Garden Office water and waste

[fatmcgav]

So as I've mentioned here, I'm currently planning a Garden Office build at the end of our 30m garden.

The building will contain a small kitchenette, for tea's/coffee's etc and a small cloakroom with hand basin, so pretty minimal requirements.

I'm now at the point where I need to start laying in the water and waste services, plus electric and internet, but they're not what I'm after some advice with here

Water:
So currently, the nearest point I could access the mains water is a 15mm copper feed behind our washing machine, which is ~27 meters from where I want the feed to enter the office.

My initial thought was to go with MDPE, however the smallest I can seem to find is 22mm, or more commonly 25mm. Is stepping up from 15mm copper to 22/25mm MDPE sensible? Am I likely to experience pressure issues due to the step up?

Alternatively, could I bury a PEX Barrier pipe underground? As I could use 15mm then to match the copper feed, and also use the same pipe for all the internal plumbing at the other end.

Waste:
So I'm going to trench in a 110mm waste pipe back to the nearest sewer access, which is ~28m. I'm pretty confident there's enough height difference to get a suitable fall from office to manhole.

As per this diagram, I'm intending on adding a mini inspection chamber just outside the garden office. The toilet and hand-basin for the cloakroom will be in the back right corner, and both will connect into a stub stack with an AAV installed.

However I'm unsure how to handle the kitchen waste.
One option would be to run an additional 110mm branch from the inspection chamber into a bottle trap which is positioned under the kitchen location, and then I just drop a 32mm waste pipe from the kitchen sink straight into that.

Alternatively, I'm wondering if I could hide a 32mm waste pipe behind the plasterboard walls, as I'm intending on battening out for a service void. However all the clips I'm finding suggest they need a depth of 50mm+, which is a lot of space to loose to a service void. Are there any other smaller clips that people know of?

Any advice greatly received.

Cheers
Gavin

 

[muggles]

20mm MDPE is the equivalent of 15mm copper. It should be buried to a depth of at least 750mm and not more than 1350mm.

Have you spoken to Building Control and your local water authority about making a new sewer connection? If you haven't, you need to do so before doing anything else - they will almost certainly want to inspect your work.

 

[fatmcgav]

20mm MDPE is the equivalent of 15mm copper. It should be buried to a depth of at least 750mm and not more than 1350mm.

Have you spoken to Building Control and your local water authority about making a new sewer connection? If you haven't, you need to do so before doing anything else - they will almost certainly want to inspect your work.

Muggles, cheers for the info.

I've spoken to local building control, and explained what I'm planning, and other then ensuring the electrics are part p, they were happy that the garden room was exempt.

He did say about contacting local water authority about a new connection, which I'm intending on doing ASAP. However I might not need to drop a new connection into the manhole, as I think there's an old soil pipe from the original outside toilet that I might be able to connect onto the end of...

 

[Hugh Jaleak]

The sink waste needs to be 40mm, so your best bet is as you describe, run a 110mm underground from the chamber to the sink position, come up, and finish with a suitable 110mm to waste connector at finished floor level.

If the existing sewer just serves your property, then it's just a matter for Building Control to approve the work, however if it is a shared drain at that point, (and you cant find/use the former outside WC connection), then you'll have to get the Water Company's permission to connect, which can open up a whole new world of pain, especially if the chamber is deep!

 

[fatmcgav]

Cheers for the responses both...

I had a couple more questions on the water connection...

Currently, I'm looking at using 25mm MDPE, as there's not much price difference, and the remainder of the 50m roll can be reused when I come to replace our existing lead water main

What I'm not sure of is the best way to actually get it inside the house. I keep coming across the Insuduct boxes (https://groundbreaker.co.uk/products/insuduct/) but at £85 for the box and MDPE "hockey stick" through wall pipe, it feels quite expensive. Though I guess it will give a nice and clean installation.

The alternative would be to just lag the pipe externally, but then I'll still need some kind of 90* elbow to get through the wall...

What other options have I got? I don't fancy coring through the internal finished floor if possible, so would like to keep the pipe on the outside and come through above floor level...

Thanks in advance.

 

[Hugh Jaleak]

Insuduct every time for me. It is a marvellous invention, saves a whole world of pain when putting new supplies into existing buildings! It's also purpose made for the job, whilst you can run the pipe using a 90 elbow to go through the wall, the problem is then insulating it to required standard.

To be honest, by the time you've bought an elbow, the insulation and material to knock up something to contain the whole lot, the £85 will probably seem money well spent!

 

[fatmcgav]

Insuduct every time for me. It is a marvellous invention, saves a whole world of pain when putting new supplies into existing buildings! It's also purpose made for the job, whilst you can run the pipe using a 90 elbow to go through the wall, the problem is then insulating it to required standard.

To be honest, by the time you've bought an elbow, the insulation and material to knock up something to contain the whole lot, the £85 will probably seem money well spent!

That's kinda where my head was at... Cheers for the vote of confidence though

 

[fatmcgav]

Is it worth getting a length of Shalloduct to run through the wall aswell, or can I just use "normal" lagging for that bit?

 

[Hugh Jaleak]

I bought a lump of thick polystyrene to go with the Insuduct when I last put one in, in was in 2 halves, and IIRC we cored a hole through the wall to the size required. You'll need some decent frost protection through the wall, (for new services the Water Inspector insists on it), although I cant see it offered now on BES's page. Maybe worth getting in touch with Groundbreaker and asking what the usual practice is now.