The Brew Cabin

I have a new plastic soil pipe running along the rear of an extension which is only about 140-150mm below ground level. I need to lay a path/patio over this area (foot traffic only!) and would like advice as to how to get a firm sub-base without damaging the pipes. Encasing in concrete is mentioned on your site, however is this strictly necessary?

Would it depend on whether block paving or slabs were being used? Could blocks be recommended at all?

Secondly, there is an IC (Hepworth with 330mm square lid) at each end of the pipe run which I intend replacing with recessed trays filled with paving/blocks. One of them has been left some 40mm above ground level so the question is will I be able to reduce the overall height when fitting the tray? Currently the lid is fitted directly onto the base so is at it's minimum height. I am hoping that after removing the lid I can cut down the chamber to allow for the recessed tray, but is there a minimum distance required between the bottom of the tray and the bottom of the IC?

Finally, there is a rodding point right next to one of the ICs. Can I reduce the height of the cover (or remove it completely?) so that I can hide this under the same tray as the IC?

Thanks in advance for your help.......

Encasing shallow drains in concrete is the recommended solution, especially when beneath a driveway, but for a path/patio, it's not essential. You could surround the pipework with 75-100mm of grit sand which then acts as a cushion between the pipe and the sub-base material. Whether the paving is blocks or flags is immaterial - if you use a sub-base, then you really ought to protect the pipework.

Secondly, as you say, the IC can be cut down as necessary to accommodate the recess tray. There is no real 'minimum' distance between the underside of the tray and the invert level of the IC, but it really isn't a good idea to have the tray impinging on the bore of the pipeline. So, assuming this was a 110mm uPVC pipe running throiugh the IC, then the bottom of the tray should be at least 120mm above invert, but,m the more space you have between tray and invert, the better.

I'm not 100% sure of what you mean in regard to your 3rd question. The Rodding Eye is adjacent to an IC - this suggests that it is two separate systems, with the IC on, say, the SW system and the RE on the FW system. In such an arrangement, it's best NOT to combine access to both SW and FW beneath one tray, as it would be confusing for future property owners and drainage surveyors.

A better solution would be to use separate recess covers and to move the RE position, if necessary, so that it doesn't clash with the location of the IC. Some stockists now how much smaller, 300x300mm trays, which would be ideal as a replacement for the RE.

Thanks.....appreciate the help!.

The pipe is laid in pea gravel which just about covers the top edge. Do I need to replace this with the grit sand or can I put something over the top?
My concern with blocks was whether I could get a firm enough sub-base and whether running a compactor over the top would damage the pipe. I have some 65mm blocks which if laid on a minimum 35mm sand bed would only leave 40mm between sand and pipe!

To try and explain my last question better......the IC is at the point where the new drain along the back wall joins the existing system which then runs underneath the extension (i.e. the new bit joins at 90 degrees to the old!). The RE is right next to this IC and joins into the same pipe that leaves the IC and heads under the building.
So the question is, can I simply remove the tops of both the IC & RE and cover them with a single 600 x 450 tray? If so, how would I finish them off under the tray - just bench round the 2 holes with concrete and leave them open?

Ideally, that pipe would be covered to a depth of around 100mm with the pea-gravel. If you have any available, you can use that, rather than grit sand, to cushion the pipe, but it's worth noting that, because pea-gravel has so many voids, there's a real risk of any bedding sand settling into those voids, and thereby causing settlement in the paving, so this is an ideal situation in which to use a separation membrane.

Assuming you get a reasonable degree of compaction, then I don't think this is going to be a big problem, as it's only a patio/path, so there are no excessive loadings or turning forces. Also, the great advantage of block paving is that, if the worst was to happen and the paving over the draina settled slightly, it can be lifted and re-laid to corrected levels with ridiculous ease. :)

I'm still not absolutely clear about the RE - are you saying that it is part of the same system as the IC? If so, surely it's redundant, as access to all pipes can be gained via the IC, can't it? Or have I missed summat?

Thanks, it's all becoming clearer now! A separation membrane below the bedding sand sounds like the way forward.

Sorry if I'm not making sense about the RE........yes it is part of the same system and gives access to the same pipe!
If you'll excuse this very poor attempt at a diagram it's like this:

l
l
l\
l \
l \
IC RE
____/ \______

i.e. a pipe feeds into each side of the IC and then it flows out straight ahead underneath the new building. The RE is attached to the pipe which goes under the building towards the main sewer.
The RE is just a few mm to the right of the IC so a 600mm tray would easily cover both.

You can lose the RE - either remove it and cap it, or fix it somehow beneath the tray.

I wonder how they managed to work out an arrangement like that? Was the IC fitted after the RE, I wonder? Or did they imagine access via the IC would be problematic? Or maybe they were on a bonus for the number of access fittings they could use up! :)

Whoops! I owe you an apology - you're right, the RE is for the surface drainage! I honestly believed otherwise, however talking to you made me go and double check today.

I pulled off the end of the RE, (since I could not get the lid off!) put a hose down it and of course the water appeared at a surface water IC not a sewage IC.
The pipe from the RE must go under the other one to join up with the surface drains under the building.

So as in your original reply I obviously need 2 covers as they are separate systems, and need to work out how I get them close together - there is 20mm at the most between them now.
I tried to look at the Clark Steel site to see what size trays were available but unfortunately it's "under construction" with no clue as to when it's coming back!

As you suggest it may mean moving the RE though I'm not sure how easy that will be. It can't move any closer to the wall but maybe I can extend the pipe to move it further away? Or would it be ok to add a shallow bend to the side? I've only got access to a short length of it before it disappears under the building!


By the way, on the subject of separation membranes, the local Builders Merchant is selling "Dupont Plantex" which claims to do the job. Would this be ok? If not can you suggest any other makes?


Again apologies for the mix up, but at least you made me stop and think!!!

http://www.pavingexpert.com/geosheet.htm

down at the bottom: Links

Without seeing the site, I can't be sure about the best solution for the encroaching RE, but it may be that the simplest solution is to extend it, by adding another half-metre of pipe to the main run, so that the cover falls outside the area that will be covered by the recess tray.

Whether you want to use another tray in place of the RE cover, or piece-in around the existing oval-shaped cover, is up to you. Some BMs and stockists have much smallers trays, say 300x300, which are more suited to replacing a RE cover, as the basic 450x600mm unit seems excessive for such a small opening.

As for the Plantex - it's a landscape fabric, intended for use as a weed membrane and originally developed for the horticultural trade rather than as a paving membrane. I don't believe Plantex is tough enough (puncture resistance measure) to be used as a separation membrane. You can get a 10-12 square metre pack of the Terram 1000 membrane from the GardenFab website, but any decent BM really ought to be selling a Terram or TDP quality product.

Can you give us an idea of what the minimum quantity a BM would sell, and what that would cost - some of us are still intimidated by BMs!

Terram do a "Mini-Pack" of their Terram 1000 offering that contains 50m².

Some Merchants, probably not the Jewsons and Travis Bloody Perkins of this world, but the more helpful local merchants and civils merchants, are willing to cut off a specific area from one of the large rolls they stock, so that you can buy, say, 40m² or 70m² as required, but it's not a widespread practice yet. They seem to be taking a lead from some of the DIY sheds that offer 'off-the-roll' lengths of Plantex or other membranes.

That GardenFab site is selling a "Mini-Pak" of just 5 sq m for £35 which I guess is the type of stuff you're recommending. Seems quite pricey, but if it does the job and prevents future problems then I guess it's worth it!

Anyway, thanks for the help, it will be a few weeks before I get a chance to do anything. No doubt more questions then!

Cheers.....

7 quid a metre? That's a rip-off!! They were selling a 10m² pack for 12 quid the last time I looked.

Try your local BM, or phone a few local contractors to see if they have any they they want to sell, because 35 quid for 5 square metres is daylight robbery!

Just a thought, but am I looking at the right stuff?

1.1m x 4.5m of "Mini-Pak" is about £30 + vat
1m x 10m of "Patio Partner" is about £13 + vat

Which one is the equivalent of Terram 1000?

Thanks....

It's them numpties doing the web design for Terram, they've dropped a bollock with the dimensions!

Patio Partner is exactly the same as Terram 1000 (and the Mini-Pak) except that they colour it brown (I bet Terram are sulking with me now for revealing this - they don't like it to be generally known!) The Patio Partner sells in 10m² lots, but the Min-Pak is 11m x 4.5m - that's eleven metres, not one point one as it states on their website - so you get almost 50m² in a Mini-Pak (what happened o the "c" in Pack - why do marketeers think dyslexia is a great selling point??), which makes it much better value than the PP roll. :)

I'll just fire off an email to Mr Terram and tell him he owes me a pint! ;)