# Trench for water, electricty and waste



## Molynoox (15 Apr 2021)

Hi All,

I am making progress with my garden room build, groundscrews have been installed and I have now started digging the trench.
The below is my current trench 'design' if you can call it that - there doesn't seem to be any clear answers on the topic of combining all 4 types of service in one trench
I have kept to 100mm spacing between the services
I may use conduits for all or some, not sure on that - maybe electricity and comms in one conduit?
I have placed water as far away from waste as I can, to avoid contamination in case of a leak, but not sure if this is really going to help or is necessary (I did read somewhere that this was advisable, but I am not sure how the waste could enter the water pipe, but anyway)

your thoughts on this?

thanks
Martin


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## Molynoox (15 Apr 2021)

It might be useful to see my overall plan for the trench position also, see pic.
The run is about 10 - 15 metres long


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## Molynoox (15 Apr 2021)

Having a nice conversation with myself here :-D just modified my design so uploading the latest.


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## MARK.B. (15 Apr 2021)

When i did mine( no waste pipe) I put them all in one trench inside 2 drainage pipes which come up flush to the inside wall and are capped flush to the floor. Easy to pull through extra cables if needed.
Having just seen the added picture it might be a better idea if you do two trenches 1 for the waste and the other for whats left ,that way you avoid those bends which could cause a problem if you need to pull through another cable .


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## Cabinetman (16 Apr 2021)

Something’s ringing a bell in my head, to not put the Wi-Fi too close to the mains, or was that hi-fi? 
Sorry not to be of more help. Ian


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## Rorton (16 Apr 2021)

yeah, split the comms away from the electrical - are you putting cat5/6 cables in or fibre?


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## Rorton (16 Apr 2021)

and also use outdoor spec cable too for the comms


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## MikeK (16 Apr 2021)

It's great that you're thinking about this now instead of a few years from now if something has to change. I've done dozens of renovation and construction projects in Europe that involve adding utilities and communications where none existed or the existing infrastructure was inadequate. 

Paying for the trench or hole in the ground tends the be the most expensive part of the project and is an event we tried to do only once for the expected life of the facility. Since you are working with distances of about 15 meters, you can easily incorporate suitable ducting in the trench that can make your shed future-proof for changes in technology or maintenance.

Keep the bends in the ducting to a minimum so pulling cable in the future will be easier. The more bends you have, the more opportunities you create for the cables to bind or break. You can never have too many pull stings in conduit. It is much better to have five unused pull strings than to need one that doesn't exist.

Keep power and communications separate. Even with fiber cable, it is standard practice here to keep power and comms separate.

Give consideration to the utilities that could fail in the future and will need access from the surface. If everything is layered in one trench, what will you not want to dig past to access what is below it? With a restriction of one trench, I would put the comms on the bottom in a suitably sized duct. We use 100mm round duct that has four internal round ducts to create separate ducts for the different communications cables. This is overkill for a residential application, but if the cost is reasonable, I would use this and install pull strings in each duct during the installation. This reduces the likelihood of a new cable snagging on existing cable later.

Make sure you use the appropriate warning tape for each utility that is placed in the trench as it is filled. This tape follows the path of the associated utility and is the first warning anyone digging in the area will see before reaching the pipe, cable, or duct buried beneath it. This is especially important for direct burial cable.

Document the location of the trench using reference points from several fixed points, such as corners of permanent structures. We use at least two reference points for several points along the path, each junction, or each bend. If the trench is straight with no junctions in the buried conduit, then we document a point one meter from each point where it enters the buildings, as well as the middle. The documentation also includes the depth below grade of the top of the conduit, pipe, or cable. This is easy to do before the trench is covered and will save lots of time later if you have to access something years from now. Based on your drawing, you have at least five permanent reference points that can be used to pinpoint any location to millimeter accuracy along the path of the ducting. Adding photos of the trenching to the documentation is also a good idea.


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## Spectric (16 Apr 2021)

Your trench depth could be dictated by the waste pipe depending on the fall and don't forget to fit a roding point, might be easier to just put this in it's own trench first along with the water and then you can keep the other trench dead straight looking at your drawing. Now all you need is a duct, soil pipe is not the cheapest but probably the easiest or rain / gutter pipe but brown underground soil is cheaper and run the Two core armoured through this with a screened and armoured data cable, or just a screened data cable depending on the type of data link and router location. Mike has made some good points about warning tape above the ducts and keeping a record of where you put it.


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## Woody2Shoes (16 Apr 2021)

Don't forget that building regs apply to the depth, fall, bedding, jointing and inspection arrangements for the foul drainage - can't remomber which approved doc it is. Where the water pipe goes from internal to external and vice versa I'd do pipe in pipe to ease installation and protect it - you've obviously spotted that it needs to be 750 deep min to protect from frost - I'd put an isolation valve outside the new build in a suitable chamber. Wiring regs apply to the type and installation method for power - I'd consult a spark to make sure that you choose the correct type of SWA cable and installation methods (the workshop may or may not also require its own earth rod, depending on what the spark recommends). I agree with the idea of putting a separate conduit for data cable, with a pulling rope installed before you bury it.
PS building regs may also require you to have an SVP or a durgo valve at the upstream end


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## Jamesc (16 Apr 2021)

A quick google for 'combined service trench detail uk' brings up a lot of results. There is a lot of good advice regarding spacing.


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## RichardG (16 Apr 2021)

This is the standard for under a U.K. pavement, not sure if building control would insist on this for a home building, worth asking as they’ll want to inspect the drains.


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## Richard_C (16 Apr 2021)

Digital photography is free at point of use, I always take loads of photos of any hidden stuff now, really useful when you come back to it years later. Copy on hard drive and well orderd copy on a USB stick in the house file box. 

If you use ducts maybe leave a pull through line in it, who knows what you might want in future. Mains coffee from a machine in the house? Steam pipe for cappuccino making....


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## Spectric (16 Apr 2021)

Electrical supply to the outbuilding depends upon the type of supply to the property which determines the means of earthing. Best leave this to the sparky doing the design and install.


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## Molynoox (17 Apr 2021)

MARK.B. said:


> When i did mine( no waste pipe) I put them all in one trench inside 2 drainage pipes which come up flush to the inside wall and are capped flush to the floor. Easy to pull through extra cables if needed.
> Having just seen the added picture it might be a better idea if you do two trenches 1 for the waste and the other for whats left ,that way you avoid those bends which could cause a problem if you need to pull through another cable .


 don't suppose you have any pictures of that conduit arrangement?


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## Molynoox (17 Apr 2021)

Rorton said:


> yeah, split the comms away from the electrical - are you putting cat5/6 cables in or fibre?





Rorton said:


> and also use outdoor spec cable too for the comms



just CAT5 I think - not sure on cost of fibre (I am getting fibre to house in May)

didn't know there was external spec cable, thanks


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## Molynoox (17 Apr 2021)

MikeK said:


> It's great that you're thinking about this now instead of a few years from now if something has to change. I've done dozens of renovation and construction projects in Europe that involve adding utilities and communications where none existed or the existing infrastructure was inadequate.
> 
> Paying for the trench or hole in the ground tends the be the most expensive part of the project and is an event we tried to do only once for the expected life of the facility. Since you are working with distances of about 15 meters, you can easily incorporate suitable ducting in the trench that can make your shed future-proof for changes in technology or maintenance.
> 
> ...


wow, thanks for the detail! excellent info.


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## Molynoox (17 Apr 2021)

Spectric said:


> Your trench depth could be dictated by the waste pipe depending on the fall and don't forget to fit a roding point, might be easier to just put this in it's own trench first along with the water and then you can keep the other trench dead straight looking at your drawing. Now all you need is a duct, soil pipe is not the cheapest but probably the easiest or rain / gutter pipe but brown underground soil is cheaper and run the Two core armoured through this with a screened and armoured data cable, or just a screened data cable depending on the type of data link and router location. Mike has made some good points about warning tape above the ducts and keeping a record of where you put it.



I admit I dont know what a rodding point is, but presumably it is someplace to access the drain to unblock it? I have a drain / manhole cover in the garden so I'm guessing that will do?

interesting you say about using screened comms cable and combining with electricty in same conduit - that is opposite of what others are saying. I guess if its screened comms cable though it should be fine.


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## Spectric (17 Apr 2021)

It really depends what the cable is carrying as far as signal. If the power cable is armoured that provides a reasonable level of screening that will reduce radiated EMC, and an armoured screened shielded CAT6 cable will protect from susceptance to EMC. Coms cables using twisted pairs like CAT 5,6 etc also reduce common mode issues. 

Have you thought about just using ethernet over power adaptors for the internet connection rather than cable?


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## Molynoox (17 Apr 2021)

Jamesc said:


> A quick google for 'combined service trench detail uk' brings up a lot of results. There is a lot of good advice regarding spacing.



I'm not so sure about that - all the searches I did returned advice about under pavement services, not gardens, and also none of them talked about combining waste with other services. Maybe its my searching that is off.


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## Molynoox (17 Apr 2021)

RichardG said:


> This is the standard for under a U.K. pavement, not sure if building control would insist on this for a home building, worth asking as they’ll want to inspect the drains.
> 
> View attachment 108427


this is a good worst case scenario, but I would prefer to keep them closer together as my trench is only 500mm wide.


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## Molynoox (17 Apr 2021)

Spectric said:


> Electrical supply to the outbuilding depends upon the type of supply to the property which determines the means of earthing. Best leave this to the sparky doing the design and install.


yes I have an electrician to do all that stuff, I have no clue.


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## Molynoox (17 Apr 2021)

Spectric said:


> It really depends what the cable is carrying as far as signal. If the power cable is armoured that provides a reasonable level of screening that will reduce radiated EMC, and an armoured screened shielded CAT6 cable will protect from susceptance to EMC. Coms cables using twisted pairs like CAT 5,6 etc also reduce common mode issues.
> 
> cool, those could be options then. I find it strange that fibre optic is not immune to EMC
> 
> Have you thought about just using ethernet over power adaptors for the internet connection rather than cable?


nope didn't consider that option - is it reliable I wonder, and at what speeds. I will have 150mbit fibre to house so would hope to keep most of that speed in the garden room


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## Molynoox (17 Apr 2021)

Woody2Shoes said:


> Don't forget that building regs apply to the depth, fall, bedding, jointing and inspection arrangements for the foul drainage - can't remomber which approved doc it is. Where the water pipe goes from internal to external and vice versa I'd do pipe in pipe to ease installation and protect it - you've obviously spotted that it needs to be 750 deep min to protect from frost - I'd put an isolation valve outside the new build in a suitable chamber. Wiring regs apply to the type and installation method for power - I'd consult a spark to make sure that you choose the correct type of SWA cable and installation methods (the workshop may or may not also require its own earth rod, depending on what the spark recommends). I agree with the idea of putting a separate conduit for data cable, with a pulling rope installed before you bury it.
> PS building regs may also require you to have an SVP or a durgo valve at the upstream end



some excellent points there thanks!

It is part H for drainage and waste, I am reading it now

plumber is sorting the SVP valve

for isolation valve, could I not just have something inside the building, like a little valve that sits in line with the pipe?


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## Inspector (17 Apr 2021)

You might want to put the wires needed for burglar alarms in there too.
Pete.


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## joshvegas (18 Apr 2021)

Your inspection chamber ( assuming that big yellow dot is a 450mm IC (not a manhole) means you don't need a rodding point as your pipe run is straight. If its existing though you might find you need a deeper one if you are including a toilet that waste pipe needs to be 1in40 from memory so you'll have a reasonable drop to get across the garden especially if the ground falls away from your house.


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## Molynoox (18 Apr 2021)

Inspector said:


> You might want to put the wires needed for burglar alarms in there too.
> Pete.


Good idea!


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## Molynoox (18 Apr 2021)

joshvegas said:


> Your inspection chamber ( assuming that big yellow dot is a 450mm IC (not a manhole) means you don't need a rodding point as your pipe run is straight. If its existing though you might find you need a deeper one if you are including a toilet that waste pipe needs to be 1in40 from memory so you'll have a reasonable drop to get across the garden especially if the ground falls away from your house.


Ah, inspection chamber, that is the terminology I was missing! Yes I read part H last night and I your comment confirms what I took from those. I have enough drop to use existing IC I think. Plumber thinks so too. And yes it's 1 in 40.


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## gmgmgm (22 Apr 2021)

Coming in a bit late here. Do you need those two 90 degree changes of direction? Much better to have straight or even gently curved trenches.

And while I'd recommend separating power from communications, realistically over 15m it won't matter. Putting them all (cat5/6, power, alarm wires(just use a couple of spare cat5)) in a single 100mm conduit won't be a problem from a crosstalk POV, but go with screened cat6 for peace of mind.

Consider also the access to conduits- for some buildings I have a manhole outside the building with a straight conduit run to the manhole outside the other building, which makes it fairly easy to check what's going on. But keep it simple


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## Molynoox (22 Apr 2021)

Cool thanks. I can avoid the 90 degree bend so I will, cheers
For alarm cable.. will cat6 have enough cores? I typed in alarm cable to Google and results ranged from 4, 6 and 8 core.

Martin


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## flying haggis (22 Apr 2021)

cat5/6 is 8 core so enough for alarms. I would put at least one spare cat5/6 in as well or put in and leave a draw rope. could you put the comms duct on the other side of the waste thereby keeping the max distance away from the power


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## MarkAW (21 May 2021)

Don't forget to account for a fall in your waste. One end of the trench will need to be deeper than the other


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