared and costed. It might be a broken drainage pipe, or a leaking water supply pipe, and nothing to do with the driveway at all, so ther's no point throwing money at that in the hope that it will rectify the sub-floor flooding.

Maybe a local builder or drainage contractor will be able to take a 'no obligation' look for you and suggest what might be the problem, but, from experience, I'd say sourcing tests (tests to identify just where the water originates ) are what's required first and foremost.

12 Sep 2002
Thanks for replying, we have actually looked at a few options ourselves, we dug a deep hole in the garden, looking for a high water table, hosed the gutters with water for ages (and seen nothing) and then pooled water on the concrete join (when it wasn't raining) which then got water under the floor a couple of hours later. I did put red tracing dye into the water but could not detect it, maybe I didn't use enough.

We actually paid a structural/civil engineer £200 to come and look at it for us, but he seemed to have less ideas than us!! I am rather loath to go back to him or anyone else, the money goes out and we are no further on.It is hard to know who to trust.


12 Sep 2002
Is the fall on your driveway away from the house? do you have a porous border around the walls? i have had my driveway overlaid with asphalt and specified to the contractor that the water must shed away from the house,as the new layer is above the dampcourse i wanted to ensure no water lay against the walls of the house or could penetrate the surface. all seems ok,but i'm not sure if this is good practice, the new surface has no seams,so logically i dont think this should be a problem.

tony whats your views on this?


Tony McCormack
13 Sep 2002
Firstly, in reply to Rach, I'm surpised that your engineer didn't produce a written report, but then, 200 quid isn't a lot for a full and proper investigation.

Two other options spring to mind - contact your local council, who can send out an engineer to asses whether there's any health/environmental risk from the sub-floor flooding, or try your Building Society, who will have a register of approved structural engineers and will put you in touch with them.

Your attempts to identify the source of the problem are along the right track, but try using a lime-green drain tracing dye, rather than the red, as it's much easier to spot that colour.

IF, and only if, it does turn out to be a problem with the driveway, then it's pretty easy to find a solution, but identifying the source of the problem must be the priority at this stage.

And so to John - if you've had a bitmac overlay and it's higher than the dpc on your property, you are asking for trouble, and, should you come to sell the property, a good surveyor will spot this immediately and you could be faced with the prospect of either dropping your asking price or forking out for remedial work.

Even if the new surfacing does fall away from the walls, there is still a damp bridge above the dpc and that is, structurally, a serious issue. Actually, I'm surprised that any surfacing company (that should be any reputable surfacing company ) agreed to lay bitmac in such a way. We would never have done it, not even with a written disclaimer from yourself, and I can't think of any local surfacing co's that would have agreed.

13 Sep 2002
Hi tony,it was a cost saving decision made by myself, otherwise excavating the existing surface would have added about 2 grand to the bill! the new surface is now about 20mm above the damp course.

the only other cheap alternative was to make a border around the walls and fill this in with chips, but i felt that it would be better having tarmac right up to the walls than have water soaking down to the founds. do you think i should make this border, or keep things as they are? what can happen if the damp course is below the finished level of tarmac? i can understand if i had a chipped driveway with the damp coarse below the chips, but with tarmac i wont have the problem of water lying in below the surface?

Tony McCormack
13 Sep 2002
Have a look at the relatively new page on damp courses: that gives a few possible solutions.

If your surfacing is above dpc, then you are inviting all sorts of problems with rising damp, possibly compromising the brickwork itself. It doesn't matter that the fall is away from the wall, the dpc itself is bridged and there is an easy-way-in for damp. sulk

Forum Question Leaking drain (salt glaze) - Strad - 15 Sep 2002
I am replacing part of an existing drain built about 1970 in saltglaze pipe, this will run under a new extension.

With 1 metre head, the leakage from the old drain section was about 6 times allowed on Test. So I replaced another 3m of the saltglaze hoping to eliminate the worst joins...but the remaining section still leaks (at proportionately slower rate). Each joint seems to have some leakage with a 1m head. What I need is Radweld for drains! The pipe itself is fine, most of the joint is OK, but it well - leaks.  Apart from getting it lined at £50/metre, is there a cheaper alternative; I can't replace too much more without vast concrete breaking etc.

forum answer Tony McCormack - 16 Sep 2002
What diameter is the pipe that's leaking?

There is no 'Radweld' for pipes - you either line them, which is just not practical on the vast majority of small residential jobs, or you replace the lot.

In fact, it's often easier, quicker and cheaper to replace the lot rather than waste time, materials and effort trying to patch knackered gaskin joints.

16 Sep 2002
Tony McCormack
17 Sep 2002
Mmmm. Sometimes, you can get a 110mm placky pipe and use that as an insert, but it's not possible with a 4" pipe. Bummer - looks like a re-lay job!
17 Sep 2002
Thanks for your comments and a very useful site indeed. Just finished relaying all the run I can get to readily. Probaly one or two old joints remain, embedded in concrete, but it tests out ok.
Forum Question Cellar flooding - Clive F - Jan 11th 2001
We have a problem with the cellar flooding intermittently. I know the cause, and I am seeking some advice about what we can do about it. Firstly I'll describe the situation.

The house is Victorian, detached and contains 4 flats. All the foul pipes from the flats route into the cellar where there is an inspection chamber, and from there the pipe goes out under the front of the house towards the street. There is an unsealed cast iron cover over the chamber in the concrete cellar floor. The problem is that every 3 or 4 years the pipe leading from the chamber out to the main sewer backs up, causing the cellar to flood via the loose inspection cover. If we spot it quickly there might only be inch or so of water, but one time it wasn't noticed for a few days and we ended up with about a foot deep of dirty water. It's not a disaster, as the cellar is used for storage and we have learnt not to put anything that might be damaged directly on the floor, but clearing up afterwards is unpleasant to say the least and I would like to stop it happening.

The obvious first question would be to ask why the pipe gets blocked. I was told by one of the drain clearance operators who came to jet it out once that the pipe is of unusually small diameter and it's probably unavoidable. I don't know the diameter, but if he's correct then clearly one option would be to excavate and lay a new pipe of the proper size. However, I suspect this would cost many thousands and I think we would take the view that it's much cheaper to get it jetted out every once in a while, even if it does flood.

I have read about double sealed inspection covers, and it seems to me this should be a way of stopping the cellar flooding. It should also stop the musty damp smell that is usually present in the cellar. However, I have a major doubt about fitting one; if we did so, wouldn't it just move the problem so that the first warning of blockage would be the ground floor flat flooding (not my flat, but still...)? If somewhere's going to flood, it's far better if it's the cellar. I suppose what I am asking is, is there a way we could get a prompt warning of the blockage occurring so that someone can call the drain clearance contractors before there's any flooding anywhere? Is it legal to fit some kind of overflow pipe, or something like that?

forum answer Tony McCormack - 17 Sep 2002
Mmmmm...I can think of one simple way to create a 'containment and alarm' system, but just how feasible it is depends on the exact layout of your system and the cellar.

Anyway, the gist of it is to raise the level of the existing IC cover, by building up with 225mm brickwork, giving, say, 1200mm of extra height to the chamber. Top this with a sealed cover, to protect the property from smells and gases, and have a float switch fitted at, say, +750mm, so that if/when the effluent starts to back up, then it will trip the float switch some time before it reaches a critical level, and you can take some action, hopefully, to minimise the risks.

An emergency overflow would be great, if you had somewhere to overflow to, but, other than the floor of the cellar, there doesn't seem to be anywhere else.

It's worth getting a drainage contractor to price a re-construction of the existing narrow drain - it might not be as scarey as you think, and at least you'd know what sort of money was involved rather than guessing.

Personally, I'd always recommend a permanent solution rather than a stop-gap, but, if that's not possible, then the 'early warning system' described above might be your best option.

Clive F
17 Sep 2002
Tony, thanks for your ideas.  Your "containment and alarm system" would be feasible, though not necessarily the most convenient.  But I like the idea of an overflow, because it would a low-tech, passively reliable solution.  It should in fact be possible because the cellar ceiling is slightly above ground level and an overflow pipe could discharge out of the front of the house.  The effluent would run across the forecourt, across the pavement and into the gutter.  I'm slightly suprised this would be permissible - even if it wasn't discharging, it would be an open vent to the foul system at ground level.  But if it is allowed, which you seem to imply, what would be the best way of doing it?  It strikes me the cheapest and easiest way would be to put a T piece at the bottom of one of the soil stacks before it disappears into the cellar floor (about 1.5m below ground level) and then run a pipe up to ground level out of the front wall.  Would that be OK?
Tony McCormack
18 Sep 2002
There seems to be a misunderstanding - you cannot discharge sewage into an open environment. Any overflow system you install must divert the sewage effluent to another sewer, not to the open air, not to run across a pavement. This is why I stated that an overflow system is fine as long as you have somewhere for it to overflow to, ie, an alternative, unblocked sewer. The only alternative is to flood the cellar floor, which is what currently happens, if I understand your first post correctly.
Clive F
18 Sep 2002
Yes, sorry, I didn't realise you meant a sewer when you said "somewhere to overflow to"... and I was surprised by what I thought you meant! But now I see there are just two alternatives - lay a new pipe, or rig up some kind of containment system in the cellar.  Thanks, that's been most helpful.
Forum Question Old Inspection Chamber - Steve W - 22 Sep 2002
I am in the process of digging foundations for a new extension.

We have encountered an old brick inspection chamber about 3 foot square that serves both my and the neighbours foul water.

The edge of the chamber would be about 2 inches into the foundation walling.

Will I have to replace the old chamber or is there a cunning plan you may be aware of, any suggestions would be gratefully accepted.

Thanks for an excellent website by the way.

Steve W

forum answer Tony McCormack - 22 Sep 2002
There's 2 options, as I see it. You either build the chamber brickwork into the foundation walling, assuming your BCO agrees, or, possibly, he/she allows you to 'nobble' the chamber brickwork to accommodate the new wall.

The second option is to replace the IC with a new camber, possibly a Polypropylene model.

Most BCOs are reasonable bods, and will try to find the easiest, least costly solution, but without seeing the set-up for myself, I can't say which would be best. If you are having additional drainage installed, the new IC might be a better option, as it would allow you to have all your new connections without having to break into existing pipelines, or create junctions, rodding eyes, etc.

Have you discussed this with the BCO?

Forum Question Connecting clayware to plastic - Toplambs - 22 Sep 2002
I have a square section yard gulley for draining the garden which has an integral bend. Looks like a cross between the yard gulley and p trap & hopper shown on the drainage page. It was probably fitted in 1940's when the house was built and it is now cracked and I intend to replace it before starting block paving.

It is connected to a clayware pipe with a mortar joint. Can someone tell me:
a) the best way to remove the fitting and mortar joint without cracking the clayware pipe.
b) the best way to connect a replacement plastic fitting to the clayware pipe.


forum answer Tony McCormack - 22 Sep 2002
Use a nangle grinder or cut-off saw to cut through the pipe downstream of the collar where you want to make the new connection. This will leave you with a clean 4" diameter clay pipe without the female collar. Next, you need an adaptor coupling  - these are readily available from the better BMs and Civils Merchants. You'll need to tell them that you;re connecting old, imperial, slatglaze clayware to new 110mm uPVC and they'll sell you the right part at a silly price (about a fiver! )

There are 'adjustable' couplings, that use something akin to giant Jubilee Clips to form a tight seal at both ends of the coupling, but these are even pricier and are normally used on larger jobs. For a simple gully connection, one of the adaptor couplings will be fine.

Forum Question Soakaways on a small site - Bob H Campbell - 25 Sep 2002
First I must say that this is an excellent web site.
I have planning approval for a 100m² self build house project. I am looking for any advice about soakaways. Most of what I need has already been said in this site but there may be some extra titbits.

Without effective soakaways I suppose that my plot is not viable; I have been informed that I cannot discharge into the public sewer but I wonder if this is negotiable?

Initially I wish to dig a trial pit and wonder if it would be possible to use an engine driven post auger rather than break my back digging a 1.2 metre deep hole.
The location for my soakaways lies about 150mm above the ground level of the new house. Am I right to assume that this means I shall have to dig my soakaways deeper or will it present other problem?

forum answer Tony McCormack - 26 Sep 2002
Hi Bob,

taking your Q's one at a time....

negotiable storm sewers - depends on your local authority. Have you spoken to them face-to-face?

There is a definite move away from allowing storm/surface water to be discharged into sewers, especially into combined or foul sewers nowadays. All part of what is known as SUDS - Sustainable Urban Drainage Sytems - which is intended to reduce loads in the sewers and the ETWs, as well as the rivers that eventually carry everything. That's why soakaways are becoming almost mandatory, in suitable areas.
But there's no harm in asking! smiley

2 - You can dig your trial pit with owt you fancy. My personal favourite is a 360degree tracked excavator, or, failing that, a JCB Sitemaster, but you can use an auger if you wish. They're great fun, until they snap your wrists!

Finally, how can a soakaway be higher than your floor level? The depth of the soakaway is determined by the formula shown on the Soakaways page, and so you need to calculate roof and paved area, add around 20-40% for safety, determine depth of water table (if applicable ) and then determnine how deep and how wide your soakaway needs to be.

Have you seen the D-rain Tanks? They're a cracking idea for you self-builders!

Bob H Campbell
26 Sep 2002
1Thanks for your reply Tony

Just one question this time. What is a D-rain tank and where do I find info?

Tony McCormack
26 Sep 2002
They're distributed by Hoofmark - see link on Drainage Links page.

I'll add a pic of them to the Soakaways page.

Forum Question Damp course - Heavyweight - 29 Sep 2002
I'm having problems sorting out a new surface for my driveway - my pipes are not very deep at all .

My question is if I concreted my driveway it would mean going to within a couple of inches of the DPC - obviously not acceptable - can I get round this by leaving a gap between the concrete drive and the bungalow wall - if yes how big a gap would I need?

The drive runs down hill and away from the bungalow so any water should disperse quickly.

Thanks Hev

forum answer Tony McCormack - 30 Sep 2002
Have a look at the DPC page - it has a few possible solutions to this problem, and it's easier looking at the drawings than trying to figure out what I mean in along drawn-out text. smiley

Post back to this thread if you've any further questions.

30 Sep 2002
Thanks Tony.

As you say the illustrations are easier to follow than text
I guess as long as I am min 200mm away from the wall and 150mm below DPC things should be OK the drive falls downwards to a drain at the end of the bungalow so all the water should run down to the drain - the drain being 5 courses of bricks below DPC.

Question. (there had to be a question!)
Would you suggest lining the bottom of the gully with slabs for the water to run down hill or would you just use some decorative shingle to enhance the look ? the fall of the gully would be something like 5 bricks depth over a distance of 30mtrs approx.

Thanks again Tony - I'm sure you have saved people loads of expense time and effort with this site - keep it up - it's very much appreciated


Tony McCormack
30 Sep 2002
If this is part of your concrete driveway job mentioned elsewhere, then use the same paving blocks to line the base of the channel. The trouble with using a deco gravel in the channel is that it collects crud, it's all but impossible to clean out any litter that collects there, and you can't see the damned stuff, anyway!
Forum Question Internal Soil vent pipe - Steve W - 14 Oct 2002
Could you let me know the advantages/disadvantages of fitting an internal svp in my new extension.
I am planning on fitting two bathrooms upstairs, and I am looking for advice.

Many thanks

forum answer Tony McCormack - 14 Oct 2002
The advanateges/disadvantages depend on the site layout. Internal SVPs are more discreet and tend to be used when a bathroom/wc facility is in an awkward position, typically when not located on an external wall. External SVPs may not be the prettiest thing in the world, but, if owt goes wrong, it's a damn sight easier to gain access and to maintain. Personally, I'd go for the external pipe everytime.
Forum Question Old Soil Pipe - Dan Bevan - 14 Oct 2002
I've got a disused (I think) soil pipe that is not connected to anything apart from the drainage system below ground. At the other side of the house is a soil pipe connected to one toilet that is open to the outside at the top. Can I cut the old cast iron pipe and cap it without causing a problem to the system. What should I look out for to see that the pipe is not needed. Eventually I will remove the pipe completely when the drive is done.


forum answer Tony McCormack - 14 Oct 2002
I assume the CI pipe you're proposing to sever is the old disused pipe? If so, and if it is unused, then yes; you can cut and cap it. However, if it is acting as a vent for the FW system or downstream connections, then you'll either have to leave it in place or provide an alternative vent. The only way to check whether it's 'live' is to excavate and follow it to where it connects to the rest of the system.
Dan Bevan
14 Oct 2002
Thanks for getting back Tony, I'm pretty sure it does go straight into the system, but it's 15 ft high and does not have any pipework coming out of the house above surface, I've sealed the top with plastic to see if by doing this a problem will occur up the way and so far nothing. Does this shed any more light on it?.
Tony McCormack
14 Oct 2002
It's not just the above ground connections you need to consider; if there are any connections below ground, they may be using the soil pipe as a vent, and, if you remove the stack, you may need to provide an alternative air admittance balancing vent. Do you think the whole line is dead?
Forum Question Selected free-draining material - R Sinden - 1 Nov 2002
What is the spec. for this, please? Would 20mm washed gravel suffice?

I understand the importance of a geo-membrane to prevent the trench material getting clagged up with soil and roots etc. But what stops the top of the geo-membrane itself getting blocked with soil and thus reducing the draining capacity? I'm particularly thinking about a collector drain scenario.

forum answer Tony McCormack - 1 Nov 2002
There's no hard and fast spec for 'selected free-draining material' - basically, if the RE (Resident Engineer) says it's OK, then it's OK, and I'd hazard a guess that any 20mm clean gravel would be more than suitable. smile

SHW (Spec for Highway Works - the groundworkers' bible) states "Natural gravel, natural sand, crushed gravel, crushed rock other than argillaceous rock, cushed concrete, chalk, well-burnt colliery spoil or any combination thereof"...and then there's a load of technical stuff about grading and plasticity indices etc, but your 20mm gravel will be fine.

Just how geo-membranes work is a PhD dissertation in itself, but, the gist of it is that, because the sediments/silts/clays are not carried into the voids between the 'selected free draining material', there is less migration of non-soluble particulates and just the groundwater passes through the membrane, under hydrostatic pressure. We may find, in 20-odd years time, that the outside of the membrane does indeed become clogged, but the indications so far are that a geo-membrane extends the working life of a land drain indefinitely.

Forum Question French drain - Brush - 22 Oct 2002

I have a question about drainage in my back garden. During periods of rain, much of my garden is under water (literally). I contacted a landscape gardener, and he suggested that I install French drains to a soakaway at the back of the garden. He also suggested that before he does all of the work, he would dig the ditches and see what happened (fortunately the garden is unfinished - no lawn or anything). The soakaway/ditch at the end he dug to about 3/4 feet and hit a layer of gravel, so was hopeful that the water would drain away. However, I think that I have a problem with the water table being very close to the surface - in the last week his drains have completely filled with water.

To add to the problem, all of the water from my house and garage (large, double) drain into soakaways in the centre of the back garden. Unfortunately, there was not enough room in the front for a soakaway there for the water from the garage. Additionally, my back garden is probably 3-6 inches below my neighbours (why o why did the builders not put another couple of courses of bricks below the DPC?!). As more background, I live in the Fens in East Anglia – very VERY flat!

I have a few questions:
1.  From what I have read, I will not be able to discharge any surface water into the sewers unless they are combined drains. How do I find out if they are combined drains or just for sewerage?

2.  Would I be able to connect into the road surface water drainage to get rid of some of my surface water if the drains are just for sewerage?

3.  Between my back and the front garden is patio – all the way round the house. Piping drainage from the back to the front will therefore involve ripping it up (is not going to happen!). Could I install something along the lines of a french drainage system from the patio towards the back of the garden into the gravel area with the addition of some sort of pump attached to the highest point of the system. I was thinking of something automatic, such as with a ball and cock valve that turned on the pump if the water backed right up the drainage system. Is this just a completely far fetched idea?

Thanks for all of your help,

forum answer Tony McCormack - 22 Oct 2002
Hi Brush,

1.  From what I have read, I will not be able to discharge any surface water into the sewers unless they are combined drains.  How do I find out if they are combined drains or just for sewerage?
Mmmm. By discharging SW into a FW sewer, you are rturning it into a Combined sewer. Your LA, as agent for the water authority, may not be best pleased with this, as it increases the load on the Effluent Treatment Works, but then again, they might accept it if there is no viable alternative. You will need to speak to the Tech Services Dept at your LA to ascertain their stance and to find out whether the existing swewer is Foul, Surface or Combined.

2.  Would I be able to connect into the road surface water drainage to get rid of some of my surface water if the drains are just for sewerage?
You need a permit to connect to a public sewer and your need a permit to excavate in a public highway which involves several million quids worth of insurance cover, a competence certificate, inspection fees to tyhe LA, and lots of other bureaucracy designed to ensure private householders are deterred and the job is left to the so-called professionals. Again, while this is a possible solution, you [b]must[/b] get approval from your LA first.

3  Pump and land drain option
I'm unsure how this would work. Using a float switch to activate a pump is straightforward enough, but to where would it pump? The excess water has to have somewhere to go - can you explain your layout a little more?

Paul T
27 Oct 2002
I have a similar problem to Brush, ie a waterlogged back garden (in my case thick Cheshire clay soil.) The garden slopes away from the house so the surface water is higher than the low point of the drains.

To a novice like myself a submersible dirty water pump with a float switch looks like a relatively simple option (£100 from Draper Tools). I know you have advised against pumping due to price and complexity. However, digging a relatively small sump and placing a pump at the bottom seems on the face of it easier than digging a large soakaway that probably wont work anyway due to the high water table.

I could bury the electric cable (RCD protected) and the waste hose under the lawn. The waste hose could discharge into an existing trap by the house that serves a downspout. This is a 1930s house, so it may be a combined waste system, I'll have to check.

Given your years of experience, is this a viable option, or wishful thinking? Thanks for the excellent website btw.

Tony McCormack
27 Oct 2002
What you're proposing is a small-scale version of what we call a Wet Well and Rising Main arrangement. Basically, the 'effluent' (in your case, surface water) is collected in a sump (the Wet Well) and, when a pre-determined volume is present in the sump, a float switch is triggered and the excess is pumped uphill, via the Rising Main, to a convenient outfall - the trap by the house, for you.

This is a proven scenario and is used on many sites up and down the country but, there can be all sorts of problems when the system is adapted for use with a residential soakaway, and I'll just guide you through the two most commonly reported 'issues'....

1 - The pump fails. Often, the water in the sump is rich in sediment and/or clay particles and, unless a suitable pump is used, the wear and tear is such that many pumps, often those commandeered from a garden pond or waterfall, just cannot cope and burn out or silt up and burst the valves. The Dirty Water pump you mention is one of the better models, but even so,  you need to check the filtration on a regular basis.

2- Where's all this bloody water coming from?
As soon as you create an effective 'outfall' for groundwater, you initiate a re-structuring of the natural groundwater channels in the surrounding area and you can find yourself draining every other bugger's garden. Think of groundwater as a gradient - we call it hydrostatic pressure. As soon as you start pumping, you are lowering the pressure at your 'sump pump' and thereby increasing the gradient within the local area. Now, all that other groundwater that once found or forced its way via the neighbouring land to a ditch or other outfall now makes a beeline for your snazzy new invention, and the next thing you know is that the damned pump is running 24-7 and you're paying for the lecky!

This is why I urge caution when considering the installation of this type of solution. Yes: it can and does work, but, in the wrong conditions, with the wrong kit, in the wrong location, it can create more problems than it solves.

If you do go for this solution, I'd strongly recommend a generous Wet Well, something like a 1050mm diameter circular MH chamber or a 1000x750 rectangular section, and, most importantly, a silt trap/catch pit to keep the Well as clean as possible.

Ensure any land drainage sytem feeding the Well is membrane-wrapped to reduce silt/sediment, and keep the rising main well buried for frost protection. We keep water supply pipes 900mm deep, but you could get away with an absolute minimum of 300mm for a small residential Wet Well and Rising main scheme - 450mm would be better still.

Also consider the outfall point. It's better to outfall within an existing IC or MH (for frost protection) than to bring the water up to surface level and dump it into a yard gully or rainwater pick-up.

If you do go ahead with this, I'd like to hear how you get on, and what your time and material costings run out at, as it's not something I would normally suggest as a DIY job.

Good luck!

Forum Question Wet Rot in Floor - Anna - 7 Nov 2002
I sincerely hope you can help us with this. We have discovered, since buying our house a couple of years ago, that we have sufficient dampness below (and in) our suspended wooden floor to be causing wet rot. Our 1930's house lies at the bottom of a long, steep field and our boundary lies across the slope - with a field drain which is probably ineffective as it's horizontal. After having read your excellent pages on drainage we suspect our field drains are insufficient to cope.  Although we have a DPC the walls are coated to ground level with render and are also then coated with Sandtex paint.  Suspect DPC being bridged! The house is cut into the hill so there is a bare minimum of 150mm below the DPC at the back - should we dig it out more? I anticipate a few days of chipping off Sandtex and exposing the DPC from under 1 inch of render.

We want to do the work ourselves but want to know what's the best plan of attack to catch all surface and below surface water. Just how low should we go? I'm not convinced a perforated pipe at 1m in a heavy clay soil will catch surface water in a heavy storm. Your advice would be invaluable.

forum answer Tony McCormack - 8 Nov 2002
The render to ground level sounds particularly naughty and that would be one of the first things I tackled, if it were my property. I suspect that, once you've got the rendering sorted, some form of dry channel arrangement (see DPC page) might be what you need.

What you need to catch all the surface water is an interceptor drain. The depth of the pipe is immaterial - it's the fact that the granular backfill comes to the surface that makes them so effective. If this is within a paved or hard-surfaced area, then a linear drain would perform the same function, but, as with all drainage issues, bear in mind that you must have a place where  you can outfall the collected water. Do you have existing drains?

8 Nov 2002
Hi, thanks for the quick reply! We have old outbuildings with various pipes leading off who knows where and the nearest point is about 30m from the edge of the house. Husband has been trying them out with a hose and they appear to run freely, so they are our probable destination for the field water rather than our septic tank which is closer.

Thanks for the tip about the dry channel - had missed that page on your wonderful site! Would you recommend a DC and an interceptor or would the latter suffice. I am concerned about the depth of the interceptor as I don't want anything coming underneath and undoing all our good work. Would you run an interceptor all the way to the outlet, or could it just run into a drainage pipe part of the way - once it has done its job.

After further reading on your site - I was up late!- am also suspicious of the solum being too low in relation to the hill at back and allowing water to penetrate both courses of brick below the DPC. The moisture level readings from our Rentokil survey even above floor level were at 'dangerous' - so there's a distinct surplus of water getting in somewhere! How high should the solum be above ground level?

Should mention we will be increasing ventilation too!

A million thanks for your time!

Tony McCormack
8 Nov 2002
You can use drain tracing dye to help you figure out which pipe runs where, but, the general rule is that surface water is never sent to a septic tank - that would just overload the system and could present a health hazard. So, it's more likely that the SW drains go to a ditch or a soakaway somewhere - it may not even be on your property!

It's difficult for me to say what would be your best option, as I'm not familiar with the property and drainage is one of those jobs that can only be properly weighed-up when you can see the ground, and even then, there's a risky element of guesswork involved, as you never know what's buried down there. However, the purpose of an interceptor drain is to intercept surface water and groundwater in the top 300-450mm or so. If the collector pipe at the base of an interceptor drain is lower than the foundations of the house, then it must be a boon, as groundwater will be collected and diverted before it can threaten the house itself. To be honest, as long as the base of the interceptor is at least 600mm below dpc, and a couple of metres away from the house, it can only have a positive influence.

So, would I use a full-length interceptor, or switch to standard drainage? Again, it depends on site conditions. No matter which option you choose, you have to dig a trench, lay a pipe and backfill it. With standard drainage, you can cover the pipe with a sprinkling of pipe-bedding material, and then backfill the rest of the trench with the excavated spoil, whereas with an interceptor drain, you have to back fill with granular material (pipe bedding) AND get rid of all the surplus excavated material, so, from a cost point of view, a standard drain is the better option.

What's this 'solum'? I'm not sure that what I call a solum is the same as what you call a solum. The standard definition of a solum (in the construction industry, anyway) is 'a piece of ground on which a building stands'. Geologists have a slightly different definition, but it still doesn't help me understand your last paragraph. Do you mean Floor Level?

9 Nov 2002
The solum I refer to is the finished level (with tar DPM) below the suspended wooden floor. I have been searching around the net and can't get details except that it must be above ground level. Have now also discovered that Sandtex - as I suspected - causes lots of moisture problems by trapping moisture behind it, above and below DPC, which can't dry out except into the house! ....Oh joy!

Hopefully if we get this drainage right it won't be such an issue. Having weighed up everything I think this is the best starting point for tackling our problems.

Many thanks for your fab site - I have been scouting around it for measurements and spec. for the interceptor drains.  Also keen to price the Terram 1BZ(?) -non permeable on one side- as it looks like it would be easier.   Can't find anything on the net - so will trying phoning around for prices on Monday - unless you can give me a ballpark figure per m - you seem to know everything about everything!!

Thanks again - we feel able to tackle the job ourselves with confidence now we know exactly what we're doing! We're hoping to start digging soon - will let you know how it goes!

Tony McCormack
Aaaah! We call that a sub-floor, but then, it's a bit out of my field so maybe it is called a solum - I've just looked it up my Dictionary of Building (rather than my Dict Civ Eng) and it says...

The ground below the lowest floor of a building. If for any reason this is not covered with oversite concrete, it must be damp-proofed in accordance with the Building Regs., in Scotland with hot pitch or asphalt, or south of the border with thick plastic sheet covered with 50mm of fine concrete (BS 2832)

Terram 1BZ is one of those products that is priced according to quantity required. Try 'phoning Terram in Pontypool on Monday and getting a direct sale price. They may have a stockist/distributor up in your part of the world.

Good luck!

Forum Question Tracing Storm Pipes - Sue - 11 Nov 2002
Please can you help?
Have a problem with rainwater coming back up pipe, towards my property. I believe the pipe is blocked, but not on my property (know this because have had hose up there). Have had all the relevant authorities out, but no one will take responsibility.
2 Questions :
1 Who is responsible for the pipe off my property?
2 No one knows where this pipe leads to, how can I find out?
Many thanks
forum answer Tony McCormack - 11 Nov 2002
Ownership of the pipeline is difficult - it may be you, it may be the local authority or it may be you and the neighbours, ie, a common sewer. The LA should have plans of your area showing who owns what and where it goes, but I know from experience that this isn't always the case. Still; that has to be your first port of call - the Tech Services Dept at your local council.

I know you've said that you've already spoken to all relevant authorities, but until the TSD say, in writing, that the pipeline isn't their responsibility and does not appear on their records, then you [b]must[/b] pursue them.

To trace just where the pipeline goes, you have to be prepared to stump up a small fortune. You could get lucky and find it on the local plans or with the aid of drain tracing dye, or you could run up a second mortgage using CCTV and/or radio-tracking systems, both of which will be available to you via local drainage contractor.

It may be worth speaking to the survey department of your bank/building society, as they sometimes authorise investigative work and charge it against your insurance policy, and it's worth a call to your local drainage company to see what sort of money they charge for their time. You may find that the local council DLO are cheaper, but that's not always the case.

I know this doesn't offer much hope, but drains are notoriously difficult, not least because they can't be seen. The age of your property also has implications, particularly if it's pre-1936. Speak again to the council, and, if they are adamant it's not their propblem, get it in writing and ask them for a recommendation as to where to go next. They'll know who are reliable and who are the clowns in your area.

Good luck!

Forum Question Pumping out soakaway - Keith Barker - 12 Nov 2002
My back lawn is in a slight dip and has always been wet in winter. 4 years ago we had our lawn re-laid, including installing a good draining first 6 inches of topsoil, clearing out one 12 ft cube soakaway and installing another smaller one. The wetter climate now overloads this, and today I've got a lake about 20x15 ft and up to 6 inch deep. There is no-where to drain this to off the property. Could I fit a pump in the large soakaway (which has a manhole and 3 foot clearance) to pump out via a trap to the foul system? If so, what pump would you recommend? Thanks,
forum answer Tony McCormack - 12 Nov 2002
Have a look at the thread entitled "Land Drainage" started by Brush - that contains answers to your questions.

However, be wary about pumping to a FW system. Make sure it's a main sewer and NOT a septic tank or cess pit.

As for choice of pump, you need to speak to your local BM and see what they have available to suit your specific requirements in terms of flow rate, voltage etc. Just ask them what they have available in sub-floor or submersible pumps.

Forum Question Linking a soakaway to surface water pipes? - Dave Evans - 16 Nov 2002

I've recently spent a lot of time and effort installing a couple of soakaways (plus drainage channels) into my back garden that ALWAYS floods in the winter. It was going well until the latest storms where it looks like the soakaways and channels are filling up and overflowing. This is putting the garden underwater once again.

The garden slopes towards the house, and I think I've made the mistake of putting the soakaways slightly closer than the 5m I saw in another thread.

But, is it possible to lay some other kind of pipework connecting the soakaways, under the patio, to the surface water pipes coming down from the roof ?

The house is about 13 years old, and appears to have plastic pipework for both surface and soil drains (I found enough under the garden when I put the channels in !).

forum answer Tony McCormack - 16 Nov 2002
Did you test whether a soakaway would work before you went to all that trouble of installing them, Dave? If your garden floods or is waterlogged for much of the year, it's highly unlikely that a soakaway is going to work, unless you have a permeable sub-strata that can be reached by the soakaway structures.

I suspect that what you've actually built is a pair of  sumps, which is a gentler way of telling you that you've dug holes that fill up with water. You might be able to connect them to the existing SW system NOT the FW system) but I can't say how feasible that is without being familiar with your garden.

If it is possible, then consider using a silt trap before connecting up to the SW system.

Dave Evans
16 Nov 2002
I did consider the fact the the water table is so high that the soakaways would fill up, but after digging them (1.5m deep) and leaving them overnight (in September) they didn't have ANY water in them by the morning.  Would it be safe to assume that the water table must have been below that level then, and that it's almost impossible for it to raise by 1.5m just in a month ? (I'm not near any rivers).

HOWEVER, I live a a big London Clay area, and from the surface down I hit the following levels....
30cm topsoil, 30cm thick yellow clay, 10cm black vegetation, 80cm blue/brown mixture (hard to tell what it was, but I'm assuming now it is clay also).

I have a feeling that the soakaways are just not draining faster than the rain has been falling recently. It still is an improvement to how it was because the garden used to stay flooded all winter, but today (after 1.5 days of dry weather) there is not any standing water, although any rain will just flood it again.

I am convinced I can run some sort of pipework relatively easily under the patio pathing slabs, but I'm going to get stuck when I need to connect the pipework securely with the Surface water pipework coming down from the roof.

Thanks for all you good advice. Extremely good web site.

Tony McCormack
17 Nov 2002
The level of a water table fluctuates during the year, and a rise of 1.5m is nothing compared to some locations. It depends on local geo-morphology; if you're in a clay syncline, then the rise in level can be astounding, especially after a period of heavy rain.

Your plan to link to the existing SW system is technically feasible. I would build the link as an overflow from the soakaway system, then take it via a catchpit/silt trap to a convenient point on the SW system. This may need to be a new access point or IC, depending on the exact layout, but it will be possible, one way or t'other.

So, where are you stuck?

Dave Evans
17 Nov 2002

Many thanks for the advice.
I was planning the link from the soakaway as an overflow, just below the level of topsoil. I think the soakaways are working reasonably well. and this overflow is only really going to be needed during periods of heavy rain.

A couple of questions...
1)  I've not heard of a catchpit/silt trap. Could you explain?
2)  Also, what's an IC? Is is some kind of joint?

Now you've put my mind at rest that this is actually possible/feasible/sensible, then my main sticking point is the knowledge and ability to link in with the sw pipe system.
As you might have gathered, I'm not a builder or gardener by trade and I'm just picking this up as I go along. Therefore the thought of mucking about with existing underground SW pipes is a little bit daunting. If it requires any kind of specialist skills then I'm inclined to get an expert in (depending on how much he'll charge).

Fear of the unknown is therefore my main sticking point, especially when I might have to bring in an expert AFTER I've screwed up the underground pipes. smilry

Once again, thanks for all the great advice.

Tony McCormack
17 Nov 2002
Dave asked...
1)  I've not heard of a catchpit/silt trap. Could you explain?

See this page

2)  Also, what's an IC?

IC means Inspection Chamber - See this page

Post back if you need any more help.

Forum Question Downpipe Problem - Colin Woodley - 18 Nov 2002
I have a blocked downpipe from my guttering. The downpipe goes directly into the ground and I assume this is going into a soakaway. We beleive the blockage is either due to silt buildup at the base or damaged underground piping from some old trees that were recently removed.

I have had 2 contractors look at the problem and they have both suggested that we reroute the guttering to a second downpipe I have at the far end of the house. This is an old brick coal shed that was converted to a joing utility room by the previous owner. This down pipe does not go directly into the ground but sits just above the drain. I do not know if this goes to a soakaway or the waste drain which is right next to it. But would this be able to take all the water from my neigbours house, my house and the utlility room.

Another contractor has suggested taking the existing downpipe and diverting that into the sewage drain which is within 4 ft of the pipe. I want to avoid digging up my new garden if possible.

Which should I go with and should my neighbour share the costs as we share the downpipe?

forum answer Tony McCormack - 18 Nov 2002
I'd definitely connect up to the sewer you know to be functional. If you get some drain tracing dye from your local BM (it costs around a fiver) you can put a couple of tablespoons into the hopper of the 'second' downspout and see whether it turns up in the Inspection Chamber or Manhole nearest, just to confirm that it is connected to the SW system. If it turns out it links to yet another soakaway, then try running a hose at a steady flow into the hopper for about an hour - if it doesn't back-up, then the soakaway should be ok.

I really wouldn't fret about digging up the garden - this is the best time of year to do such work, as by the time time spring returns, the excxavation and construction work will be all but invisible. You can't make an omelette without breaking eggs. smiley

I can't see why your neighbour should chuck in with you towards the costs, though. It's not as though they want or desperately need any of this work doing. It's for your benefit, and so, in my book, you should pay. If your neighbour benefits, then they may elect to make a contribution, but they'd be perfectly within their rights to tell you to go forth and multiply, if they were that way inclined.  wink

Forum Question SVP & Concreting-in - M Lloyd - 25 Nov 2002
I have had a massive extension/conversion on my house that has pretty much become a self-build in the latter stages due to both cost overrun and disattisfaction with the quality of work performed by the builders/plumbers.

I have two separate drainage runs, one up each side of the house. I completed the first OK thanks to your site! The second run involves a couple of new challenges.
One challenge is dropping a new internal S&V from upstairs accomodation down through floorboards at ground level and through a brick built cavity wall to connect to the new drainage I/C. I am confident I can do all this apart from installing a couple of 450x70x100 lintels above the S&V outlet.
Will I need to provide support for the wall while before removing the bricks for such a small hole? If so, how should I support the wall while doing this?
My other question is that part on the new drainage needs to pass under my front door step. I plan to encase this step area in concrete about 1100 long x 450 wide x 350 deep. Would you recommend pouring  the concrete directly next to the brickwork footings, or should I line the brickwork with a sheet of plastic or a compressible liner of some sort to allow for expansion and to stop the concrete sticking directly to the brickwork?
Later I will be laying paving areas and will face a similar question of laying concrete directly next to the house wall brickwork.

forum answer Tony McCormack - 26 Nov 2002
I'm not sure why you need to install the lintels, and, without being familiar with the site, the proposed point of entry/exit, the access etc., it's yet another of these problems where it would be unwise for me to recommend any particular modus operandi. It's sometimes possible to create a small-ish opening in a brick wall without having to resort to Acrow props or other forms of carrying the upper brickwork. In my experience, cutting a roughly 150x150mm hole to evacuate a soil pipe is straightforward enough, and does not normally require lintels or support structures, but then, your situation may be different.

Your second question brings a similar response, I'm afraid. Unless I can see the job, I can't really say what would be my plan of attack. Can you provide me with an annotated sketch of your plan?

Sorry I'm not much use on these questions, but they are so individual and site-specific, it would be unprofessional, and possibly dangerous, for me to suggest solutions when I'm not familiar with the layout.

M Lloyd
26 Nov 2002
Thanks for your comments.

Here's a bit of extra info about what I am up to.
My property was a 1950's bungalow which has been extended both outwards and upwards (Dormer windows etc). It's in a rural location with long drain runs to a septic tank. I also built 4 soakaways using your excellent advice.

Re: Why I need a lintel?
Obviously I have plans for my extension have been granted planning + building regs approval. The plans are a little lacking in detail regarding how the SVP from the new upstairs exits through the original bungalow walls.  I have 2 other SVPs which exit the newly built part of the property both of which have small lintels but obviously it is easy to to put these in a new build.
I asked my architect/building consultant if I needed to put lintels in for this SVP (having seen them in the newbuild part) and he verbally advised me it would be best, so I guess I had better put them in even if it is probably an overengineered solution.
I also need to make sure the building inspector is happy, although I guess could ask him what he would be happy with.
To be honest, it is probably unfair of me to ask you how you would put lintels in - after all you are not!
So anway, no worries and thanks for your advice on that.

Regarding the concrete, I suppose my question is not really a drainage question at all - more of a genaral question about laying concrete.
If you are laying concrete right up to a house wall  would you:
(a) Always put a liner (e.g. plastic sheeting) between the new concrete and the existing wall?
(b) Never put a liner between the concrete and the wall?
(c) Sometimes put a liner between the concrete and the wall, depending on circumstances?
If you answer (a) or (c), what materials would you use as a liner and what purpose would the liner typically serve.
(e.g. maybe one purpose of a liner to act as an expansion buffer?
another purpose may be to stop the concrete sticking to and damaging the wall the wall in case it ever needs to be broken up and removed at a later date)
Sorry if this question seems a bit vague, but I will be laying quite a lot of concrete around my house when the drainage is finished. If I understand the factors to be considered in deciding if a liner should be used then I will be able to make my own mind up in the various situautions.
Also, sorry if this question seems a bit daft.
As you can probably tell I dont know very much about laying concrete.

Tony McCormack
Somehow, the fact that an architect specc'ed the lintel comes as no great surprise. If you ever want to do things the hard way, get an architect! wink

I think you're right - ask the BCO what they would accept and go with that. The trouble with many of these types of jobs is that you can't see what you're up against until your get the ground opened up, and you could get yourself all geared up for a lintel installation only to find some prescient builder has left a 150mm dia hole in the foundations just for this sort of eventuality. Well, maybe not, but you know what I mean! smiley

So, on to the concrete - usually, we'd use a membrane between the existing brickwork and the new concrete, unless there was good reason not to, and nothing you've mentioned so far suggests such a good reason. The standard 'membrane' is a PIFA 1200 micron impermeable membrane, but we call it 'visqueen' for short. It's the blue-tinged plastic you've seen a million times on building sites and in Builder's Merchants.

You'll not need a full roll (100m²) so see if you can cadge some from a local builder in exchange for a small donation to their favourite pocket.


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